- ID:
- ivo://CDS.VizieR/J/A+A/557/A70
- Title:
- Evolved planet hosts - stellar parameters
- Short Name:
- J/A+A/557/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is still being debated whether the well-known metallicity - giant planet correlation for dwarf stars is also valid for giant stars. For this reason, having precise metallicities is very important. Precise stellar parameters are also crucial to planetary research for several other reasons. Different methods can provide different results that lead to discrepancies in the analysis of planet hosts. To study the impact of different analyses on the metallicity scale for evolved stars, we compare different iron line lists to use in the atmospheric parameter derivation of evolved stars. Therefore, we use a sample of 71 evolved stars with planets. With these new homogeneous parameters, we revisit the metallicity - giant planet connection for evolved stars. A spectroscopic analysis based on Kurucz models in local thermodynamic equilibrium (LTE) was performed through the MOOG code to derive the atmospheric parameters. Two different iron line list sets were used, one built for cool FGK stars in general, and the other for giant FGK stars. Masses were calculated through isochrone fitting, using the Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the metallicity distributions of various different samples of evolved stars and red giants. All parameters compare well using a line list set, designed specifically for cool and solar-like stars to provide more accurate temperatures. All parameters derived with this line list set are preferred and are thus adopted for future analysis. We find that evolved planet hosts are more metal-poor than dwarf stars with giant planets. However, a bias in giant stellar samples that are searched for planets is present. Because of a colour cut-off, metal-rich low-gravity stars are left out of the samples, making it hard to compare dwarf stars with giant stars. Furthermore, no metallicity enhancement is found for red giants with planets (logg<3.0dex) with respect to red giants without planets.
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- ID:
- ivo://CDS.VizieR/J/ApJ/895/140
- Title:
- EvryFlare. II. Parameters of 122 cool flare stars
- Short Name:
- J/ApJ/895/140
- Date:
- 15 Mar 2022 07:38:49
- Publisher:
- CDS
- Description:
- We measure rotation periods and sinusoidal amplitudes in Evryscope light curves for 122 two-minute K5-M4 TESS targets selected for strong flaring. The Evryscope array of telescopes has observed all bright nearby stars in the south, producing 2-minute cadence light curves since 2016. Long-term, high-cadence observations of rotating flare stars probe the complex relationship between stellar rotation, starspots, and superflares. We detect periods from 0.3487 to 104days and observe amplitudes from 0.008 to 0.216 g'mag. We find that the Evryscope amplitudes are larger than those in TESS with the effect correlated to stellar mass (p-value=0.01). We compute the Rossby number (Ro) and find that our sample selected for flaring has twice as many intermediate rotators (0.04<Ro<0.4) as fast (Ro<0.04) or slow (Ro>0.44) rotators; this may be astrophysical or a result of period detection sensitivity. We discover 30 fast, 59 intermediate, and 33 slow rotators. We measure a median starspot coverage of 13% of the stellar hemisphere and constrain the minimum magnetic field strength consistent with our flare energies and spot coverage to be 500G, with later-type stars exhibiting lower values than earlier-type stars. We observe a possible change in superflare rates at intermediate periods. However, we do not conclusively confirm the increased activity of intermediate rotators seen in previous studies. We split all rotators at Ro~0.2 into bins of PRot<10days and PRot>10 days to confirm that short-period rotators exhibit higher superflare rates, larger flare energies, and higher starspot coverage than do long-period rotators, at p-values of 3.2x10^-5^, 1.0x10^-5^, and 0.01, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A5
- Title:
- Exoplanet hosts/field stars age consistency
- Short Name:
- J/A+A/585/A5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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 Padova evolutionary models. The notable aspects of our algorithm include the treatment of element diffusion, activity checks in terms of logR'_HK_ and vsini, 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 {rho}_*_ allows us to compute stellar luminosity even if the distance is not available, by combining {rho}_* with the spectroscopic logg. The median value of the TPH ages is ~5Gyr. 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 ~4.8Gyr, respectively. Thus, these stellar samples suffer almost the same selection effects. An analysis of MS stars of the solar neighbourhood belonging to the same spectral types bring to an age distribution similar to the previous ones and centered around solar age value. Therefore, the age of our Sun is consistent with the age distribution of solar neighbourhood 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/733/68
- Title:
- Exoplanet masses derived from RVs
- Short Name:
- J/ApJ/733/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanet searches using radial velocity (RV) and microlensing (ML) produce samples of "projected" mass and orbital radius, respectively. We present a new method for estimating the probability density distribution (density) of the unprojected quantity from such samples. For a sample of n data values, the method involves solving n simultaneous linear equations to determine the weights of delta functions for the raw, unsmoothed density of the unprojected quantity that cause the associated cumulative distribution function (CDF) of the projected quantity to exactly reproduce the empirical CDF of the sample at the locations of the n data values. We smooth the raw density using nonparametric kernel density estimation with a normal kernel of bandwidth {sigma}. We calibrate the dependence of {sigma} on n by Monte Carlo experiments performed on samples drawn from a theoretical density, in which the integrated square error is minimized. We scale this calibration to the ranges of real RV samples using the Normal Reference Rule. The resolution and amplitude accuracy of the estimated density improve with n. For typical RV and ML samples, we expect the fractional noise at the PDF peak to be approximately 80n^-log2^. For illustrations, we apply the new method to 67 RV values given a similar treatment by Jorissen et al. (2001A&A...379..992J), and to the 308 RV values listed at exoplanets.org on 2010 October 20.
- ID:
- ivo://CDS.VizieR/J/ApJS/225/32
- Title:
- Extended abundance analysis of cool stars
- Short Name:
- J/ApJS/225/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of uniformly determined stellar properties and abundances for 1615 F, G, and K stars using an automated spectral synthesis modeling procedure. All stars were observed using the HIRES spectrograph at Keck Observatory. Our procedure used a single line list to fit model spectra to observations of all stars to determine effective temperature, surface gravity, metallicity, projected rotational velocity, and the abundances of 15 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni, and Y). Sixty percent of the sample had Hipparcos parallaxes and V-band photometry, which we combined with the spectroscopic results to obtain mass, radius, and luminosity. Additionally, we used the luminosity, effective temperature, metallicity and {alpha}-element enhancement to interpolate in the Yonsei-Yale isochrones to derive mass, radius, gravity, and age ranges for those stars. Finally, we determined new relations between effective temperature and macroturbulence for dwarfs and subgiants. Our analysis achieved precisions of 25K in T_eff_, 0.01dex in [M/H], 0.028dex for logg, and 0.5km/s in vsini based on multiple observations of the same stars. The abundance results were similarly precise, between ~0.01 and ~0.04dex, though trends with respect to T_eff_ remained for which we derived empirical corrections. The trends, though small, were much larger than our uncertainties and are shared with published abundances. We show that changing our model atmosphere grid accounts for most of the trend in [M/H] between 5000 and 5500K, indicating a possible problem with the atmosphere models or opacities.
- ID:
- ivo://CDS.VizieR/J/ApJS/237/38
- Title:
- Extended abundance analysis of KOIs
- Short Name:
- J/ApJS/237/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate stellar parameters and precise elemental abundances are vital pieces to correctly characterize discovered planetary systems, better understand planet formation, and trace galactic chemical evolution. We have performed a uniform spectroscopic analysis for 1127 stars, yielding accurate gravity, temperature, and projected rotational velocity in addition to precise abundances for 15 elements (C, N, O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Ni, and Y). Most of the stars in this sample are Kepler Objects of Interest, observed by the California-Kepler Survey, and include 1003 stars hosting 1562 confirmed planets. This catalog extends the uniform analysis of our previous catalog, bringing the total number of homogeneously analyzed stars to almost 2700 F, G, and K dwarfs. To ensure consistency between the catalogs, we performed an analysis of our ability to recover parameters as a function of signal-to-noise ratio (S/N) and present individual uncertainties as well as functions to calculate uncertainties for parameters derived from lower S/N spectra. With the updated parameters, we used isochrone fitting to derive new radii, masses, and ages for the stars. We use our abundance analysis to support the finding that the radius gap is likely a result of evolution rather than the result of primordial compositional differences between the two populations.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/86
- Title:
- False positive probabilities for Q1-Q17 DR24 KOIs
- Short Name:
- J/ApJ/822/86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present astrophysical false positive probability calculations for every Kepler Object of Interest (KOI) --the first large-scale demonstration of a fully automated transiting planet validation procedure. Out of 7056 KOIs, we determine that 1935 have probabilities vespa (Morton T.D. 2015ascl.soft03011M), a publicly available Python package that is able to be easily applied to any transiting exoplanet candidate.
- ID:
- ivo://CDS.VizieR/J/A+A/415/1153
- Title:
- [Fe/H] for 98 extra-solar planet-host stars
- Short Name:
- J/A+A/415/1153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present stellar parameters and metallicities, obtained from a detailed spectroscopic analysis, for a large sample of 98 stars known to be orbited by planetary mass companions (almost all known targets), as well as for a volume-limited sample of 41 stars not known to host any planet. For most of the stars the stellar parameters are revised versions of the ones presented in our previous work. However, we also present parameters for 18 stars with planets not previously published, and a compilation of stellar parameters for the remaining 4 planet-hosts for which we could not obtain a spectrum. A comparison of our stellar parameters with values of Teff, logg, and [Fe/H] available in the literature shows a remarkable agreement. In particular, our spectroscopic logg values are now very close to trigonometric logg estimates based on Hipparcos parallaxes. The derived [Fe/H] values are then used to confirm the previously known result that planets are more prevalent around metal-rich stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/71
- Title:
- Fluxes & physical param. of blended YSOs
- Short Name:
- J/ApJ/864/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Despite significant evidence suggesting that intermediate- and high-mass stars form in clustered environments, how stars form when the available resources are shared is still not well understood. A related question is whether the initial mass function (IMF) is in fact universal across galactic environments, or whether it is an average of IMFs that differ, for example, in massive versus low-mass molecular clouds. One of the long-standing problems in resolving these questions and in the study of young clusters is observational: how to accurately combine multiwavelength data sets obtained using telescopes with different spatial resolutions. The resulting confusion hinders our ability to fully characterize clustered star formation. Here we present a new method that uses Bayesian inference to fit the blended spectral energy distributions and images of individual young stellar objects (YSOs) in confused clusters. We apply this method to the infrared photometry of a sample comprising 70 Spitzer-selected, low-mass (M_cl_<100M_{sun}_) young clusters in the galactic plane, and we use the derived physical parameters to investigate how the distribution of YSO masses within each cluster relates to the total mass of the cluster. We find that for low-mass clusters this distribution is indistinguishable from a randomly sampled Kroupa IMF for this range of cluster masses. Therefore, any effects of self-regulated star formation that affect the IMF sampling are likely to play a role only at larger cluster masses. Our results are also compatible with smoothed particle hydrodynamics models that predict a dynamical termination of the accretion in protostars, with massive stars undergoing this stopping at later times in their evolution.
- ID:
- ivo://CDS.VizieR/J/AJ/147/87
- Title:
- From binaries to multiples. II. Statistical data
- Short Name:
- J/AJ/147/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Statistics of hierarchical multiplicity among solar-type dwarfs are studied using the distance-limited sample of 4847 targets presented in the accompanying Paper I. Known facts about binaries (multiplicity fraction 0.46, lognormal period distribution with median period 100yr and logarithmic dispersion 2.4, and nearly uniform mass-ratio distribution independent of the period) are confirmed with a high statistical significance. The fraction of hierarchies with three or more components is 0.13+/-0.01, and the fractions of targets with n=1,2,3,... components are 54:33:8:4:1. Subsystems in the secondary components are almost as frequent as in the primary components, but in half of such cases both inner pairs are present. The high frequency of those 2+2 hierarchies (4%) suggests that both inner pairs were formed by a common process. The statistics of hierarchies can be reproduced by simulations, assuming that the field is a mixture coming from binary-rich and binary-poor environments. Periods of the outer and inner binaries are selected recursively from the same lognormal distribution, subject to the stability constraint and accounting for the correlation between inner subsystems. The simulator can be used to evaluate the frequency of multiple systems with specified parameters. However, it does not reproduce the observed excess of inner periods shorter than 10days, caused by tidal evolution.
