This study examines the evolution of the yellow hypergiant star HR 8752 over nearly a century based on spectroscopic observations and photometry. The star underwent successive gas ejections, seen as downward excursions in effective temperature. During each ejection, a pseudo-photosphere formed with lower gravity and higher turbulence. After the ejected shells dispersed, a hotter, more compact photosphere emerged. Analysis of observations shows variation over time in the star's effective temperature, luminosity, radius, and mass, suggesting it is evolving away from an unstable region in the HR diagram known as the "yellow evolutionary void."
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.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
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.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
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.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
Uma grande equipe de astrônomos registrou uma supernova extremamente luminosa numa galáxia massiva a cerca de 3.82 bilhões de anos-luz de distância.
A explosão recém-descoberta, denominada de ASASSN-15Ih, pertence à classe mais luminosa de supernovas, chamada de supernovas superluminosas.
"Ela parece ter originado numa grande galáxia, em contraste com a maioria das supernovas superluminosas, que normalmente se originam em galáxias anãs com formação de estrelas", disse o Dr. Subo Dong, do Kavli Institute for Astronomy and Astrophysics e coautor do artigo publicado na revista Science que descreve a descoberta.
"Nós estimamos o raio efetivo para a galáxia de 7830 anos-luz e uma massa estelar de 200 bilhões de massas solares".
Também conhecida como SN 2015L, a ASASSN-15lh é aproximadamente 200 vezes mais poderosa do que uma típica explosão de supernova do Tipo Ia, cerca de 570 bilhões de vezes mais brilhante do que o nosso Sol, e vinte vezes mais brilhante do que todas as estrelas na nossa galáxia combinadas.
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.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
A estrela KIC 8462852 voltou a ser comentada na mídia astronômica essa semana, e vamos entender porque. Mas antes uma pequena recordação.
Provavelmente, você já ouviu falar da estrela KIC 8462852, que recebeu o nome carinhoso de Estrela de Tabby, em homenagem a Tabetha Boyajian que liderou a equipe que descobriu o seu estranho comportamento. Essa foi a estrela que chamou muito a atenção da imprensa no final do último ano. Os astrônomos utilizaram observações feitas com o Kepler e mediram as variações no brilho da estrela. Algumas dessas variações eram significativas, com uma queda de brilho de cerca de 20%.
Isso é muito. Não poderia ser um planeta passando em frente a estrela, pois as quedas dos brilhos também não eram periódicas, e a quantidade de luz bloqueada era diferente a cada vez. Além disso, até um planeta do tamanho de Júpiter, bloqueia menos de 1% da luz da estrela.
No artigo original, Boyajian e sua equipe discutiu uma série de hipóteses e possíveis cenários que poderiam causar a queda de brilho, eliminando algumas delas e levantando outras. Entre as hipóteses, aquela que ganhou uma força foi a de uma família de cometas passando na frente da estrela, com alguns deles colidindo entre si e gerando uma nuvem espessa que poderia bloquear a luz da estrela.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
First detection of_molecular_gas_in_shells_in_cena_galaxySérgio Sacani
This document reports the first detection of molecular gas (CO) in the shells of the galaxy Centaurus A (Cen A), located 15 kpc from the galaxy's center. The ratio of CO to HI emission in the shells matches what is found in the galaxy's central regions, which is unexpected given typical metallicity gradients in galaxies. The detection of molecular gas in the shells provides evidence that molecular gas in galaxy mergers may be spread further from nuclear regions than previously thought. The dynamics of the gas can be understood if the interstellar medium is considered clumpy and less dissipative than assumed, allowing dense gas to orbit with stars and form shells.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
This document discusses observations of six lensed starburst galaxies at redshift ~2.5 using the Atacama Large Millimeter/submillimeter Array (ALMA). The key findings are:
1) ALMA detected emission and absorption lines of the CH+ molecule in the spectra of five out of the six galaxies, indicating dense shocks and highly turbulent reservoirs of cool gas extending over 10 kiloparsecs outside the starburst regions.
2) The broad CH+ emission lines trace shocks moving at ~40 km/s within dense gas, while the absorption lines reveal turbulent reservoirs with velocities of ~400 km/s.
3) The turbulent reservoirs have radii of 10-20 kilopar
An earth sized_planet_in_the_habitable_zone_of_a_cool_starSérgio Sacani
This document describes the discovery of Kepler-186f, an Earth-sized planet orbiting within the habitable zone of its host star Kepler-186, a cool M-dwarf star. Kepler-186f receives a similar amount of stellar radiation as Earth and models suggest it could harbor liquid water on its surface if it has an Earth-like atmosphere. At 1.11 times the size of Earth, Kepler-186f is the smallest planet discovered to date within the habitable zone of its star. The five planets orbiting Kepler-186, including Kepler-186f, likely formed from the protoplanetary disk around the star and provide the first Earth-sized candidate for a habitable world.
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.
An earth sized_planet_with_an_earth_sized_densitySérgio Sacani
1) Researchers observed the exoplanet Kepler-78b using the HARPS-N spectrograph to measure its mass.
2) They measured Kepler-78b's mass to be 1.86 Earth masses, giving it a density similar to Earth, implying a rocky composition of iron and rock.
3) The small size of Kepler-78b makes it the smallest exoplanet yet measured for both mass and radius, establishing that Earth-sized planets can be terrestrial.
This document summarizes the detection of a super-Earth planet orbiting the star GJ 832. Radial velocity data from three telescopes revealed a planet, GJ 832c, with an orbital period of 35.68 days and a minimum mass of 5.4 Earth masses. GJ 832c has a low eccentricity orbit of 0.18 near the inner edge of the star's habitable zone. However, given its large mass, the planet likely has a massive atmosphere that could render it uninhabitable. The GJ 832 system resembles a miniature version of our solar system, with an interior potentially rocky planet and a distant gas giant.
No xrays from_wasp18_implications_for_its_age_activity_and_influenceSérgio Sacani
1) An 87 ks Chandra observation was performed of the star WASP-18, which hosts a very close-in hot Jupiter planet orbiting within 20 hours.
2) WASP-18 was not detected in X-rays down to a luminosity limit of 4 x 10^26 erg/s, over two orders of magnitude lower than expected for a star of its estimated age of 600 Myr.
3) This unusually low activity level for a star of WASP-18's age and mass suggests that the massive planet may play a role in disrupting the stellar magnetic dynamo generated within its thin convective layers through star-planet interaction.
1. The author measured proper motions of molecular hydrogen (H2) emission features in the Herbig-Haro 46/47 outflow system, finding tangential velocities ranging from tens to nearly 500 km/s.
2. The highest velocities were observed for H2 knots located along or near the jet/counterjet axes, while knots forming the wings of a large H2 bow shock moved more slowly.
3. Several H2 knots were found to have significantly changed luminosity over the 4-year study, indicating variability in H2 emission from young stellar object outflows for the first time.
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
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.
First discovery of_a_magnetic_field_in_a_main_sequence_delta_scuti_star_the_k...Sérgio Sacani
Coralie Neiner do Laboratory for Space Studies and Astrophysics Instrumentation, LESIA (CNRS/Observatoire de Paris/UPMC/Université Paris Diderot) e Patricia Lampens (Royual OIbservatory of Belgium), descobriram a primeira estrela magnética do tipo delta Scuti, através de observações espectropolarimétricas, realizadas com o telescópio CFHT. As estrelas do tipo delta Scuti, são estrelas pulsantes, sendo que algumas delas mostram assinaturas atribuídas para um segundo tipo de pulsação. A descoberta mostra que isso é na verdade a assinatura de um campo magnético. Essa descoberta tem importantes implicações para o entendimento do interior das estrelas.
Dois tipos de estrelas pulsantes existem entre as estrelas com massa entre 1.5 e 2.5 vezes a massa do Sol: as estrelas do tipo delta Scuti e as estrelas do tipo gamma Dor. A teoria nos diz que as estrelas com temperatura entre 6900 e 7400 graus Kelvin podem ter ambos os tipos de pulsação. Essas são então chamadas de estrelas híbridas. Contudo, o satélite Kepler da NASA tem detectado um grande número de estrelas híbridas com temperaturas maiores ou menores do que esse limite pensado anteriormente. A existência dessas estrelas híbridas com temperaturas maiores é algo muito controverso, já que desafia o nosso entendimento sobre as estrelas pulsantes do tipo delta Scuti e gamma Dor.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
- The document is a student's chemistry project on space chemistry. It thanks the teacher and school for allowing the project and providing resources.
- The project covers topics like the chemical composition of space, how space suits work, rocket propellants, and harnessing energy from space. It includes sections on stars and their properties, the life and death of stars, and references.
This document summarizes a study checking the reality of the "yellow evolutionary void" in the Hertzsprung-Russell diagram through an analysis of three stars - HD 33579, HR 8752, and IRC+10420. The study finds that HD 33579 has a large mass and stable behavior, suggesting it is a young, redward-evolving supergiant allowed in the void. HR 8752 and IRC+10420 have lower masses, placing them in a post-red blueward evolutionary loop, and they show evidence of "bouncing" as they approach the void. The photometric variations of HD 33579 and HR 8752 are attributed to pulsations.
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.
The yellow hypergiant_hr5171a_resolving_a_massive_interacting_binary_in_the_c...Sérgio Sacani
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data spanning over 60 years indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion.
A estrela KIC 8462852 voltou a ser comentada na mídia astronômica essa semana, e vamos entender porque. Mas antes uma pequena recordação.
Provavelmente, você já ouviu falar da estrela KIC 8462852, que recebeu o nome carinhoso de Estrela de Tabby, em homenagem a Tabetha Boyajian que liderou a equipe que descobriu o seu estranho comportamento. Essa foi a estrela que chamou muito a atenção da imprensa no final do último ano. Os astrônomos utilizaram observações feitas com o Kepler e mediram as variações no brilho da estrela. Algumas dessas variações eram significativas, com uma queda de brilho de cerca de 20%.
Isso é muito. Não poderia ser um planeta passando em frente a estrela, pois as quedas dos brilhos também não eram periódicas, e a quantidade de luz bloqueada era diferente a cada vez. Além disso, até um planeta do tamanho de Júpiter, bloqueia menos de 1% da luz da estrela.
No artigo original, Boyajian e sua equipe discutiu uma série de hipóteses e possíveis cenários que poderiam causar a queda de brilho, eliminando algumas delas e levantando outras. Entre as hipóteses, aquela que ganhou uma força foi a de uma família de cometas passando na frente da estrela, com alguns deles colidindo entre si e gerando uma nuvem espessa que poderia bloquear a luz da estrela.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
First detection of_molecular_gas_in_shells_in_cena_galaxySérgio Sacani
This document reports the first detection of molecular gas (CO) in the shells of the galaxy Centaurus A (Cen A), located 15 kpc from the galaxy's center. The ratio of CO to HI emission in the shells matches what is found in the galaxy's central regions, which is unexpected given typical metallicity gradients in galaxies. The detection of molecular gas in the shells provides evidence that molecular gas in galaxy mergers may be spread further from nuclear regions than previously thought. The dynamics of the gas can be understood if the interstellar medium is considered clumpy and less dissipative than assumed, allowing dense gas to orbit with stars and form shells.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
This document discusses observations of six lensed starburst galaxies at redshift ~2.5 using the Atacama Large Millimeter/submillimeter Array (ALMA). The key findings are:
1) ALMA detected emission and absorption lines of the CH+ molecule in the spectra of five out of the six galaxies, indicating dense shocks and highly turbulent reservoirs of cool gas extending over 10 kiloparsecs outside the starburst regions.
2) The broad CH+ emission lines trace shocks moving at ~40 km/s within dense gas, while the absorption lines reveal turbulent reservoirs with velocities of ~400 km/s.
3) The turbulent reservoirs have radii of 10-20 kilopar
An earth sized_planet_in_the_habitable_zone_of_a_cool_starSérgio Sacani
This document describes the discovery of Kepler-186f, an Earth-sized planet orbiting within the habitable zone of its host star Kepler-186, a cool M-dwarf star. Kepler-186f receives a similar amount of stellar radiation as Earth and models suggest it could harbor liquid water on its surface if it has an Earth-like atmosphere. At 1.11 times the size of Earth, Kepler-186f is the smallest planet discovered to date within the habitable zone of its star. The five planets orbiting Kepler-186, including Kepler-186f, likely formed from the protoplanetary disk around the star and provide the first Earth-sized candidate for a habitable world.
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.
An earth sized_planet_with_an_earth_sized_densitySérgio Sacani
1) Researchers observed the exoplanet Kepler-78b using the HARPS-N spectrograph to measure its mass.
2) They measured Kepler-78b's mass to be 1.86 Earth masses, giving it a density similar to Earth, implying a rocky composition of iron and rock.
3) The small size of Kepler-78b makes it the smallest exoplanet yet measured for both mass and radius, establishing that Earth-sized planets can be terrestrial.
This document summarizes the detection of a super-Earth planet orbiting the star GJ 832. Radial velocity data from three telescopes revealed a planet, GJ 832c, with an orbital period of 35.68 days and a minimum mass of 5.4 Earth masses. GJ 832c has a low eccentricity orbit of 0.18 near the inner edge of the star's habitable zone. However, given its large mass, the planet likely has a massive atmosphere that could render it uninhabitable. The GJ 832 system resembles a miniature version of our solar system, with an interior potentially rocky planet and a distant gas giant.
No xrays from_wasp18_implications_for_its_age_activity_and_influenceSérgio Sacani
1) An 87 ks Chandra observation was performed of the star WASP-18, which hosts a very close-in hot Jupiter planet orbiting within 20 hours.
2) WASP-18 was not detected in X-rays down to a luminosity limit of 4 x 10^26 erg/s, over two orders of magnitude lower than expected for a star of its estimated age of 600 Myr.
3) This unusually low activity level for a star of WASP-18's age and mass suggests that the massive planet may play a role in disrupting the stellar magnetic dynamo generated within its thin convective layers through star-planet interaction.
1. The author measured proper motions of molecular hydrogen (H2) emission features in the Herbig-Haro 46/47 outflow system, finding tangential velocities ranging from tens to nearly 500 km/s.
2. The highest velocities were observed for H2 knots located along or near the jet/counterjet axes, while knots forming the wings of a large H2 bow shock moved more slowly.
3. Several H2 knots were found to have significantly changed luminosity over the 4-year study, indicating variability in H2 emission from young stellar object outflows for the first time.
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
We present spectroscopic observations of the nearby dwarf galaxy AGC 198691. This object is part
of the Survey of H I in Extremely Low-Mass Dwarfs (SHIELD) project, which is a multi-wavelength
study of galaxies with H I masses in the range of 106-107:2 M discovered by the ALFALFA survey.
We have obtained spectra of the lone H II region in AGC 198691 with the new high-throughput
KPNO Ohio State Multi-Object Spectrograph (KOSMOS) on the Mayall 4-m as well as with the Blue
Channel spectrograph on the MMT 6.5-m telescope. These observations enable the measurement of the
temperature-sensitive [O III]4363 line and hence the determination of a \direct" oxygen abundance
for AGC 198691. We nd this system to be an extremely metal-decient (XMD) system with an
oxygen abundance of 12+log(O/H) = 7.02 0.03, making AGC 198691 the lowest-abundance starforming
galaxy known in the local universe. Two of the ve lowest-abundance galaxies known have
been discovered by the ALFALFA blind H I survey; this high yield of XMD galaxies represents a
paradigm shift in the search for extremely metal-poor galaxies.
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.
First discovery of_a_magnetic_field_in_a_main_sequence_delta_scuti_star_the_k...Sérgio Sacani
Coralie Neiner do Laboratory for Space Studies and Astrophysics Instrumentation, LESIA (CNRS/Observatoire de Paris/UPMC/Université Paris Diderot) e Patricia Lampens (Royual OIbservatory of Belgium), descobriram a primeira estrela magnética do tipo delta Scuti, através de observações espectropolarimétricas, realizadas com o telescópio CFHT. As estrelas do tipo delta Scuti, são estrelas pulsantes, sendo que algumas delas mostram assinaturas atribuídas para um segundo tipo de pulsação. A descoberta mostra que isso é na verdade a assinatura de um campo magnético. Essa descoberta tem importantes implicações para o entendimento do interior das estrelas.
Dois tipos de estrelas pulsantes existem entre as estrelas com massa entre 1.5 e 2.5 vezes a massa do Sol: as estrelas do tipo delta Scuti e as estrelas do tipo gamma Dor. A teoria nos diz que as estrelas com temperatura entre 6900 e 7400 graus Kelvin podem ter ambos os tipos de pulsação. Essas são então chamadas de estrelas híbridas. Contudo, o satélite Kepler da NASA tem detectado um grande número de estrelas híbridas com temperaturas maiores ou menores do que esse limite pensado anteriormente. A existência dessas estrelas híbridas com temperaturas maiores é algo muito controverso, já que desafia o nosso entendimento sobre as estrelas pulsantes do tipo delta Scuti e gamma Dor.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in th...GOASA
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion. The discovery of the
- The document is a student's chemistry project on space chemistry. It thanks the teacher and school for allowing the project and providing resources.
- The project covers topics like the chemical composition of space, how space suits work, rocket propellants, and harnessing energy from space. It includes sections on stars and their properties, the life and death of stars, and references.
This document summarizes a study checking the reality of the "yellow evolutionary void" in the Hertzsprung-Russell diagram through an analysis of three stars - HD 33579, HR 8752, and IRC+10420. The study finds that HD 33579 has a large mass and stable behavior, suggesting it is a young, redward-evolving supergiant allowed in the void. HR 8752 and IRC+10420 have lower masses, placing them in a post-red blueward evolutionary loop, and they show evidence of "bouncing" as they approach the void. The photometric variations of HD 33579 and HR 8752 are attributed to pulsations.
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.
The yellow hypergiant_hr5171a_resolving_a_massive_interacting_binary_in_the_c...Sérgio Sacani
HR 5171 A exhibits a complex appearance based on AMBER/VLTI observations. The observations reveal an unusually large star of approximately 1315 solar radii at a distance of 3.6 kiloparsecs. The source is surrounded by an extended nebula. The observations also show a high level of asymmetry in the brightness distribution, which is attributed to the discovery of a companion star located in front of the primary. Analysis of visual photometry data spanning over 60 years indicates the system has an orbital period of 1304 days, providing evidence it is a contact or over-contact eclipsing binary. Modeling suggests a total system mass of 39-79 solar masses and a high mass ratio of at least 10 for the companion.
The physical properties_of_the_dust_in_rcw120_as_seen_by_herschelSérgio Sacani
This document summarizes the results of a study using Herschel Space Observatory data to analyze the physical properties of dust in the RCW 120 H ii region. The study finds:
1) Dust temperatures in RCW 120 range from around 30 K in the interior decreasing to 20 K in the photo-dissociation region and 10 K in nearby infrared dark clouds.
2) There is tentative evidence of an anti-correlation between dust temperature and dust emissivity index β, with cooler dust having higher β values, in agreement with some previous studies.
3) RCW 120 appears to be in the process of destroying its photo-dissociation region boundary and leaked radiation may be influencing the formation of the
This document summarizes the results of a study using Herschel Space Observatory data to analyze the physical properties of dust in the RCW 120 H ii region. The study finds:
1) Dust temperatures in RCW 120 range from around 30 K in the interior decreasing to 20 K in the photo-dissociation region and 10 K in nearby infrared dark clouds.
2) There is tentative evidence of an anti-correlation between dust temperature and the dust emissivity index β, with cooler dust having higher β values, consistent with some previous studies.
3) RCW 120 appears to be in the process of destroying its photo-dissociation region boundary and leaked radiation from the interior may be influencing the
A LUMINOUS Be+WHITE DWARF SUPERSOFT SOURCE IN THE WING OF THE SMC: MAXI J0158...Carlos Bella
This document summarizes a study of the X-ray source MAXI J0158-744, which was detected by the MAXI instrument in November 2011. It exhibited an unusually bright and brief X-ray flare with a luminosity exceeding 10^39 erg/s, approaching ultraluminous X-ray source levels. Follow-up observations with Swift and other instruments over subsequent months found the source had a very soft X-ray spectrum characteristic of a supersoft source. Optical spectra of the counterpart revealed emission and absorption features consistent with a B1/2IIIe spectral type star in the Small Magellanic Cloud. The authors propose MAXI J0158-744 is a luminous supersoft source associated with
This document summarizes a study of lithium and sodium abundances in stars in the globular cluster M4. The authors obtained spectra for 91 main sequence and subgiant branch stars using the FLAMES spectrograph on the VLT. They detected a weak anti-correlation between lithium and sodium abundances among unevolved main sequence stars. Notably, one star, #37934, showed an unusually high lithium abundance, comparable to estimates of the primordial lithium abundance. This high lithium abundance, coupled with the star's sodium-rich nature, suggests the lithium may have come from pollution by a previous generation of stars, though preservation of the primordial abundance cannot be ruled out. The detection provides new evidence that globular clusters
This document summarizes a study examining the hypergiant star ρ Cassiopeiae. The researchers developed a model to explain ρ Cassiopeiae's variable mass loss rate, high microturbulent velocity, and Hα emission line profile using a stochastic field of shock waves in the star's atmosphere. Their model successfully reproduced the observed mass loss rate, microturbulent velocity, and aspects of the Hα profile using only one parameter - the maximum Mach number of shock waves in the atmosphere. The model indicates that thin, hot regions behind shock waves are responsible for the observed microturbulence and contribute to Hα emission.
The evolutionary stage of Betelgeuse inferred from its pulsation periodsSérgio Sacani
This document discusses the evolutionary stage of the red supergiant star Betelgeuse based on analyses of its pulsation periods. The authors identify Betelgeuse's longest observed period of around 2200 days as the radial fundamental mode, rather than a long secondary period of unknown origin as previously thought. Evolutionary models that excite pulsations matching Betelgeuse's four observed periods are found to be in a late stage of core carbon burning, with initial masses around 19 solar masses and current masses of about 11-12 solar masses. The authors conclude Betelgeuse is in a late evolutionary stage prior to an impending supernova explosion.
This document describes the discovery of an unusual rectangular-shaped galaxy called LEDA 074886. Some key details:
- LEDA 074886 has an absolute magnitude of -17.3 and resembles an "emerald cut diamond" in shape with very boxy isophotes.
- It contains an embedded edge-on stellar disk of extent 1.2 kpc, with a rotation to dispersion ratio of 1.4.
- The authors speculate that LEDA 074886 may be the remnant of two merged disk galaxies, where the initial gas drove inward to form the inner disk, while the stars at larger radii experienced a dissipationless merger resulting in the rectangular shape.
-
Extended x ray emission in the h i cavity of ngc 4151- galaxy-scale active ga...Sérgio Sacani
The document summarizes the discovery of diffuse soft X-ray emission extending about 2 kpc from the active nucleus of NGC 4151, filling the cavity of H i material. The X-ray emission has a luminosity of about 1039 erg s-1 and can be fit with either a thermal plasma model with a temperature of around 0.25 keV, or a photoionized model. This interaction between the AGN and interstellar medium implies the last episode of high nuclear activity occurred relatively recently, around 104 years ago.
The high albedo of the hot jupiter kepler 7 bSérgio Sacani
This document summarizes the analysis of Kepler photometry data for the exoplanet Kepler-7b. Key findings include:
1) The occultation depth is measured to be 44±5 ppm, translating to a Kepler geometric albedo of 0.32±0.03, the most precise value measured for an exoplanet.
2) The planetary orbital phase lightcurve is characterized with an amplitude of 42±4 ppm.
3) Atmospheric modeling finds it unlikely that the high albedo is due to a dominant thermal component. Two possible explanations are proposed: excess reflection from clouds/hazes, or depleted atmospheric sodium and potassium allowing Rayleigh scattering to dominate.
The document describes Hubble Space Telescope observations of Hercules A that revealed two faint, dark, interlocking rings of obscuring material located near the galaxy's nucleus and aligned along the radio jet axis. The rings are interpreted as either dust or electron scattering, and several models are discussed for their origin, including entrainment of molecular clouds by the radio jets or expansion of hot gas bubbles produced by the active galactic nucleus. The rings provide new insights into the transport of energy by powerful radio jets.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
A young protoplanet_candidate_embedded_in_the_circumstellar_disk_of_hd100546Sérgio Sacani
This document summarizes observations of HD100546 using high-contrast imaging techniques. A faint emission source was detected near the star at a projected separation of about 47 AU. The position of the source coincides with a deficit in polarization observed from the circumstellar disk. This suggests a physical link between the source and the disk. Considering various scenarios, the authors favor interpreting the source as a young protoplanet currently forming within the disk. Follow-up observations could distinguish between different possible explanations for the observed features. If confirmed, it would be a unique opportunity to study giant planet formation within an optically thick disk.
The ionized nebula_surrounding_the_w26_in_westerlund_1Sérgio Sacani
The document summarizes observations of an ionized nebula surrounding the red supergiant star W26 in the massive star cluster Westerlund 1. H-alpha images reveal a circumstellar shell or ring 0.1 pc in diameter surrounding the star, as well as a triangular nebula 0.2 pc away with a complex filamentary structure. Spectroscopy confirms the nebula is ionized but the excitation mechanism is unclear given red supergiants do not produce ionizing photons. The nebula and star's high luminosity and spectral variability suggest W26 is a highly evolved red supergiant experiencing extreme mass loss, making it an important case study for understanding the late stages of massive star evolution.
Hot white dwarfs and pre-white dwarfs discovered with SALTSérgio Sacani
The Southern African Large Telescope survey of helium-rich hot subdwarfs aims to explore evolutionary pathways among
groups of highly evolved stars. The selection criteria mean that several hot white dwarfs and related objects have also been
included. This paper reports the discovery and analysis of eight new very hot white dwarf and pre-white dwarf stars with effective
temperatures exceeding 100 000 K. They include two PG1159 stars, one DO white dwarf, three O(He), and two O(H) stars. One
of the O(H) stars is the central star of a newly discovered planetary nebula, and the other is the hottest ‘naked’ O(H) star. Both
of the PG1159 stars are GW Vir variables, one being the hottest GW Vir star measured and a crucial test for pulsation stability
models. The DO white dwarf is also the hottest in its class.
This document summarizes the discovery of two planetary companions orbiting the metal-poor star HIP 11952 based on radial velocity measurements. The star HIP 11952 was observed over a period of 16 months using the FEROS spectrograph. Analysis of the spectra revealed periodic radial velocity variations of 6.95 days and 290 days, indicating the presence of two planets with minimum masses of 0.78 MJup and 2.93 MJup orbiting at 0.07 AU and 0.81 AU, respectively. HIP 11952 is a metal-poor star with [Fe/H] of -1.95, making it one of the few known systems with planets orbiting a star with such low metallicity
Gas physical conditions_and_kinematics_of_the_giant_outflow_ou4Sérgio Sacani
This document discusses observations of the giant outflow Ou4, located near the HII region Sh 2-129. Spectroscopic observations of Ou4 reveal shock-excited gas consistent with a fast collimated outflow. Mid-infrared images show a bubble of hot dust emission inside Ou4 that corresponds to [OIII] features. The distance and properties of Ou4 are consistent with it being launched about 90,000 years ago from the young massive star cluster HR 8119, located at the center of Sh 2-129. However, the possibility that Ou4 is a planetary nebula or resulted from an eruptive event on a massive asymptotic giant branch star cannot be ruled out.
1. A&A 546, A105 (2012) Astronomy
DOI: 10.1051/0004-6361/201117166 &
c ESO 2012 Astrophysics
The hypergiant HR 8752 evolving through the yellow
evolutionary void ,
H. Nieuwenhuijzen1 , C. De Jager1,2 , I. Kolka3 , G. Israelian4 , A. Lobel5 , E. Zsoldos6 , A. Maeder7 , and G. Meynet7
1
SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
e-mail: h.nieuwenhuijzen@sron.nl; h.nieuwenhuijzen@xs4all.nl
2
NIOZ, Royal Netherlands Institute for Sea Research, PO Box 59, Den Burg, The Netherlands
e-mail: cdej@kpnplanet.nl
3
Tartu Observatory, 61602 Tõravere, Estonia
e-mail: indrek@aai.ee
4
Instituto de Astrofisica de Canarias, via Lactea s/n, 38200 La Laguna, Tenerife, Spain
e-mail: gil@iac.es
5
Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
e-mail: alobel@sdf.lonestar.org; Alex.Lobel@oma.be
6
Konkoly Observatory, PO Box 67, 1525 Budapest, Hungary
e-mail: zsoldos@konkoly.hu
7
Observatoire de Genève, 1290 Sauverny, Switzerland
e-mail: [Andre.Maeder;Georges.Meynet]@unige.ch
Received 30 April 2011 / Accepted 13 March 2012
ABSTRACT
Context. We study the time history of the yellow hypergiant HR 8752 based on high-resolution spectra (1973–2005), the observed
MK spectral classification data, B − V- and V-observations (1918–1996) and yet earlier V-observations (1840–1918).
Aims. Our local thermal equilibrium analysis of the spectra yields accurate values of the effective temperature (T eff ), the accelera-
tion of gravity (g), and the turbulent velocity (vt ) for 26 spectra. The standard deviations average are 82 K for T eff , 0.23 for log g,
and 1.1 km s−1 for vt .
Methods. A comparison of B− V observations, MK spectral types, and T eff -data yields E(B− V), “intrinsic” B− V, T eff , absorption AV ,
and the bolometric correction BC. With the additional information from simultaneous values of B − V, V, and an estimated value of R,
the ratio of specific absorption to the interstellar absorption parameter E(B − V), the “unreddened” bolometric magnitude mbol,0 can
be determined. With Hipparcos distance measurements of HR 8752, the absolute bolometric magnitude Mbol,0 can be determined.
Results. Over the period of our study, the value of T eff gradually increased during a number of downward excursions that were ob-
servable over the period of sufficient time coverage. These observations, together with those of the effective acceleration g and the
turbulent velocity vt , suggest that the star underwent a number of successive gas ejections. During each ejection, a pseudo photosphere
was produced of increasingly smaller g and higher vt values. After the dispersion into space of the ejected shells and after the restruc-
turing of the star’s atmosphere, a hotter and more compact photosphere became visible. From the B − V and V observations, the basic
stellar parameters, T eff , log M/M , log L/L , and log R/R are determined for each of the observational points. The results show the
variation in these basic stellar parameters over the past near-century.
Conclusions. We show that the atmospheric instability region in the HR-diagram that we baptize the yellow evolutionary void actually
consists of two parts. We claim that the present observations show that HR 8752 is presently climbing out of the “first” instability
region and that it is on its way to stability, but in the course of its future evolution it still has to go through the second potential unstable
region.
Key words. stars: atmospheres – stars: evolution – supergiants – stars: mass-loss – stars: fundamental parameters –
stars: variables: S Doradus
1. Introduction 1.1. The yellow hypergiants; HR 8752 in the literature
We summarize in this section the status of knowledge on The star HR 8752 is a member of a group of half a dozen massive
HR 8752 and the evolution of hypergiants and succinctly review stars, with zero age main sequence (ZAMS) masses of 20–40 or
the aims of this research. even more solar masses, the yellow hypergiants. Another well-
studied member is ρ Cas (Lobel et al. 1992, 1994, 1998, 2003;
Appendix A is available in electronic form at
http://www.aanda.org Israelian et al. 1999; Gorlova et al. 2006). These are sites of
Tables A.x and B.x are available in electronic form at the CDS via heavy mass-loss, which is sometimes episodic. The individual
anonymous ftp to stars undergo large variations in temperature. These variations
cdsarc.u-strasbg.fr (130.79.128.5) or via are the visible atmospheric manifestations of changes that are
http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A105, only semi-coupled to the star, underlying its (pseudo-) photo-
and at the external site http://www.aai.ee/HR~8752 sphere. The evolutionary changes of the underlying star have a
Article published by EDP Sciences A105, page 1 of 24
2. A&A 546, A105 (2012)
timescale that is much longer than the stability timescale of the HR 8752 and evolutionary tracks (Meynet et al., 1994)
photosphere. We associate these stars with the luminous blue 6.6 Some hypergiants near the Yellow Evolutionary Void
variables (LBVs). HD 80077 galactic hypergiant
6.4
m040e020
The extended literature on HR 8752 shows a large variabil- m025e020
ity in the spectral classification, and colour magnitudes. An early 6.2
HD Limit Yellow Void
review was written by De Jager (1980, p. 101–102). The histor- lower Teff range
log L/L sun
6.0
ical light curve from 1840 to about 1980 is shown by Zsoldos Track 4 IRC+10420
5.8 ρ Cas HD 119796
(1986a), with a bibliography on what was known about the star HD 212466
at that time. The star HR 8752 is a variable with an amplitude 5.6 40 M sun Track 3
HR 8752
HD 96918
of about 0.2 mag, and its light variation has a characteristic 5.4 Tracks 4,5
CRL 2688
timescale of about one year. It has main-sequence B1 compan-
ion (Stickland & Harmer 1978), and its circumstellar envelope 5.2 25 M sun Track 3 HD 223385
emits thermal radio emission (Smolinski et al. 1977; Higgs et al. 5.0
1978). An excellent spectral analysis of the star at one point in 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4
log T eff
its changing history was published by Luck (1975). He found
an effective temperature of 4000 K, a log g value of about –2, Fig. 1. Evolutionary tracks for 25 and 40 solar masses from Meynet
and a metal abundance that seems to have Solar-System val- et al. (1994), models with two times the mass-loss rate of De Jager
ues. A self-consistent spectrum synthesis analysis (Fry & Aller et al. (1988). Some Galactic hypergiants including HR 8752 are indi-
1975) suggests that HR 8752 has solar-type abundances. No ev- cated with their positions in the HR-diagram, some of them with ob-
idence has been found of extended structures (Schuster et al. served changes of temperature. The Humphreys-Davidson limit and
2003) for the yellow hypergiants ρ Cas, HR 8752, HR 5171a, the approximate position of the yellow evolutionary void are indi-
and μ Cep within 0. 1 of the stars and, down to the Hubble cated. For each model, evolutionary track 3 starts at the higher tem-
Wide-Field Camera (WFPC2) noise level, at about 2 . The satel- peratures and evolves redward until the “mirror point” and then returns
to higher temperatures as track 4. For the ZAMS 40 solar-mass model,
lite Hipparcos (with identification number HIP115361) has ob- track 4 goes to high temperatures, while for the ZAMS 25 solar-mass
tained colour-magnitude data that show short timescale variabil- model track 4 goes to an inversion (a secondary “mirror” point) and
ity (Nieuwenhuijzen & De Jager 2000). Its Tycho photometric thereupon goes redward as track 5.
data is given in the specific Tycho colour system that has yet to
be translated to the Johnson system for comparison purposes.
supergiant phase. The effective temperature T eff hardly changes
1.2. The evolution of hypergiant stars; the yellow during this time and large mass-losses occur.
evolutionary void An example of the timescales involved: for a model of
ZAMS mass of 25 solar masses (Meynet et al. 1994) with a lumi-
The yellow hypergiants have absolute magnitudes Mbol nosity log(L/L ) = 5.3, the time for evolution through the area
around −8 and T eff -values between 4000 K and 8000 K. In of the yellow void corresponds to 10 000 or more years, with
the HR diagram, they are situated at the low-temperature edge an increase in temperature of about 1000 K. While details differ
of an area that is virtually void of stars (Humphreys 1978; for other models, it is clear that, because of the short time span
for LMC and other galaxies cf. also Humphreys & Davidson involved, only few stars can be found inside the yellow evolu-
1979). A study of the void revealed that the few stars that tionary void.
are situated inside the void are young redward-evolving objects There may also be another reason for the existence of
(Nieuwenhuijzen & De Jager 2000). No (old) blueward evolv- this area of “avoidance”. In an earlier paper by two of us
ing stars were found inside the void. It is generally assumed (Nieuwenhuijzen & De Jager 1995), we developed a code to
that the void is an area where blueward-evolving stars are un- model geff -values over the HR-diagram using stellar mass-loss
stable (De Jager & Nieuwenhuijzen 1995; De Jager et al. 2001). data (from De Jager et al. 1988) and mass data from stellar
This area of the Hertzsprung-Russell diagram (HR-diagram) evolutionary models (Maeder & Meynet 1988). For the mass,
was baptized the yellow evolutionary void, or yellow void in we differentiated the various evolutionary phases by using the
brief. Later in this paper, we show that the void actually con- above-mentioned tracks in a specific way (Nieuwenhuijzen &
tains two limited regions: log T eff ≈ 3.8−3.95 where the ioniza- De Jager 1995). In the course of the above calculations, it ap-
tion of H might give rise to a low stability of the atmosphere, peared that massive stars of ZAMS masses between 20 and
and log T eff ≈ 4.05−4.1 where the ionization of He plays a part. about 60 solar masses are able to cross the HR diagram in their
These separate regions lie within the general yellow void. redward evolution (track 3) unimpededly, but on their return to
The position of some yellow hypergiants and the posi- the blue (track 4, cf. Fig. 1 where tracks 3 and 4 are indicated
tion of HR 8752 in the HR-diagram are given in Fig. 1, to- for a 40 M and a 25 M model) they have lost so much of
gether with evolutionary tracks (Meynet et al. 1994) for ZAMS their mass that their photospheres obtain effective accelerations
masses of 25 and 40 solar masses, respectively. The redward- close to zero and the mean weighted value of the thermody-
evolving tracks are labelled “track 3” and the blueward-evolving namic coefficient Γ1 (defined in Eq. (1), Sect. 4.1) comes in
“track 4”. These tracks are also indicated in the figure. The a range where Γ1 < 4/3 over an appreciable part of the at-
reason for choosing these models is that we position HR 8752 mosphere. Such a star may then become unstable (not neces-
(Nieuwenhuijzen & De Jager 2000) somewhere between the sarily dynamically, but generally, cf. Maeder 2009, Sect. 1.3.2).
models of a 25- and a 40-ZAMS solar-mass star (as given by In the outer layers of the hypergiant both below and above the
the models of Meynet et al. 1994). photosphere all hydrodynamic processes are strongly nonadia-
We call the transition region between these tracks the batic owing to the large radiation losses. In particular, instead of
“mirror” point, this being a region between tracks 3 and 4, in dynamical instability one may expect, for example, the strange
the time after the main-sequence and the transition to the red mode oscillations.
A105, page 2 of 24
3. H. Nieuwenhuijzen et al.: HR 8752 evolving through the void
For certain areas in the HR-diagram, that coincide with the Table 1. Observations, dates, and observers.
position of the void, no stable solution could be derived with our
code, indicating the (possible) presence of a density inversion. Observations Date JD-2 400 000 Observer
This explanation seems reasonable owing to the development of obs1 1973.08.13-17 41 911.3 Luck
the code that was defined for a monotonically decreasing atmo- obs2 1978.08.– 43 737.3 Smolinski
spheric density, with scaleheights and the concept of geff (loc. obs3 1984.07.– 45 898.3 Piters
cit. Eqs. (6)–(9)). Although the existence of a density inversion obs4 1995.04.18 49 824.3 Rutten
does not directly lead to instability (cf. Maeder 2009, Sect. 5.5.2, obs5 2000.06.06 51 702.5 Israelian
and also Maeder 1989), it might begin to explain the existence obs6 2000.10.06 51 824.4 Kolka
of (massive) shells as we discuss in Sect. 6. The existence of this obs7 2000.11.27 51 876.4 Kolka
obs8 2001.01.12 51 922.3 Kolka
phenomenon coincides with low values of Γ1 , which is the driv-
obs9 2001.02.16 51 957.3 Kolka
ing parameter in this part of our research. The low values of Γ1 obs10 2001.03.30 51 999.4 Kolka
in stars such as HR 8752 result from high radiation pressure and obs11 2001.09.25 52 178 Kolka
partial ionization effects. In Sect. 4, we discuss this parameter obs12 2001.10.01 52 184 Israelian
and its values over the HR-diagram for stellar models traversing obs13 2001.11.16 52 230.4 Kolka
the void. obs14 2002.03.25 52 359.6 Kolka
obs15 2002.08.21 52 508.5 Kolka
1.3. Aims of the present research obs16 2002.12.14 52 623.4 Kolka
obs17 2003.02.19 52 690.3 Kolka
During the past two decades, we have collected a large num- obs18 2003.03.03 52 702.3 Kolka
ber of high-resolution spectra of HR 8752 to study the details of obs19 2003.03.04 52 703.3 Kolka
its evolution. It is gratifying to note that this initiative was suc- obs20 2003.03.05 52 704.3 Kolka
cessful, because the study of these spectra allowed us, for the obs21 2003.04.18 52 748.5 Kolka
first time, to investigate the details of the evolution of a hyper- obs22 2003.07.31 52 852.5 Kolka
obs23 2004.02.11 53 047.3 Kolka
giant star during a crucial phase of its evolution. Of particular
obs24 2004.10.14 53 293.5 Kolka
interest are the various episodes of mass-loss and the recovery obs25 2005.07.22 53 574 Lobel
afterwards. That part of the investigation is completed by the in- obs26 2005.10.11 53 655.5 Kolka
clusion of occasionally obtained spectra at earlier epochs.
By analysing data on colours and magnitudes obtained in the
past century, the timeline of this research is extended, albeit not and the turbulent velocity vt , we analysed the data of the differ-
with the accuracy and details of the spectral investigations. ent observations in an identical manner, to ensure the resulting
In the following sections of this paper, we first discuss the values would be consistent and accurate, though in a relative, not
high-resolution spectra. Thereafter we deal with the colours and absolute sense.
magnitudes. After that we consider the consequences of this in- The analysis of the spectra was performed on an ensemble
vestigation for our understanding of the evolution of this partic- of measured lines and their equivalent widths. The observational
ular hypergiant and the possible consequences for the evolution data were compared to model equivalent widths obtained by in-
in general of very massive stars. terpolating equivalent widths in a grid of model spectra. The
model spectra results were based on three premises: (1) the use
2. Spectral line investigations and their results of Kurucz LTE models; (2) the use of published atomic data,
We now describe the analysis of our spectra. The reason for notably log (g f )-values, preferably from NIST data (cf. refer-
starting this systematic series of observations was that an ear- ences, Sect. 2.2), and in some cases from Kurucz line atomic data
lier study (Nieuwenhuijzen & De Jager 2000) of the time his- (cf. references, Sect. 2.2); and (3) the use of the model calcula-
tory of this star had shown the occurrence of occasional mass tion program SCAN, developed in SRON (SRON Laboratory for
ejections associated with lower T eff values, after which T eff in- Space Research) in Utrecht by L. Achmad, based on an earlier
creased gradually until another episode of mass-loss again led program Scan from Kiel, Germany, and modified by M. Burger
to another drop of T eff . This zigzag behaviour appeared to oc- at SRON (Nieuwenhuijzen & De Jager 2000). Results derived
cur for T eff values in the range from approximately 5000 K to by these three inputs LTE, NIST, and SCAN, have not been cali-
around 7500 K, which was reached in the year 2000. After this brated as a total package, so that the results can only be taken as
time, T eff increased further to ≈8000 K. It was considered in- relative in terms of accuracy.
teresting to see whether a new period of mass ejection would In this paper, we use the value of the metallicity parameter
occur, and which values of the physical parameters would be es- derived in earlier analyses (cf. Luck 1975; Fry & Aller 1975;
sential for “triggering” the ejection process. Another question Nieuwenhuijzen & De Jager 2000), where it was found that
was whether the star would asymptotically approach the high abundances were close to the solar value. We use Kurucz stellar
temperature end of the void at around T eff ≈ 9000−10 000 K. LTE models with solar abundances, thus limiting the research to
We therefore worked on a semi-regular basis to obtain new three unknowns, viz. T eff , log g, and vt .
high-resolution spectra of HR 8752. Observations listed as obs5
to obs26 were made at the La Palma and Tartu Observatories 2.1. Observations
in the period from 2000/7 to 2005/10. Table 1 lists observation
dates and observers. We included four earlier published spec- Obs5 and obs25 were obtained with the SOFIN echelle spectro-
tra (analysed the same way) from Nieuwenhuijzen & De Jager graph on the NOT, and obs12 with the UES on the WHT, both
(2000) to extend the baseline and for comparison purposes. at sites in La Palma. Obs6-obs11, obs13-24, and obs26 were
These are mentioned as obs1-obs4 in the above table. obtained at the Tartu Observatory. Four earlier published spec-
To determine the time variation in the atmospheric parame- tra (Nieuwenhuijzen & De Jager 2000) are given as obs1-obs4
ters T eff (effective temperature), log geff (effective acceleration), (cf. Table 1).
A105, page 3 of 24
4. A&A 546, A105 (2012)
Table 2. Estimated errors in the EWs, with the exception of obs4 and created to contain the polynomial terms for each observed spec-
obs25. tral line. The three-dimensional interpolation procedure is based
on our earlier two-dimensional chebychev codes (De Jager et al.
Range EW Error 1988; cf. also Appendix B.1).
10...30 mÅ 20% Thus, the parameters in the library contain information about
30...70 mÅ 10% EW-values over the complete grid for each spectral line.
70..200 mÅ 5% The modelled EW-values for the optimal set of parameters
>200 mÅ 2%...5% in the fitting procedure are given in Table A.1.3, which has the
same structure as that for the observed EWs.
Table 3. Grid of model photospheres used in the spectral line library.
2.5. Accuracy of EW data from models
−1
T eff (K) log g vt km s ... ... ... The estimated errors in the modelled lines take into account
4250–6000 0.0–2.0 4 6 13 19 the inaccuracy of the g f -values underlying the model EWs. If
6250–7500 0.5–2.5 4 6 13 19 the accuracy value Δg f is known, the influence of this value
7750–8250 1.0–3.0 4 6 13 19 on the modelled EW is found by doing calculations for g f ,
8500–9000 1.5–3.5 4 6 13 19 g f ± Δg f and taking the mean difference of the EWs as an accu-
9250–9250 2.0–4.0 4 6 13 19
racy estimate ΔEW.
The accuracies of the modelled equivalent widths are deter-
The full set of observed equivalent widths (EWs) in units mined for all the spectral lines and all models in the model grid
of mÅ are available in electronic Tables A.1.1 with columns for (cf. Table 3). These data are then reduced to N parameters for
observations obs1-obs26, and rows for spectral lines with wave- a chebychev polynomial evaluation of ΔEW and added to the
length (Å) and element number. spectral line library. There are thus two separate entries in the
library for each modelled spectral line.
The errors in the modelled EW-data for the optimal set of pa-
2.2. Spectral lines rameters in the fitting procedure are given in Table A.1.4, which
has the same structure as that for the observed EWs.
The spectral lines used in this research are given in Table A.2
in the form of wavelength, ele, ion (atomic number combined
with ionization stage), elo(cm-1), 10log(g f ), and an accuracy 2.6. Comparing observational and model EW data
value based on NIST1 data and Martin et al. (1988) publica-
tions in the form of a letter designation A-E, corresponding to For each observation, the analysis program compares observed
accuracies of 10–50%. Lines that were unavailable from NIST and modelled EWs for all relevant spectral lines, together with a
were taken from Kurucz2 . These data were used with an accu- combined σtotal derived from
racy factor of 50%, as we did not have a critical compendium of (σtotal )2 = (σobs )2 + A.(σmodel )2 .
the accuracy of these g f -values. We translated these figures into We always took A = 1.0. The total σtotal is given in Table A.1.4.
logarithmic values and added them as “accuracy” to the list in Defining the “significance” as the difference EW-value di-
Table A.2. vided by σtotal , we give the “significance” for each spectral line
and the optimal set of parameters in the fitting procedure in
2.3. Errors in observations Table A.1.5, which has the same structure as that for the ob-
served EWs.
Errors in the observed EWs were estimated following Table 2, When the significance is more than one standard deviation,
except for obs4 and obs25. For these, a different approach was this may be due to either an outlier or a line misidentification
taken, using one measurement to help determine the optimal (e.g. caused by varying temperatures when other lines appear
continuum and two measurements with a 1% difference of con- to be predominant at about the same wavelengths). We discuss
tinuum level. Multiplying this difference value by an estimate of deviations for some lines in Table A.3.
the continuum accuracy provides a measure of the observational In one case, we used a correlation technique to find the mean
accuracy in EW. The errors are given in Table A.1.2, which has wavelength shift between the observed wavelengths and mod-
the same structure as that for the observed EWs. elled lines in Table A.4.
To achieve “stable” results, we used a method of “robust
2.4. EW data from models fitting” with a Lorentzian tail distribution to ensure that large
deviations in χ2 only marginally influence the fitting process
A range of temperatures and log g’s was encountered in the anal- (cf. Press et al. 1992, chap. 15.7; Vetterling et al. 1992). In this
ysis of the observations. We decided to use a grid of LTE mod- paper, we use the merit function of the Lorentzian minimization
els and for each model created a list of lines and modelled EWs. as a “χ2 ” value.
Table 3 defines the model grid. The data of the models is rep-
resented by a three-dimensional chebychev polynomial with a
limited number of terms N. In our case, N = 45. A library was 2.7. Results of analysis
1
http://physics.nist.gov/PhysRefData/ASD/index.html The results of the best-fit analysis are given in Table 4 and in
http://physics.nist.gov/PhysRefData/datarefscover.html Fig. 2 for log T eff , in Fig. 3 for log g, and in Fig. 4 for the turbu-
http://physics.nist.gov/cgi-bin/ASBib1/TransProbBib. lent velocity vt (km s−1 ).
cgi We note that when log g-values are extrapolated outside the
2
http://cfaku5.cfa.harvard.edu/temp grid of model values of T eff , log g, and vt an asterisk is given in
http://kurucz.harvard.edu/grids.html Table 4 before the value of log g to indicate extrapolation.
A105, page 4 of 24
5. H. Nieuwenhuijzen et al.: HR 8752 evolving through the void
Table 4. Results of LTE effective temperatures T eff , Kurucz-log g- Log g from obs 1-26
values, and turbulent velocities vt . as a function of time
2.0
1975 1980 1985 1990 1995 2000 2005
Obs JD T eff log g vt
1.5
nr −2 400 000 (K) (cm sec-2) (km s−1 )
obs1 41 911.3 4913.7 ± 72.0 * –0.88 ± 0.07 11.67 ± 1.39 1.0
obs2 43 737.3 5601.7 ± 120.7 * –0.62 ± 0.08 13.10 ± 0.99
Log g
obs3 45 898.3 5334.0 ± 239.4 * –0.76 ± 0.12 14.07 ± 1.54 0.5
obs4 49 824.3 7346.2 ± 70.6 * 0.40 ± 0.19 14.23 ± 1.20
obs5 51 702.5 7611.6 ± 69.5 * 0.55 ± 0.21 11.20 ± 1.00 -0.0
obs6 51 824.4 7777.7 ± 73.3 * 0.63 ± 0.25 10.46 ± 0.98
obs7 51 876.4 7623.5 ± 61.7 * 0.56 ± 0.21 10.96 ± 0.94 -0.5
obs8 51 922.3 7747.1 ± 60.4 * 0.66 ± 0.21 9.75 ± 0.87
obs9 51 957.3 7812.1 ± 65.9 * 0.75 ± 0.20 10.61 ± 0.98 -1.0
obs10 51 999.4 8024.9 ± 76.9 1.09 ± 0.27 11.19 ± 1.16
41000 43000 45000 47000 49000 51000 53000 55000
obs11 52 178 7619.0 ± 59.9 * 0.51 ± 0.17 9.99 ± 0.80
JD - 2400000 / Year
obs12 52 184 7534.4 ± 67.7 0.51 ± 0.19 11.14 ± 0.97
obs13 52 230.4 7894.6 ± 80.9 1.02 ± 0.28 9.91 ± 0.98 Fig. 3. Results of the fitting of log g with Kurucz’s LTE models for the
obs14 52 359.6 7893.3 ± 83.8 1.20 ± 0.36 10.30 ± 1.09 observations obs1-obs26 as described in this paper.
obs15 52 508.5 7868.2 ± 80.4 * 0.88 ± 0.24 11.90 ± 1.09
obs16 52 623.4 8019.2 ± 82.6 1.30 ± 0.37 11.84 ± 1.22 vt (km/s) from obs 1-26
obs17 52 690.3 7639.2 ± 85.3 * 0.77 ± 0.33 9.88 ± 1.14
obs18 52 702.3 7576.0 ± 70.9 0.60 ± 0.22 9.57 ± 0.89 as a function of time
obs19 52 703.3 7525.1 ± 66.4 * 0.48 ± 0.21 9.49 ± 0.96 16
obs20 52 704.3 7550.3 ± 69.0 0.53 ± 0.22 9.43 ± 0.85 15
obs21 52 748.5 7894.7 ± 84.1 0.99 ± 0.26 11.95 ± 1.27 14
13
obs22 52 852.5 7909.8 ± 82.6 1.05 ± 0.25 12.46 ± 2.06
12
7942.2 ± 82.7 1.11 ± 0.31 11.15 ± 1.21
vt (km/s)
obs23 53 047.3
11
obs24 53 293.5 7998.5 ± 70.8 1.03 ± 0.23 11.22 ± 1.39 10
obs25 53 574 7639.0 ± 77.2 * 0.50 ± 0.24 11.19 ± 0.96 9
obs26 53 655.5 7907.2 ± 80.0 1.13 ± 0.26 10.00 ± 0.88 8
7
log Teff from obs 1-26 6
5 1975 1980 1985 1990 1995 2000 2005
as a function of time 4
3.92
3.90 41000 43000 45000 47000 49000 51000 53000 55000
3.88 JD - 2400000 / Year
3.86
3.84 Fig. 4. Results of the fitting of vt with Kurucz’s LTE models for the
log T eff
3.82 observations obs1-obs26 as described in this paper.
3.80
3.78
3.76
3.74 This section consists of three parts: 1) We determine the
3.72
3.70
value of E(B − V) from the overview of the colour- and
3.68 1975 1980 1985 1990 1995 2000 2005 MK-information below, and can then create a T eff time history.
2) An earlier set of multi-colour observations, together with the
41000 43000 45000 47000 49000 51000 53000 55000
synchronization of the MK-type determination (by interpola-
JD - 2400000 / Year tion) leads to a separate (re)determination of E(B−V) and allows
Fig. 2. Results of the fitting of log T eff with Kurucz’s LTE models for us to determine R, the ratio of absorption in V-colour to E(B−V).
the observations obs1-obs26 as described in this paper. 3) When the distance is known, we can then estimate absolute
magnitudes.
3. The analysis of colour observations
3.1. B – V colour, MK-, and Teff -observations
We now analyse colour data. These are transformed with stan-
dard transformation tables and graphs into effective tempera- The available B − V information has been collected in a critical
tures. A substitute for colour observations is the data on spectral compendium (Table A.7) and in a combined, ordered database of
type (MK classification). Not all data, especially the earlier data all observations after about 1973 (Table A.8) with author refer-
sets, are in the same photometric system, which is a problem that ence included for each observation. (Note: our list of references
has to be corrected. In addition, the high interstellar reddening also contains the data sources without any direct link in the main
of HR 8752 demands information on the interstellar absorption. text.)
At the same time, the star itself is changing continuously in its New observations are published in Table 5. This data is also
various spectral parameters such as the spectral type, B − V as included in Table A.8 under letter “n”. Data on some early visual
well as in its V-magnitude. We have to determine the “intrinsic” measurements is included as “early-colour”, Table A.6.
or “unreddened” B − V values that can be compared with MK In one graph, we use Tycho photometer data (cf.
spectral types, using the T eff data. To that end, information on Nieuwenhuijzen & De Jager 2000, with data on HR 8752 =
the interstellar extinction parameter E(B − V) is imperative. HIP 115 361, ESA 1997) from the Hipparcos satellite.
A105, page 5 of 24
6. A&A 546, A105 (2012)
Table 5. B − V Observations, period JD=2 448 813-2 449 299, Konkoly Teff from MK & spectral observations 1896-2005
Observatory, Budapest. 4.0 obs1-26, extra T , early T eff (1900)-reddened
eff
A: obs1- obs26->log T eff
Julian Day V B−V 3.9 B: MK->log T eff
2 448 813.532 5.088 0.872 C Teff : early T eff (1900)-reddened->log T eff
2 448 853.475 5.098 0.964 X1-4 : 4 extra T eff ’s (cf. text) ->log T eff A
Log T eff
2 448 859.374 5.113 0.973 3.8
CT
2 448 897.348 5.215 1.011
2 448 904.309 5.202 1.001
3.7
2 448 936.271 5.166 1.060
2 449 005.252 5.136 0.973 B
2 449 006.229 5.128 0.985 3.6 Gyldenkerne
X 1-4
2 449 254.380 5.095 0.894
2 449 266.368 5.089 0.888 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
2 449 289.231 5.087 0.903 3.5
11000 22000 33000 44000 55000
2 449 290.222 5.085 0.894 JD - 2400000/ Year
2 449 292.269 5.097 0.892
2 449 299.293 5.107 0.880 Fig. 5. Temperatures from T eff observations (“A”), from MK values
transformed to T eff (“B”), from extra data (“X”) and from temperature
correlation data (“CT )” form the base time-line of this study (step 1).
For the meaning of the letters A–F, X we refer to the text.
Table A.7 gives an overview of the combined sequence of
B − V measurements from 1942–1974, followed by the “intrin-
sic” or (B−V)0 value of Gyldenkerne (1955) for E(B−V) = 0.70. D: B-V
Table A.8 entitled “B − V-1976-data” (B − V) observations B-V, various types of observations F: Tycho
gives an overview of the V, (B − V) measurements in the pe- Period 1896-2005
D
C: Early colour
A: T eff ->(B-V) 0
1.8
riod 1976-1993 from various authors. A letter code gives the au- B: MK->(B-V) 0
thor reference, where the letter “n” refers to the data published 1.6 E: (B-V)
E
here. The table gives the observation date, V-magnitude, (B−V), 1.4
followed by columns with transformed values for (B − V)0, 1.2 C
mbol = V + BC, spectral parameter s, log T eff , bolometric correc- 1.0
B-V
F
tion BC and mbol , using Table B.2 “calibrate-hyper”, and finally 0.8
the author reference. 0.6 B
Table A.5 gives an overview of MK data from 1919–1987 0.4 A
with annotations and estimates of observing periods. The 0.2 Gyldenkerne
MK-data is transformed to T eff , B − V, and bolometric correction 0.0 1900 1920 1940 1960 1980 2000
BC by transforms described in Table B.2. In this analysis, we
use the continuous spectral s-parameter introduced by De Jager 10000 20000 30000 40000 50000 60000
& Nieuwenhuijzen (1987). Transforms of some older spectral JD - 2400000 / Year
class observations to MK are described in Table A.5. Except in Fig. 6. The equivalent or “intrinsic” B − V transformed from MK- (“A”),
those cases where this is indicated, the estimated accuracy in s T eff -observations (“B”), extra T eff -observations (“X”) (cf. Fig. 5), and
is about from 0.05 to 0.06 spectral steps in MK. “early-colour” B − V correlation data (“C”) from step 1 are displayed
The T eff data is derived from spectral types or s-parameter together with (from step 2) “observed” B − V’s for the period after
values. For the calibrations between the various types of mea- 1973 (“D”). The 1942–1974 (“E”) and Tycho data (“F”) have been
surement, we refer to “calibrate-hyper” in Table B.2, which dis- transformed to Johnson B − V, and have not been “unreddened”. Note
the influence of differential absorption caused by differences between
cusses the calibrations that are specific to hypergiants Ia+ or Ia0.
Johnson and Tycho pass bands.
The temperature data in our paper also consists of the follow-
ing four measurements, two measurements made in 1969 Sept. 7
of T eff = 5250 ± 250 K, and 1998 Aug. 4 T eff = 7900 ± 200 K B-V; MK & T eff ->s->(B-V) 0 period 1942-1973
from Israelian et al. (1999), one in 1970 (T eff = 5030 ± 171 K, MK&T eff -->(B-V) 0
B-V - (B-V) 0-> E(B-V)
from Schmidt 1972), and lastly an estimate of the lowest temper- 1.8 B-V observed
ature measurement (T eff = 4000 ± 300 K by Luck 1975). These 1.6 B-V- E(B-V) -> (B-V) 0
shift over
measurements are indicated by an “X” symbol in Figs. 5, 6, 1.4
B-V, Delta (B-V)
E(B-V)=0.70
and 10. The 1969 spectrum was obtained by Smolinski at the 1.2
Dominion Astrophysical Observatory, Victoria, Canada. 1.0
“Early-colour” observations with estimates of T eff and B − V 0.8
are reproduced in Table A.6. In comparing T eff , we may first
0.6
use the estimate of temperatures given there. Later in the paper,
we use the B − V information. With HR 8752’s large interstellar 0.4
absorption, the temperatures may be higher than indicated when 0.2
correcting for the shifting of colour towards the red. 0.0 1945 1950 1955 1960 1965 1970 1975
The colour observations started around 1940 and are not all
30000 32000 34000 36000 38000 40000 42000 44000
in the Johnson B−V format that we use as reference in this paper. JD - 2400000 / Year
After 1940, the measurements were made primarily in B − V.
The T eff data and the data in Tables A.5–A.8 form the basis of Fig. 7. Detail of left-hand part of Fig. 6, comparing reddened data di-
this study. rectly with “intrinsic” (B − V)’s from MK- and T eff -values.
A105, page 6 of 24
7. H. Nieuwenhuijzen et al.: HR 8752 evolving through the void
B-V; MK & T ->s->(B-V) 0 period 1973-2005 T eff from (B-V) 0 , MK & spectral observations: 1896-2005
eff
4.0 obs1-26, extra, early colour (1900):(B-V) 0 ->T eff
B-V - (B-V) 0-> E(B-V)
1.8 D, E: (B-V) 0 ->log T eff
MK&Teff-->(B-V) 0 A: obs1- obs26 ->log T eff
1.6 B-V observed 3.9 B: MK ->log T eff
1.4 B-V - E(B-V) -> (B-V) C: (B-V) 0 early colour (1900) ->log T eff
B-V, Delta (B-V)
0 A
log T eff
X1-4 : 4 extra T eff ’s (cf. text) ->log T eff
1.2 3.8
C
1.0 E
0.8 D
3.7
0.6 shift over B
E(B-V)=0.70
0.4
3.6 Gyldenkerne X1-4
0.2
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
0.0 1975 1980 1985 1990 1995 2000 2005
3.5
11000 22000 33000 44000 55000
40000 42000 44000 46000 48000 50000 52000 54000
JD - 2400000 / Year
JD - 2400000 / Year
Fig. 10. Combination of the temperatures in one plot: from B − V cor-
Fig. 8. As Fig. 7 for the right-hand part of Fig. 6. Taken together with rected for interstellar extinction, from MK –> T eff , from obs1-obs26
Fig. 7, a downward shift of the reddened data over Δ(B − V) yields a (Sect. 2), and from some extra data (indicated by “X”(X1−4 ), cf. text).
“best” data fit with the “intrinsic” (B − V)’s for Δ(B − V) = E(B − V) = The temperatures derived from the B − V and MK data combine rea-
0.70 ± 0.02. This forms step 3. sonably well. The temperatures for obs1-obs2, obs4-obs6 also seem to
follow the combined data, and the values for obs7-obs26 extend the
Delta E(B-V) for constant m bol,0 =1.86 data. The difference from obs2 is relatively large. This forms step 5.
1.2 mbol,0 =mV -AV+BC; AV=R*E(B-V), R=4.4; E(B-V)=0.70 -0.15
1.3
Delta E(B-V) with E(B-V)0=0.70
1.4
m bol,0 , Delta E(B-V) 1919-1973 -0.10 Step 4: check the measured value by verifying the value
1.5 m bol,0 , Delta E(B-V) 1973-2006 of E(B − V) required at any time to obtain a constant “unred-
1.6 dened” light output mbol,0 in Fig. 9, (with known R). We compare
m bol,0
-0.05
1.7 the identified value to literature values.
1.8
0.00
Step 5: correct the B − V observations for interstellar absorp-
1.9 tion, transform the now “intrinsic” values to T eff , and display
2.0 the MK –> T eff , the T eff , and the B − V− > T eff values along one
Reference mean m bol,0 =1.86 0.05
2.1 timeline (Fig. 10). Compare this with the “early-colour-data” T eff
2.2 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 (cf. Table A.6).
2.3 0.10 The determination of E(B − V) is done in the first three of
30000 32000 34000 36000 38000 40000 42000 44000 46000 48000 50000
the five steps mentioned at the beginning of Sect. 3. We also
JD - 2400000 / Year
perform a direct determination from available colour data and
Fig. 9. The right-hand ordinate shows the ΔE(B − V)-value needed to an interpolation of MK-data for observing date and discuss the
obtain a constant mbol,0 = 1.86. Relatively small differences in E(B − V) results in steps 4 and 5.
appear to be needed. The left-hand ordinate displays the “unreddened” Step 1. The temperature data from 1896 to 2005 are pre-
bolometric magnitude given as mbol = V − AV + BC, with AV = R ×
E(B − V), for the timeframe 1942–1996. The mean value of mbol,0 for
sented in Fig. 5. The T eff values are given for MK-data (“B”,
1919–1973 seem to cluster around a value near to mbol,0 = 1.86, while cf. Table A.5), observed T eff (“A”, cf. Table 4), extra T eff (“X”),
for 1973–1996 a larger range of values is involved. This forms step 4. and the “early-colour” temperature correlation data (“CT ”, cf.
Table A.6). The “CT ” data have to be corrected for reddening
and are expected to be somewhat higher than given. The “C” data
for “early-colour”, experimentally corrected for interstellar red-
3.2. Determining the interstellar extinction E(B – V) dening with E(B − V) = 0.70 shows (cf. Fig. 10) a somewhat
higher temperature. In Fig. 5 at “B” and “A”, the different types
Values of E(B − V) in the literature for HR 8752 vary from 0.27 of temperature measurements (MK and spectral models) can be
to 0.82. In this paper, we try to get a direct measure by comparing compared. The error bars of the two types seem to overlap at
between the timelines of the observed B − V values and the T eff nearly coincident (synchronous) timeframes, and although ob-
and MK data transformed to T eff data, and then transform them served T eff -values could be somewhat higher than the MK –>
to “intrinsic” B − V values, i.e. without the effects of interstellar s –> T eff values (but for those at the time of the minimum around
absorption. JD 24 419 000, ≈1973), we consider the agreement between the
This procedure is performed in the following five steps: two types as reasonable. We suggest that the temperature is pos-
Step 1: transform MK data to T eff ; carry these over to the sibly log T eff = 3.65 around 1900, about log T eff = 3.68 around
observed T eff ’s from Sect. 2, and display them in a graph (Fig. 5). 1925, and log T eff = 3.7 from 1940–1960 with dramatic changes
Transform the various data to B − V, and display this in step 2 between 1960–1980 and a sharp increase to log T eff = 3.9 dur-
(Fig. 6, lower line). ing 1990–2000. The measurement of Gyldenkerne (Gyldenkerne
Step 2: add the observed B − V data to the graph (Fig. 6, 1955, 1958; Strömgren & Gyldenkerne 1955) is incorporated
upper line). from B−V –> T eff using a 1/5 sensitivity of influence of E(B−V)
Step 3: compare the two time segments of the graph (Fig. 7, with first approximations of E(B − V), but is actually used in
Fig. 8) and find a value for the difference Δ(B − V) such that a Fig. 6 as an intrinsic (B − V) value. It is indicated by an arrow in
reasonable overlay is obtained. the figure.
A105, page 7 of 24
8. A&A 546, A105 (2012)
Table 6. Characteristics of four types of variations in the observations, cf. also Figs. 6, 11, and Sect. 5.6.
Type Days/years Variation Reference Year
1 300–500 d sawtooth 1975–1995: D, F 1940–1995
2 2–3 y smaller episodes 1960: E, B, 1980: D, A 1960, 1980
3 20 y special episode 1973 minimum T eff 1965–1980
4 100 y incomplete Geyser-model? before 1840–1973?
HR 8752 : B-V from 1976-1993 as type 2). These deviations are possibly not the semi-regular
0.8 Tycho Photometry is uncorrected for differential reddening “sawtooth” variations seen in Sects. “D” and “F” (type 1), but
0.9 they seem to be larger-scale, longer-time duration disturbances
1.0 that influence the atmospheric parameters. Finally, there is an
1.1
overall structure (of changes ≈instability?) with a timescale of
more than a century (100 years) (type 4).
1.2
In the approach outlined below, we assume a constant
B-V
1.3 bolometric magnitude to test and limit the choices of values
1.4 B-V of E(B − V). For this reason we employ data for which simul-
1.5
Tycho
B-V Lowess
taneous B − V- and V-magnitudes are available. These data are
1.6 Tycho Lowess effectively only available in the time range 1942–1996.
1.7
Step 3. In Fig. 6, the curves “E” and “D” are at some dis-
1980 1985 1990
tance from the curves “B” and “A”. For time-synchronous data,
1.8
43000 44000 45000 46000 47000 48000 49000 50000 this distance defines the excess E(B − V). To get a better view,
JD - 2400000 / Year we combine the data as two streams called the B − V data
Fig. 11. Detail of B − V and Tycho photometry observations showing (upper graphs) and “intrinsic” data (lower graphs), and split the
“saw-tooth” variations with an amplitude of ≈0.2 m, and a sequence timeline into two parts (Figs. 7, 8). A shift over E(B − V) =
time of a few hundred days. The difference between the Tycho and B−V 0.70 ± 0.02 brings a reasonable correlation with the observed
mean values is due to differential pass-band reddening; the Tycho data B − V values over the intrinsic B − V values. We use this lat-
points have been obtained at small time differences and may indicate a ter value in our paper, but first do a test to see where there are
field of shockwaves. differences and if they depend on changes in bolometric magni-
tude over time. This value is also found when synchronization
with interpolation is used to correct the E(B − V) published by
In Fig. 6, the T eff values from Fig. 5 have been transformed Johnson (mentioned below as a direct determination). However,
to B − V (lower curves) for MK-data (“B”) and observed T eff , the difference measurement given here is applicable to all avail-
(“A”). From the “early-colour” data the B−V correlation data are able data. We from hereon use E(B − V) = 0.70 ± 0.02.
displayed (“C”). The “C” data have been corrected for redden- We also note the difference of about 0.15 m between the
ing; in the first instance, one could expect an excess colour that is two data streams for the observations before 1960, the dips be-
near to the value of E(B − V) found later in this study, but this is tween 1960–1965, between 1970–1980, and the smaller bump
uncertain. We note that the measurement of Gyldenkerne (1955, (negative) difference between 1985–1995.
1958) lies in a reasonable position of temperature and B − V val- Step 4: Checking E(B – V) in the case of a constant bolo-
ues, after having been corrected for an appropriate excess, cf. the metric magnitude: Here we use the concepts and values of R and
discussion in Table A.7. AV developed and determined in the next subsection. In Fig. 9,
Step 2. In Fig. 6, we now add the observations from “(B−V)- we show how much variation in E(B − V) is needed to obtain a
1973-data” (“D”, cf. Table A.8), from “(B − V)-1950-data” constant value of mbol,0 = V + BC − AV , i.e. assuming that the
(“E”, cf. Table A.7) and finally the (transformed, still reddened) “unreddened” light output of the star stays constant. The energy
Tycho B − V data (“F”, cf. Nieuwenhuijzen & De Jager 2000). output also consists of internal-, movement-, and perhaps other
These data lie in the upper part of Fig. 6. The Tycho data energies, and we wish to check the constancy of E(B−V) and AV .
has been transformed to Johnson B − V representation and has It appears that only relatively small variations in Δ(B−V) around
not been corrected for interstellar absorption. Some differential E(B − V) = 0.7 are needed to obtain a constant value of mbol,0
absorption is visible due to differences between Johnson- and for the data clustering around the E(B − V) = 0.70 line. After a
Tycho passbands. The Tycho data set coincides closely in time number of trials, it appears that a constant value of mbol,0 = 1.86
with the “(B − V)-1973-data” (“D”, cf. Table A.8). In this paper, gives results that can be accurately compared with our observa-
we do not apply the somewhat complex dereddening procedures tions of Δ(B − V) to find E(B − V).
for the Tycho data. We define the “mean” of the “early observations” during
Leaving aside the plot named “C”, we characterize the “B”-, 1950–1965 as a “mean” reference value with which other obser-
“A”-, and “X”-plots as indicating initially a medium tempera- vations should be compared. We use this value in various places
ture, after which the star becomes cooler with a minimum around throughout this paper. Their averages can be given as V = 5.11,
1973 followed by a growth toward higher temperature in “D”, V0 = 2.03, mbol = 4.94, and mbol,0 = 1.856.
and continuing in nearly a straight line in section “F”. The time We note that the observations show a structure about the
between about 1965 and 1980 may indicate a special episode in “mean” line: points below the line have less or negative absorp-
the star’s evolution (type 3, cf. Table 6 for an overview of four tion (AV = R × E(B − V)), while points above the line have more
types of variations that we identify in Figs. 6 and 11). absorption than the mean value. These changes indicate that
There also seem to be shorter episodes around 1960 in “E” some form of energy interaction is taking place in the processes
and “B” and around 1980 in “D” and “A” (which we indicate before, during and after the 1965–1980 episode. This exercise
A105, page 8 of 24
9. H. Nieuwenhuijzen et al.: HR 8752 evolving through the void
also shows that the derived value for (constant) E(B − V) is a 3.3. Direct determination of E(B – V) and R-ratio
useful starting point.
A direct measurement is also available from colour observa-
We conclude that the apparent changes in bolometric magni- tions of HR 8752 (Johnson 1968) by comparing with an (inter-
tude are due to changes in the luminosity, and that AV is to first polated) MK-spectral type, instead of using the (classic value)
approximation constant. We have indeed two possibilities: MK type G0 as a reference. To synchronize the observing
dates for the colour and the MK-observations, we interpolate
1) Either we have the colour excess decreases by 0.05 between for the date JD 2 438 300 (27 Sept. 1963) in the sequence of
1978 and 1995 with a constant luminosity or MK measurements in our Table A.5 (codes 3:-6a:) between
2) We have a constant E(B − V) and a variation in L. JD 2 436 462–2 439 080 for MK G0Ia and G3 respectively, to get
It is unclear whether the grain distribution and the grain sizes spectral type G2. When combined with the calibration data from
close to the star could experience enough change over that Schmidt-Kaler (1982, Sect. 4.1.2.1), and the observations of
period of time for possibility 1) to apply. It is similarly un- Johnson (1966, Table 4), this leads to E(B − V) = 0.70± ≈ 0.02.
clear whether the large increase in T eff as more UV radiation The two techniques to time-synchronize the different types
is emitted could affect the grain properties or whether any of observations result in the same number for E(B − V) and en-
difference in absorption could be caused by matter ejection. hance our confidence in the measured value.
For the time being, we decided to use option 2) above. Literature values: apart from Johnson (1968), there are two
direct determinations of E(B − V), by Kron (1958) with E(B −
It also remains unclear whether modelling of the R-ratio for the V) ≈ E(P − V) = 0.53, transformed to E(B − V) = 0.58 (Fernie
extremely large changes in the atmosphere of HR 8752 might 1972) and by Schmidt (1972) with E(B − V) = 0.66. This last
not lead to some change in Av. It seems that both later types and value is practically identical to the value we find here.
higher luminosities can correspond to higher R-ratios, as demon- Another result is that with the given time-synchronization
strated by Fig. 8 of Crawford & Mandwewala (1976), cf. also the other observed colour excesses can be redetermined, lead-
Table A.9. ing to a direct determination of the R-ratio, thus with known
Step 5, the last step in finding Teff : determining the T eff E(B − V) the value of AV . The corrected R-ratio is R = 4.4± ≈ 0.2
variation over the twentieth century. Transformation of B − V (cf. Table A.9 for details of the correction of the various colour
to temperature can now be done with the “unreddened” or “in- excesses and the graphical determination of the R-ratio R).
trinsic” (B − V)0 from the observed B − V as (B − V)0 = Hence, AV = R × E(B − V) = 3.08 ± 0.16. The “unreddened”
B − V − E(B − V) using the transforms in Table B.2 to trans- visual and bolometric magnitudes are V0 = V − 3.08 and mbol,0 =
form (B − V)0 –> s, and s –> T eff and finding the appropriate V + BC − 3.08, respectively.
errors caused by measurement errors and transformation errors. We note that the high value for the R-ratio contrasts with the
Figure 10 shows the equivalent temperatures T eff transformed values of R = 3.0 to 3.1 that are usually attributed to O, B stars
from B − V, together with T eff from obs1-obs26, the MK clas- (cf. e.g. Fitzpatrick & Massa 2007). There are two possible rea-
sifications, and the early-colour B − V. Both MK- and B − V- sons for this:
transformed temperatures give nearly identical temperature in-
1) This high value (if it is true) points unambiguously to a
formation, while the star is continuously changing. The data
non-canonical IS reddening curve along the line-of-sight to-
obs3-obs8 show how the temperature at the end of the B − V ob-
wards HR 8752 whatever the reason for that (it may well be
servations rises extremely rapidly until the flattening out at the
the parameters of dust close to HR 8752). In addition, we
end of the observations at about log T eff = 3.9. Obs2 indicates
note the result of Johnson (1968) who found strong varia-
a jump in temperature. In the plot, the early colour B − V in-
tions in the line-of-sight reddening for different regions in
formation is transformed to temperature using the same value of
Cepheus, a result that should indeed be the topic of a sepa-
E(B − V) as for the other data. The temperatures are higher than
rate investigation.
those mentioned in Sect. 3.1.2 and step 1 for the temperature-
2) The variation in the R-ratio with spectral class/ type found
correlation data (cf. Fig. 5).
by some studies, from combining stellar energy fluxes for
Here the position of the measurement by Gyldenkerne is in- various spectral types with filter transmission curves, as pre-
dicated by an arrow. The four extra temperature measurements sented in Table A.9.
are indicated by four blocks (“X1−4 ”). The first measurement is
somewhat high (Israelian et al. 1999), the second (Schmidt 1972) We note that the above values for R and AV are used in the pre-
and fourth (Israelian et al. 1999) are in the line of the other ob- vious subsection at the start of step 4.
servations, and the third (Luck 1975) shows an estimate of the
low temperature.
3.4. Absolute magnitude
Figure 11 shows relatively large saw-tooth variations in
B − V observations with a magnitude of ≈0.2 m, with various Following a redetermination of the distance of HR 8752
frequency components and time-spans. The Tycho observations (Van Leeuwen 2007) giving a parallax π = 0.73 ± 0.25
show large variations over all measurements, probably indicat- (milliarcsec), distance log d = 3.137 ± 0.149 (parsec), and a
ing shockwaves going through the stellar atmosphere. The small distance modulus m − M = 10.685 ± 0.746, the absolute val-
offset visible in the Tycho data is due to differential reddening of ues for the “mean” reference is MV,0 = −8.65 ± 0.75 and
the differing pass bands of the Tycho photometer. The ordinate Mbol,0 = −8.82 ± 0.75.
is inverted with respect to Figs. 6–9 to comply with the usual The spectral parameter s for the “mean” reference is s =
plots. The two Lowess curves in Fig. 11 characterize the run- 4.976 ± .068 corresponding to a MK classification of F9-G0.5
ning means for the B − V and the Tycho data. The term Lowess with MV = −8.9± ≈ 0.03. Schmidt-Kaler (1982, section 4.1.2,
refers to a method for smoothing scatter plots with the help of Table 13) found for the absolute magnitudes of the MK system
robust locally weighted regression, (cf. Cleveland 1979, 1985; of class Ia0 that F0-F8 –> MV = −9.0, G0 –> MV = −8.9,
Cleveland & Devlin 1988). and G2 –> MV = −8.8. We note that the “mean” reference
A105, page 9 of 24
10. A&A 546, A105 (2012)
HR8752: V, M V: 1942-1996; m - M= 10.69 HR8752: V in period ~1840-1996
4.5 R=4.4, E(B-V)=0.7, parallax =0.73 milli arcsec -9.27 4.5
4.7
4.6 -9.17
4.9
4.7 -9.07
5.1
4.8 -8.97
MV
5.3
Reference mean
V
Reference mean
V
4.9 -8.87 5.5 V = 5.1
V = 5.11
5.0 -8.77 5.7
V in period 1942-1996
5.9 V in period 1860-1930
5.1 -8.67
6.1
5.2 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 -8.57
6.3 1840 1860 1880 1900 1920 1940 1960 1980 2000
5.3 -8.47 6.5
32000 34000 36000 38000 40000 42000 44000 46000 48000 50000
-10000 0 10000 20000 30000 40000 50000 60000
JD - 2400000 / Year JD - 2400000 / Year
Fig. 12. The visual observed resp. absolute magnitudes mV and MV Fig. 13. Long time visual magnitude as a function of time, in the time-
are given for the timeframe 1942–1996 as one plot with two ordi- frame 1840–1996. The “mean” reference value (Sect. 3, step 4) for V is
nate values. The absolute visual magnitude is given as “unreddened” indicated by a short horizontal line within the period 1942–1996.
MV = V − AV − (m − M), for AV = R × E(B − V) with the observed
values of R and E(B − V). The mean value of V for 1919–1973 appears
to cluster around a value near V = 5.1 and is indicated by a line at the that before 1840 the star was invisible to the naked eye. We quote
left lower side of the figure. from Zsoldos (1986a): “It is interesting that HR 8752 is not in-
cluded in several catalogues compiled mainly before 1850. The
star has neither a Flamsteed number, nor a Bayer letter. It is not
we indicate here is thus compatible with a MK value of MK ≈ in the catalogues of Piazzi or Baily. Several reasons can be men-
G0 − Ia0± ≈ 0.7 spectral step. tioned to explain why the star is not in these catalogues: (i) the
For the Galactic supergiant HR 8752, Mantegazza (1988, star was fainter than 6 m. ... ... Bearing in mind Fig. 1, I sug-
1991, 1992, Eq. (4) resp. Eq. (5)) gives absolute visual mag- gest that the most likely explanation is the first possibility”. This
nitudes of MV = −8.87 ± 0.53 and MV = −9.04 ± 0.34. The implies that the star was fainter than the sixth magnitude.
MK spectral class of F7-Ia0 was measured on September Are these variations due to a form of Γ1 -instability? We carry
22, 1987, while the CP-indices were measured over this question forward to the next section.
December 15–18, 1987, to ensure that time synchroniza- The main conclusions of this section can be summarized as:
tion between the spectral type and CP-index has been achieved.
This spectral class is also near to that of the “mean” reference 1) We have derived a time-history of T eff (cf. Fig. 10) that allows
given above, so that a near comparison can be made. us to determine:
Within the measurement errors, the different observations are 2) Four different timescales (cf. Table 6) identified and dis-
both consistent with each other and with the data of the MK ref- cussed in Sect. 5.6.
erence system for the luminosity class Ia0. This enhances the 3) That measurements E(B − V), R, and AV can help us to
confidence in the combination of values found for E(B − V), R, measure absolute magnitudes for a subset of the data (cf.
AV , and distance modulus m − M. Sects. 5.2 and 6).
We note that it is possible the luminosity given by our value
for MV is somewhat low. The MV -value depends directly on the
value of the the “mean” reference of the “early observations”
4. Atmospheric (in)stability and the yellow
from 1950–1965 as defined earlier and may depend on how that evolutionary void
was derived. We tried to find a meaningful value for the absolute To understand the evolutionary scenario of HR 8752 and other
magnitudes when the star varies strongly in time, and other pro- hypergiants, we start from models of Meynet et al. (1994), which
cesses exist that use or give extra energy in the time line of the form part of a series of evolutionary models with different au-
star. thors. In the following, we use unpublished evolutionary data
from one of us (GM) and models from Meynet et al. (1994)
3.5. Extending the V-coverage back to 1840 with rates of mass-loss twice as high as the mass-loss given in
De Jager et al. (1988). The factor of two may seem arbitrary
In Fig. 12, we give the values of the visual- and visual ab- but was taken to achieve the best mean time fit of models com-
solute magnitude as a function of time, during the timeframe pared to observations. The mean time fit is the average of the
1942–1996. total mass-loss, hence includes “regular” mass-loss during “sta-
Extending the 1942–1996 V-data backwards in time with ble” periods of mass-loss and periods of massive loss of mass
data from Zsoldos (1986a, Table I) and adding three data points during a time of “instability”.
from the literature (cf. end of Table A.5) leads to Fig. 13. The We note that this “instability” mass-loss occurs during the
“mean” reference value (Sect. 3, step 4) for V is indicated evolution of the models along track 4, and not along track 3. The
by short horizontal lines within the period 1942–1996 in both text below refers to track 4 unless otherwise indicated.
Figs. 12 and 13. It seems that the process time for the indicated We now empirically check the condition (3 Γ1 − 4 ) < 0 for
changing situation is longer than the time of the record, more a stellar model traversing the region of the yellow evolutionary
than 150 years. void. As an example for this study, we take the Meynet et al.
The V-observations indicate a visual brightness growing (1994) model m040e020 that gives L, T eff , mass, and mass-loss
from below V ≈ 6 to around V ≈ 5.1 in some 60 years. It seems as a function of age to find the physical parameters including Γ1
A105, page 10 of 24