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- 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.
- 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/ApJ/895/52
- Title:
- EW and chemical abundances in 211 stars with HARPS
- Short Name:
- J/ApJ/895/52
- Date:
- 15 Mar 2022 07:30:10
- Publisher:
- CDS
- Description:
- Magnetic fields and stellar spots can alter the equivalent widths of absorption lines in stellar spectra, varying during the activity cycle. This also influences the information that we derive through spectroscopic analysis. In this study, we analyze high-resolution spectra of 211 sunlike stars observed at different phases of their activity cycles, in order to investigate how stellar activity affects the spectroscopic determination of stellar parameters and chemical abundances. We observe that the equivalent widths of lines can increase as a function of the activity index log R_HK_' during the stellar cycle, which also produces an artificial growth of the stellar microturbulence and a decrease in effective temperature and metallicity. This effect is visible for stars with activity indexes log R_HK_'>=-5.0 (i.e., younger than 4-5Gyr), and it is more significant at higher activity levels. These results have fundamental implications on several topics in astrophysics that are discussed in the paper, including stellar nucleosynthesis, chemical tagging, the study of Galactic chemical evolution, chemically anomalous stars, the structure of the Milky Way disk, stellar formation rates, photoevaporation of circumstellar disks, and planet hunting.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A94
- Title:
- Exoplanetary parameters for 18 bright stars
- Short Name:
- J/A+A/586/A94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the interferometric angular diameters of 18 bright stars: HD3651 , HD9826, HD19994, HD75732, HD167042, HD170693, HD173416, HD185395, HD190360, HD217014, HD221345, HD1367, HD1671, HD154633, HD161178, HD161151, HD209369, HD218560. The first 11 host exoplanets (except HD185395). We combined these angular diameters {theta}_LD_ with the stellar distances to estimate the stellar radii. We perform SED fitting of the photometry to derive the stars bolometric flux Fbol with and without stellar extinction Av. We then give the effective temperature Teff_SED_ and angular diameter {theta}_SED_ from this SED fit, considering fixed Av, metallicity [Fe/H] and gravity log(g). Then, taking into account the stellar extinction, we derived from the bolometric flux and the measured angular diameters the effective temperature and luminosity to place the stars on the H-R diagram. We then used the PARSEC models to derive the best fit ages and masses of the stars, with error bars derived from Monte Carlo calculations. Typically, for main sequence stars, two distinct sets of solutions appear (an old and a young age). For stars that host known exoplanets, we also derive the exoplanets parameters considering the two different solutions (old and young): semi-major axis, planetary minimum mass and habitable zone of the host stars. Finally, we give the true mass, radius and density of the transiting exoplanet 55 Cnc e using the inteferometric radius and photometry.
- 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/MNRAS/475/2480
- Title:
- Extremely-low mass white dwarf star
- Short Name:
- J/MNRAS/475/2480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The so-called sdA stars are defined by having H-rich spectra and surface gravities similar to hot subdwarf stars, but effective temperature below the zero-age horizontal branch. Their evolutionary history is an enigma: their surface gravity is too high for main-sequence stars, but too low for single evolution white dwarfs. They are most likely byproducts of binary evolution, including blue-stragglers, extremely-low mass white dwarf stars (ELMs) and their precursors (pre-ELMs). A small number of ELMs with similar properties to sdAs is known. Other possibilities include metal-poor A/F dwarfs, second generation stars, or even stars accreted from dwarf galaxies. In this work, we analyse colours, proper motions, and spacial velocities of a sample of sdAs from the Sloan Digital Sky Survey to assess their nature and evolutionary origin. We define a probability of belonging to the main sequence and a probability of being a (pre-)ELM based on these properties. We find that 7 per cent of the sdAs are more likely to be (pre-)ELMs than main-sequence stars. However, the spacial velocity distribution suggests that over 35 per cent of them cannot be explained as single metal-poor A/F stars.
- ID:
- ivo://CDS.VizieR/J/A+A/522/A79
- Title:
- Faint, high-Galactic-latitude red clump stars
- Short Name:
- J/A+A/522/A79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With this survey we aim to derive accurate, multi-epoch radial velocities and atmospheric parameters (Teff, logg, [M/H] and V_rot_sini) of a large sample of carefully selected red clump (RC) stars located over a great circle at high Galactic latitudes. We acquired data of the program stars of high signal-to-noise ratio and high resolution with the Asiago Echelle spectrograph. We obtained radial velocities by applying cross-correlation and atmospheric parameters via chi2 fitting to a synthetic spectral library. Extensive tests were carried out by re-observing with the same instrument a large number of standard stars taken from a variety of sources in literature.
- ID:
- ivo://CDS.VizieR/J/A+A/527/A40
- Title:
- Faint, high-Galactic-latitude red clump stars
- Short Name:
- J/A+A/527/A40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal of our survey is to provide accurate and multi-epoch radial velocities, atmospheric parameters (Teff, logg and [M/H]), distances, and space velocities of faint red clump (RC) stars. We recorded high signal-to-noise (S/N>=200) spectra of RC stars over the 4750-5950{AA} range at a resolving power 5500. The target stars are distributed across the great circle of the celestial equator. Radial velocities were obtained via cross-correlation with IAU radial velocity standards. Atmospheric parameters were derived via {chi}^2^ fit to a synthetic spectral library. A large number of RC stars from other surveys were re-observed to check the consistency of our results and the absence of offsets and trends.
- 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.
