115 research outputs found
Age consistency between exoplanet hosts and field stars
Transiting planets around stars are discovered mostly through photometric
surveys. Unlike radial velocity surveys, photometric surveys do not tend to
target slow rotators, inactive or metal-rich stars. Nevertheless, we suspect
that observational biases could also impact transiting-planet hosts. This paper
aims to evaluate how selection effects reflect on the evolutionary stage of
both a limited sample of transiting-planet host stars (TPH) and a wider sample
of planet-hosting stars detected through radial velocity analysis. Then, thanks
to uniform derivation of stellar ages, a homogeneous comparison between
exoplanet hosts and field star age distributions is developed. Stellar
parameters have been computed through our custom-developed isochrone placement
algorithm, according to PARSEC models. The notable aspects of our algorithm
include the treatment of element diffusion, activity checks in terms of
and , and the evaluation of the stellar evolutionary
speed in the Hertzsprung-Russel diagram in order to better constrain age.
Working with TPH, the observational stellar mean density allows
us to compute stellar luminosity even if the distance is not available, by
combining with the spectroscopic . The median value of
the TPH ages is Gyr. Even if this sample is not very large, however,
the result is very similar to what we found for the sample of spectroscopic
hosts, whose modal and median values are [3, 3.5) Gyr and Gyr,
respectively. Thus, these stellar samples suffer almost the same selection
effects. We also conclude that the age of our Sun is consistent with the age
distribution of solar neighbourhood MS stars with spectral types from late F to
early K, regardless of whether they harbour planets or not. We considered the
possibility that our selected samples are older than the average disc
population.Comment: 13 pages, 1 longtable, 9 figures. Accepted by A&
Revising the ages of planet-hosting stars
This article aims to measure the age of planet-hosting stars (SWP) through
stellar tracks and isochrones computed with the \textsl{PA}dova \&
T\textsl{R}ieste \textsl{S}tellar \textsl{E}volutionary \textsl{C}ode (PARSEC).
We developed algorithms based on two different techniques for determining the
ages of field stars: \emph{isochrone placement} and \emph{Bayesian estimation}.
Their application to a synthetic sample of coeval stars shows the intrinsic
limits of each method. For instance, the Bayesian computation of the modal age
tends to select the extreme age values in the isochrones grid. Therefore, we
used the isochrone placement technique to measure the ages of 317 SWP. We found
that of SWP have ages lower than 0.5 Gyr. The age distribution peaks
in the interval [1.5, 2) Gyr, then it decreases. However, of the
stars are older than 11 Gyr. The Sun turns out to be a common star that hosts
planets, when considering its evolutionary stage. Our SWP age distribution is
less peaked and slightly shifted towards lower ages if compared with ages in
the literature and based on the isochrone fit. In particular, there are no ages
below 0.5 Gyr in the literature.Comment: 16 pages, 18 figures. Accepted by A&
Atmospheric Parameters and Metallicities for 2191 stars in the Globular Cluster M4
We report new metallicities for stars of Galactic globular cluster M4 using
the largest number of stars ever observed at high spectral resolution in any
cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the VLT
FLAMES+GIRAFFE spectrograph at VLT. These medium resolution spectra cover by a
small wavelength range, and often have very low signal-to-noise ratios. We
attacked this dataset by reconsidering the whole method of abundance analysis
of large stellar samples from beginning to end. We developed a new algorithm
that automatically determines the atmospheric parameters of a star. Nearly all
data preparation steps for spectroscopic analyses are processed on the
syntheses, not the observed spectra. For 322 Red Giant Branch stars with we obtain a nearly constant metallicity, ( = 0.02). No difference in the metallicity at the level of
is observed between the two RGB sequences identified by
\cite{Monelli:2013us}. For 1869 Subgiant and Main Sequence Stars we
obtain ( = 0.09) after fixing the
microturbulent velocity. These values are consistent with previous studies that
have performed detailed analyses of brighter RGB stars at higher spectroscopic
resolution and wavelength coverage. It is not clear if the small mean
metallicity difference between brighter and fainter M4 members is real or is
the result of the low signal-to-noise characteristics of the fainter stars. The
strength of our approach is shown by recovering a metallicity close to a single
value for more than two thousand stars, using a dataset that is non-optimal for
atmospheric analyses. This technique is particularly suitable for noisy data
taken in difficult observing conditions.Comment: 17 pages, 20 figures, 3 tables. Accepted for publication in The
Astronomical Journa
TOSC: an algorithm for the tomography of spotted transit chords
Photometric observations of planetary transits may show localized bumps,
called transit anomalies, due to the possible crossing of photospheric
starspots. The aim of this work is to analyze the transit anomalies and derive
the temperature profile inside the transit belt along the transit direction. We
develop the algorithm TOSC, a tomographic inverse-approach tool which, by means
of simple algebra, reconstructs the flux distribution along the transit belt.
We test TOSC against some simulated scenarios. We find that TOSC provides
robust results for light curves with photometric accuracies better than 1~mmag,
returning the spot-photosphere temperature contrast with an accuracy better
than 100~K. TOSC is also robust against the presence of unocculted spots,
provided that the apparent planetary radius given by the fit of the transit
light curve is used in place of the true radius. The analysis of real data with
TOSC returns results consistent with previous studies
TRADES: A new software to derive orbital parameters from observed transit times and radial velocities. Revisiting Kepler-11 and Kepler-9
Aims. With the purpose of determining the orbital parameters of exoplanetary
systems from observational data, we have developed a software, named TRADES
(TRAnsits and Dynamics of Exoplanetary Systems), to simultaneously fit observed
radial velocities and transit times data. Methods. We implemented a dynamical
simulator for N-body systems, which also fits the available data during the
orbital integration and determines the best combination of the orbital
parameters using grid search, minimization, genetic algorithms,
particle swarm optimization, and bootstrap analysis. Results. To validate
TRADES, we tested the code on a synthetic three-body system and on two real
systems discovered by the Kepler mission: Kepler-9 and Kepler-11. These systems
are good benchmarks to test multiple exoplanet systems showing transit time
variations (TTVs) due to the gravitational interaction among planets. We have
found that orbital parameters of Kepler-11 planets agree well with the values
proposed in the discovery paper and with a a recent work from the same authors.
We analyzed the first three quarters of Kepler-9 system and found parameters in
partial agreement with discovery paper. Analyzing transit times (T0s) covering
12 quarters of Kepler data, that we have found a new best-fit solution. This
solution outputs masses that are about 55% of the values proposed in the
discovery paper; this leads to a reduced semi-amplitude of the radial
velocities of about 12.80 m/s.Comment: 14 pages, 13 figures, 6 tables; accepted for publication in Astronomy
& Astrophysics, and corrected by the Language Edito
A PSF-based approach to Kepler/K2data – III. Search for exoplanets and variable stars within the open cluster M 67 (NGC 2682)
In the third paper of this series we continue the exploitation of Kepler/K2
data in dense stellar fields using our PSF-based method. This work is focused
on a ~720-arcmin^2 region centred on the Solar-metallicity and Solar-age open
cluster M 67. We extracted light curves for all detectable sources in the
Kepler channels 13 and 14, adopting our technique based on the usage of a
high-angular-resolution input catalogue and target-neighbour subtraction. We
detrended light curves for systematic errors, and searched for variables and
exoplanets using several tools. We found 451 variables, of which 299 are new
detection. Three planetary candidates were detected by our pipeline in this
field. Raw and detrended light curves, catalogues, and K2 stacked images used
in this work will be released to the community.Comment: 14 pages, 9 figures (1 at low resolution), 3 tables. Accepted for
publication in MNRAS on August 24, 2016. Electronic materials are available
at http://groups.dfa.unipd.it/ESPG/Kepler-K2.htm
Validation of TESS exoplanet candidates orbiting solar analogues in the all-sky PLATO input catalogue
Funding: G.M. acknowledges the support of the Erasmus+ Programme of the European Union and of the doctoral grant funded by the University of Padova and by the Italian Ministry of Education, University and Research (MIUR). G.M. is also grateful to the Centre for Exoplanet Science, University of St Andrews (StA-CES) for hospitality and computing resources. GPi, LBo, VNa, and FZM acknowledge the funding support from Italian Space Agency (ASI) regulated by ‘Accordo ASI-INAF n. 2013-016-R.0 del 9 luglio 2013 e integrazione del 9 luglio 2015 CHEOPS Fasi A/B/C’. We acknowledge the support of PLATO ASI-INAF agreements n.2015-019-R0-2015 and n. 2015-019-R.1-2018. T.G.W. and A.C.C. acknowledge support from STFC consolidated grant number ST/V000861/1, and UKSA grant ST/R003203/1.The Transiting Exoplanet Survey Satellite (TESS) is focusing on relatively bright stars and has found thousands of planet candidates. However, mainly because of the low spatial resolution of its cameras (≈ 21 arcsec/pixel), TESS is expected to detect several false positives (FPs); hence, vetting needs to be done. Here, we present a follow-up program of TESS candidates orbiting solar-analogue stars that are in the all-sky PLATO input catalogue. Using Gaia photometry and astrometry we built an absolute colour-magnitude diagram and isolated solar-analogue candidates’ hosts. We performed a probabilistic validation of each candidate using the vespa software and produced a prioritized list of objects that have the highest probability of being genuine transiting planets. Following this procedure, we eliminated the majority of FPs and statistically vetted 23 candidates. For this remaining set, we performed a stellar neighbourhood analysis using Gaia Early Data Release 3 and centroid motion tests, greatly enhancing the on-target probability of 12 of them. We then used publicly available high-resolution imaging data to confirm their transit source and found five new, fully validated planets. For the remaining candidates, we propose on-off photometry to further refine the list of genuine candidates and prepare for the subsequent radial velocity follow-up.Publisher PDFPeer reviewe
VizieR Online Data Catalog: BR light curves of GJ1214b (Nascimbeni+, 2015)
We observed two complete transits of GJ1214b during the nights of March 29 and May 17, 2012 with the LBC camera mounted at the double 8.4m Large Binocular Telescope (LBT). We mounted a Bessel B and Bessel R filter on the blue and red channel, respectively. (4 data files)
The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
Kepler-10b was the first rocky planet detected by the Kepler satellite and
con- firmed with radial velocity follow-up observations from Keck-HIRES. The
mass of the planet was measured with a precision of around 30%, which was
insufficient to constrain models of its internal structure and composition in
detail. In addition to Kepler-10b, a second planet transiting the same star
with a period of 45 days was sta- tistically validated, but the radial
velocities were only good enough to set an upper limit of 20 Mearth for the
mass of Kepler-10c. To improve the precision on the mass for planet b, the
HARPS-N Collaboration decided to observe Kepler-10 intensively with the HARPS-N
spectrograph on the Telescopio Nazionale Galileo on La Palma. In to- tal, 148
high-quality radial-velocity measurements were obtained over two observing
seasons. These new data allow us to improve the precision of the mass
determina- tion for Kepler-10b to 15%. With a mass of 3.33 +/- 0.49 Mearth and
an updated radius of 1.47 +0.03 -0.02 Rearth, Kepler-10b has a density of 5.8
+/- 0.8 g cm-3, very close to the value -0.02 predicted by models with the same
internal structure and composition as the Earth. We were also able to determine
a mass for the 45-day period planet Kepler-10c, with an even better precision
of 11%. With a mass of 17.2 +/- 1.9 Mearth and radius of 2.35 +0.09 -0.04
Rearth, -0.04 Kepler-10c has a density of 7.1 +/- 1.0 g cm-3. Kepler-10c
appears to be the first strong evidence of a class of more massive solid
planets with longer orbital periods.Comment: 44 pages, 8 figures, accepted for publication in Ap
HAYDN: High-precision AsteroseismologY of DeNse stellar fields
In the last decade, the Kepler and CoRoT space-photometry missions have demonstrated the potential of asteroseismology as a novel, versatile and powerful tool to perform exquisite tests of stellar physics, and to enable precise and accurate characterisations of stellar properties, with impact on both exoplanetary and Galactic astrophysics. Based on our improved understanding of the strengths and limitations of such a tool, we argue for a new small/medium space mission dedicated to gathering high-precision, high-cadence, long photometric series in dense stellar fields. Such a mission will lead to breakthroughs in stellar astrophysics, especially in the metal poor regime, will elucidate the evolution and formation of open and globular clusters, and aid our understanding of the assembly history and chemodynamics of the Milky Way’s bulge and a few nearby dwarf galaxies
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