- ID:
- ivo://CDS.VizieR/J/AJ/156/264
- Title:
- California-Kepler Survey. VII. Planet radius gap
- Short Name:
- J/AJ/156/264
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of planet sizes encodes details of planet formation and evolution. We present the most precise planet size distribution to date based on Gaia parallaxes, Kepler photometry, and spectroscopic temperatures from the California-Kepler Survey. Previously, we measured stellar radii to 11% precision using high-resolution spectroscopy; by adding Gaia astrometry, the errors are now 3%. Planet radius measurements are, in turn, improved to 5% precision. With a catalog of ~1000 planets with precise properties, we probed in fine detail the gap in the planet size distribution that separates two classes of small planets, rocky super-Earths and gas-dominated sub-Neptunes. Our previous study and others suggested that the gap may be observationally under-resolved and inherently flat-bottomed, with a band of forbidden planet sizes. Analysis based on our new catalog refutes this; the gap is partially filled in. Two other important factors that sculpt the distribution are a planet's orbital distance and its host-star mass, both of which are related to a planet's X-ray/UV irradiation history. For lower-mass stars, the bimodal planet distribution shifts to smaller sizes, consistent with smaller stars producing smaller planet cores. Details of the size distribution including the extent of the "sub-Neptune desert" and the width and slope of the gap support the view that photoevaporation of low-density atmospheres is the dominant evolutionary determinant of the planet size distribution.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/770/90
- Title:
- Candidate planets in the habitable zones
- Short Name:
- J/ApJ/770/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A key goal of the Kepler mission is the discovery of Earth-size transiting planets in "habitable zones" where stellar irradiance maintains a temperate climate on an Earth-like planet. Robust estimates of planet radius and irradiance require accurate stellar parameters, but most Kepler systems are faint, making spectroscopy difficult and prioritization of targets desirable. The parameters of 2035 host stars were estimated by Bayesian analysis and the probabilities p_HZ_ that 2738 candidate or confirmed planets orbit in the habitable zone were calculated. Dartmouth Stellar Evolution Program models were compared to photometry from the Kepler Input Catalog, priors for stellar mass, age, metallicity and distance, and planet transit duration. The analysis yielded probability density functions for calculating confidence intervals of planet radius and stellar irradiance, as well as p_HZ_. Sixty-two planets have p_HZ_>0.5 and a most probable stellar irradiance within habitable zone limits. Fourteen of these have radii less than twice the Earth; the objects most resembling Earth in terms of radius and irradiance are KOIs 2626.01 and 3010.01, which orbit late K/M-type dwarf stars. The fraction of Kepler dwarf stars with Earth-size planets in the habitable zone ({eta}_{Earth}_) is 0.46, with a 95% confidence interval of 0.31-0.64. Parallaxes from the Gaia mission will reduce uncertainties by more than a factor of five and permit definitive assignments of transiting planets to the habitable zones of Kepler stars.
- ID:
- ivo://CDS.VizieR/J/AJ/158/235
- Title:
- Candidate X-ray sources in IRAS 09002-4732 region
- Short Name:
- J/AJ/158/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- IRAS 09002-4732 is a poorly studied embedded cluster of stars in the Vela Molecular Ridge at a distance of 1.7 kpc. Deep observations with the Chandra X-ray Observatory, combined with existing optical and infrared surveys, produce a catalog of 441 probable pre-main-sequence members of the region. The stellar spatial distribution has two components: most stars reside in a rich, compact, elliptical cluster, but a minority reside within a molecular filament several parsecs long that straddles the cluster. The filament has active distributed star formation with dozens of unclustered protostars. The cluster pre-main-sequence population is =<0.8 Myr old and deeply embedded; its most massive member is extremely young, producing an ultracompact H II region. The cluster total population deduced from the X-ray luminosity function is surprisingly rich, twice that of the Orion Nebula Cluster. The cluster core is remarkably dense where strong N-body interactions should be occurring; its initial mass function may be deficient in massive stars. We infer that IRAS 09002-4732 is a rare case where a rich cluster is forming today in a molecular filament, consistent with astrophysical models of cluster formation in clouds that involve the hierarchical formation and merging of groups in molecular filaments.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A112
- Title:
- Carbon and oxygen in 107 dwarf stars
- Short Name:
- J/A+A/621/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results from the determination of stellar masses, carbon and oxygen abundances in the atmospheres of 107 stars from the CHEPS program. Our stars are drawn from a population with a significantly super-solar metallicity. At least 10 of these stars are known to host orbiting planets. In this work, we set out to understand the behavior of carbon and oxygen abundance in stars with different spectral classes, metallicities and Vsini, within the metal-rich stellar population. Masses of these stars were determined using the data from Gaia DR2 release. The oxygen and carbon abundances were determined by fitting the absorption lines. Oxygen abundances were determined by fits to the 6300.304{AA} OI line, and for the determination of the carbon abundances we used 3 lines of the CI atom and 12 lines of C_2_ molecule for the determination of carbon abundances. We determine masses and abundances of 107 CHEPS stars. There is no evidence that the [C/O] ratio depends on V sin i or the mass of the star, within our constrained range of masses, i.e. 0.82<M*/M_{sun}_<1.5 and metallicities -0.27<[Fe/H]<+0.39 and we confirm that metal-rich dwarf stars with planets are more carbon-rich in comparison with non-planet host stars, with a statistical significance of 96%. We find tentative evidence that there is a slight offset to lower abundance and a greater dispersion in oxygen abundances relative to carbon, and interpret this as potentially arising from the production of the oxygen being more effective at more metal-poor epochs. We also find evidence that for lower mass star's the angular momentum loss in star's with planets as measured by Vsini is steeper than star's without planets. In general, we find that the fast rotators (Vsini>5km/s) are massive stars.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A109
- Title:
- Carina nebula optically identified YSOs
- Short Name:
- J/A+A/567/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The low obscuration and proximity of the Carina nebula make it an ideal place to study the ongoing star formation process and impact of massive stars on low-mass stars in their surroundings. To investigate this process, we have generated a new catalogue of the pre-main-sequence (PMS) stars in the Carina west (CrW) region and studied their nature and spatial distribution. We have also determined various parameters (reddening, reddening law, age, mass) which are further used to estimate the initial mass function (IMF) and K-band luminosity function (KLF) for the region under study. We obtained deep UBVRI H{alpha} photometric data of the field situated to the west of the main Carina nebula and centered around WR22. Medium-resolution optical spectroscopy of a subsample of X-ray selected objects along with archival data sets from Chandra, XMM-Newton and 2MASS surveys are used for the present study. Our spectroscopic results indicate that the majority of the X-ray sources are late spectral type stars. The region shows a large amount of differential reddening with minimum and maximum values of E(B-V) as 0.25 and 1.1mag, respectively. Our analysis reveals that the total to selective absorption ratio R_V_ is ~3.7+/-0.1 suggesting an abnormal grain size in the observed region. We identify 467 young stellar objects (YSOs) and study their characteristics. The ages and masses of the 241 optically identified YSOs range from ~0.1 to 10Myr and ~0.3 to 4.8M_{sun}_, respectively. However, the majority of them are younger than 1Myr and have masses below 2M_{sun}_. The high mass star WR22 does not seem to have contributed to the formation of YSOs in the CrW region. The initial mass function slope, Gamma in this region is found to be -1.13+/-0.20 in the mass range of 0.5<M/M_{sun}_<4.8. The K-band luminosity function slope ({alpha}) is also estimated as 0.31+/-0.01. We also performed minimum spanning tree analysis of the YSOs in this region which reveals that there are at least ten YSO cores associated with the molecular cloud and that leads to an average core radius and median branch length 0.43pc and 0.28pc, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/161/189
- Title:
- Catalog of gyro-kinematic ages for ~30000 Kepler stars
- Short Name:
- J/AJ/161/189
- Date:
- 09 Mar 2022 22:00:00
- Publisher:
- CDS
- Description:
- Estimating stellar ages is important for advancing our understanding of stellar and exoplanet evolution and investigating the history of the Milky Way. However, ages for low-mass stars are hard to infer as they evolve slowly on the main sequence. In addition, empirical dating methods are difficult to calibrate for low-mass stars as they are faint. In this work, we calculate ages for Kepler F, G, and crucially K and M-dwarfs, using their rotation and kinematic properties. We apply the simple assumption that the velocity dispersion of stars increases over time and adopt an age-velocity-dispersion relation (AVR) to estimate average stellar ages for groupings of coeval stars. We calculate the vertical velocity dispersion of stars in bins of absolute magnitude, temperature, rotation period, and Rossby number and then convert velocity dispersion to kinematic age via an AVR. Using this method, we estimate gyro-kinematic ages for 29949 Kepler stars with measured rotation periods. We are able to estimate ages for clusters and asteroseismic stars with an rms of 1.22Gyr and 0.26Gyr respectively. With our Astraea machine-learning algorithm, which predicts rotation periods, we suggest a new selection criterion (a weight of 0.15) to increase the size of the McQuillan et al. catalog of Kepler rotation periods by up to 25%. Using predicted rotation periods, we estimated gyro-kinematic ages for stars without measured rotation periods and found promising results by comparing 12 detailed age-element abundance trends with literature values.
- ID:
- ivo://CDS.VizieR/J/ApJS/245/13
- Title:
- CDIPS. I. LCs from TESS sectors 6 and 7
- Short Name:
- J/ApJS/245/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Transiting Exoplanet Survey Satellite (TESS) is providing precise time-series photometry for most star clusters in the solar neighborhood. Using the TESS images, we have begun a Cluster Difference Imaging Photometric Survey, in which we are focusing both on stars that are candidate cluster members and on stars that show indications of youth. Our aims are to discover giant transiting planets with known ages, and to provide light curves suitable for studies in stellar astrophysics. For this work, we made 159343 light curves of candidate young stars, across 596 distinct clusters. Each light curve represents between 20 and 25 days of observations of a star brighter than G_Rp_=16, with 30-minute sampling. We describe the image-subtraction and time-series analysis techniques we used to create the light curves, which have noise properties that agree with theoretical expectations. We also comment on the possible utility of the light-curve sample for studies of stellar rotation evolution and binary eccentricity damping.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/2238
- Title:
- Cepheids in open clusters
- Short Name:
- J/MNRAS/434/2238
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cepheids in open clusters (cluster Cepheids: CCs) are of great importance as zero-point calibrators of the Galactic Cepheid period-luminosity relationship (PLR). We perform an 8-dimensional all-sky census that aims to identify new bona-fide CCs and provide a ranking of membership confidence for known CC candidates according to membership probabilities. The probabilities are computed for combinations of known Galactic open clusters and classical Cepheid candidates, based on spatial, kinematic, and population-specific membership constraints. Data employed in this analysis are taken largely from published literature and supplemented by a year-round observing program on both hemispheres dedicated to determining systemic radial velocities of Cepheids. In total, we find 23 bona-fide CCs, 5 of which are candidates identified for the first time, including an overtone-Cepheid member in NGC 129. We discuss a subset of CC candidates in detail, some of which have been previously mentioned in the literature. Our results indicate unlikely membership for 7 Cepheids that have been previously discussed in terms of cluster membership. We furthermore revisit the Galactic PLR using our bona fide CC sample and obtain a result consistent with the recent calibration by Turner (2010). However, our calibration remains limited mainly by cluster uncertainties and the small number of long-period calibrators. In the near future, Gaia will enable our study to be carried out in much greater detail and accuracy, thanks to data homogeneity and greater levels of completeness.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A71
- Title:
- Chemical abundances of solar neighbourhood dwarfs
- Short Name:
- J/A+A/562/A71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed elemental abundance study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The analysis is based on high-resolution spectra obtained with MIKE on the Magellan telescope, FEROS on the ESO 1.5m and 2.2m telescopes, HARPS on the ESO 3.6m telescope, UVES on the ESO Very Large Telescope, SOFIN and FIES on the Nordic Optical Telescope. Our data show that there is an old and alpha-enhanced disk population, and a younger and less alpha-enhanced disk population. While they overlap greatly in metallicity between -0.7<[Fe/H]<+0.1, they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff<5400K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. In addition, we find that the alpha-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk, fully consistent with the recent claims of a short scale-length for the alpha-enhanced Galactic thick disk. We have also investigated the properties of the Hercules stream and the Arcturus moving group.
- ID:
- ivo://CDS.VizieR/J/A+A/275/101
- Title:
- Chemical evolution of the galactic disk I.
- Short Name:
- J/A+A/275/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From high resolution, high S/N spectroscopic observations of carefully selected northern and southern stars, abundances of O, Na, Mg, Al, Si, Ca, Ti, Fe, Ni, Y, Zr, Ba and Nd, as well as photometric ages, are derived for 189 nearby field F and G stars.
