Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
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 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.
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
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
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 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.
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
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
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.
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.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Quase 900 galáxias próximas, porém escondidas, têm sido estudadas por uma equipe internacional de astrônomos, levando uma nova luz sobre o entendimento do Grande Atrator - uma concentração difusa de massa a 250 milhões de anos-luz de distância, que está puxando a nossa Via Láctea, e milhares de outras galáxias em sua direção.
Usando o Multibeam Receiver, instalado no rádio telescópio Parkes de 64 m, pertencente à instituição CSIRO na Austrália, a equipe foi capaz de ver através das estrelas e da poeira da nossa galáxia, vasculhando assim uma região inexplorada do espaço, conhecida pelos astrônomos como Zone of Avoidance (Zona de Anulação).
“Nós descobrimos 883 galáxias, um terço das quais nunca tinham sido vistas anteriormente”, disse o Professor Lister Staveley-Smith, membro da equipe, do ARC Centre of Excellence for All-sky Astrophysics, e da University of Western Australia, um dos nós do International Centre for Radio Astronomy Research.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
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 importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This
satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the
Hubble Space Telescope’s Wide Field Camera 3 on UTC April 27, 2015 at 7.80±0.04 magnitudes
fainter than Makemake. It likely evaded detection in previous satellite searches due to a nearly edgeon
orbital configuration, placing it deep within the glare of Makemake during a substantial fraction
of its orbital period. This configuration would place Makemake and its satellite near a mutual event
season. Insufficient orbital motion was detected to make a detailed characterization of its orbital
properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary
analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days, and
must have a semi-major axis &21,000 km. We find that the properties of Makemake’s moon suggest
that the majority of the dark material detected in the system by thermal observations may not reside
on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform
dark surface. This “dark moon hypothesis” can be directly tested with future JWST observations.
We discuss the implications of this discovery for the spin state, figure, and thermal properties of
Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
Evidence for a_distant_giant_planet_in_the_solar_systemSérgio Sacani
A descoberta de um novo planeta, atualmente não é uma manchete que chama tanto assim a atenção das pessoas. Muito disso, graças ao Telescópio Espacial Kepler, que já descobriu quase 2000 exoplanetas e todo instante uma nova descoberta é anunciada, certo? Mais ou menos, a descoberta anunciada hoje, dia 20 de Janeiro de 2016, é um pouco diferente, pois não se trata de um exoplaneta, e sim de um novo planeta no Sistema Solar, e esse é um fato que intriga os astrônomos a muitos e muitos anos.
Porém, temos que ir com calma com esses anúncios. No artigo aceito para publicação no The Astronomical Journal (artigo no final do post), os autores, Mike Brown e Konstantin Batygin, do Instituto de Tecnologia da Califórnia, apresentaram o que eles dizem ser evidências circunstâncias fortes para a existência de um grande planeta ainda não descoberto, talvez, com uma massa 10 vezes a massa da Terra, orbitando os confins do nosso Sistema Solar, muito além da órbita de Plutão. Os cientistas inferiram sua presença, por meio de anomalias encontradas nas órbitas de seis objetos do chamado Cinturão de Kuiper.
O objeto, que os pesquisadores estão chamando de Planeta Nove, não chega muito perto do Sol, no ponto mais próximo da sua órbita ele fica a 30.5 bilhões de quilômetros, ou seja, cinco vezes a distância entre o Sol e Plutão. Apesar do seu grande tamanho, ele é muito apagado, e por isso ninguém até o momento conseguiu observá-lo.
Não existe ainda uma confirmação observacional da descoberta, mas as evidências são tão fortes que fizeram com que outros especialistas como Chad Trujilo do Observatório Gemini no Havaí e David Nesvorny, do Southwest Research Institute em Boulder no Colorado, ficassem impressionados e bem convencidos de que deve mesmo haver um grande planeta nas fronteiras da nossa vizinhança cósmica.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
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.
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.
Evidence for reflected_lightfrom_the_most_eccentric_exoplanet_knownSérgio Sacani
Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is > 1.22◦, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations may be caused by reflected light from the planet’s atmosphere and the dramatic change in star–planet separation surrounding the periastron passage.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Quase 900 galáxias próximas, porém escondidas, têm sido estudadas por uma equipe internacional de astrônomos, levando uma nova luz sobre o entendimento do Grande Atrator - uma concentração difusa de massa a 250 milhões de anos-luz de distância, que está puxando a nossa Via Láctea, e milhares de outras galáxias em sua direção.
Usando o Multibeam Receiver, instalado no rádio telescópio Parkes de 64 m, pertencente à instituição CSIRO na Austrália, a equipe foi capaz de ver através das estrelas e da poeira da nossa galáxia, vasculhando assim uma região inexplorada do espaço, conhecida pelos astrônomos como Zone of Avoidance (Zona de Anulação).
“Nós descobrimos 883 galáxias, um terço das quais nunca tinham sido vistas anteriormente”, disse o Professor Lister Staveley-Smith, membro da equipe, do ARC Centre of Excellence for All-sky Astrophysics, e da University of Western Australia, um dos nós do International Centre for Radio Astronomy Research.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
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 importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
Probing the innermost_regions_of_agn_jets_and_their_magnetic_fields_with_radi...Sérgio Sacani
Desde 1974, observações feitas com o chamado Long Baseline Interferometry, ou VLBI, combinaram sinais de um objeto cósmico recebidos em diferentes rádio telescópios espalhados pelo globo para criar uma antena com o tamanho equivalente à maior separação entre elas. Isso fez com que fosse possível fazer imagens com uma nitidez sem precedentes, com uma resolução 1000 vezes melhor do que Hubble consegue na luz visível. Agora, uma equipe internacional de astrônomos quebrou todos os recordes combinando 15 rádio telescópios na Terra e a antena de rádio da missão RadioAstron, da agência espacial russa, na órbita da Terra. O trabalho, liderado pelo Instituto de Astrofísica de Andalucía, o IAA-CSIC, forneceu novas ideias sobre a natureza das galáxias ativas, onde um buraco negro extremamente massivo engole a matéria ao redor enquanto simultaneamente emite um par de jatos de partículas de alta energia e campos magnéticos a velocidades próximas da velocidade da luz.
Observações feitas no comprimento de onda das micro-ondas são essenciais para explorar esses jatos, já que os elétrons de alta energia se movendo em campos magnéticos são mais proficientes em produzir micro-ondas. Mas a maioria das galáxias ativas com jatos brilhantes estão a bilhões de anos-luz de distância da Terra, de modo que esses jatos são minúsculos no céu. Desse modo a alta resolução é essencial para observar esses jatos em ação e então revelar fenômenos como as ondas de choque e a turbulência que controla o quanto de luz é produzida num dado tempo. “Combinando pela primeira vez rádio telescópios na Terra com rádio telescópios no espaço, operando na máxima resolução, tem permitido que a nossa equipe crie uma antena que tem um tamanho equivalente a 8 vezes o diâmetro da Terra, correspondendo a 20 micro arcos de segundo”, disse José L; Gómez, o líder da equipe no Instituto de Astrofísica de Andalucía, IAA-CSIC.
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
We describe the discovery of a satellite in orbit about the dwarf planet (136472) Makemake. This
satellite, provisionally designated S/2015 (136472) 1, was detected in imaging data collected with the
Hubble Space Telescope’s Wide Field Camera 3 on UTC April 27, 2015 at 7.80±0.04 magnitudes
fainter than Makemake. It likely evaded detection in previous satellite searches due to a nearly edgeon
orbital configuration, placing it deep within the glare of Makemake during a substantial fraction
of its orbital period. This configuration would place Makemake and its satellite near a mutual event
season. Insufficient orbital motion was detected to make a detailed characterization of its orbital
properties, prohibiting a measurement of the system mass with the discovery data alone. Preliminary
analysis indicates that if the orbit is circular, its orbital period must be longer than 12.4 days, and
must have a semi-major axis &21,000 km. We find that the properties of Makemake’s moon suggest
that the majority of the dark material detected in the system by thermal observations may not reside
on the surface of Makemake, but may instead be attributable to S/2015 (136472) 1 having a uniform
dark surface. This “dark moon hypothesis” can be directly tested with future JWST observations.
We discuss the implications of this discovery for the spin state, figure, and thermal properties of
Makemake and the apparent ubiquity of trans-Neptunian dwarf planet satellites.
Us college access programs complex adaptives system nov2011CHEARS
AEA Presentation explores US college access education system as a complex system with a special focus on inequality. Simple models are included using vensim of achieving Obama goals of US being first in college attainment by 2020
Preparé este material para un Taller de Redes Sociales que he organizado en varias ocasiones para trabajar con las familias del alumnado de centros educativos.
Las fuentes de origen del material multimedia están en la parte final de cada presentación.
Jona Oboza of SMILDS.com.ph shared their experience in rolling out social e-commerce service to SMEs. This was presented at Carl Duisberg Association of the Philippines E-Commerce Project Planning & E-Store Creation Workshop last November 19, 2010 at Oxford Suites Makati City.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
Artigo descreve a descoberta do exoplaneta HATS-6b, um exoplaneta parecido com Saturno, porém pesado como Júpiter ao redor de uma estrela anã-M, o tipo de estrela mais abundante na nossa galáxia.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Beyond the Drake Equation: A Time-Dependent Inventory of Habitable Planets an...Sérgio Sacani
We introduce a mathematical framework for statistical exoplanet population and astrobiology studies
that may help directing future observational efforts and experiments. The approach is based on a
set of differential equations and provides a time-dependent mapping between star formation, metal
enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemopopulation history of the solar neighborhood. Our results are summarized as follows: 1) the formation
of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about
11 Gyr ago; 2) within 100 pc from the Sun, there are as many as 11, 000 (η⊕/0.24) Earth-size planets
in the habitable zone (“temperate terrestrial planets” or TTPs) of K-type stars. The solar system is
younger than the median TTP, and was created in a star formation surge that peaked 5.5 Gyr ago and
was triggered by an external agent; 3) the metallicity modulation of the giant planet occurrence rate
results in a later typical formation time, with TTPs outnumbering giant planets at early times; 4) the
closest, life-harboring Earth-like planet would be ∼
< 20 pc away if microbial life arose as soon as it did
on Earth in ∼
> 1% of the TTPs around K stars. If simple life is abundant (fast abiogenesis), it is also
old, as it would have emerged more than 8 Gyr ago in about one third of all life-bearing planets today.
Older Earth analogs are more likely to have developed sufficiently complex life capable of altering the
environment and producing detectable oxygenic biosignatures.
TOI-4600 b and c: Two Long-period Giant Planets Orbiting an Early K DwarfSérgio Sacani
We report the discovery and validation of two long-period giant exoplanets orbiting the early K dwarf TOI-4600
(V = 12.6, T = 11.9), first detected using observations from the Transiting Exoplanet Survey Satellite (TESS) by
the TESS Single Transit Planet Candidate Working Group. The inner planet, TOI-4600 b, has a radius of
6.80 ± 0.31 R⊕ and an orbital period of 82.69 days. The outer planet, TOI-4600 c, has a radius of 9.42 ± 0.42 R⊕
and an orbital period of 482.82 days, making it the longest-period confirmed or validated planet discovered by
TESS to date. We combine TESS photometry and ground-based spectroscopy, photometry, and high-resolution
imaging to validate the two planets. With equilibrium temperatures of 347 K and 191 K, respectively, TOI-4600 b
and c add to the small but growing population of temperate giant exoplanets that bridge the gap between hot/warm
Jupiters and the solar system’s gas giants. TOI-4600 is a promising target for further transit and precise RV
observations to measure the masses and orbits of the planets as well as search for additional nontransiting planets.
Additionally, with Transit Spectroscopy Metric values of ∼30, both planets are amenable for atmospheric
characterization with JWST. Together, these will lend insight into the formation and evolution of planet systems
with multiple giant exoplanets.
Uma equipe formada por astrônomos de Israel, da Europa, da Coreia e dos EUA, anunciou a descoberta de um exoplaneta gigante gasoso circumbinário, na zona habitável de seu par de estrelas, uma ocorrência surpreendentemente comum para os exoplanetas circumbinários descobertos pela missão Kepler/K2 da NASA.
Lembrando o planeta da ficção, Tatooine, exoplanetas circumbinários orbitam duas estrelas e assim têm dois sóis em seu céu.
O exoplaneta circumbinário, recém-descoberto, denominado de Kepler-453b, leva 240.5 dias para orbitar suas estrelas, enquanto as estrelas orbitam uma com relação a outra a cada 27.3 dias.
A estrela maior, a Kepler-453A, é similar ao nosso Sol, contendo 94% da massa do Sol, enquanto que a estrela menor, a Kepler-453B, tem cerca de 20% da massa e é mais fria e mais apagada.
O sistema binário, localiza-se na constelação de Lyra, e está a aproximadamente 1400 anos-luz de distância da Terra. Estima-se que esse sistema tenha entre 1 e 2 bilhões de anos de vida, sendo bem mais novo que o nosso Sistema Solar.
Também conhecido como KIC 9632895b, o Kepler-453b tem um raio 6.2 vezes maior que o da Terra. Sua massa não foi medida nos dados atuais, mas provavelmente ele deve ter cerca de 16 vezes a massa da Terra.
De acordo com os astrônomos, o Kepler-453b, é o terceiro planeta circumbinário da missão Kepler, descoberto na zona habitável de um par de estrelas.
Devido ao seu tamanho, e a sua natureza gasosa, o planeta pouco provavelmente deve abrigar a vida como nós a conhecemos. Contudo, ele pode, como os gigantes gasosos do Sistema Solar, ter grandes luas, e essas luas poderiam ser habitáveis. Sua órbita se manterá estável por 10 milhões de anos, aumentando a possibilidade da vida se formar nas suas luas.
Com o número de exoplanetas circumbinários conhecidos agora em dez, os cientistas podem começar a comparar diferentes sistemas e procurar uma tendência. Os sistemas tendem a ser bem compactos e podem aparecer num grande número de configurações.
Uma vez pensados como sendo raros e até mesmo impossíveis de existir, essa e outras descobertas do Kepler, confirmam que esses planetas são comuns na nossa Via Láctea.
“A diversidade e complexidade desses sistemas circumbinários é algo maravilhoso. Cada novo planeta circumbinário, é uma joia, revelando algo inesperado e desafiador”, disse o Prof. William Welsh da Universidade Estadual de San Diego, e o primeiro autor do artigo que descreve a descoberta, publicado no Astrophysical Journal.
Fonte:
http://www.sci-news.com/astronomy/science-kepler453b-circumbinary-exoplanet-03117.html
Validation of twelve_small_kepler_transiting_planets_in_the_habitable_zoneSérgio Sacani
Artigo descreve a análise dos mais novos exoplanetas descobertos pela missão Kepler, incluindo o Kepler-438b, o exoplaneta mais parecido com a Terra já descoberto até o momento.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Efficient spin-up of Earth System Models usingsequence accelerationSérgio Sacani
Marine and terrestrial biogeochemical models are key components of the Earth System Models (ESMs) used toproject future environmental changes. However, their slow adjustment time also hinders effective use of ESMsbecause of the enormous computational resources required to integrate them to a pre-industrial equilibrium. Here,a solution to this "spin-up" problem based on "sequence acceleration", is shown to accelerate equilibration of state-of-the-art marine biogeochemical models by over an order of magnitude. The technique can be applied in a "blackbox" fashion to existing models. Even under the challenging spin-up protocols used for Intergovernmental Panelon Climate Change (IPCC) simulations, this algorithm is 5 times faster. Preliminary results suggest that terrestrialmodels can be similarly accelerated, enabling a quantification of major parametric uncertainties in ESMs, improvedestimates of metrics such as climate sensitivity, and higher model resolution than currently feasible.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
2. FIS05). Moreover, by comparing the host-star metallicity of 20
sub-stellar companions from the literature with the metallicity
distribution of the Lick sample, Hekker et al. (2007) showed
that planet-hosting stars are on average more metal rich by 0.13
± 0.03 dex, suggesting that the PMC might also be valid for
giant stars. However, recent works have obtained conflicting re-
sults, particularly from planet search programs focusing on post-
main-sequence (MS) stars. For instance, Pasquini et al. (2007),
based on a sample of 10 planet-hosting giant stars2
, showed that
exoplanets around evolved stars are not found preferentially in
metal-rich systems, arguing that the planet-metallicity correla-
tion might be explained by an atmospheric pollution effect, due
to the ingestion of iron-rich material or metal-rich giant plan-
ets (Murray & Chaboyer 2002). Similarly, Hekker et al. (2008)
showed a lack of correlation between the planet occurrence rate
and the stellar metallicity, although they included in the analy-
sis all of the giant stars with observable periodic radial velocity
(RV) variations, instead of only including those stars with se-
cure planets. Thus, it might be expected that the Hekker et al.
sample is contaminated with non-planet-hosting variable stars.
Döllinger et al. (2009) showed that planet-hosting giant stars
from the Tautenburg survey tend to be metal-poor. In contrast,
based on a small sample of subgiant stars with M⋆> 1.4 M⊙ ,
Johnson et al. (2010; hereafter JOHN10) found that their data
are consistent with the planet-metallicity correlation observed
among dwarf stars. Also, Maldonado et al. (2013) showed that
the planet-metallicity correlation is observed in evolved stars
with M⋆> 1.5M⊙ , while for the lower mass stars this trend is
absent. Finally, based on a much larger sample analyzed in a ho-
mogeneous way, Reffert et al. (2015; hereafter REF15) showed
that giant planets around giant stars are preferentially formed
around metal-rich stars.
On the other hand, different RV surveys have also shown a
direct correlation between the occurrence rate of giant planets
and the stellar mass. Johnson et al. (2007), claimed that there
is a positive correlation between the fraction of planets and stel-
lar mass. They showed that the fraction increases from f = 1.8
± 1.0 %, for stars with M⋆∼ 0.4 M⊙ to a significantly higher
value of f = 8.9 ± 2.9 %, for stars with M⋆∼ 1.6 M⊙ . These
results were confirmed by JOHN10, who showed that there is
a linear increase in the fraction of giant planets with the stellar
mass, characterized by f = 2.5 ± 0.9 %, for M⋆∼ 0.4 M⊙ and
f = 11.0 ± 2.0 %, for M⋆∼ 1.6 M⊙ . In a similar study, Bowler
et al. (2010) showed that the fraction of giant planets hosted by
stars with mass between 1.5 - 1.9 M⊙ is f = 26+9
−8 %, signifi-
cantly higher than the value obtained by JOHN10.
In this paper we present the discovery of four giant planets
around giant stars that are part of the EXPRESS (EXoPlanets
aRound Evolved StarS) radial velocity program (Jones et al.
2011; hereafter JON11). The minimum masses of the substel-
lar companions range between 2.4 and 5.5 MJ , and have orbital
periods in the range 562-1560 days. All of them have low eccen-
tricity values e < 0.16. In addition to these planet discoveries, we
present a detailed analysis of the mass-metallicity correlations
of the planet-hosting and non-planet-hosting stars in our sample,
along with studying the fraction of multiple-planet systems ob-
served in giant stars.
This paper is organized as follows. Section 2 briefly de-
scribes the observations and radial velocity computation tech-
niques. In Section 3 we summarize the main properties of the
host stars. In Section 4, we present a detailed analysis of the or-
2
One of those planets (HD 122430 b) was shown not be a real planet
(Soto et al. 2015).
bital fits and stellar activity analysis. In Section 5 we present a
statistical analysis of the mass-metallicity correlation of our host
stars. Also, we discuss about the occurrence rate of multiple-
planet systems. The summary and discussion are presented in
Section 6.
2. Observations and RV calculation
Since 2009 we have been monitoring a sample of 166 bright gi-
ant stars that are observable from the southern hemisphere. The
selection criteria of the sample are presented in JON11. We
have been using two telescopes located in the Atacama desert
in Chile, namely the 1.5 m telescope at the Cerro Tololo Inter-
American Observatory and the 2.2 m telescope at La Silla ob-
servatory. The former was initially equipped with the fiber-fed
echelle spectrograph (FECH), which was replaced in 2011 by
CHIRON (Tokovinin et al. 2013), a much higher resolution3
and
more stable spectrograph. These two spectrographs are equipped
with an I2 cell, which is used as a precision wavelength refer-
ence.
The 2.2 m telescope is connected to the Fiber-fed Extended
Range Optical Spectrograph (FEROS; Kaufer et al. 1999) via
optical fibres to stabilise the pupil entering the spectrograph.
FEROS offers a unique observing mode, delivering a spectral
resolution of ∼ 48,000, and does not require the beam be passed
through an I2 cell for precise wavelength calibration, using a
Thorium-Argon gas lamp instead.
We have taken several spectra for each of the stars in our
sample using these instruments. In the case of FECH and CH-
IRON, we have computed precision radial velocities using the
iodine cell method (Butler et al. 1996). We achieve typi-
cally a precision of ∼ 10-15 m s−1
from FECH data, and ∼ 5
m s−1
for CHIRON. On the other hand, for FEROS spectra, we
used the simultaneous calibration method (Baranne et al. 1996)
to extract the stellar radial velocities, reaching a typical preci-
sion of ∼ 5 m s−1
. Details on the data reduction and RV cal-
culations have been given in several papers (e.g. Jones et al.
2013; 2014; 2015a; 2015b). In addition, we present comple-
mentary observations from the Pan-Pacific Planet Search (PPPS;
Wittenmyer et al. 2011). These spectroscopic data have been
taken with the UCLES spectrograph (Diego et al. 1990), which
delivers a resolution of R ∼ 45,000, using a 1 arcsec slit. The
instrument is mounted on the 3.9 m Anglo-Australian telescope
and is also equipped with an I2 cell for wavelength calibration.
Details on the reduction procedure and RV calculations can be
found in Tinney et al. (2001) and Wittenmyer et al. (2012).
3. Host stars properties
Table 1 lists the stellar properties of HIP 8541 (= HD 11343
), HIP 74890 (= HD 135760), HIP 84056 (= HD 155233) and
HIP 95124 (= HD 181342). The spectral type, B − V color, vi-
sual magnitude, and parallax of these stars were taken from the
Hipparcos catalog (Van Leeuwen 2007). The atmospheric pa-
rameters (Te f f , logg, [Fe/H], vsini) were computed using the
MOOG code4
(Sneden 1973), following the methodology de-
scribed in JON11. The stellar mass and radius was derived by
comparing the position of the star in the HR diagram with the
evolutionary tracks from Salasnich et al. (2000). A detailed de-
scription of the method is presented in Jones et al. (2011; 2015b)
3
CHIRON delivers a maximum resolution of ∼ 130,000 using the nar-
row slit mode.
4
http://www.as.utexas.edu/~chris/moog.html
Article number, page 2 of 11
3. M. I. Jones et al.: Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars.
Table 1. Atmosperic parameters and physical properties of the host stars.
HIP 8541 HIP 74890 HIP 84056 HIP 95124
Spectral Type K2III/IV K1III K1III K0III
B − V (mag) 1.08 1.05 1.03 1.02
V (mag) 7.88 7.05 6.81 7.55
Parallax (mas) 5.93 ± 0.61 10.93 ± 0.63 13.31 ± 0.59 9.04 ± 0.61
Teff (K) 4670 ± 100 4850 ± 100 4960 ± 100 5040 ± 100
L (L⊙) 25.4 ± 5.8 16.4 ± 2.4 13.45 ± 1.73 14.99 ± 2.46
log g (cm s−2
) 2.7 ± 0.2 3.1 ± 0.2 3.17 ± 0.2 3.3 ± 0.2
[Fe/H] (dex) -0.15 ± 0.08 0.20 ± 0.13 0.08 ± 0.07 0.20 ± 0.08
v sini (km s−1
) 1.3 ± 0.9 2.2 ± 0.9 1.67 ± 0.9 1.90 ± 0.9
M⋆ (M⊙ ) 1.17 ± 0.28 1.74 ± 0.21 1.69 ± 0.14 1.89 ± 0.11
R⋆ (R⊙) 7.83 ± 1.02 5.77 ± 0.53 5.03 ± 0.39 5.12 ± 0.49
4. Orbital parameters and activity analysis
4.1. HIP8541 b
We have computed a total of 36 precision RVs of HIP8541, from
FEROS, CHIRON, and UCLES spectra taken between 2009 and
2015. These velocities are listed in Table A.1, and are shown
in Figure 1. As can be seen, there is a large RV signal with
an amplitude that exceeds the instrumental uncertainties, and
the RV jitter expected for the spectral type of this star (e.g.
Sato et al. 2005), by an order of magnitude. A Lomb-Scargle
(LS) periodogram (Scargle 1982) revealed a strong peak around
∼ 1600 days. Starting from this orbital period, we computed
the Keplerian solution using the Systemic Console version 2.17
(Meschiari et al. 2009). To do this, we added a 5 m s−1
error in
quadrature to the internal instrumental uncertainties. This value
is the typical level of RV noise induced by stellar pulsations in
these type of giant stars (Kjeldsen & Bedding 1995). We ob-
tained a single-planet solution with the following parameters: P
= 1560.2 ± 53.9 d, mb sini= 5.5 ± 1.0 MJ and e = 0.16 ± 0.06.
The post-fit RMS is 9.1 m s−1
, and no significant periodicity or
linear trend is observed in the RV residuals. The RV uncertain-
ties were computed using the Systemic bootstrap tool. In the
case of the planet mass and semi-major axis, the uncertainty was
computed by error propagation, including both the uncertainties
in the fit (from the bootstrap tool) and also the uncertainty in the
stellar mass. The full set of orbital parameters and their corre-
sponding uncertainties are listed in Table 2.
Since stellar intrinsic phenomena can mimic the presence of
a sub-stellar companion (e.g. Huelamo et al. 2008; Figueira et
al. 2010; Boisse et al. 2011), we examined the All Sky Auto-
matic Survey (ASAS; Pojmanski 1997) V-band photometry and
the Hipparcos photometric data of HIP 8541. For both datasets,
we included only the best quality data (grade A and quality flag
equal to 0 and 1, respectively). We also filtered the ASAS data
using a 3-σ rejection method to remove outliers, which are typ-
ically due to CCD saturation. The photometric stability of the
ASAS and Hipparcos data are 0.013 and 0.012 mag, respec-
tively. Moreover, a periodogram analysis of these two datasets
show no significant peak around the period obtained from the
RV time-series. Similarly, we computed the bisector velocity
span (BVS; Toner & Gray 1988; Queloz et al. 2001) and the
full width at half maximum (FWHM) variations of the cross-
correlation function (CCF), from FEROS spectra. None of these
activity indicators show any significant correlation with the ob-
served RVs. Finally, we computed the S-index variations from
the reversal core emission of the Ca ii H and K lines, according
5500 6000 6500 7000
Fig. 1. Radial velocity measurements of HIP 8541. The black circles,
blue triangles and red squares represent the UCLES, FEROS and CHI-
RON velocities, respectively. The best Keplerian solution is overplotted
(black solid line). The post-fit residuals are shown in the lower panel.
to the method presented in Jenkins et al. (2008; 2011), revealing
no significant correlation with the measured velocities.
4.2. HIP 74890 b
The velocity variations of HIP 74890 are listed in Table A.2. The
RVs were computed from FEROS and UCLES spectra, taken be-
tween the beginning of 2009 and mid 2015. A detailed analysis
of the RV data revealed a periodic signal, which is superimposed
onto a linear trend. The best Keplerian fit is best explained by a
giant planet with a projected mass of 2.4 ± 0.3 MJ , in a 822-day
orbit with a low eccentricity of e = 0.07 ± 0.07. A third ob-
ject in the system induces a linear acceleration of -33.23 ± 1.46
m s−1
yr
−1
. The full set of parameters with their uncertainties are
listed in Table 2. Using the Winn et al. (2009) relationship,
we obtained a mass and orbital distance of the outer object of
mcsini > 7.9 MJ and ac > 6.5 AU, respectively. Figure 2 shows
the HIP 74890 radial velocities.
The Hipparcos and ASAS photometric datasets of this stars
present a stability of 0.008 mag and 0.013 mag, respectively. No
Article number, page 3 of 11
4. 5000 5500 6000 6500 7000
Fig. 2. Radial velocity measurements of HIP 74890. The black filled
circles and blue triangles correspond to UCLES and FEROS measure-
ments, respectively. The solid line is the best Keplerian solution. The
residuals around the fit are shown in the lower panel.
significant peak is observed in the LS periodogram of these two
datasets. Similarly, the BVS analysis, CCF variations, and chro-
mospheric activity analysis show neither an indication of peri-
odic variability, nor any correlation with the radial velocities.
4.3. HIP84056 b
The velocity variations of HIP 84056 are listed in Table A.3 and
Figure 3 shows its RV curve. The best orbital solution leads to:
P = 818.8 ± 12.1 d, mb sini = 2.6 ± 0.3 and e = 0.04 ± 0.04.
The full orbital elements solution are listed in Table 2. This
planet was independently detected by the PPPS (Wittenmyer et
al. 2016). Based on 21 RV epochs, they obtained an orbital
period of 885 ± 63 days, minimum mass of 2.0 ± 0.5 MJ , and
eccentricity of 0.03 ± 0.2, in good agreement with our results.
To determine the nature of the periodic RV signal observed
in HIP84056, we performed an activity analysis, as described in
section 4.1. We found no significant periodicity or variability
of the activity indicators with the observed RVs. Moreover, the
photometric analysis of the Hipparcos data reveals a stability of
0.009 mag. Similarly, the RMS of the ASAS data is 0.012 mag.
These results support the planet hypothesis of the periodic signal
detected in the RVs.
4.4. HIP95124 b
Figure 4 shows the RV variations of HIP95124. The orbital pa-
rameters are listed in Table 2. The RV variations of HIP 8541
are best explained by the presence of a 2.9 ± 0.2 MJ planet, with
orbital period of P = 562.1 ± 6.0 d and eccentricity e = 0.1 ±
0.07. The radial velocities are also listed in Table A.4. As for
the other stars described here, we scrutinized the Hipparcos and
ASAS photometry to search for any signal with a period similar
to that observed in the RV timeseries, finding a null result. More-
over, the Hipparcos and ASAS RMS is 0.007 mag and 0.013
mag. According to Hatzes (2002), this photometric variability is
well below the level to mimic the RV amplitude observed in this
5500 6000 6500 7000
Fig. 3. Upper panel: Radial velocity measurements of HIP 84056.
The blue triangles and red squares correspond to FEROS and CHIRON
data, respectively. The best Keplerian solution is overplotted (black
solid line). Lower panel: Residuals from the Keplerian fit.
5500 6000 6500 7000
Fig. 4. Radial velocities of HIP 95124. The black filled circles, blue
triangles and red open circles correspond to UCLES, FEROS and CH-
IRON data, respectively. The solid line is the best Keplerian solution.
The residuals around the fit are shown in the lower panel.
star. Additionally, the BVS, CCF variations, and S-index vari-
ations show no significant correlation with the observed radial
velocities.
5. Preliminary statistical results of the EXPRESS
project
After 6 years of continuous monitoring of a sample comprised
by 166 giant stars, we have published a total of 11 substellar
companions (including this work), orbiting 10 different stars. In
addition to this, using combined data of the EXPRESS and PPPS
surveys, we have detected a two-planet system in a 3:5 mean-
motion resonance (Wittenmyer et al. 2015) around the giant
star HIP 24275. Moreover, Trifonov et al. (2014), recently an-
Article number, page 4 of 11
5. M. I. Jones et al.: Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars.
Table 2. Orbital parameters
HIP8541 b HIP74890b HIP84056b HIP95124b
P (days) 1560.2 ± 53.9 822.3 ± 16.8 818.8 ± 12.1 562.1 ± 6.0
K (m s−1
) 87.4 ± 6.4 36.5 ± 2.7 40.5 ± 3.1 46.5 ± 1.8
a (AU) 2.8 ± 0.25 2.1 ± 0.09 2.0 ± 0.06 1.65 ± 0.04
e 0.16 ± 0.06 0.07 ± 0.07 0.04 ± 0.04 0.10 ± 0.07
MP sini (MJ ) 5.5 ± 1.0 2.4 ± 0.3 2.6 ± 0.3 2.9 ± 0.2
ω (deg) 293.9 ± 15.2 181.9 ± 93.9 120.0 ± 71.9 311.8 ± 35.8
TP-2455000 4346.9 ± 93.4 4820.4 ± 379.8 5282.0 ± 192.1 4915.5 ± 54.3
˙γ (m s−1
yr−1
) - - - -33.23 ± 1.46 - - - - - -
γ1 (m s−1
) (CHIRON) 58.8 ± 4.1 - - - 6.7 ± 2.3 24.6 ± 3.0
γ2 (m s−1
) (FEROS) -56.8 ± 5.6 78.1 ± 3.6 3.6 ± 2.7 -1.4 ± 2.6
γ3 (m s−1
) (UCLES) -14.3 ± 5.0 80.3 ± 4.3 - - - 4.8 ± 5.0
RMS (m s−1
) 9.1 6.5 9.9 7.2
χ2
red 2.4 1.5 2.7 1.7
nounced the discovery of a two-planet systems around HIP 5364,
as part of the Lick Survey (Frink et al. 2002). Since this star is
part of our RV program, we have also taken several FECH and
CHIRON spectra. The resulting velocities will be presented in a
forthcoming paper (Jones et al., in preparation).
In summary, a total of 15 substellar companions to 12 differ-
ent stars in our sample have been confirmed, plus a number of
candidate systems that are currently being followed-up (Jones et
al. in preparation). These objects have projected masses in the
range 1.4 - 20.0 MJ , and orbital periods between 89 d (0.46 AU)
and 2132 d (3.82 AU).
Figure 5 shows the orbital distance versus stellar mass for
these 12 systems. The red and blue dashed lines represent radial
velocity amplitudes of K = 30 m s−1
(assuming circular orbits),
which correspond to ∼ 3-σ detection limits5
. It can be seen that
we can detect planets with MP 3.0 MJ up to a ∼ 3 AU (or MP
2.5 MJ at a ∼ 2.5 AU) around stars with M⋆ 2.5 M⊙ . For
more massive stars, we can only detect such planets but at closer
orbital distance (a 2.5 AU for M⋆= 3.0 M⊙ ). We note that we
have collected at least 15 RV epochs for each of our targets, with
a typical timespan of ∼ 2-3 years, which allow us to efficiently
detect periodic RV signals with K 30 m s−1
and e 0.6 via
periodogram analysis and visual inspection. Moreover, we have
obtained additional data for our targets showing RV variability
20 m s−1
, including those presenting linear trends. In fact, some
of these linear trend systems are brown-dwarf candidates, with
orbital periods exceeding the total observational timespan of our
survey (P 2200 d; see Bluhm et al., submitted). We also note
that in the case of HIP 67851c (Jones et al. 2015b), we used
ESO archive data to fully cover its orbital period (P = 2132 d; a
= 3.82 AU).
5.1. Stellar mass and metallicity
Figure 6 shows a histogram of the planetary occurrence rate as
a function of the stellar mass in our sample. The bin width is
0.4 M⊙ and the stellar masses range from 0.9 M⊙ to 3.5 M⊙ . The
uncertainties were computed according to Cameron (2011), and
5
For FEROS and CHIRON data, the RV noise is dominated by stellar
pulsations, that induce velocity variability of ∼ 5-10 m s−1
level in our
targets. In fact, according to Kjeldsen & Bedding (1995), only 4 of our
targets are expected to present velocity variations larger than 10 m s−1
.
In the case of FECH data, the instrumental uncertainty is comparable to
the stellar pulsations noise.
1 2 3 4
Fig. 5. Stellar mass versus semi-major axis of the 12 planetary sys-
tems in our sample. The size of the circles is proportional to the planet
mass. Multi-planet systems are connected by the dotted lines. The red,
green and blue dashed lines correspond to K = 30 m s−1
, for 1, 2 and 3
MJ planets, respectively.
correspond to 68.3% equal-tailed confidence limits. As can be
seen, there is an increase in the detection fraction with the stellar
mass, between ∼ 1.0 -2.1 M⊙ , reaching a peak in the occurrence
rate of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ . In addition, there is a
sharp drop in the occurrence rate at stellar masses 2.5 M⊙ . In
fact, there are 17 stars in our survey in this mass regime, but none
of them host a planet. We note that, although the observed lack
of planets around these stars might be in part explained by the re-
duced RV sensitivity (see Figure 5), all of our targets more mas-
sive than 2.5 M⊙ present RV variability 15 m s−1
. This means
that we can also discard the presence of planets with MP 3.0
MJ interior to a ∼ 3 AU, otherwise we would expect to observe
doppler-induced variability at the 20 m s−1
level.6
Following
the REF15 results, we fitted a Gaussian function to the data, of
6
The RMS of a cosine function (circular orbit) is ∼ 0.71 K, where
K is the semi-amplitude of the signal. Thus, for a K = 30 m s−1
semi-
amplitude RV signal, we expect to observe a variability (RMS) of ∼ 21
m s−1
, while for K = 21 m s−1
is ∼ 15 m s−1
.
Article number, page 5 of 11
6. Fig. 6. Normalized occurrence rate versus stellar mass for EXPRESS
targets with published planets. The dashed blue line corresponds to the
parent sample distribution. The solid curve corresponds to the Gaussian
fit (equation 1).
the form:
f(M⋆) = C exp
−(M⋆ − µ)2
2 σ2
. (1)
To obtain the values of C, µ and σ, we generated 10000 syn-
thetic datasets, computing the confidence limits for each realiza-
tion following the Cameron (2011) prescription. After fitting C,
µ and σ for each synthetic dataset, we end-up with a probabil-
ity density distribution for each of these three parameters. We
note that we first computed C, and then we fixed it to compute
µ and σ, restricting these two parameters to: µ ∈ [1.5,3.0] and
σ ∈ [0.0,1.5]. Figure 7 shows our results for the three param-
eters. The red lines correspond to the smoothed distributions.
We obtained the following values: C = 0.14 +0.08
−0.01, µ = 2.29 +0.44
−0.06
M⊙ , and σ = 0.64 +0.44
−0.03 M⊙ . The parameters were derived from
the maximum value and equal-tailed confidence limits of each
smoothed distribution, respectively.
Despite the fact that we are dealing with low number statis-
tics, particularly for the upper mass bin, these results are in ex-
cellent agreement with previous works. JOHN10, based on a
sample of 1266 stars with M⋆∼ 0.5 -2.0 M⊙ , showed that the oc-
currence rate of planets increases linearly with the mass of the
host star, reaching a fraction of ∼ 14 % at M⋆∼ 2.0 M⊙ . Sim-
ilarly, based on a sample of 373 giant stars with M⋆∼ 1.0 - 5.0
M⊙ , REF15 showed that the detection fraction of giant plan-
ets present a Gaussian distribution, with a peak in the detec-
tion fraction of ∼ 8 % at ∼ 1.9 M⊙ . Additionally, they showed
that the occurrence rate around stars more massive than ∼ 2.7
M⊙ is consistent with zero, in good agreement with our findings,
and also with theoretical predictions. For instance, based on a
semi-analytic calculation of an evolving snow-line, Kennedy &
Kenyon (2008) showed that the formation efficiency increases
linearly from 0.4 to 3.0 M⊙ . For stars more massive than 3.0
M⊙ , the formation of gas giant planets in the inner region of
the protoplanetary disk is strongly reduced. Because of the fast
stellar evolution timescale for those massive stars, the snow line
moves rapidly to 10-15 AU, preventing the formation of the gi-
ant planets in this region.
Figure 8 shows the planet occurrence rate as a function of
the stellar metallicity. The symbols and lines are the same as in
Fig. 7. Probability density functions for µ, σ, and C, obtained from
a total of 10000 synthetic datasets. The red lines correspond to the
smoothed distributions.
Figure 6. The width of the bins is 0.15 dex. It can be seen, that
the occurrence rate increases with the stellar metallicity, with a
peak of f = 16.7+15.5
−5.9 % around stars with [Fe/H] = 0.35 dex.
This trend seems to be real, despite a relatively high fraction ob-
served in the bin centered at -0.25 dex, which might be explained
by the low number statistics for that specific bin. Following the
prescription of FIS05, we fitted the metallicity dependence of
the occurrence fraction, with a function of the form:
f([Fe/H]) = α 10β [Fe/H]
. (2)
Using a similar approach for fitting equation 1, we obtained the
following values: α = 0.061+0.028
−0.003, and β = 1.27+0.83
−0.42 dex−1
. Fig-
ure 9 shows the probability density distribution of α and β ob-
tained after fitting the synthetic datasets. The functional depen-
dence of the occurrence rate with [Fe/H] (equation 2) is over-
plotted (solid curve).
This relationship between the occurrence rate and the stellar
metallicity is also observed in solar-type stars (Gonzalez 1997;
Santos et al. 2001). Moreover, according to REF15, this trend
is also present in giant stars. Interestingly, they also showed
that there is an overabundance of planets around giant stars with
[Fe/H] ∼ -0.3, similarly to what we found in our sample.
To investigate whether one of the two correlations presented
above are spurious, we investigated the level of correlation be-
tween the stellar mass and metallicity in our sample. Figure 10
shows the mass of the star as a function of the metallicity for
all of our targets (filled dots). The open circles are the planet-
hosting stars. In the top left corner is shown the mean uncertainty
in [Fe/H] and M⋆. From Figure 10, it is clear that there is some
dependence between these two quantities. The Pearson linear
coefficient is r = 0.27, which means that there is an insignificant
level of correlation. Moreover, if we restrict our analysis to stars
with M⋆< 2.5 M⊙ , the r-value drops to 0.22, and we obtain a
steeper rise of the occurrence rate with the stellar metallicity.
Thus, we conclude that the two correlations presented in Figures
6 and 8 are valid.
In addition, we computed the fraction of our stars hosting
planets in the stellar mass-metallicity space, using the same bins
size presented in REF15. These results are listed in Table 3.
Columns 1 and 2 correspond to the stellar metallicity and mass
bins, each of 0.16 dex and 0.8 M⊙ , respectively. The number of
Article number, page 6 of 11
7. M. I. Jones et al.: Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars.
-0.4 -0.2 0 0.2 0.4
Fig. 8. Normalized occurrence rate versus stellar metallicity for
EXPRESS targets with published planets. The dashed blue line cor-
responds to the parent sample distribution. The solid curve is our best
fit to equation 2.
stars with detected planets (np), number of stars in the bin (ns)
and the fraction of stars with planets in each bin (f), are listed in
columns 3-5. It can be seen that the highest fraction is obtained
in the bin centered at 1.4 M⊙ and 0.12 dex (f = 9.4+8.3
−5.1), which
is slightly higher than the value of the bin with the same metal-
licity, but centered at 2.2 M⊙ (f = 9.1+10.8
−5.8 ). Interestingly, REF15
found a similar trend, i.e., they also obtained the highest fraction
in these two mass-metallicity bins, although they claim higher
values for f. Also, we analyzed the combined results of the two
surveys. These are listed in columns 6-8 in Table 3. It can be
seen that the overall trend is unaffected, but the uncertainties in
the planet fraction are smaller.
Finally, to understand whether the combined results are af-
fected by systematic differences in the stellar parameters derived
independently by the two surveys, we compared the resulting
metallicities of the Lick Survey (listed in REF15) with those de-
rived using our method. We used a total of 16 stars, from which
12 of them are common targets. We measured a difference of
∆([Fe/H]) = 0.03 dex ± 0.11 dex, showing the good agreement
between the two methods7
. Similarly, we compared the masses
of the stars derived by the two surveys. We found that our stel-
lar masses are on average larger by ∆(M⋆) = 0.15 ± 0.37 M⊙ ,
which corresponds to a ratio of 1.07 ± 0.18. For comparison,
Niedzielski et al. (2016) also found that our stellar masses are
overestimated with respect to their values by a factor 1.15 ± 0.10.
We also note that the planet-hosting star HIP 5364 is a common
target of the two surveys. They obtained Teff = 4528 ± 19 K and
[Fe/H] = 0.07 ± 0.1 dex. Using these values they derived a mass
of 1.7 ± 0.1 M⊙ for this star (Trifonov et al. 2014), significantly
lower than our value of 2.4 ± 0.3 M⊙ . This shows that the com-
bined results of the Lick and EXPRESS surveys should be taken
with caution. Certainly, a more detailed comparison between the
stellar parameters derived independently by the two surveys, as
well as their completeness, will allow us to check the validity of
these combined results.
7
Our typical dispersion (RMS) in the metallicity derived by each of
the ∼ 150 Fe i individual lines is ∼ 0.1 dex, corresponding to an internal
error 0.01 dex.
Fig. 9. Probability density functions for α and β obtained from a total
of 10000 synthetic datasets. The red lines correspond to the smoothed
distributions.
-0.4 0 0.4
Fig. 10. Mass versus metallicity of the 166 giant stars in our survey.
The red open circles correspond to the planet-hosting stars.
5.2. Multiple-planet systems.
Out of the 12 planet-hosting stars in our sample, HIP 5364,
HIP 24275 and HIP 67851 host planetary systems with at least
two giant planets. This means that 25% of the parent stars, host
a multiple system. Considering the full sample, it yields a ∼ 2 %
fraction of multiple systems, comprised by two or more giant
planets (Mp > 1.0 MJ ). This number is a lower limit, since there
are several other systems in our sample whose velocities are
compatible with the presence of a distant giant planet, but still
need confirmation (e.g. HIP 74890, presented in section 4.2).
If we consider all of the known planet-hosting giant stars
(logg 3.6), around 10% of them host a planetary system com-
prised by at least two giant planets. This fraction is significantly
higher compared to solar-type stars. In fact, there are only 21
such systems among dwarf stars8
, despite the fact that most of
8
source: http://exoplanets.org
Article number, page 7 of 11
8. Table 3. Detection fraction in different stellar mass-metallicity bins.
EXPRESS EXPRESS + LICK
[Fe/H] M⋆ np ns f np ns f
(dex) (M⊙ ) (%) (%)
-0.20 1.4 1 17 5.9+11.3
−1.9 1 58 1.7+3.8
−0.5
-0.20 2.2 0 5 0.0+26.4
−0.0 2 34 5.9+6.9
−1.9
-0.20 3.0 0 0 - - - 0 21 0.0+8.0
−0.0
-0.04 1.4 1 25 4.0+8.1
−1.3 3 54 5.6+4.9
−1.7
-0.04 2.2 1 19 5.3+10.3
−1.7 2 70 2.9+3.6
−0.9
-0.04 3.0 0 1 0.0+60.2
−0.0 0 30 0.0+5.8
−0.0
+0.12 1.4 3 32 9.4+7.8
−3.0 7 48 14.6+6.5
−3.7
+0.12 2.2 2 22 9.1+9.9
−3.1 6 46 13.0+6.6
−3.5
+0.12 3.0 0 14 0.0+11.5
−0.0 2 36 5.6+6.5
−1.8
the RV surveys have targeted those type of stars. Moreover, plan-
ets are easier to be detected via precision RVs around solar-type
stars, because they are on average less massive and have p-modes
oscillations much weaker than giant stars (Kjeldsen & Bedding
1995), which translates into larger amplitudes with a lower level
of RV noise. This observational result is a natural extension of
the known mass distribution of single-planet systems orbiting
evolved stars, which is characterized by an overabundance of
super-Jupiter-like planets (e.g. Lovis & Mayor 2007; Döllinger
et al. 2009; Jones et al. 2014). This result also reinforces the
observed positive correlation between the stellar and planetary
mass, in the sense that more massive stars not only tend to form
more massive single planets, but also more massive multi-planet
systems.
6. Summary and discussion
In this work we present precision radial velocities of four giant
stars that have been targeted by the EXPRESS project, during the
past six years. These velocities show periodic signals, with semi-
amplitudes between ∼ 50 - 100 m s−1
, which are likely caused by
the doppler shift induced by orbiting companions. We performed
standard tests (chromospheric emission, line bisector analysis
and photometric variability) aimed at studying whether these RV
signals have an intrinsic stellar origin. We found no correlation
between the stellar intrinsic indicator with the observed veloci-
ties. Therefore, we conclude that the most probable explanation
of the periodic RV signals observed in these stars is the presence
of substellar companions. The best Keplerian fit to the RV data
of the four stars leads to minimum masses between mb sini= 2.4 -
5.5 MJ and orbital periods P = 562 - 1560 days. Interestingly, all
of them have low eccentricities (e ≤ 0.16), confirming that most
of the giant planets orbiting evolved stars present orbital eccen-
tricities 0.2 (Schlaufman & Winn 2013; Jones et al. 2014).
The RVs of HIP 74890 also reveal the presence of a third object
at large orbital separation (a > 6.5 AU). The RV trend induced
by this object is most likely explained by a brown dwarf or a
stellar companion.
We also present a statistical analysis of the mass-metallicity
correlations of the planet-hosting stars in our sample. This sub-
sample is comprised of 12 stars, drawn from a parent sample of
166 stars, which host a total of 15 giant planets. We show that
the fraction of giant planets f, increases with the stellar mass in
the range between ∼ 1.0 - 2.1 M⊙ , despite the fact that planets
are more easily detected around less massive stars. For compar-
ison, we obtained f = 2.6+5.4
−0.8 % for M⋆∼ 1.3 M⊙ , and a peak of
f = 13.0+10.1
−4.2 % for stars with M⋆∼ 2.1 M⊙ . These results are
in good agreement with previous works showing that the occur-
rence rate of giant planets exhibit a positive correlation with the
stellar mass, up to M⋆∼ 2.0 M⊙ (e.g. JOHN10; REF15). For
stars more massive than ∼ 2.5 M⊙ , the fraction of planets is con-
sistent with zero. We fitted the overall occurrence distribution
with a Gaussian function (see Eq. 1), obtaining the following
parameters: C = 0.14 +0.08
−0.01, µ = 2.29 +0.44
−0.06 M⊙ , and σ = 0.64 +0.44
−0.03
M⊙ .
Similarly, we studied the occurrence rate of giant planets as a
function of the stellar metallicity. We found an overabundanceof
planets around metal-rich stars, with a peak of f = 16.7+15.5
−5.9 %
for stars with [Fe/H] ∼ 0.35 dex. We fitted the metallicity de-
pendence of the occurrence rate with a function of the form
f = α10β [Fe/H]
, obtaining the following parameter values: α =
0.061+0.028
−0.003, and β = 1.27+0.83
−0.42 dex−1
. Our power-law index β
lies in between the values measured by JOHN10 (β = 1.2 ± 0.2)
and FIS05 (β = 2.0). Thus, our results suggest that the planet-
metallicity correlation observed in solar-type stars is also present
in intermediate-mass (M⋆ 1.5 M⊙ ) evolved stars, in agreement
with REF15 results.
Finally, we investigated the fraction of multiple planetary
systems comprised by two or more giant planets. Out of the
12 systems presented above, three of them contain two giant
planets, which is a significant fraction of the total number of
these planetary systems. If we also consider multi-planet sys-
tems published by other RV surveys, we found that there is a
significantly higher fraction of them around intermediate-mass
evolved stars in comparison to solar-type stars. This result is not
surprising, since different works have shown that giant planets
are more frequent around intermediate-mass stars (Döllinger et
al. 2009; Bowler et al. 2010), which is also supported by the-
oretical predictions (Kennedy & Kenyon 2008). Also, planets
tend to be more massive around intermediate-mass stars com-
pared to those around solar-type stars (e.g. Lovis & Mayor 2007;
Döllinger et al. 2009; Jones et al. 2014). Thus, we conclude that
the high fraction of multiple systems observed in giant stars is a
Article number, page 8 of 11
9. M. I. Jones et al.: Four new planets around giant stars and the mass-metallicity correlation of planet-hosting stars.
natural consequence of the planet formation mechanism around
intermediate-mass stars.
Acknowledgements. M.J. acknowledges financial support from Fondecyt project
#3140607 and FONDEF project CA13I10203. A.J. acknowledges support
from Fondecyt project #1130857, the Ministry of Economy, Development, and
Tourism’s Millennium Science Initiative through grant IC120009, awarded to
The Millennium Institute of Astrophysics (MAS). P.R acknowledges funding
by the Fondecyt project #1120299. F.O acknowledges financial support from
Fondecyt project #3140326 and from the MAS. J.J., P.R and A.J acknowledge
support from CATA-Basal PFB-06. HD acknowledges financial support from
FONDECYT project #3150314. This research has made use of the SIMBAD
database and the VizieR catalogue access tool, operated at CDS, Strasbourg,
France.
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