1) The authors conducted a radial velocity survey of stars in the young massive cluster Westerlund 1 to search for a potential pre-supernova companion to the magnetar CXO J1647-10.2-455216 located within the cluster.
2) They identified a candidate star, Wd1-5, that has anomalous velocities compared to other stars in the cluster, suggesting it was impacted by the supernova that created the magnetar.
3) Analysis of Wd1-5 found evidence of chemical enrichment that is difficult to explain by single star evolution, but could be explained if Wd1-5 was once part of a close binary system where it accreted material from
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
Young remmants of_type_ia_supernovae_and_their_progenitors_a_study_of_snr_g19_03Sérgio Sacani
Type Ia supernovae, with their remarkably homogeneous light curves and spectra, have been used as
standardizable candles to measure the accelerating expansion of the Universe. Yet, their progenitors
remain elusive. Common explanations invoke a degenerate star (white dwarf) which explodes upon
reaching close to the Chandrasekhar limit, by either steadily accreting mass from a companion star
or violently merging with another degenerate star. We show that circumstellar interaction in young
Galactic supernova remnants can be used to distinguish between these single and double degenerate
progenitor scenarios. Here we propose a new diagnostic, the Surface Brightness Index, which can
be computed from theory and compared with Chandra and VLA observations. We use this method
to demonstrate that a double degenerate progenitor can explain the decades-long
ux rise and size
increase of the youngest known Galactic SNR G1.9+0.3. We disfavor a single degenerate scenario.
We attribute the observed properties to the interaction between a steep ejecta prole and a constant
density environment. We suggest using the upgraded VLA to detect circumstellar interaction in
the remnants of historical Type Ia supernovae in the Local Group of galaxies. This may settle the
long-standing debate over their progenitors.
Subject headings: ISM: supernova remnants | radio continuum: general | X-rays: general | bi-
naries: general | circumstellar matter | supernovae: general | ISM: individual
objects(SNR G1.9+0.3)
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
We present long-baseline Atacama Large Millimeter/submillimeter Array (ALMA) observations of
the 870 m continuum emission from the nearest gas-rich protoplanetary disk, around TW Hya, that
trace millimeter-sized particles down to spatial scales as small as 1 AU (20 mas). These data reveal
a series of concentric ring-shaped substructures in the form of bright zones and narrow dark annuli
(1{6AU) with modest contrasts (5{30%). We associate these features with concentrations of solids
that have had their inward radial drift slowed or stopped, presumably at local gas pressure maxima.
No signicant non-axisymmetric structures are detected. Some of the observed features occur near
temperatures that may be associated with the condensation fronts of major volatile species, but the
relatively small brightness contrasts may also be a consequence of magnetized disk evolution (the
so-called zonal
ows). Other features, particularly a narrow dark annulus located only 1 AU from the
star, could indicate interactions between the disk and young planets. These data signal that ordered
substructures on AU scales can be common, fundamental factors in disk evolution, and that high
resolution microwave imaging can help characterize them during the epoch of planet formation.
Keywords: protoplanetary disks | planet-disk interactions | stars: individual (TW Hydrae)
We discovered two transient events in the Kepler eld with light curves that strongly suggest they
are type II-P supernovae. Using the fast cadence of the Kepler observations we precisely estimate
the rise time to maximum for KSN2011a and KSN2011d as 10.50:4 and 13.30:4 rest-frame days
respectively. Based on ts to idealized analytic models, we nd the progenitor radius of KSN2011a
(28020 R) to be signicantly smaller than that for KSN2011d (49020 R) but both have similar
explosion energies of 2.00:3 1051 erg.
The rising light curve of KSN2011d is an excellent match to that predicted by simple models of
exploding red supergiants (RSG). However, the early rise of KSN2011a is faster than the models
predict possibly due to the supernova shockwave moving into pre-existing wind or mass-loss from the
RSG. A mass loss rate of 10 4 M yr 1 from the RSG can explain the fast rise without impacting
the optical
ux at maximum light or the shape of the post-maximum light curve.
No shock breakout emission is seen in KSN2011a, but this is likely due to the circumstellar inter-
action suspected in the fast rising light curve. The early light curve of KSN2011d does show excess
emission consistent with model predictions of a shock breakout. This is the rst optical detection of
a shock breakout from a type II-P supernova.
Periodic mass extinctions_and_the_planet_x_model_reconsideredSérgio Sacani
The 27 Myr periodicity in the fossil extinction record has been con-
firmed in modern data bases dating back 500 Myr, which is twice the time
interval of the original analysis from thirty years ago. The surprising regularity
of this period has been used to reject the Nemesis model. A second
model based on the sun’s vertical galactic oscillations has been challenged
on the basis of an inconsistency in period and phasing. The third astronomical
model originally proposed to explain the periodicity is the Planet
X model in which the period is associated with the perihelion precession
of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated
to mass extinctions, a trans-Neptunian super-Earth planet has been proposed
to explain the observation that the inner Oort cloud objects Sedna
and 2012VP113 have perihelia that lie near the ecliptic plane. In this
Letter we reconsider the Planet X model in light of the confluence of the
modern palaeontological and outer solar system dynamical evidence.
Key Words: astrobiology - planets and satellites - Kuiper belt:
general - comets: general
The xmm newton-view_of_the_central_degrees_of_the_milk_waySérgio Sacani
Novas imagens do Observatório de Raios-X XMM-Newton da ESA revelaram alguns dos processos mais intensos que acontecem no coração da nossa Via Láctea.
As fontes brilhantes e pontuais que se destacam por toda imagem indicam os sistemas estelares binários onde uma das estrelas atingiu o final de sua vida, desenvolvendo para um objeto compacto e denso – uma estrela de nêutrons ou um buraco negro.
A região central da Via Láctea também contém jovens estrelas e aglomerados estelares e algumas dessas fontes são visíveis como pontos brancos e vermelhos brilhando na imagem, que se espalha por 1000 anos-luz.
A maior parte da ação ocorre no centro, onde nuvens difusas de gás estão sendo cavadas por ventos poderosos soprados por estrelas jovens, bem como por supernovas.
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
Destruction of galactic_globular_cluster_systemSérgio Sacani
This document summarizes research on the destruction of globular clusters in the Milky Way galaxy. The researchers used a Fokker-Planck code to model the evolution of individual clusters, taking into account two-body relaxation, tidal truncation, gravitational shocks from passing through the disk and bulge. They modeled the orbits of globular clusters over Hubble time and found destruction rates are significantly higher than previous estimates, with over half of current clusters being destroyed in the next Hubble time. This could indicate that the initial population was much larger, with remnants of destroyed clusters now making up a large part of the spheroid stellar population.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
1) High-resolution N-body simulations were conducted of isolated disk galaxies to explore the origin of spiral arms. Mass concentrations similar to giant molecular clouds were included to perturb the disks.
2) The simulations demonstrated that the disks developed long-lived, multi-armed spiral structures in response to the perturbations. This challenges the expectation that spiral arms should fade quickly once perturbations are removed.
3) Contrary to linear theories of spiral structure formation, the response of the disks to local perturbations was found to be highly non-linear and time-variable, significantly modifying the formation and longevity of spiral patterns.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
Radio imaging obserations_of_psr_j1023_0038_in_an_lmxb_stateSérgio Sacani
Uma estrela super densa formada depois da explosão de uma supernova está expelindo poderosos jatos de material no espaço, sugerem pesquisas recentes.
Num estudo publicado no dia 6 de Agosto de 2015, uma equipe de cientistas na Austrália e na Holanda descobriram poderosos jatos sendo expelidos de uma sistema estelar duplo conhecido como PSR J1023+0038.
Pensava-se anteriormente que os únicos objetos no universo capazes de formar jatos poderosos eram os buracos negros.
O sistema PSR J1023+0038 contém uma estrela extremamente densa que os astrônomos chamam de estrela de nêutrons, numa órbita próxima com uma estrela normal.
Ela foi identificada primeiro como uma estrela de nêutrons em 2009, mas foi somente quando a equipe de pesquisa observou a estrela com o rádio telescópio Very Large Array nos EUA em 2013 e 2014 que eles perceberam que a estrela estava produzindo jatos mais fortes do que se esperava.
Os astrônomos James Miller-Jones, do International Centre for Radio Astronomy Research (ICRAR), disse que as estrelas de nêutrons podem ser pensadas como cadáveres estelares.
“Elas são formadas quando uma estrela massiva esgota todo o seu combustível e vira uma supernova, e as partes centrais da estrela colapsam sobre sua própria gravidade”, disse ele.
“Essas coisas tem normalmente entre uma vez e meia a massa do Sol e somente entre 10 a 15 km de diâmetro, de modo que são extremamente densas”.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
This document describes the discovery of a giant ring-like structure in the observable universe displayed by 9 gamma ray bursts (GRBs) between redshifts of 0.78 and 0.86. The ring has a diameter of 1720 Mpc, over five times larger than the expected transition scale to homogeneity. The ring lies at a distance of 2770 Mpc with major and minor diameters of 43° and 30°, respectively. The probability of this structure occurring by random chance is calculated to be 2 × 10-6. This ring-shaped feature contradicts the cosmological principle of large-scale homogeneity and isotropy, and the physical mechanism responsible is unknown.
The document summarizes findings from the Microwave Instrument on the Rosetta Orbiter (MIRO) regarding the subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko. Key points:
- MIRO detected water vapor emissions from the comet beginning in early June 2014 and measured the total water production rate, which varied from 0.3 kg/s to 1.2 kg/s between June and August.
- Water outgassing displayed periodic variations correlated with the comet's 12.4-hour rotation period and seemed to originate primarily from the comet's "neck" region.
- Subsurface temperatures measured by MIRO showed seasonal and diurnal variations, indicating radiation
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
This document summarizes an article that proposes an alternative explanation for dark energy and dark matter based on a modified theory of gravity. It begins by providing background on dark matter and dark energy in standard cosmology and the evidence that supports their existence. It then outlines the proposed alternative theory, which modifies Einstein's field equations by adding a function of the Ricci scalar. This introduces new curvature terms that could potentially drive accelerated expansion, providing an alternative to dark energy. The theory aims to match observations without requiring dark matter or energy, but reduces to general relativity in the solar system scale where it has been tightly tested.
The colision between_the_milky_way_and_andromedaSérgio Sacani
The document summarizes a simulation of the future collision between the Milky Way and Andromeda galaxies. It finds that given current observational constraints on their distance, velocity, and masses:
1) The Milky Way and Andromeda are likely to collide in a few billion years, within the lifetime of the Sun.
2) During the interaction, there is a chance the Sun could be pulled into an extended tidal tail between the galaxies.
3) Eventually, after the merger is complete, the Sun would most likely be scattered to the outer halo of the merged galaxy at a distance over 30 kpc.
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
Destruction of galactic_globular_cluster_systemSérgio Sacani
This document summarizes research on the destruction of globular clusters in the Milky Way galaxy. The researchers used a Fokker-Planck code to model the evolution of individual clusters, taking into account two-body relaxation, tidal truncation, gravitational shocks from passing through the disk and bulge. They modeled the orbits of globular clusters over Hubble time and found destruction rates are significantly higher than previous estimates, with over half of current clusters being destroyed in the next Hubble time. This could indicate that the initial population was much larger, with remnants of destroyed clusters now making up a large part of the spheroid stellar population.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
First identification of_direct_collapse_black_holes_candidates_in_the_early_u...Sérgio Sacani
The first black hole seeds, formed when the Universe was younger than ⇠ 500Myr, are recognized
to play an important role for the growth of early (z ⇠ 7) super-massive black holes.
While progresses have been made in understanding their formation and growth, their observational
signatures remain largely unexplored. As a result, no detection of such sources has been
confirmed so far. Supported by numerical simulations, we present a novel photometric method
to identify black hole seed candidates in deep multi-wavelength surveys.We predict that these
highly-obscured sources are characterized by a steep spectrum in the infrared (1.6−4.5μm),
i.e. by very red colors. The method selects the only 2 objects with a robust X-ray detection
found in the CANDELS/GOODS-S survey with a photometric redshift z & 6. Fitting their
infrared spectra only with a stellar component would require unrealistic star formation rates
(& 2000M# yr−1). To date, the selected objects represent the most promising black hole seed
candidates, possibly formed via the direct collapse black hole scenario, with predicted mass
> 105M#. While this result is based on the best photometric observations of high-z sources
available to date, additional progress is expected from spectroscopic and deeper X-ray data.
Upcoming observatories, like the JWST, will greatly expand the scope of this work.
1) High-resolution N-body simulations were conducted of isolated disk galaxies to explore the origin of spiral arms. Mass concentrations similar to giant molecular clouds were included to perturb the disks.
2) The simulations demonstrated that the disks developed long-lived, multi-armed spiral structures in response to the perturbations. This challenges the expectation that spiral arms should fade quickly once perturbations are removed.
3) Contrary to linear theories of spiral structure formation, the response of the disks to local perturbations was found to be highly non-linear and time-variable, significantly modifying the formation and longevity of spiral patterns.
Detection of lyman_alpha_emission_from_a_triply_imaged_z_6_85_galaxy_behind_m...Sérgio Sacani
We report the detection of Ly emission at 9538A
in the Keck/DEIMOS and HST WFC3
G102 grism data from a triply-imaged galaxy at z = 6:846 0:001 behind galaxy cluster MACS
J2129.4 0741. Combining the emission line wavelength with broadband photometry, line ratio upper
limits, and lens modeling, we rule out the scenario that this emission line is [O II] at z = 1:57. After
accounting for magnication, we calculate the weighted average of the intrinsic Ly luminosity to be
1:31042 erg s 1 and Ly equivalent width to be 7415A. Its intrinsic UV absolute magnitude at
1600A
is 18:60:2 mag and stellar mass (1:50:3)107 M, making it one of the faintest (intrinsic
LUV 0:14 L
UV) galaxies with Ly detection at z 7 to date. Its stellar mass is in the typical range
for the galaxies thought to dominate the reionization photon budget at z & 7; the inferred Ly escape
fraction is high (& 10%), which could be common for sub-L z & 7 galaxies with Ly emission. This
galaxy oers a glimpse of the galaxy population that is thought to drive reionization, and it shows
that gravitational lensing is an important avenue to probe the sub-L galaxy population.
Radio imaging obserations_of_psr_j1023_0038_in_an_lmxb_stateSérgio Sacani
Uma estrela super densa formada depois da explosão de uma supernova está expelindo poderosos jatos de material no espaço, sugerem pesquisas recentes.
Num estudo publicado no dia 6 de Agosto de 2015, uma equipe de cientistas na Austrália e na Holanda descobriram poderosos jatos sendo expelidos de uma sistema estelar duplo conhecido como PSR J1023+0038.
Pensava-se anteriormente que os únicos objetos no universo capazes de formar jatos poderosos eram os buracos negros.
O sistema PSR J1023+0038 contém uma estrela extremamente densa que os astrônomos chamam de estrela de nêutrons, numa órbita próxima com uma estrela normal.
Ela foi identificada primeiro como uma estrela de nêutrons em 2009, mas foi somente quando a equipe de pesquisa observou a estrela com o rádio telescópio Very Large Array nos EUA em 2013 e 2014 que eles perceberam que a estrela estava produzindo jatos mais fortes do que se esperava.
Os astrônomos James Miller-Jones, do International Centre for Radio Astronomy Research (ICRAR), disse que as estrelas de nêutrons podem ser pensadas como cadáveres estelares.
“Elas são formadas quando uma estrela massiva esgota todo o seu combustível e vira uma supernova, e as partes centrais da estrela colapsam sobre sua própria gravidade”, disse ele.
“Essas coisas tem normalmente entre uma vez e meia a massa do Sol e somente entre 10 a 15 km de diâmetro, de modo que são extremamente densas”.
The identification of_93_day_periodic_photometric_variability_for_yso_ylw_16aSérgio Sacani
This study identifies a 93 day periodic photometric variability in the Class I young stellar object (YSO) YLW 16A in the Rho Ophiuchus star forming region. Light curve analysis reveals variations of ~0.5 magnitudes in the Ks band over this period. The authors propose a triple system model consisting of an inner binary with a 93 day period eclipsed by a warped circumbinary disk, with a tertiary companion at ~40 AU responsible for warping the disk. This model is similar to one previously proposed for another YSO, WL 4, and may indicate such triple systems with eclipsing disks are common around young stars. Understanding these systems can provide insights into stellar and planetary formation and evolution.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
This document describes the discovery of a giant ring-like structure in the observable universe displayed by 9 gamma ray bursts (GRBs) between redshifts of 0.78 and 0.86. The ring has a diameter of 1720 Mpc, over five times larger than the expected transition scale to homogeneity. The ring lies at a distance of 2770 Mpc with major and minor diameters of 43° and 30°, respectively. The probability of this structure occurring by random chance is calculated to be 2 × 10-6. This ring-shaped feature contradicts the cosmological principle of large-scale homogeneity and isotropy, and the physical mechanism responsible is unknown.
The document summarizes findings from the Microwave Instrument on the Rosetta Orbiter (MIRO) regarding the subsurface properties and early activity of comet 67P/Churyumov-Gerasimenko. Key points:
- MIRO detected water vapor emissions from the comet beginning in early June 2014 and measured the total water production rate, which varied from 0.3 kg/s to 1.2 kg/s between June and August.
- Water outgassing displayed periodic variations correlated with the comet's 12.4-hour rotation period and seemed to originate primarily from the comet's "neck" region.
- Subsurface temperatures measured by MIRO showed seasonal and diurnal variations, indicating radiation
- The document derives the second order Friedmann equations from the quantum corrected Raychaudhuri equation (QRE), which includes quantum corrections terms.
- One correction term can be interpreted as dark energy/cosmological constant with the observed density value, providing an explanation for the coincidence problem.
- The other correction term can be interpreted as a radiation term in the early universe that prevents the formation of a big bang singularity and predicts an infinite age for the universe by avoiding a divergence in the Hubble parameter or its derivative at any finite time in the past.
Alma observations of_feed_and_feedback_in_nearby_seyfert_galaxiesSérgio Sacani
The ALMA observations of NGC 1433 reveal a nuclear gaseous spiral structure within the central kpc. This spiral winds up into a pseudo-ring at ~200 pc from the center. Near the nucleus, there is intense high-velocity CO emission up to 200 km/s that is interpreted as an outflow, involving 3.6 million solar masses of molecular gas and a flow rate of ~7 solar masses per year. The outflow could be driven by both the central star formation and AGN through its radio jets. Continuum emission at 0.87 mm is detected only at the very center and likely comes from thermal dust emission from the molecular torus expected in this Seyfert 2 galaxy.
This document summarizes observations of the W49 giant molecular cloud (GMC) using the PMO 14m telescope and the Submillimeter Array (SMA). The PMO observations mapped the entire GMC in various molecular lines at scales up to 113 pc, while the SMA mosaic mapped the central star-forming region W49N at scales down to 0.5 pc. The observations are used to derive the mass structure of the GMC across all scales. The main findings are that the W49 GMC has a total gas mass of 1.1 million solar masses within 60 pc and 2x10^5 solar masses within 6 pc. The mass is distributed in a hierarchical network of filaments converging toward the central
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
This document presents a sample of 20 extremely luminous galaxies discovered by the Wide-field Infrared Survey Explorer (WISE). Five of these galaxies have infrared luminosities exceeding 1014 solar luminosities, the highest infrared luminosity threshold yet observed. They were selected using criteria requiring weak or no detection in the first two WISE bands but strong detections in the third and fourth bands. Spectral energy distribution modeling suggests their high luminosities are powered by obscured active galactic nuclei with hot dust temperatures around 450 Kelvin. The existence of such luminous galaxies at redshifts above 3 provides constraints on the early growth of supermassive black holes through rapid accretion.
Detectcion of noble_gas_molecular_ion_arh_in_the_crab_nebulaSérgio Sacani
Scientists detected emission lines from the ionized argon hydride (36ArH+) molecule in spectra of the Crab Nebula obtained with the Herschel Space Observatory. The detection of 36ArH+ confirms that argon originated from explosive nucleosynthesis during the core-collapse supernova that created the Crab Nebula. The likely excitation mechanism is electron collisions in partially ionized regions with electron densities of a few hundred per cubic centimeter. This is the first detection of a noble gas molecule in space.
Assymetries in core_collapse_supernovae_from_maps_of_radioactive_ti_in_cassio...Sérgio Sacani
The document summarizes findings from observations of Cassiopeia A using the Nuclear Spectroscopic Telescope Array (NuSTAR).
1) NuSTAR detected two clear emission lines from the decay of radioactive titanium-44, confirming previous measurements of titanium-44 yield with high significance. The spatial distribution of titanium-44 emission shows it is clumpy and extended along the jet axis seen in X-ray images, with knots off the jet axis.
2) There is no correlation between the distribution of titanium-44 and iron detected by Chandra X-ray Observatory. This suggests much of the iron-rich ejecta has not been shock-heated and is "invisible", constraining models of the remnant.
An ultraluminous quasar_with_a_twelve_billion_solar_mass_black_hole_at_redshi...Sérgio Sacani
1) Researchers discovered an ultraluminous quasar, SDSS J010013.021280225.8, at a redshift of 6.30, making it the most distant and luminous quasar known.
2) Spectral analysis estimates the black hole at its center has a mass of 1.2 billion solar masses, consistent with an Eddington-limited accretion rate.
3) The quasar has an ionized proximity zone estimated to be 26 million light years across, significantly larger than found for other high-redshift quasars, suggesting its high luminosity.
Detection of an_unidentified_emission_line_in_the_stacked_xray_spectrum_of_ga...Sérgio Sacani
This document describes the detection of an unidentified emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. The line was detected at an energy of 3.55-3.57 keV in independent analyses of the MOS and PN instruments. The line was also seen in Chandra observations of the Perseus cluster. Possible explanations discussed include an atomic transition in thermal plasma, or the decay of sterile neutrino dark matter particles. However, the origin is unclear and requires further observation.
Asymmetrical tidal tails of open star clusters: stars crossing their cluster’...Sérgio Sacani
The document discusses asymmetrical tidal tails observed around five open star clusters, which challenges Newtonian gravity. It summarizes how tidal tails form as stars escape clusters due to energy equipartition. Observations of the Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, and NGC 752 clusters found more stars in the leading tidal tails within 50 pc of the clusters. Simulations show that in Newtonian gravity, tidal tails should be symmetrical, but asymmetries can arise in Milgromian dynamics. Future work is needed to better map tidal tails and develop Milgromian simulations.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
Studies of ngc_6720_with_calibrated_hst_wfc3_emission_line_filter_imagesSérgio Sacani
This study uses calibrated Hubble Space Telescope images of the Ring Nebula (NGC 6720) taken 12.925 years apart to measure tangential motions within the nebula. Individual features were measured in nitrogen emission line images as well as dark knots seen against oxygen emission. The results indicate that the nebula is expanding homologously, but at a faster rate along its major axis. Dark knots were found to expand more slowly than the nebular gas. The tangential motion measurements allow estimates of the nebula's distance and dynamic age to be about 720 pc and 4000 years, respectively.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
The puzzling source_in_ngc6388_a_possible_planetary_tidal_disruption_eventSérgio Sacani
Artigo descreve a descoberta da destruição de um planeta ao passar próximo a uma estrela do tipo anã branca presente dentro do aglomerado globular de estrelas NGC 6388. Para isso os astrônomos utilizaram um arsenal de telescópios.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
The massive relic galaxy NGC 1277 is dark matter deficient From dynamical mod...Sérgio Sacani
According to the Λ cold dark matter (ΛCDM) cosmology, present-day galaxies with stellar masses M? > 1011 M should contain
a sizable fraction of dark matter within their stellar body. Models indicate that in massive early-type galaxies (ETGs) with M? ≈
1.5 × 1011 M, dark matter should account for ∼15% of the dynamical mass within one effective radius (1 Re) and for ∼60% within
5 Re
. Most massive ETGs have been shaped through a two-phase process: the rapid growth of a compact core was followed by the
accretion of an extended envelope through mergers. The exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG population at z & 2. The best relic galaxy candidate discovered
to date is NGC 1277, in the Perseus cluster. We used deep integral field George and Cynthia Mitchel Spectrograph (GCMS) data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to 5 Re). By using Jeans anisotropic modelling, we find
a negligible dark matter fraction within 5 Re (fDM(5 Re) < 0.05; two-sigma confidence level), which is in tension with the ΛCDM
expectation. Since the lack of an extended envelope would reduce dynamical friction and prevent the accretion of an envelope, we
propose that NGC 1277 lost its dark matter very early or that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals, suggesting that some relic galaxies may result from dark matter stripping as they fell in and interacted
within galaxy clusters. Alternatively, NGC 1277 might have been born in a high-velocity collision of gas-rich proto-galactic fragments,
where dark matter left behind a disc of dissipative baryons. We speculate that the relative velocities of ≈2000 km s−1
required for the
latter process to happen were possible in the progenitors of the present-day rich galaxy clusters.
This document summarizes the results of a 180 ks Chandra-LETGS observation of Mrk 509 as part of a larger multi-wavelength campaign. The observation detected several absorption features in the X-ray spectrum originating from an ionized absorber, including ions with three distinct ionization degrees. The lowest ionized component is slightly redshifted and not in pressure equilibrium with the others, likely belonging to the host galaxy's interstellar medium. The other two components are outflowing at velocities of around -200 and -455 km/s. Simultaneous HST-COS observations detected 13 UV kinematic components, and at least three can be associated with the X-ray components, providing evidence that the UV and X-
The physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
The document summarizes a study of an extreme molecular cloud in the Antennae galaxies that has properties consistent with forming a globular cluster. ALMA observations reveal a cloud with a radius of 24 pc and mass greater than 5 million solar masses. While capable of forming a globular cluster, a lack of associated thermal radio emission indicates star formation has not yet begun to alter the environment, suggesting the cloud is in an early stage of evolution. For the cloud to be confined as observed, an external pressure over 10,000 times greater than typical interstellar pressure is required, supporting the theory that high pressures are needed to form globular clusters in extreme environments like mergers.
1. VFTS 682 is a very massive star located 29 pc in projection from the young massive cluster R136 in the Tarantula Nebula of the LMC.
2. Spectral modeling finds it has an unusually high luminosity of log(L/L) = 6.5, corresponding to a present-day mass of ~150 solar masses.
3. Its isolation and mass pose the question of whether it formed in situ, which would profoundly impact theories of massive star formation, or if it was ejected from R136, making it the most massive runaway star known.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Sdss1133 an unsually_perssitent_transient_in_a_nearby_dwarf_galaxySérgio Sacani
This document summarizes observations of SDSS1133, an unusual transient object offset from the center of a nearby dwarf galaxy. SDSS1133 has been detected in observations spanning 63 years, and exhibits broad emission lines and strong variability. While initially classified as a supernova due to its non-detection in 2005, more recent observations over the past decade show it has rebrightened over a magnitude and displays properties consistent with both an active galactic nucleus and luminous blue variable star eruptions. Its nature remains ambiguous between an extreme example of pre-supernova mass loss or a potential candidate for a recoiling supermassive black hole.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
Artigo que descreve a descoberta do exoplaneta Kepler-432b, um exoplaneta mais massivo que Júpiter que orbita uma estrela gigante vermelha bem próximo e numa órbita extremamente alongada.
Radio continum emission_of_35_edge_on_galaxies_observed_with_the_vlaSérgio Sacani
Usando um dos maiores rádio observatórios do mundo, o Very Large Array do National Radio Astronomy, um grupo de astrônomos descobriram que os halos ao redor dos discos das galáxias espirais são muito mais comuns do que se pensava anteriormente.
A equipe, dirigida pela Dra. Judith Irwin, da Universidade de Queens, em Kingston, ON, Canadá, observou 35 galáxias espirais próximas de lado, de 11 a 137 milhões de anos-luz de distância da Terra.
As galáxias espirais, como a nossa própria Via Láctea ou a famosa Galáxia de Andrômeda, possuem uma vasta maioria de suas estrelas, gás, e poeira num disco plano em rotação com braços espirais. A maior parte da luz e das ondas de rádio observadas com telescópios veem de objetos localizados nesse disco.
“Nós sabíamos antes que alguns halos existiam, mas, usando o poder total do VLA atualizado e o poder total de algumas técnicas de processamento de imagens, nós descobrimos que esses halos são muito mais comuns entre as galáxias espirais do que nós pensávamos antes”, explicou a Dra. Irwin.
Similar to A vlt flames_survey_for_massive_binaries_in_westerlund_1 (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
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Exploiting Artificial Intelligence for Empowering Researchers and Faculty, In...Dr. Vinod Kumar Kanvaria
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A vlt flames_survey_for_massive_binaries_in_westerlund_1
1. Astronomy & Astrophysics manuscript no. aa21771-13 c ESO 2014
May 12, 2014
A VLT/FLAMES survey for massive binaries in Westerlund 1
IV. Wd1-5 – binary product and a pre-supernova companion for the magnetar
CXOU J1647-45? ,
J. S. Clark1, B. W. Ritchie1,2, F. Najarro3, N. Langer4, and I. Negueruela5
1
Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
e-mail: s.clark@open.ac.uk
2
Lockheed Martin Integrated Systems, Building 1500, Langstone, Hampshire, PO9 1SA, UK
3
Departamento de Astrofísica, Centro de Astrobiología, (CSIC-INTA), Ctra. Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz,
Madrid, Spain
4
Argelander Institut für Astronomie, Auf den Hügel 71, 53121 Bonn, Germany
5
Departamento de Física, Ingenaría de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
Received 25 April 2013 / Accepted 12 March 2014
ABSTRACT
Context. The first soft gamma-ray repeater was discovered over three decades ago, and was subsequently identified as a magnetar,
a class of highly magnetised neutron star. It has been hypothesised that these stars power some of the brightest supernovae known,
and that they may form the central engines of some long duration gamma-ray bursts. However there is currently no consenus on the
formation channel(s) of these objects.
Aims. The presence of a magnetar in the starburst cluster Westerlund 1 implies a progenitor with a mass ≥40 M , which favours
its formation in a binary that was disrupted at supernova. To test this hypothesis we conducted a search for the putative pre-SN
companion.
Methods. This was accomplished via a radial velocity survey to identify high-velocity runaways, with subsequent non-LTE model
atmosphere analysis of the resultant candidate, Wd1-5.
Results. Wd1-5 closely resembles the primaries in the short-period binaries, Wd1-13 and 44, suggesting a similar evolution-
ary history, although it currently appears single. It is overluminous for its spectroscopic mass and we find evidence of He- and
N-enrichement, O-depletion, and critically C-enrichment, a combination of properties that is difficult to explain under single star evo-
lutionary paradigms. We infer a pre-SN history for Wd1-5 which supposes an initial close binary comprising two stars of comparable
(∼41 M + 35 M ) masses. Efficient mass transfer from the initially more massive component leads to the mass-gainer evolving more
rapidly, initiating luminous blue variable/common envelope evolution. Reverse, wind-driven mass transfer during its subsequent WC
Wolf-Rayet phase leads to the carbon pollution of Wd1-5, before a type Ibc supernova disrupts the binary system. Under the as-
sumption of a physical association between Wd1-5 and J1647-45, the secondary is identified as the magnetar progenitor; its common
envelope evolutionary phase prevents spin-down of its core prior to SN and the seed magnetic field for the magnetar forms either in
this phase or during the earlier episode of mass transfer in which it was spun-up.
Conclusions. Our results suggest that binarity is a key ingredient in the formation of at least a subset of magnetars by preventing
spin-down via core-coupling and potentially generating a seed magnetic field. The apparent formation of a magnetar in a Type Ibc
supernova is consistent with recent suggestions that superluminous Type Ibc supernovae are powered by the rapid spin-down of these
objects.
Key words. stars: individual: CXOU J1647-45 – binaries: close – stars: evolution – stars: magnetars – stars: fundamental parameters –
stars: abundances
1. Introduction
A major uncertainty in our current understanding of massive
stellar evolution is the mapping of initial stellar mass onto super-
nova (SN) type and the resultant relativistic remnant (i.e. neutron
star (NS) or black hole (BH)). The key driver for both relation-
ships is the magnitude of pre-SN mass loss; historically this has
been assumed to be mediated by a radiatively driven wind but
recently other modes, such as impulsive events and binary mass
transfer have received increasing attention.
Based on observations made at the European Southern Observatory,
Paranal, Chile, under programmes ESO 81.D-0324, 383.D-0633,
087.D-0440, and 087.D-0673.
Appendix A is available in electronic form at
http://www.aanda.org
Three approaches can be taken to resolve this issue (e.g.
Muno 2007). First, given the association of a SN remnant with
a relativistic object, one can attempt to infer the properties of
the progenitor object from the former; a classic example be-
ing the Crab nebula (Nomoto et al. 1982). However, this ap-
proach is model dependent, with Cas A, for example, being in-
terpreted as originating from both single and binary progenitors
of differing masses (Laming & Hwang 2003; Young et al. 2006).
Second, theoretical reconstruction of the evolutionary history of
(high-mass) X-ray binaries such as GX301-2 (=BP Cru) and
4U1700-37 (=HD 153919) from their current physical proper-
ties may be attempted (e.g. Wellstein & Langer 1999; Clark et al.
2002) although once again this methodology is heavily depen-
dant on assumptions made regarding processes such as binary
mass transfer.
Article number, page 1 of 17
2. A&A proofs: manuscript no. aa21771-13
The final approach is to identify relativistic objects within
their natal stellar aggregates and hence use the cluster proper-
ties to infer the nature of the progenitor. This methodology is
challenging. Many compact objects are ejected from their na-
tal association due to SNe kicks; the host association must be
demonstrated to be co-eval and in general the properties of the
cluster population must be determined via comparison to stel-
lar evolutionary models. Nevertheless, this procedure has been
successfully implemented for three clusters, each hosting a mag-
netar. The brief lifetime inferred for such objects (e.g. ≤104
yr;
Kouveliotou et al. 1994; Woods & Thompson 2006) implies they
should still be associated with their birthsite, hence minimis-
ing false coincidences and allowing us to infer that their pro-
genitor was derived from the subset of the most massive stars
currently present. Moreover, this also allows us to address the
parallel problem of determining the mechanism by which the
extreme magnetic fields (B > 1015
G; Duncan & Thompson
1992; Thompson & Duncan 1993) present in magnetars are gen-
erated (Sect. 6). The first two examples identified appear to orig-
inate from very different progenitors, with SGR1806-20 evolv-
ing from a high-mass star (48+20
−8 M star; Bibby et al. 2008)1
and SGR1900+14 from a much lower mass object (∼17 ± 2 M ;
Clark et al. 2008; Davies et al. 2009). However, in neither case
has the cluster Main Sequence (MS) been identified, meaning
that progenitor masses have been inferred from post-MS objects
via comparison to evolutionary theory, while co-evality has also
yet to be demonstrated.
The third association is the magnetar CXO J164710.2-
455216 (henceforth J1647-45; Muno et al. 2006a) with the
young (∼5 Myr) massive (∼105
M ) cluster Westerlund 1 (Wd1;
Clark et al. 2005)2
. Unlike the previous examples, its co-evality
has been confirmed from studies of both its high- and low-
mass stellar cohorts (Negueruela et al. 2010; Kudryavtseva et al.
2012); thus we may safely infer the properties of the magne-
tar progenitor from the current stellar population. An absolute,
dynamically determined lower limit to the progenitor mass of
J1647-45 is provided by the 23.2+3.3
−3.0 M + 35.4+5.0
−4.6 M eclips-
ing binary Wd1-13 (Ritchie et al. 2010). Given that the cur-
rent binary period and evolutionary states of both components
of Wd1-13 require the lower mass component to have been the
initially more massive star, and adopting plausible assumptions
regarding pre-SN binary mass transfer (Petrovic et al. 2005), this
rises to ∼40 M . This in turn is consistent with masses inferred
from the spectroscopic classification of the high mass compo-
nent of Wd1 (e.g. Clark et al. 2005).
Given the expected downwards revision of stellar mass loss
rates due to wind clumping (Fullerton et al. 2006; Mokiem et al.
2007) the production of a NS from a >40 M progenitor appears
difficult. However, several theoretical studies suggest that binary
driven mass loss can yield such an outcome, even for very mas-
sive (∼60 M ) progenitors (e.g. Brown et al. 2001; Fryer et al.
2002; Yoon et al. 2010). While no stellar counterpart is visible at
the location of the magnetar (Muno et al. 2006a) such an absence
could plausibly be explained by the disruption of a putative bi-
nary at SN. If this were correct, one would expect the companion
to have a lower velocity than the magnetar and hence also remain
1
The association of 1E 1048.1-5937 with a stellar wind bubble also
points to a high-mass (∼30−40 M ) progenitor (Gaensler et al. 2005).
2
We also highlight the recent detection of a transient magnetar in the
vicinity of the Galactic Centre cluster (Mori et al. 2013). However, as
highlighted by these authors, two potential progenitor populations exist
in this region, complicating the assignment of a unique progenitor mass
for SGR J1745-29.
within Wd1. Therefore, the presence of the pre-SN companion
is a clear observational prediction of this hypothesis and in this
paper we describe the identification and analysis of a potential
candidate.
2. Data reduction and presentation
2.1. Radial velocity survey
An obvious prediction for a putative pre-SN companion to the
magnetar is that it should have acquired an anomalous velocity
with respect to the cluster as a result of the SN, i.e. it should be
a “runaway” star (Blaauw 1961).
Various authors have attempted to determine the mean sys-
temic velocity of Wd1 via two distinct methodologies. The first
employs observations of neutral H i and molecular material in
the vicinity of Wd1 with Kothes & Dougherty (2007) associat-
ing Wd1 with the Scutum-Crux arm (vsys ∼ −55 ± 3 km s−1
)
and Luna et al. (2009) with the Norma arm (vsys ∼ −90 kms−1
).
However, by their nature they rely on the additional assumption
of an association of kinematic and/or morphological features of
the interstellar medium with Wd 1 and do not directly sample
the velocities of the constituent stars (and hence do not yield a
velocity dispersion).
Three additional studies have attempted to measure the
velocities of individual cluster members and hence the clus-
ter systemic velocity and velocity dispersion. Mengel &
Tacconi-Garmann (2009) employ single epoch observations of
3 red supergiants (RSGs), 5 yellow hypergiants (YHGs) and
the supergiant B[e] star Wd1-9 to determine vsys ∼ −53.0 ±
9.2 km s−1
, while Cottaar et al. (2012) utilise 3 epochs of ob-
servations of the luminous blue variable (LBV) Wd1-243 and
six YHGs, of which 5 are in common with the previous study,
to estimate a velocity dispersion of ∼2.1+3.3
−2.1 km s−1
(but no sys-
temic velocity determination). However, both studies are ham-
pered by small sample sizes, which comprise stars which are
known pulsators and hence radial velocity (RV) variables (cf.
Clark et al. 2010), potentially leading to significantly biased
RV determinations. Finally Koumpia & Bonanos (2007) make
multiple observations of four eclipsing binaries within Wd1 to
determine their orbital parameters, from which mean values of
vsys ∼ −40 ± 6 km s−1
are found (or vsys ∼ −45 ± 14 km s−1
depending on the assumptions made regarding the twin compo-
nents of Wd1-13).
Between 2008-9 we undertook a multi-epoch RV survey of
Wd1, utilising ESO VLT/FLAMES (Pasquini et al. 2002), with
the primary goal of constraining the properties of the OB star
binary population, but which also permits us to provide a sig-
nificantly more robust estimate of its bulk kinematic proper-
ties (Clark et al., in prep.). Full details of target selection and
data acquisition and reduction may be found in Ritchie et al.
(2009a). Subsequently, in 2011 we extended this to include the
Wolf-Rayet (WR) population (Ritchie et al., in prep.), which
also permited the observation of additional OB stars in the spare
fibres. Two other configurations were employed encompassing
∼20 new stars, with observations made in service mode on 2011
April 17, May 20 and 22 and June 24 with an identical instru-
mental setup to previous observations3
.
Given the breadth of the emission lines in the Wolf-Rayets,
these were excluded from further analysis, as were
the pulsationally-prone YHGs and the LBV Wd1-243
3
The GIRAFFE spectrograph operated in MEDUSA mode (HR21
setup), yielding a spectral resolution of ∼16 200 between 8484−9001 Å.
Article number, page 2 of 17
3. J. S. Clark et al.: A VLT/FLAMES survey for massive binaries in Westerlund 1. IV.
(Clark et al. 2010, noting that no blue hypergiants (BHGs)
or RSGs were observed). Of the remainder, RVs were de-
termined via Gaussian fits to the line cores of the Paschen
series (individually weighted by line strength). Previous model
atmosphere analysis of stars in such a temperature regime
indicated that significant wind contamination of the Paschen
series is only an issue for hypergiants (Clark et al. 2012),
giving us confidence in this approach. Unfortunately, the He i
photospheric transitions were too weak to be employed for such
an analysis for stars of spectral types earlier than B2 (which
form the majority of our remaining sample); we note that they
are also subject to broadening, which is not included in the
model-atmosphere code employed here for such high lying lines
(Hillier & Miller 1998, 1999)4
.
This analysis permitted the determination of the systemic ve-
locity of individual objects and hence the cluster as a whole.
In order to accomplish this, newly identified pulsators (in addi-
tion to the hypergiants) were excluded from further analysis, as
were candidate binaries detected via reflex motion but for which
orbital solutions could not be determined and those stars with
3 or fewer epochs of observations. This left a total of 61 stars
from which we find vsys ∼ −42.5 ± 4.6 km s−1
; if we also ex-
clude all stars which show any indication of binarity in terms
of RV variability, spectral morphology, X-ray and/or radio prop-
erties (Clark et al. 2008; Dougherty et al. 2010; Ritchie et al.,
in prep.; Clark et al., in prep.) we are left with a reduced subset
of 39 stars that yields vsys ∼ −42.9 ± 4.6 km s−1
. We regard the
velocity dispersion as an upper limit given that our limited time-
base of observations will not be sensitive to long period binaries.
The unusual emission line BHG Wd1-5 was identified as
having a highly discrepant systemic velocity – RV ∼ −99.8 ±
1.3 km s−1
, or ∼−56.9 km s−1
relative to the cluster mean – sug-
gestive of a runaway nature. No epoch to epoch RV shifts in-
dicative of reflex binary motion were observed. Informed by the
results of quantitative analysis of Wd1-5, we return to a discus-
sion of its runaway nature in Sects. 3 and 5.
2.2. Dedicated observations
Upon the identification of Wd1-5 as a potential runaway we col-
lated existing data to constrain its nature. Photometric data were
taken from Clark et al. (2005) and Crowther et al. (2006a) and
are reproduced in Fig. 1. Our primary spectroscopic resource
were observations made on 2011 May 21 with VLT/FORS2
(Appenzeler et al. 1998). Grisms 1028z (7730−9480 Å), 1200 R
(5750−7310 Å) and 1400V (4560−5860 Å) were employed with
exposure times of 2 × 60 s, 2 × 600 s and 2 × 980 s respec-
tively. The longslit mode with a 0.3 slit was used for all obser-
vations, yielding a resolution of ∼7000. Data reduction was ac-
complished following the methodology described in Negueruela
et al. (2010). The resultant spectra from both this, our higher res-
olution VLT/FLAMES run (Ritchie et al. 2009a) and published
JHK-band observations (Crowther et al. 2006a) are presented in
Figs. 2−4; we note that low S/N as a result of interstellar redden-
ing precludes meaningful discussion of the spectrum shortwards
of ∼5000 Å.
4
The missing broadening mechanisms are relevent to the high mem-
bers of the HeI Paschen-like series (n → 3) in the I band. These mem-
bers approach hydrogen-like transitions and their theoretical profiles are
expected to depart from a pure Doppler profile towards a more Stark-
broadened one. Moreover, our current He i atom splits the L ≤ 3 states
only up to n = 7, and packs all L states into a single Singlet or Triplet
term for n > 7. Thus, populations of the high lying HeI levels involved
in the I band may not be accurately accounted for in our models.
Fig. 1. Comparison of the observed and synthetic spectral energy dis-
tributions of Wd1-5. Broadband photometry is given by the yellow di-
amonds, with the corresponding bandpasses given by the dashed green
lines. The observed and synthetic spectra are given by the black and
blue lines, respectively.
Wd1-5 shares a similar spectral morphology to Wd1-13 and
-44 (Figs. 2−4) and consequently was initially assigned a “hy-
brid” classification of early-B hypergiant/WNVLh (e.g. Clark
et al. 2005). Negueruela at al. (2010) subsequently amended this
to B0.5 Ia+
, primarily on the basis of the similarity of the I-band
spectrum to those of the B0.5 supergiants within the cluster; the
hypergiant classification being allocated due to the presence of
spectroscopic signatures of a high mass loss rate (e.g. strong
Hα emission). Note, however, that it is significantly fainter than
the cooler (B5-9) hypergiants such as Wd1-33, although com-
parable to other OB supergiants within Wd1 (Fig. 5). Bonanos
(2007) found Wd1-5 to be an aperiodic photometric variable
over short timescales but we find no evidence of secular pho-
tometric or spectroscopic changes over the past decade (Clark
et al. 2010). At other wavelengths Wd1-5 does not appear to
support a near-IR excess (characteristic of colliding wind bina-
ries containing a WC star; Crowther et al. 2006a), has a marginal
X-ray detection (Clark et al. 2008) and may be associated with a
weak, apparently thermal radio source (Dougherty et al. 2010).
Thus we find no observational evidence for a binary companion
via either direct or indirect diagnostics. In contrast, of the spec-
troscopically similar stars, Wd-13 is a short-period eclipsing bi-
nary (Ritchie et al. 2010) while recent spectroscopy of Wd1-44
suggests a similar conclusion (Ritchie et al., in prep.) and both
are rather hard and bright X-ray sources, presumbly due to the
presence of shocks in wind collision zones.
Finally we address whether Wd1-5 could be a chance su-
perposition with Wd1. Foreshadowing the following sections,
the reddening of Wd1-5 is fully consistent with the mean clus-
ter value (Negueruela et al. 2010). Moreover, both the 8620 Å
Diffuse Interstellar Band and the Phillips (2−0) C2 band lines
overlapping Pa-12 are identical to other B supergiants in the
cluster; furthermore the C2 lines in Wd1-5 also have radial ve-
locities comparable to the cluster mean suggesting the material
responsible for the absorption is the same in both cases. The
dereddened magnitudes of Wd1-5, the spectroscopically sim-
ilar stars Wd1-13 and -44 and the OB supergiant population
within Wd1 are likewise directly comparable. Indeed, the sole
example of an interloper to have been identified, the O9 Iab
star HD 151018 ∼2.4 arcmin to south of the nominal clus-
ter centre, is easily distinguished by its discrepant colours and
Article number, page 3 of 17
4. A&A proofs: manuscript no. aa21771-13
Wd1-5 + synthetic spectrum
Zeta Sco + BP Cru (B1 Ia+)
Wd1-5 + synthetic spectrum
Zeta Sco + BP Cru (B1 Ia+)
Wd1-44 (WN9h & ?)
Wd1-13 (WNL/B Ia+ & ?)
Fig. 2. Comparison of the observed (black, solid line) to synthetic (red,
dotted line) spectrum of Wd1-5. Illustrative spectra of selected, closely
related early-B hypergiants and WNVLh stars are also shown (with
BP Cru and Wd1-13 overplotted in dashed cyan and green lines, re-
spectively, to save space). Spectra of Wd1-13 and 44 were not available
in the 5600−6000 Å window, while data on ζ1
Sco and BP Cru were
from Clark et al. (2012) and Kaper et al. (2006). Both Wd1-13 and -44
are SB2 binaries, although a precise spectral classification of their sec-
ondaries is uncertain at this time.
Fig. 3. Continuation of Fig. 2 encompassing the I band. Please note the
difference in resolutions of the VLT/FORS2 and FLAMES data – the
latter plotted longwards of 8475 Å.
Wd1-5 + synthetic spectrum
Wd1-44 (WN9h & ?)
Wd1-5 + synthetic spectrum
Zeta Sco (B1 Ia+)
Wd1-44 (WN9h & ?)
Fig. 4. Continuation of Fig. 2 encompassing the near-IR window (spec-
tra from Crowther et al. 2006a); the spectra are of lower resolution than
other wavebands (∼1000 versus >7000).
magnitude. Regarding kinematic evidence, we note that under
the assumption that Wd1-5 is an interloping field star its ra-
dial velocity would place it in an inter-arm void between the
Scutum-Crux and Norma arms (Kothes & Dougherty 2007); a
less intuitive scenario than the assumption it is a runaway from
Wd1. Finally, our quantitative modelling of Wd1-5 (Sect. 3) in-
dicates an anomalous pattern of chemical abudances, which is
only replicated in two other Galactic stars and that argues for
a specific binary evolutionary pathway consistent with cluster
membership (Sect. 4). Given the rarity of such objects, the simi-
larity of Wd1-5 to other cluster members in terms of magnitude
and reddening and the explicability of the properties of Wd1-5
in terms of binary evolution as a cluster member, we consider it
highly unlikely that it is a distant interloper and hence continue
under the hypothesis that it is a runaway star.
3. Stellar properties
3.1. Quantitative modelling
In order to further understand the nature and evolutionary history
of Wd1-5 we undertook a quantitative non-LTE model atmo-
sphere analysis of it with the CMFGEN code (Hillier & Miller
1998, 1999), utilising a spectroscopic and photometric dataset
Article number, page 4 of 17
5. J. S. Clark et al.: A VLT/FLAMES survey for massive binaries in Westerlund 1. IV.
10000150002000025000300003500040000
Teff
(K)
-9
-8
-7
-6
-5
-4
-3
MV
Fig. 5. Semi-empirical HR diagram for Wd1-5 (diamond) and the pop-
ulation of bright OB supergiants (circles) and hypergiants (Wd1-33 and
42; diamonds) within Wd1 (following Negueruela et al. 2010). The
solid lines represent the Geneva isochrones (Meynet & Maeder 2000)
without rotation for log t = 6.7 (5 Myr; top, blue) and log t = 6.8
(6.3 Myr; bottom, brown). The dash-dotted line is the log t = 6.7
isochrone for high initial rotational velocity. We note that no correction
has been made for binary contamination in the sample, which might be
expected to contribute to the scatter in absolute magnitudes. Errorbars
for Wd1-5 are those quoted in the text, while representative errorbars
for the remaining stars are presented in the lower right corner of the
plot. These represent typical uncertainties associated with an incorrect
assignment of spectral type by ±0.5 subtypes (in Teff), and 0.5 mag in
MV to take into account the absolute magnitude and bolometric correc-
tion calibrations (as the difference in MV is negligible between spectral
types at Ia luminosity class).
assembled from the above sources. Given the spectroscopic sim-
ilarity to galactic BHGs such as ζ1
Sco and BP Cru (Figs. 2−4)
we adopted the methodology employed by Clark et al. (2012).
One key result of our analysis is the close proximity of
Wd1-5 to the Eddington limit, with Γ ∼ 0.9 being adopted
as a conservative lower limit (where Γe ∼ 0.52 is the con-
tribution from electron scattering). Moreover, since the star
displays a strong wind, the stellar radius moves towards the
wind/photosphere transition region, R(τ = 2/3) ∼ 0.1vsound.
These findings imply a sensitivity of the models to the
Teff vs. log g pairings and hence particular care was taken in
the determination of both parameters.
3.1.1. Temperature determination
To estimate the effective temperature of Wd1-5 and hence con-
strain the ionisation structure, we made use of several ionisa-
tion equilibria, utilizing both Si iv/Si iii and C iii/C ii line ra-
tios simultaneously. The proximity of Wd1-5 to the Eddington
limit, together with influence of the wind/photosphere transition
region translates into a relatively large uncertainty in our de-
rived value at Teff = 21 900+1500
−1200 K (cf. comparable modelling
of the early BHGs Cyg OB2 #12, ζ1
Sco and HD 190603; Clark
et al. 2012). This process is shown in detail in Fig. 6, where
we display the reaction of the key lines to changes in Teff im-
plied by our estimated uncertainties. In this parameter domain,
we found that Si iii 5740 Å is extremely sensitive to changes
in temperature, while the Si iv 8957 Å line places a firm lower
limit. Furthermore, for the high Teff value (Teff = 23 400 K) both
the Si iv 6667 Å and 6701 Å transitions should be strongly in
emission, but are not present in our data. Similar behaviour is
observed in the C iii/C ii line ratios (see Fig. 6). A high tempera-
ture makes the C ii 8683Å line vanish and produces excessively
strong C iii 5695 Å and 9718 Å emission. Likewise, several
C iii lines, not detected in our spectra, appear in emission (e.g.
5826 Å, 6727 Å and 6515 Å). While no N iii and He ii lines are
detected, N iii/N ii and He ii/He i equilibria may be used as well
(see Fig. 6). Many N ii lines react strongly to changes in Teff,
while several N iii lines (not detected) appear in emission for
the high temperature models (e.g. 6395 Å, 8485 Å and 8572 Å).
The He ii 10124 Å diagnostic line suffers from poor S/N ratio
and spectral resolution; however, from Fig. 6, the high Teff value
is clearly excluded.
3.1.2. Surface gravity determination
To estimate log g we made use of the Paschen lines in the high-
resolution and signal to noise (S/N) I-band spectrum, as they
provide the best constraints for the surface gravity, especially
the run of the line overlap among the higher members (see Clark
et al. 2012; Fig. 3). The high Paschen lines indeed provide reli-
able estimates of the stellar surface gravity, as is apparent from
Fig. 7, where our current best model together with the upper and
lower log g values – log g = 2.33+0.17
−0.10 – are compared with the
observations. We highlight that low gravity values push the star
to the Eddington limit and modify the upper photospheric and
transition regions with considerable impact on the lines forming
there (lower panels of Fig. 7). Specifically, the lack of emission
in N ii, Al iii, Si iii and He ii all exclude a lower surface gravity.
3.1.3. Radius and mass determination
Once the effective temperature and gravity were obtained, and
assuming a distance of d ∼ 5.0 kpc to Westerlund 1, we pro-
ceeded to fit the observed optical and near-IR spectral energy
distribution (SED) of Wd1-5 (see Fig. 1) and hence derived
the reddening, stellar radius and, therefore, the stellar luminos-
ity. We used the extinction law from Cardelli (1989). Several
tests and comparisons with other laws were carried out, and
very good agreement was also found with the latest extinc-
tion law from CHORIZOS (Maiz-Apellaniz, priv. comm.). We
found E(B − V) = 4.54 and a reddening parameter RV = 2.35,
corresponding to AV = 10.66. Such a finding is fully consis-
tent with the mean value found for OB supergiants within Wd1
(E(B − V) = 4.2 ± 0.4 with a 1σ standard deviation; Negueruela
et al. 2010).
Figure 1 also displays the excellent agreement between our
model and the near-IR flux calibrated spectra obtained with
SOFI, together with the filters used in the photometry (green-
dashed lines). From these values we obtained a stellar radius of
34+5.0
−4.4 R , corresponding to a spectroscopic mass of M = 9+4
−2 M
and a final luminosity of 2.39+0.78
−0.56 × 105
L . We note that the er-
ror in the luminosity is dominated by the uncertainty in the red-
dening determination. Finally, while we strongly favour a dis-
tance to Wd1 of ≥5 kpc (Negueruela et al. 2010), a value of
4 kpc (the lower end of literature values) would lead to a re-
vision in radius by a factor of (d/5 kpc) ∼ 0.8, luminosity by
(d/5 kpc)1.72
∼ 0.68 and mass by (d/5 kpc)2.0
∼ 0.64.
3.1.4. Determination of wind properties
Although the moderate reddening affecting Wd1-5 prevents us
from securing UV observations from which we might derive
firm v∞ estimates, the dense stellar wind provides alternative v∞
Article number, page 5 of 17
6. A&A proofs: manuscript no. aa21771-13
Fig. 6. Plot showing the determination of Teff for Wd1-5. The best-fit synthetic spectrum is given in red, with spectra utilising the upper and lower
error-bounds given in Table 1 presented in blue and green respectively.
diagnostic lines such as Hα, He i 10830 Å and He i 20581 Å.
Since the latter two were observed at relatively low (∼1000)
resolution and moderate (∼50) S/N, we basically rely on Hα as
primary diagnostic to derive v∞ and β, the parameter controlling
the shape of the velocity field. We obtain v∞ = 430+20
−40 km s−1
and
β = 2.5+0.5
−0.25. The uncertainties are mainly driven by the moder-
ate S/N at Hα due to the reddening.
The main observational constraints which set the mass-loss
rate and clumping are the optical Hα, He i 5875 Å, He i 6678 Å
and He i 7065 Å lines and the near-IR Paβ, Brγ, He i 10830 Å
and He i 20581 Å emission lines. As shown by Najarro et al.
(1997, 2006) the latter is extremely sensitive to modelling as-
sumptions and atomic data and is less reliable as an ˙M di-
agnostic; nevertheless, we are still able to reproduce this fea-
ture in our synthetic spectrum (Fig. 4). Thus, we were able to
derive a mass-loss rate of ˙M = 2.16+0.06
−0.07 × 10−6
M yr−1
(see
Table 1) and a clumping factor of fcl = 0.25+0.75
−0.15. The latter
is essentially set by the electron scattering wings of Hα and
its error estimates are dominated by the uncertainties in Teff
and log g together with the error in the normalisation of the
spectra as a result of the S/N in the line. Note that the mass
loss scales as (d/5 kpc)−1.43
. We may compare the unclumped
˙M = (2.16/0.250.5
)×10−6
M yr−1
= 4.32 ×10−6
M yr−1
to the
theoretically predicted one (Vink et al. 2000). For Wd1-5 stel-
lar parameters we obtain ˙M = 3.0 × 10−5
M yr−1
, a factor of 7
above our value. However, if we just increase our derived mass
from 9 to 10.5 M (a change of 0.07 in log g), the theoretically
predicted ˙M drops to ˙M = 7.1 × 10−6
M yr−1
(i.e. just a factor
of 1.6 above our value). Thus, we conclude that Wd1-5 may lie
in the bi-stability jump region.
Article number, page 6 of 17
7. J. S. Clark et al.: A VLT/FLAMES survey for massive binaries in Westerlund 1. IV.
Table 1. Model parameters for Wd1-5.
log (L∗) R∗ Teff
˙M v∞ β fcl log g M∗ H/He N/N C/C O/O
(L ) (R ) (kK) (10−6
M yr−1
) (km s−1
) (M )
5.38+0.12
−0.12 34.0+5.0
−4.4 21.9+1.5
−1.2 2.16+0.06
−0.07 430+20
−40 2.50+0.50
−0.25 0.25+0.75
−0.15 2.33+0.17
−0.10 9.0+4.0
−2.0 4.0+2.7
−1.1 9+0.15
−0.15 1.40+0.15
−0.15 0.3+0.2
−0.3
Notes. We adopt a distance of ∼5 kpc (Negueruela et al. 2010) and with AV ∼ 10.66 (Sect. 3) determine that MV = −6.63 (implying a bolometric
correction of −2.1 mag). We note that R∗ corresponds to R(τRoss = 2/3). The H/He ratio is given by number and other abundances are relative to
solar values from Anders & Grevesse (1989); if we use the values from Asplund et al. (2006) as a reference, the derived ratios need to be scaled by
1.38, 1.537 and 1.86 for C, N and O respectively. Finally, our derived H/He abundance corresponds to a surface helium mass fraction, Ys = 0.49.
Fig. 7. Determination of log g for Wd1-5. The best-fit synthetic spec-
trum is given in red, with spectra utilising the upper and lower error-
bounds in Table 1 presented in blue and green respectively.
3.1.5. Abundance determinations
As the derived abundances play a crucial role in our conclu-
sions regarding the nature of Wd1-5, we describe their determi-
nation here. In all cases the uncertainties in the abundances take
into account the uncertainties in Teff and log g – i.e. they are
estimated considering possible combinations of Teff and log g
within the accepted range. The helium abundance is set by the
relative strength of the H i and He i emission lines. We derive
He/H = 0.25 by number (49% by mass) with 0.15 and 0.35 as
lower and upper limits.
A relatively enhanced carbon abundance (∼1.4× solar) is
obtained from the C ii 6578−6583 Å, C ii 7231−7236 Å and
C ii 8683−8697 Å lines. The C iii 9717 Å and the C ii 9904 Å
lines present in the low resolution noisy J band spectrum are
used as a consistency check. Figure 8 illustrates the sensitiv-
ity of the available carbon lines to changes in the abundance.
As with Figs. 6 and 7, models labeled as C+/− correspond to
Fig. 8. Determination of the carbon abundance for Wd1-5. The best-fit
synthetic spectrum is given in red, with spectra utilising the upper and
lower error-bounds given in Table 1 presented in blue and green respec-
tively. Additionally, we provide spectra produced using more extreme,
observationally unsupported upper and lower error-bounds (±0.35 dex;
orange and dark green respectively).
changes in ±0.15 dex (our estimated uncertainty), while those
labeled as C++/− – have variations of ±0.35 dex in the car-
bon abundance. The C iii line at 5695.9 Å is blended with the
Al iii 5696.6 Å transition, while the C iii 8500 Å line is located
within the blue absorption wing of Pa-16, and therefore both are
used as secondary abundance diagnostics. The same weighting
is given to the C ii 6578−6583 Å lines in the red wing of Hα, as
they are polluted by the electron scattering emission wing and
to C ii 8696.7 Å, as it is blended with N ii 8697.8 Å. Following
from Fig. 8 we therefore estimate an uncertainty of ∼0.15 dex for
our derived carbon abundance, confirming the abnormally high
value for the present evolutionary stage of the object. We return
to this in Sect. 3.2.
Article number, page 7 of 17
8. A&A proofs: manuscript no. aa21771-13
The nitrogen abundance is basically constrained from the
large number of N ii lines throughout the full spectral range
covered by our observations. We find a significant enhancement
(∼9× solar) consistent with moderate CNO processing. Again a
value of 0.15 dex should be regarded as a safe estimate for the er-
ror in the N abundance. Finally, to derive the oxygen abundance
we make use of the weakly detected O ii emission lines at 6641
and 6721 Å and the O ii absorption lines at 8564 and 8687 Å
and obtain a value corresponding to ∼0.3 solar. In this case, the
uncertainty on the derived abundance is much higher and we ob-
tain 0.2 and 0.3 dex respectively for the higher and lower error
estimates.
3.1.6. Additional implications
The close proximity of Wd1-5 to the Eddington limit implies
that even moderate rotation may place Wd1-5 close to critical, or
breakup velocity (vcrit; Langer 1998b; Maeder & Meynet 2000).
Utilising the stellar parameters from Table 1 and assuming Γ ∼
0.9 we may estimate vcrit ∼ 80 km−1
. We obtain an upper limit
to the projected rotational velocity of vrot ∼ 60 km s−1
from the
profile of the narrow C ii 8683 Å photospheric emission line,
which would be consistent with vcrit for inclinations, i < 49o
;
unfortunately we currently have no constraints on the inclination
of Wd1-5. In this regard we note that the spectroscopic mass
given in Table 1, derived from logg has consequently not been
corrected for rotation and hence should properly be regarded as a
lower limit; of importance for comparison to the stellar structure
scenarios presented for Wd1-5 in Sect. 3.3.
Finally, an important finding from this analysis was that
cross correlation of the synthetic to the high-resolution spec-
trum (∼8484−9000 Å) resulted in a significantly lower RV shift
of ∼−68 ± 4 km s−1
relative to rest-wavelength when compared
to that determined from Gaussian line-core fitting (∼−99.8 ±
1.3 km s−1
; Sect. 2.1). We suspect this is due to the presence
of excess emission in the red flanks of the Paschen series pho-
tospheric lines (due to heavy mass loss), which systematically
drives the line centres to shorter wavelengths. Indeed, cross cor-
relation of the spectrum of Wd1-5 to that of a normal super-
giant (the BI.5 Ia star Wd1-8b) and a synthetic spectrum of a
supergiant of comparable temperature but of higher surface grav-
ity and weaker wind resulted in an RV offset relative to rest-
wavelength of over −90 km s−1
in both cases. We conclude that
the true RV shift of Wd1-5 relative to the cluster mean is smaller
than the initial determination of ∼56.9 km s−1
, but in the absence
of an observational template, its determination is dependant on
the model parameters adopted for the generation of the synthetic
spectrum. We therefore adopt a conservative lower limit to the
offset from the cluster systemic velocity of >25.1 km s−1
; dis-
crepant at the ∼5.5σ level with the mean velocity dispersion of
stars within Wd1.
Following from the initial discussion regarding the identifi-
cation of runaways (Blaauw et al. 1961), various studies have
refined the criterion for runaway status for 1-dimensional ra-
dial velocity data (Vitrichenko et al. 1965; Cruz-Gonzalez et al.
1974; Tetzlaff et al. 2011). These have resulted in a downwards
revision in the absolute radial velocity threshold to 25 km s−1
and also the adoption of a more generic threshold of v > 3σ,
where σ is the 1-dimensional mean velocity dispersion of low-
velocity stars. Wd1-5 appears to satisfy both criteria, although
we note that the former is defined via the motion of field stars
within 3 kpc of the Sun (Tetzlaff et al. 2011) and hence there is
no a priori reason for this to match the mean velocity dispersion
of stars within Wd1.
3.2. Comparison to related objects
In order to place Wd1-5 into an astrophysical context it is in-
structive to compare its physical properties to those of other
galactic BSGs, BHGs, LBVs and Ofpe/WNL (=WN9-11h) stars
and related objects. Quantitative analyses of such stars have
been undertaken by a number of authors and are summarised in
Table A.1. The temperature and radius (and hence luminosity)
of Wd1-5 are directly comparable to those of early spectral-type
field BSGs; conversely, both BHGs and LBVs appear signifi-
cantly more physically extended than Wd1-5, which also lies at
the high temperature extreme found for these stars. Ofpe/WNLh
stars span a wide range of temperatures and luminosities – pre-
sumably corresponding to a spread in initial masses – and the
temperature and radius of Wd1-5 appears comparable to the least
luminous examples, subject to the large uncertainties in these pa-
rameters (Table A.1).
Systematic quantitative analysis has yet to be undertaken
for the wider population of massive evolved stars within Wd1.
Nevertheless, following Negueruela et al. (2010) we may con-
struct a semi-empirical HR diagram for Wd1 (Fig. 5), which
demonstrates the close correspondance between Wd1-5 and the
cluster OB supergiants, noting that we might expect all these ob-
jects to be of similar mass given the co-evality of the population.
Conversely, the wind properties of Wd1-5 do not closely
resemble those of either BSGs or Ofpe/WNLh stars, despite sim-
ilarities in temperature and luminosity. With regard to the for-
mer, the wind terminal velocity of Wd1-5 is significantly lower
than found for BSGs of comparable spectral type (Fig. 9). In
comparison to Ofpe/WNLh stars, both the terminal velocity and
mass loss rate of Wd1-5 are at the extreme lower bounds expe-
rienced by such stars. A similar discrepancy is found in compar-
ison to the LBVs, which drive slower winds with higher mass
loss rates than Wd1-5 (Fig. 9). Indeed, as expected from their
spectroscopic similarity, Wd1-5 most closely resembles other
BHGs in terms of wind properties, despite being significantly
more physically compact than such stars (Table A.1). Finally,
while we may not readily determine the surface gravity of LBVs
and Ofpe/WNLh stars due to the lack of suitable spectroscopic
diagnostics, the surface gravity of Wd1-5 appears lower than any
of the 20 O9-B0.7 Ia stars sampled in Table A.1, but once again
consistent with those found for BHGs.
Therefore, in terms of the combination of both stellar (tem-
perature, radius and surface gravity) and wind (mass loss rate,
terminal velocity) properties we are unable to identify a compa-
rable star to Wd1-5, which resembles an OB supergiant in terms
of radius but a BHG in terms of surface gravity and wind proper-
ties. We return to the implications of these findings in Sect. 3.3.
Lastly we turn to chemical abundances. Both Crowther et al.
(2006b) and Searle et al. (2008) assume moderate H-depletion
(H/He ∼ 4.0) for Galactic BSGs, and find N-enrichment and
C- and O-depletion, consistent with the products of CNO burn-
ing. Clark et al. (2012) provide a detailed analysis of the abun-
dance patterns of early-B hypergiants. As with BSGs, the three
stars studied – Cyg OB2 #12, ζ1
Sco and HD 190603 – exhibit
the products of CNO burning, with carbon being very depleted
(C/C ∼ 0.21 ± 0.2, 0.33 ± 0.2 and 0.33 ± 0.2 respectively).
This differs from the super-solar abundances we infer for Wd1-5
(C/C ∼ 1.4 ± 0.15) at >5σ level. A similar pattern is also ob-
served for those LBVs for which similar analyses have been
performed – C/C ∼ 0.11 ± 0.03, 0.31 and trace for AG Car,
Article number, page 8 of 17
9. J. S. Clark et al.: A VLT/FLAMES survey for massive binaries in Westerlund 1. IV.
Fig. 9. Comparison of the wind properties of Wd1-5 to field BHGs,
BSGs (both plotted according to spectral type, with BHGs given by
solid symbols), LBVs and WNLh (=Ofpe/WNL) stars. The data and
references employed are summarised in Table A.1. Unfortunately, given
the diverse sources employed to construct this figure, it is not possible
to plot representative errors for all the objects. In all cases clumping
corrected mass loss rates are used to enable direct comparison between
individual objects. We estimate log ˙M ∼ −5.36+0.3
−0.2 M yr−1
for Wd1-5
since the errors on the clumping factor in Table 1 are conservative and
once this parameter is set the mass loss rate is also determined to a high
precision.
P Cygni and Wd1-243 respectively (Groh et al. 2009a; Najarro
2001; Ritchie et al. 2009a).
This behaviour (He and N enhancement and C and O de-
peletion) is also predicted for single stars by current evolution-
ary codes (Ekström et al. 2012). Stars of comparable luminosity
to Wd1-5 are expected to encounter the BHG phase either side
of a red-loop across the HR diagram; prior to this they are ex-
pected to exhibit moderately sub-solar (C/C ∼ 0.2−0.5) carbon
abundances and after this passage they are extremely depleted
(C/C ∼ 0.02−0.03) due to mass-stripping as a RSG (Jose Groh,
priv. comm.).
Therefore, the C-abundance of Wd1-5 is unexpected on both
theoretical and observational grounds. We highlight that even
in the absence of our quantitative analysis, the evidence for a
high C-abundance is compelling; simple comparison of the op-
tical spectra of Wd1-5 to the two other cluster BHG/WNLh
stars – Wd1-13 and -44 – reveals the anomalous strength of
the C ii 7231 Å and 7236 Å lines in Wd1-5, with these lines
being essentially absent in its spectroscopic twins (Fig. 2). All
three stars are expected to share the same natal metalicity and
evolutionary pathway (since Wd-1 appears essentially co-eval;
Negeuruela et al. 2010; Kudryavtseva et al. 2012) and so it is
difficult to account for this observational finding unless Wd1-5
has a greater C-abundance than these objects.
To date, the sole exceptions to these abundance patterns are
the B1 Ia+
hypergiant BP Cru (=Wra977) and the O6.5Iaf+
star HD 153919; the mass donors in the high mass X-ray bi-
naries GX301-2 and 4U1700-37 respectively. In addition to
the expected He- and N-enrichment, both show significant
C-enrichment over CNO equilibrium values (C/C ∼ 2 and 1 re-
spectively; Kaper et al. 2006; Clark et al. 2002) in an analagous
manner to Wd1-5; the implications of this finding are discussed
below.
3.3. Internal structure and evolutionary state
Given the discrepancies in the properties of Wd1-5 when com-
pared to other massive evolved stars we may also employ our
quantitative analysis to try to determine the internal structure –
and hence evolutionary state – of Wd1-5 via comparison to theo-
retical predictions. An immediate difficulty is encountered when
attempting to reconcile the high intrinsic luminosity with the
spectroscopic mass estimate, in the sense that it appears signif-
icantly overluminous for a star of normal composition. If Wd-1
were found at a lower distance than the 5 kpc adopted here this
discrepancy becomes worse in the sense that stellar mass de-
creases more rapidly as a function of distance than luminosity
does. Thus, while the absolute masses of the models described
below would be reduced, our qualitative conclusions would re-
main entirely unchanged.
In order to replicate our modelling results we investigated
three different scenarios to overcome this limitation:
Scenario (i): Wd1-5 is chemically homogeneous.From Eq. (11)
of Graefener et al. (2011) we derive M = 32.5 M , leading
to log g = 2.79, Γe = 0.168, and an escape velocity, vesc =
520 km s−1
.
Scenario (ii): Wd1-5 is core-helium burning and possesses a
shallow H-envelope. From Eq. (18) of Langer (1989a) we find
M = 13.7 M , resulting in log g = 2.41, Γe = 0.40 and
vesc = 290 km s−1
.
Scenario (iii): consisting of a hybrid of the above, whereby
Wd1-5 has burnt hydrogen in the core to the stage of Xcore = 0.1.
and has little envelope mass. Then we may again employ
Eq. (11) of Graefener et al. (2011) to determine M = 18.6 M ,
log g = 2.54, Γe = 0.30, and vesc = 360 km s−1
.
Scenario (i) appears excluded on the basis of pronounced
discrepancies between the predicted and observed values of log g
(and hence stellar mass), wind velocity (vesc versus v∞) and Γe.
However, scenarios (ii) and (iii) – that Wd1-5 is essentially
an He-star with relatively shallow H-envelope – appear more
acceptable in terms of these properties. In such a picture v∞
exceeds the predicted vesc, as might be expected and Γe ap-
proaches the value of 0.5 determined via modelling, noting that
for Galactic metallicities, the Eddington factor based on the full
Rosseland mean opacity in the atmosphere of hot massive stars
is larger by ∼0.3 compared to the case when only electron scat-
tering is considered as an opacity source. Likewise, the discrep-
ancy between predicted and spectroscopic masses (Table 1) may
be ameliorated by the inclusion of the (uncertain) correction due
to the effects of stellar rotation, given the proximity of Wd1-5 to
the Eddington limit (Sect. 3.1).
Nevertheless, if Wd1-5 were born with a mass at the main
sequence turn-off of Wd1 (∼40 M ; Ritchie et al. 2010), we
would find it difficult to account simultaneously for the lumi-
nosity of Wd1-5 and the observed, He-rich surface chemistry
under the assumption of mass loss driven by stellar winds (Brott
et al. 2011). Moreover, we would not expected it to achieve such
Article number, page 9 of 17
10. A&A proofs: manuscript no. aa21771-13
an apparently low mass while retaining such a high hydrogen
content. Conversely, while the current mass would be explica-
ble if Wd1-5 was born with a lower initial mass (∼20 M ), we
would not expect such a star to have evolved from the main se-
quence given the current age of Wd1 (Negueruela et al. 2010).
Furthermore, the requirement for stellar winds to yield the ob-
served surface chemistry would be even more implausible.
As well as He-enrichment, Wd1-5 is also N- and, critically,
C-enriched. Unlike the He- and N-enrichment, which in princi-
ple might be understood as the result of products of the CNO
cycle being transported to the surface via rotational mixing, the
C-enhancement over CNO equilibrium values cannot arise from
such a mechanism, since any carbon produced by He-burning
would have to pass through overlying H-burning layers prior to
reaching the surface where it would be converted into nitrogen
(e.g. Clark et al. 2002). Consequently, this cannot be the result
of the evolution of a single star and must be the result of mass-
transfer from a C-rich bianry companion.
Therefore, in order to reconcile the luminosity, mass and sur-
face composition, we are forced to conclude that Wd1-5 must
have been subject to an additional source of mass-loss, which
we suppose was binary-induced, since we also must infer (sub-
sequent) mass-transfer from a putative binary companion.
4. The nature and formation of Wd1-5
4.1. A pre-SN binary evolutionary pathway
At first glance, the dual requirements of binary driven mass loss
and gain required to explain the abundance pattern of Wd1-5 ap-
pear contradictory. Nevertheless we believe they may both be ac-
comodated in a single evolutionary scheme, which we describe
here. We first consider the mass loss mechanism responsible for
the removal of the majority of the H-mantle of Wd1-5. Case B
and case C mass transfer would have quickly yielded unaccept-
ably high surface He-abundances (e.g. Ys = 0.8 in 104
yr for
case C), which would have subsequently increased very quickly,
resulting in a low likelihood of catching Wd1-5 in its current
state. Conversely, while case A mass transfer also produces stars
with He-abundances comparable to that of Wd1-5, crucially the
state persists for a significant fraction of the stellar lifetime
(∼106
yr; Fig. 10, following Wellstein & Langer 1999); we there-
fore conclude that Wd1-5 likely evolved via case A evolution.
The requirement for the mass-gainer to both avoid merger
and explode first to unbind Wd1-5 places important constraints
on the pre-SN system. Assuming a ∼41 M primary (Ritchie
et al. 2010), a rather massive companion is required to avoid
merger during the binary interaction, but even in a Minit ∼
41 M + ∼ 30 M system – as suggested for the eclipsing
BHG/WNLh+O supergiant binary Wd1-13 (Ritchie et al. 2010)
– we would still expect the initial primary and mass donor to
undergo SN first, despite the companion accreting significant
quantities of matter. This behaviour results from the fact that the
evolution of the mass-gainer is rather sensitive to the assumed
timescale for semiconvective mixing; while the mass-gainer at-
tempts to increase its convective core mass in response to the ac-
cretion of material, this rejuvenation process is hindered by the
chemical barrier imposed by the presence of (accreted) H-rich
matter on top of He-rich material (see Braun & Langer 1995).
However, if the initial mass ratio of the putative binary sys-
tem instead approached unity, a reversal of the supernova order
would be expected (Wellstein et al. 2001), while rejuvenation of
the mass gainer would still not occur. We note that such a mass
ratio would not be expected to affect the case A evolution of
Fig. 10. Evolution of the helium abundance of a 41 M primary in an
initial 6 d orbital period massive binary under the case A evolution-
ary scenario described in Sect. 4.1, where mass loss and He-enrichment
is driven by both stellar wind and binary induced mass transfer (solid
red line). The dashed line represents our prediction of the evolution of
Wd1-5 in a post-common envelope phase, whereby only stellar wind
mass loss is present; for completeness the dotted line represents the
continuation of the specific evolutionary model of Petrovic et al. (2005)
if a common envelope had not formed. Finally, a brief episode of wind-
driven reverse mass transfer during the pre-SN WC phase of the com-
panion star accounts for the anomalous C-rich chemistry of Wd1-5.
the mass donor, which would still evolve into the same He-rich
overluminous state that we currently find Wd1-5 to be in.
So, we might suppose an hypothetical binary initially com-
prising two ∼41 M + 35 M stars – where the more massive
component represents Wd1-5 – in a compact (initial orbital pe-
riod Pinit < ∼8 d) configuration in order to permit case A mass
transfer. Following the approach of Petrovic et al. (2005), such
an evolutionary pathway would lead to the 41 M primary los-
ing ∼20 M by t ∼ 3.5 Myr during fast case A mass transfer,
corresponding to the fast rise in Ys at that time (e.g. system #4
of Petrovic et al. 2005; Fig. 10). The original secondary accretes
a sizable fraction of this material and becomes a ∼55 M star.
Because it is so luminous as a result of this process and as it
does not rejuvenate, it finishes core H-burning well before the
donor star does (i.e. before t = 4.25 Myr). During the remaining
core H-burning stage of the mass-gainer, the system is of Algol
type, meaning that the mass-donor (corresponding to Wd1-5)
fills its Roche lobe and undergoes slow case A mass transfer.
During that phase, the surface helium abundance subsequently
rises from about Ys = 0.34 to a value of up to Ys = 0.47; in
excellent agreement to that found for Wd1-5 (Sect. 3.1).
Petrovic et al. (2005) showed that the mass-gainer is signif-
icantly spun-up by such an accretion process. In their 56 M +
33 M system, the mass-gainer subsequently spins down again
after accretion due to its long remaining core hydrogen burning
life time after rejuvenation. In our case, with a mass ratio close
to 1 and without rejuvenation, the mass-gainer is not likely to
have the time to do so, but will instead keep a high specific an-
gular momentum until core hydrogen exhaustion.
When the mass-gainer finishes core H-burning, the quantita-
tive predictions of the model end. The mass-gainer will certainly
Article number, page 10 of 17
11. J. S. Clark et al.: A VLT/FLAMES survey for massive binaries in Westerlund 1. IV.
expand after core H-exhaustion and, with an orbital period in
the ∼10−20 day range, it will interact with Wd1-5, likely en-
gulfing it. While one would typically expect such interaction
to lead to merger, we emphasise that the mass (∼55 M ) and
hence luminosity of the mass-gainer will be so high that its
envelope will approach the Eddington limit and hence be only
lightly bound. Therefore we suggest that both stars survive this
phase, with the H-rich mantle of the mass-gainer ejected in a
LBV/common envelope phase analagous to those driven by the
RSG phase in lower mass systems as the orbital period of the
binary decreases. This process will result in its transition to a
WR state. Unfortunately, current simulations of binary evolution
do not include such a phase due to the complexity of the physics.
However, in support of this assertion we emphasise that the cur-
rent configurations of the high-mass X-ray binaries 4U1700-37
and OAO 1657-415 also require the occurrence of exactly such a
process in systems containing stars too massive to pass through
a RSG phase (Clark et al. 2002; Mason et al. 2012); demonstrat-
ing that such a scheme is indeed viable and has observational
precedents.
Subsequently, due to the short period of our binary – and
guided by the evolution of the analagous pre-SN binary progen-
itor of 4U1700-37 (Clark et al. 2002) – we might expect pol-
lution of the atmosphere of Wd1-5 by the carbon-rich stellar
wind of the pre-SN WC phase of the mass-gainer; this repre-
senting the second phase of (reverse) wind-driven mass trans-
fer required to yield the observed surface abundance pattern of
Wd1-5. Approximately 0.05 M of carbon would be required to
have been accreted to replicate the current chemistry5
; hydrody-
namical simulations (Dessart et al. 2003) suggest such a process
is possible and it indeed appears to have occured in 4U1700-37,
despite the more powerful wind of the recipient in this system
(HD 153919; Clark et al. 2002). Finally, the WC mass-gainer
will explode as a Type Ibc SN and will likely unbind the binary.
The absence of rejuvenation during the case A accretion and the
subsequent early exposure of the core results in a sufficiently
low pre-SN iron core mass to form a NS rather than a BH (e.g.
Fryer et al. 2002). We explore this phase of the binary evolution
in more detail in Sects. 5 and 6.
4.2. Evolutionary pathways for massive stars in Wd1
Building on the evolutionary schemes delineated in Clark et al.
(2011) we might suppose an additional pathway for close bi-
naries comprising two stars of comparable masses, such that
for stars within Wd1 current evolving from the MS (Minit ∼
35−50 M ):
Case A binary, similar masses: O6-7 V (primary) + O6-
7 V (secondary) → case A mass transfer → BHG/WNLh +
O III-V → BHG/WNLh + LBV → LBV/common envelope
evolution → BHG/WNLh + WN/WC (+ wind driven mass
transfer) → SN + binary disruption → BHG/WNLh + mag-
netar/NS.
Case A binary, disimilar masses: O6-7 V (primary) + OB V
(secondary) → late case A/B mass transfer → BHG/WNLh +
OB III-V → WNo + OB III-V → WC + OB III-V → SN +
binary disruption → NS + OB I-III.
Single channel: O6-7 V → O8-9 III → O9-B3 Ia →
B5-9 Ia+
/YHG → RSG → B5-9 Ia+
/YHG/LBV → WN →
WC(/WO?) → SN (leading to BH formation?)
5
Similar quantities of helium would also be transfered but would have
a negligible effect on the abundances of Wd1-5
Comprising two distinct populations, the BHGs within Wd 1
provide an elegant illustration of this scheme. The first, consist-
ing of the late B5-9 Ia+
stars Wd1-7, -33 and -42a, lack obser-
vational signatures of binarity and appear to originate via single
star evolution as the stars evolve from the main sequence and
execute a red loop across the HR diagram.
The second, made up of the hybrid early BHG/WNLh ob-
jects Wd1-5, -13 and -44, all show clear signatures of current or
historic binarity (e.g. periodic RV variability and/or hard, over-
luminous X-ray emission; Clark et al. 2008; Ritchie et al. 2010;
and in prep.). Indeed, their spectral similarity (Figs. 2−4) sug-
gest they have all experienced binary driven mass loss. With an
orbital period of ∼9.13 days, Wd1-13 is likely to undergo late
case A/case B mass transfer and with Minit ∼ 41 M + ∼ 30 M
will not experience the reversal of SNe order we anticipate for
our putative Wd1-5 binary (Ritchie et al. 2010).
Initial analysis of multi-epoch RV observations of Wd1-44
(Ritchie et al., in prep.) suggests a period of <∼9 d, which is po-
tentially consistent with the case A mass transfer we propose for
Wd1-5. Moreover, with a secondary of apparently earlier spec-
tral type – and hence more massive – than the O supergiant com-
panion in Wd1-13 (for which we find Mcurrent ∼ 35.4+5.0
−4.6 M ) it
may represent a precursor of our putative Wd1-5 binary prior to
the common envelope phase (and subsequent brief episode of re-
verse mass transfer that distinguishes Wd1-5 from the other two
stars via the resultant C-enrichment).
We also identify a larger population of massive compact, in-
teracting OB+OB binaries within Wd1 (e.g. Wd1-30a, -36 and
-53; Clark et al. 2008; Ritchie et al., in prep.) that provide a rich
reservoir of progenitors from which systems such as Wd1-5, -13
and -44 may be drawn. In particular we highlight the binary
supergiant B[e] star Wd1-9, which currently appears to be un-
dergoing the rapid case A evolution we hypothesise for Wd1-5
(Fig. 10; Clark et al. 2013).
5. A physical connection between Wd1-5
and CXOU J1647-45?
Two mechanisms have been invoked to explain the runaway
phenomenon; dynamical ejection from dense stellar systems;
(Poveda et al. 1967) and SN kicks in binary systems (Blaauw
1961). N-body simulations of both Wd1 and the young massive
cluster R136 demonstrate that dynamical ejection of massive
stars with velocities ranging up to ∼300 km s−1
is well underway
by ∼3 Myr (Banerjee et al. 2012; Fujii et al. 2012). Conversely,at
the age of Wd 1 we would expect SNe every 7−13 000 yr (Muno
et al. 2006a,b); trivially, the presence of the magnetar confirms
the recent occurrence of a SN.
Both mechanisms therefore appear viable for the ejection
of Wd1-5, although a key discriminator between dynamical
and SN ejection mechanisms is that under the latter scenario
mass transfer from the SN progenitor may result in anomalous
physical properties of the runaway. Wd1-5 shows evidence of
C-enrichment that can only be understood via binary interac-
tion, strongly favouring the SN kick model for the formation of
Wd1-5. Indeed, if Wd1-5 were ejected via dynamical interaction,
it must still have followed an identical binary evolution to that
described in Sect. 4 prior to this event, which would also have
had to unbind the requisite evolved companion. Therefore, while
such a sequence is in principle possible, it appears unnecessarily
contrived in comparison to the SN scenario.
If the peculiar velocity imparted to Wd1-5 was the result of
a SN kick, an obvious question is whether this was the event that
Article number, page 11 of 17
12. A&A proofs: manuscript no. aa21771-13
produced the magnetar J1647-45? Given the rarity of magnetars,
a compelling case for cluster membership rather than chance
superposition may be made for J1647-45 (Muno et al. 2006a).
Moreover, spectral modelling of J1647-45 shows that the col-
umn density towards it is consistent both with that inferred for
Wd1 (determined from optical reddening), as well as the column
density towards other X-ray bright cluster members (Clark et al.
2008). Following these lines of argument, we adopt the hypoth-
esis that it is a cluster member for the remainder of this study.
Therefore, if J1647-45 resides within Wd1, one would ex-
pect the putative pre-SN companion to also remain within the
cluster; indeed if such an object were not present, the hypothe-
sis that binary driven mass loss permitted the formation of a NS
rather than a BH would be seriously challenged. Are the physi-
cal properties of Wd1-5 – e.g. composition, luminosity, temper-
ature, surface gravity and velocity relative to J1647-45 – consis-
tent with such an hypothesis?
The displacement between J1645-47 and Wd1-5 of ∼139
implies a minimum separation of ∼3.4 pc at a distance of 5 kpc.
Assuming a characteristic age of the order of 104
yr for mag-
netars (e.g. Kouveliotou et al. 1994; Woods et al. 2006) leads
to a relative projected velocity between the two objects of
∼325 km s−1
. To date direct measurements of the transverse ve-
locities of six magnetars have been made, all of which are en-
couragingly modest (≤350 km s−1
)6
and hence consistent with
the above estimate for the J1645-47/Wd1-5 system. Moreover,
the association of three anomalous X-ray pulsars with super-
novae remnants further supports the adoption of rather low mag-
netar kick velocities (despite theoretical predictions to the con-
trary; Mereghetti 2008). For comparison, a mean velocity of
∼400 km s−1
has been reported for young (<3 Myr) pulsars, with
a maximum velocity of ∼1600 km s−1
(Hobbs et al. 2005). Given
these findings, the separation of both Wd1-5 and J1645-47 ap-
pears consistent with a common origin.
Moreover, as highlighted in Sect. 3.2, the anomalous
C-abundance of Wd1-5 (C/C ∼ 1.4) is also present in the
B1 Ia+
and O6.5 Iaf+
hypergiant mass donors in the X-ray bi-
naries GX301-2 and 4U1700-37. As with our putative Wd1-5 +
J1647-45 binary, the current physical properties of both bina-
ries imply pre-SN mass transfer onto the current mass donor
(Wellstein & Langer 1999; Clark et al. 2002; Kaper et al.
2006). Additionally, the lifetime of the C-abundance anomaly
is expected to be rather short. Critically, acting on the thermal
timescale (e.g. Wellstein et al. 2001; Petrovic et al. 2005), ther-
mohaline, rather than rotational, mixing is expected to act to
rapidly dilute the carbon overabundance resulting from the pre-
SN mass transfer. So one would expect that dilution would al-
ready be well advanced after only 104
yr; a timescale directly
comparable to the lifetime inferred for magnetars. Indeed, the
similarity in the timescale for carbon dilution to the lifetime
of a magnetar implies that the cessation of mass transfer to
Wd1-5 and the event that formed J1647-45 must have occurred
quasi-simultaneously.
We can also advance three additional arguments to bolster
this association. No other magnetar or young cooling neutron
star candidate that could have formed the requisite companion
to Wd1-5 has been identified in either the original dataset or
6
v = 212 ± 35(d/3.5 kpc) km s−1
for XTE J1810-197 (Helfand et al.
2007), v = 280+130
−120 km s−1
for PSR J1550-5418 (Deller et al. 2012),
v = 350 ± 100(d/9 kpc) km s−1
for SGR 1806-20 and v = 130 ±
30(d/12.5 kpc) km s−1
for SGR 1900+14 (both Tendulkar et al. 2012)
and v = 157±17 km s−1
for AXP 1E 2259+586 and v = 102±26 km s−1
for AXP 4U 0142+61 (both Tendulkar et al. 2013).
subsequent multi-epoch X-ray observations (Muno et al. 2006a;
Clark et al. 2008; Woods et al. 2011). Conversely, despite ex-
tensive optical and near-IR surveys (Negueruela et al. 2010;
Crowther et al. 2006a), no other plausible pre-SN binary com-
panion to J1647-45 has been identified within the massive stel-
lar population of Wd1. Moreover, given the preceding estimate
of the mean interval between consecutive SNe within Wd1 at
this epoch, one would expect the observed runaway velocity of
Wd1-5 to carry it beyond the cluster confines before the next
such event – i.e. if the velocity of Wd1-5 is representative of that
imparted to runaway stars at SN, on average one would expect
only one such object to be present within Wd1 at this time – and
hence on statistical grounds we would expect both magnetar and
Wd1-5 to be physically associated with one another.
So in summary, all the available evidence points to the
anomalous RV of Wd1-5 as being the result of a SNe kick. In
particular, the carbon abundance points to a recent episode of
mass transfer from a close companion, although currently there
is no observational evidence of such an object. Moreover, the
timescale for dilution of the abundance anomalies is comparable
to the duration of the magnetar phase, while the angular separa-
tion of both Wd1-5 and J1647-45 is also consistent with known
magnetar and pulsar kick velocities. Therefore, while the ab-
sence of transverse velocity measurements prevents a definitive
association, we can identify strong lines of argument to posit a
physical association between Wd1-5 and J1647-45 in a pre-SN
binary system.
6. Implications for magnetar formation
If the hypothesis that Wd1-5 and the magnetar J1647-45 com-
prised a pre-SN binary system is correct, what are the physical
implications? No consensus yet exists on the formation mecha-
nism for magnetars. Gaensler et al. (2005) suggested their pro-
genitors were limited to particularly massive stars (>∼40 M );
however, more recent observations suggest that they instead span
a wide range of masses (∼17−50 M ; Sect. 1), implying that ad-
ditional physical factors must drive this process.
Duncan & Thompson (1992) and Thompson & Duncan
(1993) argued for their formation via rapidly rotating (P ∼ 1 ms)
proto-NSs, when a large-scale convective dynamo may generate
an extreme magnetic field in the first few seconds after birth.
However, if magnetic torques are successful at removing angu-
lar momentum from the core via coupling to the extended atmo-
sphere present in a pre-SN RSG phase, then the core will not be
rotating rapidly enough at SN for this mechanism to operate (e.g.
Heger et al. 2005). Moreover such a scenario would predict both
highly energetic SNe and high spatial velocities for the resul-
tant magnetars (e.g. Duncan & Thompson 1992) which appear
to be in conflict with observations (e.g. Mereghetti 2008; Vink
& Kuiper 2006). An alternative suggestion is the “fossil field”
hypothesis, whereby a pre-existing magenetic field acquired at
the birth of the progenitor is amplified during stellar collapse.
Spruit (2008) argued against this mechanism given the lack of
sufficient numbers of highly magnetised stars to explain the ex-
pected formation rate of magnetars and, once again, the fact that
core-envelope coupling will result in spin down of the core.
How does J1647-45 inform the debate? The Wd1 RSGs co-
hort implies that if the progenitor of J1647-45 had been a single
star, it would have passed through such a phase and hence have
been subject to spin-down via core-envelope coupling. While we
cannot exclude an unusually strong (fossil) magnetic field in the
progenitor of J1647-45, we find no evidence of a corresponding
Article number, page 12 of 17
13. J. S. Clark et al.: A VLT/FLAMES survey for massive binaries in Westerlund 1. IV.
population of highly magnetic massive stars within Wd1 at this
time7
.
Binarity has been invoked under both scenarios as an addi-
tional ingredient in order to avoid core-envelope coupling, by re-
moving the outer layers of the SN progenitor and thus preventing
a RSG phase, so that sufficient angular momentum is retained in
the core to form a magnetar8
. Moreover, the high mass implied
for the progenitors of both J1647-45 and SGR1806-20 (Sect. 1)
suggests that binary driven mass loss resulting in the early onset
of WR mass loss rates and hence the production of a low-mass
pre-SN core was likewise essential to the formation of a magne-
tar rather than a BH (cf. Fryer et al. 2002).
An additional point of interest is whether the pre-SN evo-
lution of a massive compact binary system – such as we infer
for J1647-45 – favours the production of a seed magnetic field,
which is subsequently amplified during or shortly after core col-
lapse to yield a magnetar (e.g. Spruit 2008). Following Langer
(2012), both mass transfer and stellar merger in compact binaries
may lead to dramatic spin-up of the mass-gainer/merger rem-
nant, potentially favouring the formation of a magnetic field via
dynamo action. In support of such an hypothesis we highlight the
detection of a magnetic field in the rapidly rotating secondary in
Plaskett’s star (Grunhut et al. 2013); a higher mass analogue of
our putative Wd1-5+J1647-45 binary, which has also undergone
case A mass transfer (e.g. Linder et al. 2008).
Alternatively, Tout et al. (2008) suggested that high magnetic
field white dwarfs may form via strong binary interactions be-
tween a main sequence and red giant (and hence white-dwarf
progenitor) in a common envelope phase. In this scenario as
the orbital period of the 2 components decreases, differential
rotation within the convective common envelope generates the
magnetic field via dynamo action; one might speculate that a
comparable process also occurs in high mass analogues, such
as the pre-SN LBV/common envelope phase we propose here
(Sect. 4.1).
A binary mediated formation scenario would suppose that
if merger is avoided9
one could anticipate identifying the pre-
SN magnetar companion. The proper motion study of Tendulkar
et al. (2012; footnote 6) places the birthsite of SGR1806-20
within the confines of the eponymous host cluster, with the po-
sitional uncertainty elipse encompassing three stars. Of these,
object D has been classified as an OB supergiant, and hence po-
tentially the massive pre-SN companion we predict; classifica-
tion spectroscopy of the remaining stars in combination with an
RV survey of the full cluster population would be of considerable
interest to determine if any of the three are indeed overluminous
chemically peculiar runaway analogues to Wd1-5. Alternatively,
if disruption is avoided, binaries containing magnetars should
7
By analogy to the optical properties of Of?p stars, Clark et al. (2010)
cited Wd1-24 as a possible highly magnetic star, based on the vari-
able C iii+Pa 16 ∼8500 Å blend. However, further observations have
revealed that this behaviour is instead due to a variable contribution
from a late-O binary companion (Ritchie et al., in prep.). Known mag-
netic OB stars are expected to demonstrate hard, overluminous X-ray
emission (e.g. Clark et al. 2009a, and refences therein); while several
overluminous OB stars are present within Wd 1 (Clark et al. 2008),
they all demonstrate rather soft X-ray spectra; the sole exception being
W30a, a known (colliding wind) binary.
8
Although simulations by Yoon et al. (2010) suggests that such a
mechanism is ineffective for stars below 25 M .
9
Under such a scenario we might suppose the lack of a luminous stel-
lar source associated with the wind blown bubble hosting the magentar
1E 1048.1-5937 (Gaensler et al. 2005) would be explicable if the binary
merged prior to SN.
also exist. In this regard the suggestion of Reig et al. (2012) that
the neutron star within the X-ray binary 4U2206+54 is a magne-
tar is of considerable interest, moreso given that the combination
of short (Porb ∼ 10 day) period and He-rich nature of the primary
is suggestive of pre-SN binary interaction in the system.
Potential observational biases in the detection of quiescent
magnetars hamper a direct determination of their birth rate, al-
though several authors have suggested it may be comparable to
that of radio pulsars (e.g. Muno et al. 2008; Woods 2008); confir-
mation of a binary channel for magnetar formation would allow
us to address this issue. Intriguingly, recent observations sug-
gest a high (≥40%; e.g. Sana et al. 2012; Kiminki & Kobulnicky
2012; Chini et al. 2012; Ritchie et al., in prep.) binary fraction
amongst OB stars, an orbital period distribution favouring short-
period systems with respect to the classical Öpik’s Law (a flat
distribution of orbital separations in logarithmic space) and a
mass ratio favouring more massive companions (i.e. inconsistent
with random selection from a Kroupa type initial mass function);
all factors potentially favouring the production of magnetars un-
der the above scenario. Indeed, the presence of a number of com-
pact OB+OB binaries and a massive binary fraction of >70%
amongst the WR population (Clark et al. 2008) potentially pro-
vides a rich progenitor reservoir within Wd1, with Wd1-44 being
the most compelling example currently identified (Sect. 4.2).
7. Concluding remarks
The presence of a magnetar with a progenitor mass >∼40 M
within Wd 1 requires a mechanism by which significant mass
loss can occur prior to SN, with binary interaction a leading can-
didate. Therefore, the identification of a pre-SN companion to
J1647-45 provides a critical test of the theory. As part of our
RV survey of the cluster we identified the single star Wd1-5 as a
runaway – and hence a potential candidate.
To date no other massive star – either within Wd1 or part
of the wider Galactic population – completely reproduces the
spectral morphology and/or combination of physical properties
of Wd1-5. Quantitative analysis reveals physical properties in-
consistent with the evolution of a single star (Sect. 3). In partic-
ular the anomalously high C-abundance of Wd1-5 in compari-
son to the predicted CNO abundances is inexplicable under such
a scenario and has previously only been observed in the mass
donors of the X-ray binaries GX301-2 and 4U1700-37. In both
cases this is thought to result from a brief episode of wind driven
mass transfer from a C-rich WC Wolf-Rayet binary companion
which, post-SN, formed the relativistic companion.
Motivated by these findings, we used the combination of
spectroscopic mass, luminosity and chemical abundances of
Wd1-5 to infer a pre-SN evolutionary history for the putative
binary (Sect. 4). Significant case A mass transfer from Wd1-5
leads to spin-up of the companion, which consequently evolves
more rapidly than the mass donor, resulting in a subsequent
LBV-driven common-envelope phase which strips its H-rich
mantle. The initially less massive companion then enters the
WR phase, triggering an enrichment of the atmosphere of Wd1-5
by the stellar wind of the by then WC star, which then explodes
as a type Ibc SN, unbinding the binary. In support of this hypoth-
esis we highlight that the observational properties of the remain-
ing early-BHG/WNLhs within Wd1 – Wd1-13 and -44 – reveal
them both to be short-period interacting binaries, while a large
reservoir of progenitor binaries has also been identified (Ritchie
et al., in prep.).
Given this, a natural explanation for the runaway nature for
Wd1-5 is that it was ejected via a SN kick and we present a
Article number, page 13 of 17
14. A&A proofs: manuscript no. aa21771-13
number of lines of argument to support a physical association
with the magnetar J1647-45 (noting that the conclusions above
are not dependant on such a connection). Under this hypothesis,
binarity plays a critical role in the formation of the magnetar by
(i) preventing the spin-down which happens in single stars via
core-envelope coupling because the envelope is removed and
(ii) enabling the formation of a low-mass pre-SN core via the
prolonged action of WR-phase winds. Moreover, we may specu-
late that the binary interaction results in the generation of a seed
magnetic field in the magnetar progenitor via dynamo action, ei-
ther during the spin up of the mass gainer or in a subsequent
LBV/common envelope phase.
If correct, while the BHG/WNLh stars Wd1-5, -13 and -44
might be expected to form a NS rather than a BH as a result
of their binary driven mass loss, they have not been spun up by
mass transfer and therefore do not replicate the properties of our
putative magnetar progenitor. While the secondary in Wd-13 has
been spun up via mass transfer, it remains insufficiently massive
for the SN order to be reversed, as we propose for Wd1-5, and
consequently will follow a different evolutionary path whereby
magnetic core-envelope coupling is not avoided. However, the
secondary in Wd1-44 appears more massive and we might sup-
pose this system will follow a similar pathway to Wd1-5, and
hence potentially yield a magnetar.
As well as permitting a determination of the magnetar for-
mation rate via the identification of the binary progenitor pop-
ulation, the presence of carbon pollution in the atmosphere of
Wd1-5 supposes an H-depleted WC Wolf-Rayet as the immedi-
ate magnetar progenitor, which would have exploded as a type
Ibc SN. This would be the first association of the birth of a mag-
netar with such an event and would also support the assertion
that massive close binary evolution is a promising channel for
the production of a subset of type Ibc SNe. Indeed current ob-
servational studies suggest that binary stripping is important in
the production of the majority of type Ibc SNe, albeit from a
population of lower mass (≤20−25 M ) progenitors than we as-
sume here (Smith et al. 2011; Eldridge et al. 2013; Kuncarayakti
et al. 2013).
Expanding upon this and a number of authors have suggested
that magnetars may power superluminous type II and Ibc SNe
(Thompson et al. 2004; Woosley 2010; Kasen & Bildsten 2010;
Gal-Yam 2012; Quimby et al. 2011); indeed the 7.29 M progen-
itor model of Woosley (2010) is directly motivated by the pres-
ence of J1647-45 within Wd1. Moreover, Inserra et al. (2013)
studied the late-time lightcurves of five superluminous type Ic
SNe, finding that the data are indeed consistent with these events
being powered by the rapid spin-down of newly born magnetars
(see also McCrum et al. 2013; Nicholl et al. 2013) Additionally,
magnetars have also been proposed as the central engines of
some gamma-ray bursts (GRBs; e.g. Usov 1992; Duncan &
Thompson 1992; Metzger et al. 2011, and refs. therein). Given
the latter suggestion it is therefore intriguing that long duration
GRBs have been associated with type Ibc SNe (e.g. Della Valle
2006).
If such an hypothesis is viable, one might ask why such su-
perluminous events are not more common in the local Universe
if the magnetar formation rate is indeed a substantial percent-
age of that of neutron stars (e.g. Muno et al. 2008)? One plau-
sible explanation may be that the superluminous SNe occur in
low metallicity environments where correspondingly weak stel-
lar winds minimise pre-SNe angular momentum losses, leading
to systematically more rapidly rotating magnetars and hence a
greater deposition of energy in the SNe in comparison to the
higher metallicity local environment. In any event, given the
apparent ubiquity of massive compact binaries, additional the-
oretical and observational investigations of the potential link
between binary mediated formation channels for magnetars,
(superluminous) type Ibc SNe and GRBs would clearly be of
considerable interest.
Acknowledgements. This research is partially supported by the Spanish
Ministerio de Ciencia e Innovación (MICINN) under grant AYA2012-39364-
C02-02.
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16. A&A proofs: manuscript no. aa21771-13
Appendix A: Summary of stellar comparison data to Wd1-5
Table A.1. Comparison of basic stellar parameters of Wd1-5 to those of related galactic stars.
Name Spec. log(L∗) R∗ Teff log g log( ˙M) v∞ Reference
Type (L ) (R ) (kK) (M yr−1
) (km s−1
)
Wd1-5 B0.5 Ia+
5.38+0.12
−0.12 34.0+5.0
−4.4 21.05+1.5
−1.2 2.33+0.17
−0.10 −5.36+0.3
−0.2 430+20
−40 This work
HD 30614 O9.5 Ia 5.63 26.0 29.0 ± 1.0 3.0 ± 0.15 −5.30+0.11
−0.15 1560 1
HD 168183 O9.5 Ib 5.42 ± 0.22 19.0+4.3
−3.5 30.0 ± 1.0 3.3 ± 0.1 −6.82+0.24
−0.24 1700 ± 510 2
HD 37128 B0 Ia 5.44 24.0 27.0 ± 1.0 2.9 ± 0.15 −5.60+0.11
−0.15 1910 1
HD 89767 B0 Ia 5.35 ± 0.22 30.0+6.7
−5.5 23.0 ± 1.0 2.55 ± 0.1 −6.07+0.24
−0.24 1600 ± 480 2
HD 91969 B0 Ia 5.52 25.3 27.5 ± 1.0 2.75 ± 0.14 −6.00+0.11
−0.15 1470 1
HD 94909 B0 Ia 5.49 25.5 27.0 ± 1.0 2.9 ± 0.14 −5.70+0.11
−0.15 1050 1
HD 122879 B0 Ia 5.52 24.4 28.0 ± 1.0 2.95 ± 0.14 −5.52+0.11
−0.15 1620 1
HD 192660 B0 Ib 5.74 ± 0.13 23.4 ± 1.0 30.0 ± 1.0 3.25 −5.30+0.00
−0.40 1850 3
HD 204172 B0.2 Ia 5.48 ± 0.27 22.4 ± 3.2 28.5 ± 1.0 3.13 −6.24+0.34
−0.40 1685 3
HD 38771 B0.5 Ia 5.35 22.2 26.5 ± 1.0 2.9 ± 0.14 −6.05+0.11
−0.15 1525 1
HD 115842 B0.5 Ia 5.65 34.2 25.5 ± 1.0 2.85 ± 0.14 −5.70+0.11
−0.15
1180 1
HD 152234 B0.5 Ia 5.87 42.4 26.0 ± 1.0 2.85 ± 0.14 −5.57+0.11
−0.15
1450 1
HD 185859 B0.5 Ia 5.54 ± 0.14 29.1 ± 1.3 26.0 ± 1.0 3.13 −6.30+0.08
−0.10 1830 3
HD 64760 B0.5 Ib 5.48 ± 0.26 23.3 ± 2.2 28.0 ± 2.0 3.38 −5.96+0.28
−1.04 1600 3
HD 93619 B0.5 Ib 5.30 ± 0.22 22.0+4.9
−4.1 26.0 ± 1.0 2.9 ± 0.1 −6.12+0.24
−0.24 1470 ± 441 2
HD 213087 B0.5 Ib 5.69 ± 0.11 32.0 ± 0.01 27.0 ± 1.0 3.13 −6.15+0.19
−0.0 1520 3
HD 2905 BC0.7 Ia 5.52 41.4 21.5 ± 1.0 2.6 ± 0.14 −5.70+0.11
−0.15
1105 1
HD 91943 B0.7 Ia 5.35 26.3 24.5 ± 1.0 2.8 ± 0.14 −6.12+0.11
−0.15
1470 1
HD 152235 B0.7 Ia 5.76 47.1 23.0 ± 1.0 2.65 ± 0.14 −5.90+0.11
−0.15 850 1
HD 154090 B0.7 Ia 5.48 36.0 22.5 ± 1.0 2.65 ± 0.14 −6.02+0.11
−0.15 915 1
HD 96880 B1 Ia 5.42 ± 0.11 43.0+9.7
−7.9 20.0 ± 1.0 2.4 ± 0.1 −6.40+0.24
−0.24 1200 ± 360 2
HD 115363 B1 Ia 5.42 ± 0.11 43.0+9.7
−7.9 20.0 ± 1.0 2.4 ± 0.1 −5.92+0.24
−0.24 1200 ± 360 2
HD 148688 B1 Ia 5.45 36.7 22.0 ± 1.0 2.60 ± 0.14 −5.76+0.11
−0.15 725 1
HD 170938 B1 Ia 5.42 ± 0.11 43.0+9.7
−7.9 20.0 ± 1.0 2.4 ± 0.1 −6.15+0.24
−0.24 1200 ± 360 2
HD 13854 B1 Iab 5.43 37.4 21.5 ± 1.0 2.55 ± 0.14 −6.07+0.11
−0.15 920 1
HD 91316 B1 Iab 5.47 37.4 22.0 ± 1.0 2.55 ± 0.14 −6.46+0.11
−0.15 1110 1
HD 109867 B1 Iab 5.56 ± 0.22 38.0+8.5
−7.0 23.0 ± 1.0 2.6 ± 0.1 −6.30+0.24
−0.24 1400 ± 420 2
HD 190066 B1 Iab 5.54 ± 0.20 41.4 ± 1.9 21.0 ± 1.0 2.88 −6.15+0.05
−0.07 1275 3
HD 47240 B1 Ib 4.93 ± 0.22 27.0+6.1
−5.0 19.0 ± 1.0 2.4 ± 0.1 −6.77+0.24
−0.24 1000 ± 300 2
HD 154043 B1 Ib 4.98 ± 0.22 26.0+5.8
−5.3 20.0 ± 1.0 2.5 ± 0.1 −6.70+0.24
−0.24 1300 ± 390 2
HD 54764 B1 Ib/II 4.90 ± 0.22 26.0+5.8
−5.3 19.0 ± 1.0 2.45 ± 0.10 −7.52+0.24
−0.24 900 ± 270 2
HD 14956 B1.5 Ia 5.65 50.6 21.0 ± 1.0 2.5 ± 0.14 −6.00+0.11
−0.15 500 1
HD 106343 B1.5 Ia 5.40 ± 0.22 42.0+9.4
−7.7 20.0 ± 1.0 2.50 ± 0.1 −6.28+0.24
−0.24 800 ± 240 2
HD 193183 B1.5 Ib 5.00 ± 0.26 30.8 ± 2.8 18.5 ± 1.0 2.63 −6.64+0.40
−0.00 565 3
HD 111990 B1/2 Ib 4.91 ± 0.22 25.0+5.6
−4.5 19.5 ± 1.0 2.55 ± 0.10 −6.85+0.24
−0.24 750 ± 225 2
HD 14143 B2 Ia 5.42 52.9 18.0 ± 1.0 2.25 ± 0.14 −5.98+0.11
−0.15 645 1
HD 14818 B2 Ia 5.35 46.1 18.5 ± 1.0 2.4 ± 0.14 −6.26+0.11
−0.15 565 1
HD 41117 B2 Ia 5.65 61.9 19.0 ± 1.0 2.35 ± 0.14 −6.05+0.11
−0.15 510 1
HD 194279 B2 Ia 5.37 44.7 19.0 ± 1.0 2.3 ± 0.14 −5.98+0.11
−0.15 550 1
HD 206165 B2 Ib 5.18 ± 0.26 39.8 ± 5.5 18.0 ± 0.5 2.50 −6.30+0.00
−0.22 640 3
HD 141318 B2 II 4.56 ± 0.11 16.0 20.0 ± 1.0 2.90 ± 0.1 −7.52+0.24
−0.24 900 ± 270 2
HD 92964 B2.5 Iae 5.33 ± 0.11 48.0 18.0 ± 1.0 2.1 ± 0.1 −6.55+0.24
−0.24 520 ± 156 2
HD 198478 B2.5 Ia 5.03 40.0 16.5 ± 1.0 2.15 ± 0.14 −6.64+0.11
−0.15
470 1
HD 42087 B2.5 Ib 5.11 ± 0.24 36.6 ± 1.7 18.0 ± 1.0 2.50 −6.70+0.00
−0.40 650 3
Notes. Stars are presented from early to late spectral types for BSGs and BHGs and from hottest to coolest for the LBVs and WNLh stars. The
lack of suitable absorption profiles prevents a determination of the surface gravity of the LBVs and WNLh stars. Throughout the table we employ
the clumping corrected mass loss rate ( ˙M/ f ) to allow direct comparison between individual stars; hence the difference between this table and
Table 1 for Wd1-5. Unfortunately errors are not presented for all physical parameters of all individual stars by the studies used in the construction
of this table. Values for both high and low temperature states of AG Car are provided.
References. (1)
Crowther et al. (2006b); (2)
Lefever et al. (2007); (3)
Searle et al. (2008); (4)
Markova & Puls (2008); (5)
Kaper et al. (2006); (6)
Clark
et al. (2012); (7)
Groh et al. (2009a); (8)
Najarro (2001); (9)
Groh et al. (2009b); (10)
Najarro et al. (2009); (11)
Clark et al. (2009b); (12)
Bohannan &
Crowther (1999); (13)
Martins et al. (2007).
Article number, page 16 of 17