- ID:
- ivo://CDS.VizieR/J/ApJ/809/25
- Title:
- Stellar and planet properties for K2 candidates
- Short Name:
- J/ApJ/809/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The extended Kepler mission, K2, is now providing photometry of new fields every three months in a search for transiting planets. In a recent study, Foreman-Mackey and collaborators presented a list of 36 planet candidates orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar and planetary properties for all systems. We combine ground-based seeing-limited survey data and adaptive optics imaging with an automated transit analysis scheme to validate 21 candidates as planets, 17 for the first time, and identify 6 candidates as likely false positives. Of particular interest is K2-18 (EPIC 201912552), a bright (K=8.9) M2.8 dwarf hosting a 2.23+/-0.25 R_{earth}_ planet with T_eq_=272+/-15 K and an orbital period of 33 days. We also present two new open-source software packages which enable this analysis. The first, isochrones, is a flexible tool for fitting theoretical stellar models to observational data to determine stellar properties using a nested sampling scheme to capture the multimodal nature of the posterior distributions of the physical parameters of stars that may plausibly be evolved. The second is vespa, a new general-purpose procedure to calculate false positive probabilities and statistically validate transiting exoplanets.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/374/664
- Title:
- Stellar atmospheric parameters in MILES library
- Short Name:
- J/MNRAS/374/664
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous set of stellar atmospheric parameters (Teff, logg, [Fe/H]) for MILES, a new spectral stellar library covering the range {lambda}{lambda}3525-7500{AA} at 2.3{AA} (FWHM) spectral resolution. The library consists of 985 stars spanning a large range in atmospheric parameters, from super-metal-rich, cool stars to hot, metal-poor stars. The spectral resolution, spectral type coverage and number of stars represent a substantial improvement over previous libraries used in population synthesis models. The atmospheric parameters that we present here are the result of a previous, extensive compilation from the literature. In order to construct a homogeneous data set of atmospheric parameters we have taken the sample of stars of Soubiran, Katz & Cayrel (1998, Cat. <J/A+AS/133/221>, which has very well determined fundamental parameters, as the standard reference system for our field stars, and have calibrated and bootstrapped the data from other papers against it. The atmospheric parameters for our cluster stars have also been revised and updated according to recent metallicity scales, colour-temperature relations and improved set of isochrones.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/15
- Title:
- Stellar mass-metallicity relation. I.
- Short Name:
- J/ApJ/856/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the stellar mass-stellar metallicity relationship (MZR) in the galaxy cluster Cl0024+1654 at z~0.4 using full-spectrum stellar population synthesis modeling of individual quiescent galaxies. The lower limit of our stellar mass range is M*=10^9.7^M_{sun}_, the lowest galaxy mass at which individual stellar metallicity has been measured beyond the local universe. We report a detection of an evolution of the stellar MZR with observed redshift at 0.037+/-0.007dex per Gyr, consistent with the predictions from hydrodynamical simulations. Additionally, we find that the evolution of the stellar MZR with observed redshift can be explained by an evolution of the stellar MZR with the formation time of galaxies, i.e., when the single stellar population (SSP)-equivalent ages of galaxies are taken into account. This behavior is consistent with stars forming out of gas that also has an MZR with a normalization that decreases with redshift. Lastly, we find that over the observed mass range, the MZR can be described by a linear function with a shallow slope ([Fe/H]{propto}(0.16+/-0.03)logM*). The slope suggests that galaxy feedback, in terms of mass-loading factor, might be mass-independent over the observed mass and redshift range.
- ID:
- ivo://CDS.VizieR/J/PASP/115/22
- Title:
- Stellar parameters for 134 cool subdwarfs
- Short Name:
- J/PASP/115/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a search for cool subdwarfs are presented. Kinematic (U, V, and W) and stellar parameters (Teff, logg, [Fe/H], and Vturb) are derived for 134 candidate subdwarfs based on high-resolution spectra. The observed stars span 4200K<Teff<6400K and -2.70<[Fe/H]<0.25 including only eight giants (logg<4.0). Of the sample, 100 stars have MgH bands present in their spectra. The targets were selected by their large reduced proper motion, by the offset from the solar-metallicity main sequence, or from the literature. We confirm the claims made by Ryan (1989, Cat. <J/AJ/98/1693>) that the NLTT catalog is a rich source of subdwarfs and verify the success of the reduced proper-motion constraint in identifying metal-poor stars.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A68
- Title:
- Stellar parameters for CoRoT exoplanet field stars
- Short Name:
- J/A+A/581/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic observations represent a fundamental step in the physical characterization of stars and, in particular, in the precise location of stars in the HR diagram. Rotation is also a key parameter, impacting stellar properties and evolution, which modulates the interior and manifests itself on the surface of stars. To date, the lack of analysis based on large samples has prevented our understanding of the real impact of stellar parameters and rotation on the stellar evolution as well as on the behavior of surface abundances. The space missions, CoRoT and Kepler, are providing us with rotation periods for thousands of stars, thus enabling a robust assessment of the behavior of rotation for different populations and evolutionary stages. For these reasons, the follow-up programs are fundamental to increasing the returns of these space missions. An analysis that combines spectroscopic data and rotation/modulation periods obtained from these space missions provides the basis for establishing the evolutionary behavior of the angular momentum of solar-like stars at different evolutionary stages, and the relation of rotation with other relevant physical and chemical parameters. To support the computation and evolutionary interpretation of periods associated with the rotational modulation, oscillations, and variability of stars located in the CoRoT fields, we are conducting a spectroscopic survey for stars located in the fields already observed by the satellite. These observations allow us to compute physical and chemical parameters for our stellar sample. Using spectroscopic observations obtained with UVES/VLT and Hydra/Blanco, and based on standard analysis techniques, we computed physical and chemical parameters (T_eff_, log(g), [Fe/H], v_mic_, v_rad_, vsin(i), and A(Li)) for a large sample of CoRoT targets. We provide physical and chemical parameters for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in our sample are located in different evolutionary stages, ranging from the main sequence to the red giant branch, and range in spectral type from F to K. The physical and chemical properties for the stellar sample are in agreement with typical values reported for FGK stars. However, we report three stars presenting abnormal lithium behavior in the CoRoT fields. These parameters allow us to properly characterize the intrinsic properties of the stars in these fields. Our results reveal important differences in the distributions of metallicity, T_eff_, and evolutionary status for stars belonging to different CoRoT fields, in agreement with results obtained independently from ground-based photometric surveys. Our spectroscopic catalog, by providing much-needed spectroscopic information for a large sample of CoRoT targets, will be of key importance for the successful accomplishment of several different programs related to the CoRoT mission, thus it will help further boost the scientific return associated with this space mission.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A141
- Title:
- Stellar parameters for 582 HARPS FGK stars
- Short Name:
- J/A+A/533/A141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the formation and evolution of solar-type stars and planets in the solar neighborhood, we need to obtain their stellar parameters with high precision. We present a catalog of precise stellar parameters for low-activity FGK single stars in a volume-limited sample followed by the HARPS spectrograph in the quest to identify extra-solar planets. The spectroscopic analysis was completed assuming LTE with a grid of Kurucz atmosphere models and using the ARES code to perform an automatic measurement of the line equivalent widths. The results are compared with different independent methods and also with other values found in the literature for common stars. Both comparisons are consistent and illustrate the homogeneity of the parameters derived by our team. The derived metallicities of this sample reveal a somewhat different distribution for the present planet hosts, but still indicates the already known higher frequency of planets observed for the more metal-rich stars. We combine the results derived in this sample with the one from the CORALIE survey to present the largest homogeneous spectroscopic study of the metallicity-giant-planet relation using a total of 1830 stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/899/62
- Title:
- Stellar parameters from the 1st release of the MaSTar
- Short Name:
- J/ApJ/899/62
- Date:
- 14 Mar 2022 07:12:49
- Publisher:
- CDS
- Description:
- We report the stellar atmospheric parameters for 7503 spectra contained in the first release of the Mapping Nearby Galaxies at Apache Point Observatory survey (MaNGA) stellar library (MaStar) in Sloan Digital Sky Survey DR15. The first release of MaStar contains 8646 spectra measured from 3321 unique stars, each covering the wavelength range 3622-10354{AA} with a resolving power of R~1800. In this work, we first determined the basic stellar parameters: effective temperature (Teff), surface gravity (logg), and metallicity ([Fe/H]), which best fit the data using an empirical interpolator based on the Medium-resolution Isaac Newton Telescope library of empirical spectra (MILES), as implemented by the University of Lyon Spectroscopic analysis Software package. While we analyzed all 8646 spectra from the first release of MaStar, since MaStar has a wider parameter-space coverage than MILES, not all of these fits are robust. In addition, not all parameter regions covered by MILES yield robust results, likely due to the nonuniform coverage of the parameter space by MILES. We tested the robustness of the method using the MILES spectra itself and identified a proxy based on the local density of the training set. With this proxy, we identified 7503 MaStar spectra with robust fitting results. They cover the range from 3179 to 20517K in effective temperature (Teff), from 0.40 to 5.0 in surface gravity (logg), and from -2.49 to +0.73 in metallicity ([Fe/H]).
- ID:
- ivo://CDS.VizieR/J/A+A/577/A132
- Title:
- Stellar parameters of early M dwarfs
- Short Name:
- J/A+A/577/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. As a consequence, Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. We aim to calibrate empirical relationships to determine accurate stellar parameters for early M dwarfs (spectral types M0-M4.5) using the same spectra that are used for the radial velocity determinations. Our methodology consists in the use of ratios of pseudo equivalent widths of spectral features. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A194
- Title:
- Stellar parameters of 18 M dwarfs
- Short Name:
- J/A+A/658/A194
- Date:
- 24 Feb 2022 06:38:20
- Publisher:
- CDS
- Description:
- Deriving metallicities for solar-like stars follows well-established methods, but for cooler stars such as M dwarfs, the determination is much more complicated due to forests of molecular lines that are present. Several methods have been developed in recent years to determine accurate stellar parameters for these cool stars (Teff<4000K). However, significant differences can be found at times when comparing metallicities for the same star derived using different methods. In this work, we determine the effective temperatures, surface gravities, and metallicities of 18 well-studied M dwarfs observed with the CARMENES high-resolution spectrograph following different approaches, including synthetic spectral fitting, analysis of pseudo-equivalent widths, and machine learning. We analyzed the discrepancies in the derived stellar parameters, including metallicity, in several analysis runs. Our goal is to minimize these discrepancies and find stellar parameters that are more consistent with the literature values. We attempted to achieve this consistency by standardizing the most commonly used components, such as wavelength ranges, synthetic model spectra, continuum normalization methods, and stellar parameters. We conclude that although such modifications work quite well for hotter main-sequence stars, they do not improve the consistency in stellar parameters for M dwarfs, leading to mean deviations of around 50-200K in temperature and 0.1-0.3dex in metallicity. In particular, M dwarfs are much more complex and a standardization of the aforementioned components cannot be considered as a straightforward recipe for bringing consistency to the derived parameters. Further in-depth investigations of the employed methods would be necessary in order to identify and correct for the discrepancies that remain.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A156
- Title:
- Stellar populations of quiescent galaxies
- Short Name:
- J/A+A/631/A156
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Our aim is to determine the distribution of stellar population parameters (extinction, age, metallicity, and star formation rates) of quiescent galaxies within the rest-frame stellar mass-colour diagrams and UVJ colour-colour diagrams corrected for extinction up to z~1. These novel diagrams reduce the contamination in samples of quiescent galaxies owing to dust-reddened galaxies, and they provide useful constraints on stellar population parameters only using rest-frame colours and stellar mass. We set constraints on the stellar population parameters of quiescent galaxies combining the ALHAMBRA multi-filter photo-spectra with our fitting code for spectral energy distribution, MUlti-Filter FITting (MUFFIT), making use of composite stellar population models based on two independent sets of simple stellar population (SSP) models. The extinction obtained by MUFFIT allowed us to remove dusty star-forming (DSF) galaxies from the sample of red UVJ galaxies. The distributions of stellar population parameters across these rest-frame diagrams are revealed after the dust correction and are fitted by LOESS, a bi-dimensional and locally weighted regression method, to reduce uncertainty effects. Quiescent galaxy samples defined via classical UVJ diagrams are typically contaminated by a 20% fraction of DSF galaxies. A significant part of the galaxies in the green valley are actually obscured star-forming galaxies (30-65%). Consequently, the transition of galaxies from the blue cloud to the red sequence, and hence the related mechanisms for quenching, seems to be much more efficient and faster than previously reported. The rest-frame stellar mass-colour and UVJ colour-colour diagrams are useful for constraining the age, metallicity, extinction, and star formation rate of quiescent galaxies by only their redshift, rest-frame colours, and/or stellar mass. Dust correction plays an important role in understanding how quiescent galaxies are distributed in these diagrams and is key to performing a pure selection of quiescent galaxies via intrinsic colours.
