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14671. Stars of very low metal abundance. VI. Abundances
ID:
ivo://CDS.VizieR/J/AJ/147/136
Title:
Stars of very low metal abundance. VI. Abundances
Short Name:
J/AJ/147/136
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coude Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by {approx}0.25dex for red giants and {approx}0.04dex for subgiants. Our sample contains 19 stars with [Fe/H]<=-3.5, 84 stars with [Fe/H]<=-3.0, and 210 stars with [Fe/H]<=-2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H]<=-2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.
14672. Starspot rotation rates vs. activity cycle phase
ID:
ivo://CDS.VizieR/J/A+A/622/A85
Title:
Starspot rotation rates vs. activity cycle phase
Short Name:
J/A+A/622/A85
Date:
21 Oct 2021
Publisher:
CDS
Description:
During the solar magnetic activity cycle the emergence latitudes of sunspots change, leading to the well-known butterfly diagram. This phenomenon is poorly understood for other stars since starspot latitudes are generally unknown. The related changes in starspot rotation rates caused by latitudinal differential rotation can however be measured. Using the set of 3093 Kepler stars with activity cycles identified by Reinhold et al. (2017A&A...603A..52R, Cat. J/A+A/603/A52), we aim to study the temporal change in starspot rotation rates over magnetic activity cycles, and how this relates to the activity level, the mean rotation rate of the star, and its effective temperature. We measured the photometric variability as a proxy for the magnetic activity and the spot rotation rate in each quarter over the duration of the Kepler mission. We phase-fold these measurements with the cycle period. To reduce random errors we perform averages over stars with comparable mean rotation rates and effective temperature at fixed activity-cycle phases. We detect a clear correlation between the variation of activity level and the variation of the starspot rotation rate. The sign and amplitude of this correlation depends on the mean stellar rotation and -- to a lesser extent -- on the effective temperature. For slowly rotating stars (rotation periods between 15-28 days) the starspot rotation rates are clearly anti-correlated with the level of activity during the activity cycles. A transition is observed around rotation periods of 10-15 days, where stars with effective temperature above 4200K instead show positive correlation. Our measurements can be interpreted in terms of a stellar "butterfly diagram", but these appear different from the Sun's since the starspot rotation rates are either in phase or anti-phase with the activity level. Alternatively, the activity cycle periods observed by Kepler are short (around 2.5 years) and may therefore be secondary cycles, perhaps analogous to the solar quasi-biennial oscillations.
14673. Starspots in short-period Kepler binaries
ID:
ivo://CDS.VizieR/J/MNRAS/448/429
Title:
Starspots in short-period Kepler binaries
Short Name:
J/MNRAS/448/429
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report on a new method for tracking the phases of the orbital modulations in very short-period, near-contact, and contact binary systems in order to follow starspots. We apply this technique to Kepler light curves for 414 binary systems that were identified as having anticorrelated O-C curves for the mid-times of the primary and secondary eclipses, or in the case of non-eclipsing systems, their light-curve minima. This phase tracking approach extracts more information about starspot and binary system behaviour than may be easily obtained from the O-C curves. We confirm the hypothesis of Tran et al. that we can successfully follow the rotational motions of spots on the surfaces of the stars in these binaries. In ~34% of the systems, the spot rotation is retrograde as viewed in the frame rotating with the orbital motion, while ~13% show significant prograde spot rotation. The remaining systems show either little spot rotation or erratic behaviour, or sometimes include intervals of both types of behaviour. We discuss the possibility that the relative motions of spots are related to differential rotation of the stars. It is clear from this study that the motions of the starspots in at least 50% of these short-period binaries are not exactly synchronized with the orbits.
14674. Starspots on A stars
ID:
ivo://CDS.VizieR/J/MNRAS/467/1830
Title:
Starspots on A stars
Short Name:
J/MNRAS/467/1830
Date:
21 Oct 2021
Publisher:
CDS
Description:
Rotation modulation of Kepler light curves in mid-A to late-B stars is shown to be present. This is demonstrated by the high correlation of projected rotational velocities with photometric frequencies in 30 stars. The time-frequency diagrams show stochastic variations in all respects similar to those in spotted cool stars. This disposes of any explanation in terms of binary proximity effects. More than half of the sample of stars with effective temperatures in the range of 8300-12000K show rotational modulation, indicating that starspots are the rule rather than the exception among A stars. The periodograms of a subset of these stars show a characteristic pattern in which a broad peak is flanked by a sharp peak at a slightly higher frequency. It is demonstrated that the sharp peak has the same width as the spectral window, indicating a stable period over the duration of the 4-yr Kepler observations. It is speculated that this might be a signature of a reflection effect in a non-transiting planet. These observations suggest that the presence of localized magnetic fields in A and B stars and that current views of radiative stellar envelopes need to be revised.
14675. Starspot variability as X-ray radiation proxy
ID:
ivo://CDS.VizieR/J/MNRAS/476/1224
Title:
Starspot variability as X-ray radiation proxy
Short Name:
J/MNRAS/476/1224
Date:
21 Oct 2021
Publisher:
CDS
Description:
Stellar X-ray emission plays an important role in the study of exoplanets as a proxy for stellar winds and as a basis for the prediction of extreme ultraviolet (EUV) flux, unavailable for direct measurements, which in their turn are important factors for the mass-loss of planetary atmospheres. Unfortunately, the detection thresholds limit the number of stars with the directly measured X-ray fluxes. At the same time, the known connection between the sunspots and X-ray sources allows using of the starspot variability as an accessible proxy for the stellar X-ray emission. To realize this approach, we analysed the light curves of 1729 main-sequence stars with rotation periods 0.5<P<30d and effective temperatures 3236<Teff<7166K observed by the Kepler mission. It was found that the squared amplitude of the first rotational harmonic of a stellar light curve may be used as a kind of activity index. This averaged index revealed practically the same relation with the Rossby number as that in the case of the X-ray to bolometric luminosity ratio R_x_. As a result, the regressions for stellar X-ray luminosity L_x_(P, T_eff_) and its related EUV analogue L_EUV_ were obtained for the main-sequence stars. It was shown that these regressions allow prediction of average (over the considered stars) values of log(L_x_) and log(L_EUV_) with typical errors of 0.26 and 0.22dex, respectively. This, however, does not include the activity variations in particular stars related to their individual magnetic activity cycles.
14676. Stars with CaII H and K emission
ID:
ivo://CDS.VizieR/III/120
Title:
Stars with CaII H and K emission
Short Name:
III/120
Date:
21 Oct 2021
Publisher:
CDS
Description:
Intensities and widths of emission cores of H and K lines from the literature are presented for over 1400 stars of spectral types F, G, K and M.
14677. Stars with Debris Disks and Planets
ID:
ivo://svo.cab/debris
Title:
Stars with Debris Disks and Planets
Date:
23 Jan 2017 10:09:28
Publisher:
SVO CAB
Description:
Planetary systems are built by planets and planetesimals formed in circumstellar disks surrounding young pre-main sequence stars. Once in the main-sequence collisions of planetesimals produce small dust particles giving rise to the so-called debris disks. The mutual interaction among planets, planetesimals and debris disks, and with their host stars determines the fate of planetary systems. Currently thousands of main-sequence stars are known to host planets and debris disks. The Solar System with its peculiarities is just one of such planetary systems. However, only few tens of stars are known to host simultaneously both planets and debris disks. Therefore, the study of those systems is particularly valuable to widen our knowledge of planetary systems and their evolution. This page just collects some of the properties of the known, to our knowledge, solar-type stars hosting both planets and debris disk.
14678. Stars with hot Jupiter exoplanets
ID:
ivo://CDS.VizieR/J/MNRAS/474/5158
Title:
Stars with hot Jupiter exoplanets
Short Name:
J/MNRAS/474/5158
Date:
07 Dec 2021 00:40:26
Publisher:
CDS
Description:
We present a grid of forward model transmission spectra, adopting an isothermal temperature-pressure profile, alongside corresponding equilibrium chemical abundances for 117 observationally significant hot exoplanets (equilibrium temperatures of 547-2710K). This model grid has been developed using a 1D radiative-convective-chemical equilibrium model termed ATMO, with up-to-date high-temperature opacities. We present an interpretation of observations of 10 exoplanets, including best-fitting parameters and {chi}^2^ maps. In agreement with previous works, we find a continuum from clear to hazy/cloudy atmospheres for this sample of hot Jupiters. The data for all the 10 planets are consistent with subsolar to solar C/O ratio, 0.005 to 10 times solar metallicity and water rather than methane-dominated infrared spectra. We then explore the range of simulated atmospheric spectra for different exoplanets, based on characteristics such as temperature, metallicity, C/O ratio, haziness and cloudiness. We find a transition value for the metallicity between 10 and 50 times solar, which leads to substantial changes in the transmission spectra. We also find a transition value of C/O ratio, from water to carbon species dominated infrared spectra, as found by previous works, revealing a temperature dependence of this transition point ranging from ~0.56 to ~1-1.3 for equilibrium temperatures from ~900 to ~2600K. We highlight the potential of the spectral features of HCN and C2H2 to constrain the metallicities and C/O ratios of planets, using James Webb Space Telescope (JWST) observations. Finally, our entire grid (~460000 simulations) is publicly available and can be used directly with the JWST simulator PandExo for planning observations.
14679. Stars within 25 pc of the Sun
ID:
ivo://CDS.VizieR/V/32A
Title:
Stars within 25 pc of the Sun
Short Name:
V/32A
Date:
21 Oct 2021
Publisher:
CDS
Description:
This catalog was constructed at the Royal Greenwich Observatory in order to enlarge the Gliese (1957) compilation. It contains data on stars nearer than 25 pc that are not included in Gliese's catalog, plus additional information published since 1957 on stars in the Gliese catalog. The machine version contains essentially all information given in Table Ia of the published catalog, plus positional data, and most cross references to other catalogs given in Table IIa. The notes flags in Table Ia are not included because the notes are not machine-readable. Omitted from Table IIa are the finding-chart indicators (Lowell G numbers or notes references) and miscellaneous cross identifications to other names and catalog identifiers. Tables Ib and IIb, containing 21 systems originally included in Gliese's (1957) catalog but for which revised parallaxes have placed them farther than 25 pc are not included in the machine version. Data in the machine version are Gliese number (Newly added stars begin with 9001, but new parallaxes have removed 9419 and added 9849 and 9850; the Sun [first record] has number 0); component identifications for multiple systems; parallax; annual proper motions; radial velocity; (U,V,W) space velocities; box orbit parameters (omega, e, i); spectral type; UBV data; absolute visual magnitude; right ascension (B1950) declination, GCTP (Jenkins 1952, 1963); HD DM, GCRV (Wilson 1953) and other catalog identifiers; BS (= HR) (Hoffleit 1964) numbers; and remarks codes for SB, doubles, variables, etc. Please note that the first entry is for the Sun, and thus it lacks fields such as RA and Dec.
14680. Stars within 8 pc of the Sun
ID:
ivo://CDS.VizieR/J/AJ/121/2189
Title:
Stars within 8 pc of the Sun
Short Name:
J/AJ/121/2189
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the technique and results of a survey of stars within 8pc of the Sun with declinations {delta}>-35{deg} (J2000.00). The survey, designed to find without color bias faint companions, consists of optical coronagraphic images of the 1 field of view centered on each star and infrared direct images with a 32" field of view. The images were obtained through the optical Gunn r and z filters and the infrared J and K filters. The survey achieves sensitivities up to 4 absolute magnitudes fainter than the prototype brown dwarf, Gliese 229B. However, this sensitivity varies with the seeing conditions, the intrinsic brightness of the star observed, and the angular distance from the star. As a result, we tabulate sensitivity limits for each star in the survey. We used the criterion of common proper motion to distinguish companions and to determine their luminosities. In addition to the brown dwarf Gl 229B, we have identified six new stellar companions of the sample stars. Since the survey began, accurate trigonometric parallax measurements for most of the stars have become available. As a result, some of the stars we originally included should no longer be included in the 8pc sample. In addition, the 8pc sample is incomplete at the faint end of the main sequence, complicating our calculation of the binary fraction of brown dwarfs. We assess the sensitivity of the survey to stellar companions and to brown dwarf companions of different masses and ages.

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