- ID:
- ivo://CDS.VizieR/J/ApJ/901/169
- Title:
- Photometric obs. & LAMOST sp. of 4 W UMa binaries
- Short Name:
- J/ApJ/901/169
- Date:
- 22 Feb 2022 00:36:07
- Publisher:
- CDS
- Description:
- We present new photometric data and LAMOST spectra for the W UMa binaries UV Lyn, V781 Tau, NSVS 4484038, and 2MASS J15471055+5302107. The orbital and starspot parameters are obtained using the Wilson-Devinney program. Comparing the starspot parameters at different times, there are magnetic activities in these four binaries. The orbital period of UV Lyn is increasing at a rate of dP/dt=+8.9(5)x10^-8^d/yr, which maybe due to mass transfer from the less massive component to the more massive component (dM1/dt=-6.4x10^-8^M_{sun}_/yr). The period variation of 2MASSJ15471055+5302107 is also increasing at a rate of 6.0(4)x10^-7^d/yr, which can be explained by mass transfer from the less massive component to the more massive component (dM1/dt=-2.8x10^-7^M_{sun}_/yr). The period variation of V781 Tau presents the downward parabola superimposed the cyclic oscillation. The period of V781 Tau is decreasing (dP/dt=-3.2(4)x10^-8^d/yr), which can be explained by mass transfer from the more massive component to the less massive component (dM2/dt=-2.2x10^-8^M_{sun}_/yr). The cyclic oscillation may be due to the magnetic activity with a period of 30.8(5)yr rather than a third body. The period variation of NSVS4484038 also shows the cyclic oscillation, which could be explained by the magnetic activity with 10.8(1)yr or a black hole candidate. Interestingly, there is a depth variation between the light minimum times of NSVS 4484038, which may also be caused by stellar magnetic activity.
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- ID:
- ivo://CDS.VizieR/J/AJ/150/200
- Title:
- Photometry and spectroscopy of stars in Cz 30
- Short Name:
- J/AJ/150/200
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new photometric and spectroscopic data of the old open cluster Czernik 30. Wide field BVI photometry allows us to correct for the high field contamination by statistical subtraction to produce a color-magnitude diagram (CMD) that clearly reveals the cluster sequence. From spectra of stars in the cluster field obtained with the Hydra spectrograph on the Wisconsin-Indiana-Yale-NOAO 3.5m telescope we determine a mean cluster velocity of +79.9+/-1.5km/s and provide membership information that helps further define the cluster giant branch and red clump. Stellar abundances for the brighter giants in the cluster indicate a mean metallicity of [Fe/H]=-0.2+/-0.15. Fitting theoretical isochrones to the CMD we determine the following properties of Czernik 30: age=2.8+/-0.3Gyr, (m-M)_v_=14.8+/-0.1, E(B-V)=0.24+/-0.06, and E(V-I)=0.36+/-0.04. Czernik 30 is an old, sub-solar metallicity cluster located at a Galactocentric radius of R_gc_~13.3kpc. Given its age and position just beyond the transition to a flat abundance gradient seen in the open cluster population, Czernik 30 provides an interesting target for future observations.
- ID:
- ivo://CDS.VizieR/J/A+A/615/A6
- Title:
- Photospheric parameters of CARMENES stars
- Short Name:
- J/A+A/615/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The new CARMENES instrument comprises two high-resolution and high-stability spectrographs that are used to search for habitable planets around M dwarfs in the visible and near-infrared regime via the Doppler technique. Characterising our target sample is important for constraining the physical properties of any planetary systems that are detected. The aim of this paper is to determine the fundamental stellar parameters of the CARMENES M-dwarf target sample from high-resolution spectra observed with CARMENES. We also include several M-dwarf spectra observed with other high-resolution spectrographs, that is CAFE, FEROS, and HRS, for completeness. We used a {chi}^2^ method to derive the stellar parameters effective temperature T_eff, surface gravity log g, and metallicity [Fe/H] of the target stars by fitting the most recent version of the PHOENIX-ACES models to high-resolution spectroscopic data. These stellar atmosphere models incorporate a new equation of state to describe spectral features of low-temperature stellar atmospheres. Since Teff, logg, and [Fe/H] show degeneracies, the surface gravity is determined independently using stellar evolutionary models. We derive the stellar parameters for a total of 300 stars. The fits achieve very good agreement between the PHOENIX models and observed spectra. We estimate that our method provides parameters with uncertainties of {sigma}_Teff_=51K, {sigma}_logg_=0.07, and {sigma}_[Fe/H]_=0.16, and show that atmosphere models for low-mass stars have significantly improved in the last years. Our work also provides an independent test of the new PHOENIX-ACES models, and a comparison for other methods using low-resolution spectra. In particular, our effective temperatures agree well with literature values, while metallicities determined with our method exhibit a larger spread when compared to literature results.
- ID:
- ivo://CDS.VizieR/J/A+A/555/A150
- Title:
- Physical parameters of cool solar-type stars
- Short Name:
- J/A+A/555/A150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Temperature, surface gravity, and metallicity are basic stellar atmospheric parameters necessary to characterize a star. There are several methods to derive these parameters and a comparison of their results often shows considerable discrepancies, even in the restricted group of solar-type FGK dwarfs. We want to check the differences in temperature between the standard spectroscopic technique based on iron lines and the infrared flux method (IRFM). We aim to improve the description of the spectroscopic temperatures especially for the cooler stars where the differences between the two methods are higher, as presented in a previous work. Our spectroscopic analysis was based on the iron excitation and ionization balance, assuming Kurucz model atmospheres in LTE. The abundance analysis was determined using the code MOOG. We optimized the line list using a cool star (HD 21749) with high resolution and high signal-to-noise spectrum, as a reference in order to check for weak, isolated lines. We test the quality of the new line list by re-deriving stellar parameters for 451 stars with high resolution and signal-to-noise HARPS spectra, that were analyzed in a previous work with a larger line list. The comparison in temperatures between this work and the latest IRFM for the stars in common shows that the differences for the cooler stars are significantly smaller and more homogeneously distributed than in previous studies for stars with temperatures below 5000K.
- ID:
- ivo://CDS.VizieR/J/AJ/155/21
- Title:
- Planet candidates from K2 campaigns 5-8
- Short Name:
- J/AJ/155/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 151 planet candidates orbiting 141 stars from K2 campaigns 5-8 (C5-C8), identified through a systematic search of K2 photometry. In addition, we identify 16 targets as likely eclipsing binaries, based on their light curve morphology. We obtained follow-up optical spectra of 105/141 candidate host stars and 8/16 eclipsing binaries to improve stellar properties and to identify spectroscopic binaries. Importantly, spectroscopy enables measurements of host star radii with ~10% precision, compared to ~40% precision when only broadband photometry is available. The improved stellar radii enable improved planet radii. Our curated catalog of planet candidates provides a starting point for future efforts to confirm and characterize K2 discoveries.
- ID:
- ivo://CDS.VizieR/J/AJ/152/187
- Title:
- Planet occurrence and stellar metallicity for KOIs
- Short Name:
- J/AJ/152/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Host star metallicity provides a measure of the conditions in protoplanetary disks at the time of planet formation. Using a sample of over 20000 Kepler stars with spectroscopic metallicities from the LAMOST survey, we explore how the exoplanet population depends on host star metallicity as a function of orbital period and planet size. We find that exoplanets with orbital periods less than 10 days are preferentially found around metal-rich stars ([Fe/H]{simeq}0.15+/-0.05dex). The occurrence rates of these hot exoplanets increases to ~30% for super-solar metallicity stars from ~10% for stars with a sub-solar metallicity. Cooler exoplanets, which reside at longer orbital periods and constitute the bulk of the exoplanet population with an occurrence rate of >~90%, have host star metallicities consistent with solar. At short orbital periods, P<10days, the difference in host star metallicity is largest for hot rocky planets (<1.7R_{Earth}_), where the metallicity difference is [Fe/H]{simeq}0.25+/-0.07dex. The excess of hot rocky planets around metal-rich stars implies they either share a formation mechanism with hot Jupiters, or trace a planet trap at the protoplanetary disk inner edge, which is metallicity dependent. We do not find statistically significant evidence for a previously identified trend that small planets toward the habitable zone are preferentially found around low-metallicity stars. Refuting or confirming this trend requires a larger sample of spectroscopic metallicities.
- ID:
- ivo://CDS.VizieR/J/AJ/153/136
- Title:
- Planets and their host stars with Gaia parallaxes
- Short Name:
- J/AJ/153/136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present empirical measurements of the radii of 116 stars that host transiting planets. These radii are determined using only direct observables - the bolometric flux at Earth, the effective temperature, and the parallax provided by the Gaia first data release - and thus are virtually model independent, with extinction being the only free parameter. We also determine each star's mass using our newly determined radius and the stellar density, a virtually model independent quantity itself from previously published transit analyses. These stellar radii and masses are in turn used to redetermine the transiting-planet radii and masses, again using only direct observables. The median uncertainties on the stellar radii and masses are 8% and 30%, respectively, and the resulting uncertainties on the planet radii and masses are 9% and 22%, respectively. These accuracies are generally larger than previously published model-dependent precisions of 5% and 6% on the planet radii and masses, respectively, but the newly determined values are purely empirical. We additionally report radii for 242 stars hosting radial-velocity (non-transiting) planets, with a median achieved accuracy of ~2%. Using our empirical stellar masses we verify that the majority of putative "retired A stars" in the sample are indeed more massive than ~1.2 M_{sun}_. Most importantly, the bolometric fluxes and angular radii reported here for a total of 498 planet host stars-with median accuracies of 1.7% and 1.8%, respectively-serve as a fundamental data set to permit the re-determination of transiting-planet radii and masses with the Gaia second data release to ~3% and ~5% accuracy, better than currently published precisions, and determined in an entirely empirical fashion.
- ID:
- ivo://CDS.VizieR/J/ApJ/697/544
- Title:
- Planets orbiting metal-poor dwarfs. II.
- Short Name:
- J/ApJ/697/544
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of three years of precision radial velocity (RV) measurements of 160 metal-poor stars observed with HIRES on the Keck 1 telescope. We report on variability and long-term velocity trends for each star in our sample. We identify several long-term, low-amplitude RV variables worthy of followup with direct imaging techniques. We place lower limits on the detectable companion mass as a function of orbital period. Our survey would have detected, with a 99.5% confidence level, over 95% of all companions on low-eccentricity orbits with velocity semiamplitude K>~100m/s, or M_p_sini>~3.0M_J_(P/yr)^(1/3)^, for orbital periods P<~3yr. None of the stars in our sample exhibits RV variations compatible with the presence of Jovian planets with periods shorter than the survey duration.
- ID:
- ivo://CDS.VizieR/J/ApJ/419/596
- Title:
- Pop I UV radiation models
- Short Name:
- J/ApJ/419/596
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This series of papers comprises a systematic exploration of the hypothesis that the far-ultraviolet radiation from star clusters and elliptical galaxies originates from extremely hot horizontal-branch (HB) stars and their post-HB progeny. This first paper presents an extensive grid of calculations of stellar models from the zero-age horizontal branch (ZAHB) through to a point late in post-HB evolution or a point on the white dwarf cooling track. The grid will be used to produce synthesized UV fluxes for the interpretation of existing and future short-wavelength (900-3000A) observations. Our sequences have been computed for a range of masses which concentrates on models that begin their HB evolution very close to the hot end of the ZAHB. We have calculated tracks for three metal-poor compositions ([Fe/H]=-2.26, -1.48, -0.47 with [O/Fe]>0), for use with globular cluster observations. We have also chosen three metal rich compositions (Z=0.017=Z_{sun}_, Z=0.04, 0.06) for use in the study of elliptical galaxy populations. For each of the two super-metal-rich compositions, for which the helium abundance is unconstrained by observation, we have computed two sets of sequences: one assuming no additional helium, and a second with a large enhancement (Y(HB)=0.29 and 0.36 for Z=0.04), and (Y(HB)=0.29 and 0.46 for Z=0.06). For each set of sequences, our lowest ZAHB envelope masses (M^0^_env_) are in the range 0.002M_{sun}_<M^0^_env_<0.006M_{sun}_. We use the term extreme horizontal branch (EHB) to refer to HB sequences of constant mass that do not reach the thermally pulsing stage on the AGB. These models evolve after core helium exhaustion into post-early asymptotic giant branch (AGB) stars, which leave the AGB before thermal pulsing, and AGB-manque stars, which never reach the AGB. We describe various features of the evolution of post-HB stars, discussing the correspondence between slow phases of evolution at high temperature and the early-AGB evolution. We note that the relationship between core mass and luminosity for stars on the upper AGB is not straightforward, because stars arrive on the ZAHB with a range of masses and subsequently burn different amounts of fuel. We determine from our models an upper bound to the masses of EHB stars, finding that it varies little for [Fe/H]<0, but that it is sensitive to the helium abundance. We show that for each composition there is a range of M^0^_env_ (at least a few hundredths M_{sun}) in which the models have a slow phase of evolution at high temperature. The duration of this phase is found to increase with the metallicity, but its luminosity is lower, so that total UV energy output is not significantly different from metal-poor sequences. The properties of very metal rich stars are, however, made uncertain by our lack of knowledge of the helium abundance for [Fe/H]>0; the range of stellar masses in which high temperatures are attained for significant periods of time increases with Y. There is no intrinsic composition dependence of the peak UV output from evolved stars; the output from a stellar population depends most directly on the mass distribution of stars arriving on the ZAHB. This is determined mainly by the mass loss that occurs on the red giant branch.
- ID:
- ivo://CDS.VizieR/J/AJ/155/149
- Title:
- Properties of co-moving stars observed by Gaia
- Short Name:
- J/AJ/155/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have estimated fundamental parameters for a sample of co-moving stars observed by Gaia and identified by Oh et al (2017, J/AJ/153/257). We matched the Gaia observations to the 2MASS and Wide-Field Infrared Survey Explorer catalogs and fit MIST isochrones to the data, deriving estimates of the mass, radius, [Fe/H], age, distance, and extinction to 9754 stars in the original sample of 10606 stars. We verify these estimates by comparing our new results to previous analyses of nearby stars, examining fiducial cluster properties, and estimating the power-law slope of the local present-day mass function. A comparison to previous studies suggests that our mass estimates are robust, while metallicity and age estimates are increasingly uncertain. We use our calculated masses to examine the properties of binaries in the sample and show that separation of the pairs dominates the observed binding energies and expected lifetimes.
