- ID:
- ivo://CDS.VizieR/J/ApJ/835/172
- Title:
- Kepler asteroseismic LEGACY sample. I. Oscillations
- Short Name:
- J/ApJ/835/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The advent of space-based missions like Kepler has revolutionized the study of solar-type stars, particularly through the measurement and modeling of their resonant modes of oscillation. Here we analyze a sample of 66 Kepler main-sequence stars showing solar-like oscillations as part of the Kepler seismic LEGACY project. We use Kepler short-cadence data, of which each star has at least 12 months, to create frequency-power spectra optimized for asteroseismology. For each star, we identify its modes of oscillation and extract parameters such as frequency, amplitude, and line width using a Bayesian Markov chain Monte Carlo "peak-bagging" approach. We report the extracted mode parameters for all 66 stars, as well as derived quantities such as frequency difference ratios, the large and small separations {Delta}{nu} and {delta}{nu}_02_; the behavior of line widths with frequency and line widths at {nu}_max_ with T_eff_, for which we derive parametrizations; and behavior of mode visibilities. These average properties can be applied in future peak-bagging exercises to better constrain the parameters of the stellar oscillation spectra. The frequencies and frequency ratios can tightly constrain the fundamental parameters of these solar-type stars, and mode line widths and amplitudes can test models of mode damping and excitation.
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- ID:
- ivo://CDS.VizieR/J/AJ/157/143
- Title:
- Kepler GK dwarf planet candidate samples
- Short Name:
- J/AJ/157/143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We re-examine the statistical confirmation of small long-period Kepler planet candidates in light of recent improvements in our understanding of the occurrence of systematic false alarms in this regime. Using the final Data Release 25 (DR25, Twicken et al. 2016, J/AJ/152/158) Kepler planet candidate catalog statistics, we find that the previously confirmed single-planet system Kepler-452b no longer achieves a 99% confidence in the planetary hypothesis and is not considered statistically validated in agreement with the finding of Mullally et al. (2018AJ....155..210M). For multiple planet systems, we find that the planet prior enhancement for belonging to a multiple-planet system is suppressed relative to previous Kepler catalogs, and we also find that the multiple-planet system member, Kepler-186f, no longer achieves a 99% confidence level in the planetary hypothesis. Because of the numerous confounding factors in the data analysis process that leads to the detection and characterization of a signal, it is difficult to determine whether any one planetary candidate achieves a strict criterion for confirmation relative to systematic false alarms. For instance, when taking into account a simplified model of processing variations, the additional single-planet systems Kepler-443b, Kepler-441b, Kepler-1633b, Kepler-1178b, and Kepler-1653b have a non-negligible probability of falling below 99% confidence in the planetary hypothesis. The systematic false alarm hypothesis must be taken into account when employing statistical validation techniques in order to confirm planet candidates that approach the detection threshold of a survey. We encourage those performing transit searches of K2, TESS, and other similar data sets to quantify their systematic false alarm rates. Alternatively, independent photometric detection of the transit signal or radial velocity measurements can eliminate the false alarm hypothesis.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/19
- Title:
- Kepler planetary candidates. II.
- Short Name:
- J/ApJ/736/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On 2011 February 1 the Kepler mission released data for 156453 stars observed from the beginning of the science observations on 2009 May 2 through September 16. There are 1235 planetary candidates with transit-like signatures detected in this period. These are associated with 997 host stars. Distributions of the characteristics of the planetary candidates are separated into five class sizes: 68 candidates of approximately Earth-size (R_p_<1.25R_{earth}_), 288 super-Earth-size (1.25R_{earth}_<=R_p_<2R_{earth}_), 662 Neptune-size (2R_{earth}_<=R_p_<6R_{earth}_), 165 Jupiter-size (6R_{earth}<=R_p_<15R_{earth}_), and 19 up to twice the size of Jupiter (15R_{earth}_<=R_p_<22R_{earth}_). In the temperature range appropriate for the habitable zone, 54 candidates are found with sizes ranging from Earth-size to larger than that of Jupiter. Six are less than twice the size of the Earth. Over 74% of the planetary candidates are smaller than Neptune. Multi-candidate, transiting systems are frequent; 17% of the host stars have multi-candidate systems, and 34% of all the candidates are part of multi-candidate systems.
- ID:
- ivo://CDS.VizieR/J/ApJS/204/24
- Title:
- Kepler planetary candidates. III.
- Short Name:
- J/ApJS/204/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New transiting planet candidates are identified in 16 months (2009 May-2010 September) of data from the Kepler spacecraft. Nearly 5000 periodic transit-like signals are vetted against astrophysical and instrumental false positives yielding 1108 viable new planet candidates, bringing the total count up to over 2300. Improved vetting metrics are employed, contributing to higher catalog reliability. Most notable is the noise-weighted robust averaging of multi-quarter photo-center offsets derived from difference image analysis that identifies likely background eclipsing binaries. Twenty-two months of photometry are used for the purpose of characterizing each of the candidates. Ephemerides (transit epoch, T_0_, and orbital period, P) are tabulated as well as the products of light curve modeling: reduced radius (R_P_/R_*_), reduced semimajor axis (d/R_*_), and impact parameter (b).
- ID:
- ivo://CDS.VizieR/J/A+A/601/A67
- Title:
- Kepler solar-type stars modeling
- Short Name:
- J/A+A/601/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kepler space telescope yielded unprecedented data for the study of solar-like oscillations in other stars. The large samples of multi-year observations posed an enormous data analysis challenge that has only recently been surmounted. Asteroseismic modeling has become more sophisticated over time, with better methods gradually developing alongside the extended observations and improved data analysis techniques. We apply the latest version of the Asteroseismic Modeling Portal (AMP) to the full-length Kepler data sets for 57 stars, comprising planetary hosts, binaries, solar-analogs, active stars, and for validation purposes, the Sun. From an analysis of the derived stellar properties for the full sample, we identify a variation of the mixing-length parameter with atmospheric properties. We also derive a linear relation between the stellar age and a characteristic frequency separation ratio. In addition, we find that the empirical correction for surface effects suggested by Kjeldsen and coworkers is adequate for solar-type stars that are not much hotter (Teff<~6200K) or significantly more evolved (logg>~4.2, <{Delta}{nu}> >~80uHz80) than the Sun. Precise parallaxes from the Gaia mission and future observations from TESS and PLATO promise to improve the reliability of stellar properties derived from asteroseismology.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/83
- Title:
- K2 GAP data release. I. Campaign 1
- Short Name:
- J/ApJ/835/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NASA's K2 mission is observing tens of thousands of stars along the ecliptic, providing data suitable for large-scale asteroseismic analyses to inform galactic archaeology studies. Its first campaign covered a field near the north Galactic cap, a region never covered before by large asteroseismic-ensemble investigations, and was therefore of particular interest for exploring this part of our Galaxy. Here we report the asteroseismic analysis of all stars selected by the K2 Galactic Archaeology Program during the mission's "north Galactic cap" campaign 1. Our consolidated analysis uses six independent methods to measure the global seismic properties, in particular the large frequency separation and the frequency of maximum power. From the full target sample of 8630 stars we find about 1200 oscillating red giants, a number comparable with estimates from galactic synthesis modeling. Thus, as a valuable by-product we find roughly 7500 stars to be dwarfs, which provide a sample well suited for galactic exoplanet occurrence studies because they originate from our simple and easily reproducible selection function.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A124
- Title:
- K-G-F dwarfs stellar granulation variability
- Short Name:
- J/A+A/607/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The inhibition of small-scale convection in the Sun dominates the long-term radial velocity (RV) variability: it therefore has a critical effect on light exoplanet detectability using RV techniques. We here extend our previous analysis of stellar convective blueshift and its dependence on magnetic activity to a larger sample of stars in order to extend the Teff range, to study the impact of other stellar properties, and finally to improve the comparison between observed RV jitter and expected RV variations. Methods. We estimate a differential velocity shift for Fe and Ti lines of different depths and derive an absolute convective blueshift using the Sun as a reference for a sample of 360 F7-K4 stars with different properties (age, Teff, metallicity). We confirm the strong variation in convective blueshift with Teff and its dependence on (as shown in the line list in Paper I) activity level. Although we do not observe a significant effect of age or cyclic activity, stars with a higher metallicity tend to have a lower convective blueshift, with a larger effect than expected from numerical simulations. Finally, we estimate that for 71% of the stars in our sample the RV and LogR'_HK_ variations are compatible with the effect of activity on convection, as observed in the solar case, while for the other stars, other sources (such as binarity or companions) must be invoked to explain the large RV variations. We also confirm a relationship between LogR'_HK_ and metallicity, which may affect discussions of the possible relationship between metallicity and exoplanets, as RV surveys are biased toward low LogR'_HK_ and possibly toward high-metallicity stars. We conclude that activity and metallicity strongly affect the small-scale convection levels in stars in the F7-K4 range, with a lower amplitude for the lower mass stars and a larger amplitude for low-metallicity stars.
- ID:
- ivo://CDS.VizieR/J/AJ/154/207
- Title:
- K2 planetary systems orbiting low-mass stars
- Short Name:
- J/AJ/154/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We recently used near-infrared spectroscopy to improve the characterization of 76 low-mass stars around which K2 had detected 79 candidate transiting planets. 29 of these worlds were new discoveries that had not previously been published. We calculate the false positive probabilities that the transit-like signals are actually caused by non-planetary astrophysical phenomena and reject five new transit-like events and three previously reported events as false positives. We also statistically validate 17 planets (7 of which were previously unpublished), confirm the earlier validation of 22 planets, and announce 17 newly discovered planet candidates. Revising the properties of the associated planet candidates based on the updated host star characteristics and refitting the transit photometry, we find that our sample contains 21 planets or planet candidates with radii smaller than 1.25 R_{Earth}_, 18 super-Earths (1.25-2 R_{Earth}_), 21 small Neptunes (2-4 R_{Earth}_), three large Neptunes (4-6 R_{Earth}_), and eight giant planets (>6 R_{Earth}_). Most of these planets are highly irradiated, but EPIC 206209135.04 (K2-72e, 1.29_-0.13_^+0.14^ R_{Earth}_), EPIC 211988320.01 (R_p_=2.86_-0.15_^+0.16^ R_{Earth}_), and EPIC 212690867.01 (2.20_-0.18_^+0.19^ R_{Earth}_) orbit within optimistic habitable zone boundaries set by the "recent Venus" inner limit and the "early Mars" outer limit. In total, our planet sample includes eight moderately irradiated 1.5-3 R_{Earth}_ planet candidates (F_p_~<20 F_{Earth}_) orbiting brighter stars (Ks<11) that are well-suited for atmospheric investigations with the Hubble, Spitzer, and/or James Webb Space Telescopes. Five validated planets orbit relatively bright stars (Kp<12.5) and are expected to yield radial velocity semi-amplitudes of at least 2 m/s. Accordingly, they are possible targets for radial velocity mass measurement with current facilities or the upcoming generation of red optical and near-infrared high-precision RV spectrographs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/4641
- Title:
- LAMOST DR5 White dwarf-main sequence binaries
- Short Name:
- J/MNRAS/477/4641
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the data release (DR) 5 catalogue of white dwarf-main sequence (WDMS) binaries from the Large sky Area Multi-Object fibre Spectroscopic Telescope (LAMOST). The catalogue contains 876 WDMS binaries, of which 757 are additions to our previous LAMOST DR1 sample and 357 are systems that have not been published before. We also describe a LAMOST-dedicated survey that aims at obtaining spectra of photometrically selected WDMS binaries from the Sloan Digital Sky Survey (SDSS) that are expected to contain cool white dwarfs and/or early-type M dwarf companions. This is a population under-represented in previous SDSS WDMS binary catalogues. We determine the stellar parameters (white dwarf effective temperatures, surface gravities and masses, and M dwarf spectral types) of the LAMOST DR5 WDMS binaries and make use of the parameter distributions to analyse the properties of the sample. We find that, despite our efforts, systems containing cool white dwarfs remain under-represented. Moreover, we make use of LAMOST DR5 and SDSS DR14 (when available) spectra to measure the NaI {lambda}{lambda} 8183.27, 8194.81 absorption doublet and/or H{alpha} emission radial velocities of our systems. This allows identifying 128 binaries displaying significant radial velocity variations, 76 of which are new. Finally, we cross-match our catalogue with the Catalina Surveys and identify 57 systems displaying light-curve variations. These include 16 eclipsing systems, two of which are new, and nine binaries that are new eclipsing candidates. We calculate periodograms from the photometric data and measure (estimate) the orbital periods of 30 (15) WDMS binaries.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/3651
- Title:
- L and T dwarfs from UKIDSS LAS
- Short Name:
- J/MNRAS/449/3651
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from the United Kingdom Deep Infrared Sky Survey. Using the YJHK photometry from the Large Area Survey and the red-optical photometry from the Sloan Digital Sky Survey we selected a sample of 262 brown dwarf candidates and we have followed-up 196 of them using the echelle spectrograph X-shooter on the Very Large Telescope. The large wavelength coverage (0.30-2.48um) and moderate resolution (R~5000-9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low-gravity M dwarfs. Using a spectral indices-based technique, we identified 27 unresolved binary candidates, for which we have determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity of our targets, and we determined the distribution of the sample, which is centred at -1.7+/-1.2km/s with a dispersion of 31.5km/s. Using our results, we estimated the space density of field brown dwarfs and compared it with the results of numerical simulations. Depending on the binary fraction, we found that there are (0.85+/-0.55)x10^-3^ to (1.00+/-0.64)x10^-3^ objects per cubic parsec in the L4-L6.5 range, (0.73+/-0.47)x10^-3^ to (0.85+/-0.55)x10^-3^ objects per cubic parsec in the L7-T0.5 range, and (0.74+/-0.48)x10^-3^ to (0.88+/-0.56)x10^-3^ objects per cubic parsec in the T1-T4.5 range. We notice that there seems to be an excess of objects in the L-T transition with respect to the late-T dwarfs, a discrepancy that could be explained assuming a higher binary fraction than expected for the L-T transition, or that objects in the high-mass end and low-mass end of this regime form in different environments, i.e. following different initial mass functions.
