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14851. Stellar surface gravity measures of KIC stars
ID:
ivo://CDS.VizieR/J/ApJ/818/43
Title:
Stellar surface gravity measures of KIC stars
Short Name:
J/ApJ/818/43
Date:
21 Oct 2021
Publisher:
CDS
Description:
In our previous work we found that high-quality light curves, such as those obtained by Kepler, may be used to measure stellar surface gravity via granulation-driven light curve "flicker" (F_8_). Here, we update and extend the relation originally presented by Bastien et al. (2013Natur.500..427B) after calibrating F_8_ against a more robust set of asteroseismically derived surface gravities. We describe in detail how we extract the F_8_ signal from the light curves, including how we treat phenomena, such as exoplanet transits and shot noise, that adversely affect the measurement of F_8_. We examine the limitations of the technique, and, as a result, we now provide an updated treatment of the F_8_-based log g error. We briefly highlight further applications of the technique, such as astrodensity profiling or its use in other types of stars with convective outer layers. We discuss potential uses in current and upcoming space-based photometric missions. Finally, we supply F_8_-based log g values, and their uncertainties, for 27628 Kepler stars not identified as hosts of transiting planets, with 4500K<T_eff_<7150K, 2.5<logg<4.6, K_p_<=13.5, and overall photometric amplitudes <10 parts per thousand.
14852. Stellar twins in RAVE with Gaia
ID:
ivo://CDS.VizieR/J/MNRAS/472/2517
Title:
Stellar twins in RAVE with Gaia
Short Name:
J/MNRAS/472/2517
Date:
21 Oct 2021
Publisher:
CDS
Description:
We apply the twin method to determine parallaxes to 232 545 stars of the RAVE survey using the parallaxes of Gaia DR1 as a reference. To search for twins in this large data set, we apply the t-student stochastic neighbour embedding projection that distributes the data according to their spectral morphology on a two-dimensional map. From this map, we choose the twin candidates for which we calculate a {chi}^2^ to select the best sets of twins. Our results show a competitive performance when compared to other model-dependent methods relying on stellar parameters and isochrones. The power of the method is shown by finding that the accuracy of our results is not significantly affected if the stars are normal or peculiar since the method is model free. We find twins for 60 per cent of the RAVE sample that are not contained in Tycho-Gaia Astrometric Solution (TGAS) or that have TGAS uncertainties that are larger than 20 per cent. We could determine parallaxes with typical errors of 28 per cent. We provide a complementary data set for the RAVE stars not covered by TGAS, or that have TGAS uncertainties which are larger than 20 per cent, with model-free parallaxes scaled to the Gaia measurements.
14853. Stellar variability in field stars
ID:
ivo://CDS.VizieR/J/PASP/114/656
Title:
Stellar variability in field stars
Short Name:
J/PASP/114/656
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from a 5 night wide-field time-series photometric survey that detects variable field stars. We find that the fraction of stars whose light curves show variations depends on color and magnitude, reaching 17% for the brightest stars in this survey (V~4) for which the photometric precision is best. The fraction of stars found to be variable is relatively high at colors bluer than the Sun and relatively low at colors similar to the Sun and increases again for stars redder than the Sun. We present light curves for a sample of the pulsating and eclipsing variables. Most of the stars identified as pulsating variables have low amplitudes ({Delta}V=0.01-0.05), relatively blue colors, and multiple periods. There are 13 stars we identify as either SX Phoenicis or {delta} Scuti stars. These classes represent a significant contribution to the total number of blue variables found in this survey. Another 17 stars are identified as eclipsing variables, which have a wide range in color, magnitude, and amplitude. Two variable giants are observed, and both show night-to-night ~1% variations. We present data for 222 variables in total, most of which are not classified. Implications of surveys for stellar variability and interferometry are briefly discussed. On 2000 March 16-20 UT we observed a time series of images in V and one or two images each in UBRI toward two 59'x59' fields using the NOAO Mosaic Camera at the Kitt Peak 0.9 m telescope.
14854. Stellar variability in Galactic Center
ID:
ivo://CDS.VizieR/J/ApJ/659/1241
Title:
Stellar variability in Galactic Center
Short Name:
J/ApJ/659/1241
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the results of a diffraction-limited, photometric variability study of the central 5"x5" of the Galaxy conducted over the past 10-years using speckle imaging techniques on the W.M. Keck I 10 m telescope. Within our limiting magnitude of m_K_<16mag for images made from a single night of data, we find a minimum of 15K[2.2um]-band variable stars out of 131 monitored stars. The only periodic source in our sample is the previously identified variable IRS 16SW, for which we measure an orbital period of 19.448+/-0.002-days.
14855. Stellar variability towards Galactic Bulge
ID:
ivo://CDS.VizieR/J/A+AS/139/321
Title:
Stellar variability towards Galactic Bulge
Short Name:
J/A+AS/139/321
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Table "stars.dat" contains the catalogue of variable stars discovered and/or observed for the 12 low-extinction fields towards the galactic bulge, with the IAG/USP Meridian Circle. The first column of the catalog indicates the star label, formed by a name that identifies the window (see Table 1) and a sequential number that indicates the position of the object in the corresponding database. The following columns display successively the mean right ascension, the mean declination, their standard deviations (in seconds and in arcseconds, respectively) (J2000); the mean magnitude observed (m_{Val}), the difference between the maximum and the minimum magnitude value observed, the number of observations, a estimative for the period, if possible, or a indication "NF" when the stars show periodic characteristics but we aren't able to found a period, or "NC" when the star can be aperiodic or have few observations. The next column have the tentative classification and the last are the remarks about the previous known variables. Finding charts will be available upon request from the authors.
14856. Stellar X-ray flares from the 2XMM catalog
ID:
ivo://CDS.VizieR/J/A+A/581/A28
Title:
Stellar X-ray flares from the 2XMM catalog
Short Name:
J/A+A/581/A28
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a uniform, large-scale survey of X-ray flare emission, based on the XMM-Newton Serendipitous Source Catalogue and its associated data products. Our survey comprises both XMM-targeted active stars and those observed serendipitously in the field-of-view of each observation. The 2XMM Catalogue and the associated time-series ('light-curve') data products have been used as the basis for the survey of X-ray flares from cool stars in the Hipparcos Tycho-2 catalogue. Our sample contains ~130 flares with well-observed profiles; they originate from ~70 stars.
14857. Stellar X-ray sources in the COSMOS survey
ID:
ivo://CDS.VizieR/J/ApJ/725/480
Title:
Stellar X-ray sources in the COSMOS survey
Short Name:
J/ApJ/725/480
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of the X-ray properties of a sample of solar- and late-type field stars identified in the Chandra Cosmic Evolution Survey (COSMOS), a deep (160ks) and wide (~0.9deg^2^) extragalactic survey. The sample of 60 sources was identified using both morphological and photometric star/galaxy separation methods. We determine X-ray count rates, extract spectra and light curves, and perform spectral fits to determine fluxes and plasma temperatures. Complementary optical and near-IR photometry is also presented and combined with spectroscopy for 48 of the sources to determine spectral types and distances for the sample. We find distances ranging from 30pc to ~12kpc, including a number of the most distant and highly active stellar X-ray sources ever detected. Overall the sample is typically more luminous than the active Sun, representing the high-luminosity end of the disk and halo X-ray luminosity functions. The halo population appears to include both low-activity spectrally hard sources that may be emitting through thermal bremsstrahlung, as well as a number of highly active sources in close binaries.
14858. Stellar yields of rotating first stars. II.
ID:
ivo://CDS.VizieR/J/ApJ/857/111
Title:
Stellar yields of rotating first stars. II.
Short Name:
J/ApJ/857/111
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recent theory predicts that first stars are born with a massive initial mass of >~100M_{sun}_. Pair-instability supernova (PISN) is a common fate for such massive stars. Our final goal is to prove the existence of PISNe and thus the high-mass nature of the initial mass function in the early universe by conducting abundance profiling, in which properties of a hypothetical first star is constrained by metal-poor star abundances. In order to determine reliable and useful abundances, we investigate the PISN nucleosynthesis taking both rotating and nonrotating progenitors for the first time. We show that the initial and CO core mass ranges for PISNe depend on the envelope structures: nonmagnetic rotating models developing inflated envelopes have a lower shifted CO mass range of ~70-125_M{sun}_, while nonrotating and magnetic rotating models with deflated envelopes have a range of ~80-135_M{sun}_. However, we find no significant difference in explosive yields from rotating and nonrotating progenitors, except for large nitrogen production in nonmagnetic rotating models. Furthermore, we conduct the first systematic comparison between theoretical yields and a large sample of metal-poor star abundances. We find that the predicted low [Na/Mg]~-1.5 and high [Ca/Mg]~0.5-1.3 abundance ratios are the most important to discriminate PISN signatures from normal metal-poor star abundances, and confirm that no currently observed metal-poor star matches with the PISN abundance. An extensive discussion on the nondetection is presented.
14859. Stephenson H{alpha} stars
ID:
ivo://CDS.VizieR/J/A+A/402/963
Title:
Stephenson H{alpha} stars
Short Name:
J/A+A/402/963
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of spectroscopic observations for 52 objects from the list of H{alpha} emission stars of Stephenson (1986ApJ...300..779S). Out of six known T Tauri stars observed, five showed H{alpha} in emission and in one (StHa 40), H{alpha} changed from being in absorption to emission over a period of two years, accompanied by photometric and spectral type variability. We confirm the T Tauri nature of one Stephenson object (StHa 48) on the basis of the presence of H{alpha} and H{beta} in emission, Li I {lambda}6708 in absorption, infrared excess and X-ray emission. Among the 52 objects observed, there were other emission line objects: 1 Ke star, 1 BQ[] star, 2 galaxies and 2 Be stars. We present a higher-resolution spectrum of StHa 62 showing permitted and forbidden lines in emission typical of BQ[] stars. Twenty five out of 30 newly observed objects failed to show H{alpha} in emission. We also present 2MASS observations for 112 StHa objects. We suggest three Stephenson objects (StHa 52, 125 and 129) to be YSOs on the basis of 2MASS, IRAS and ROSAT observations. These and all other known YSOs amongst StHa stars are found in regions of star-forming clouds in Taurus, Orion and Ophiuchus. YSOs at high galactic latitudes in other parts of the sky are therefore rare.
14860. STEREO magnetic chemically peculiar stars
ID:
ivo://CDS.VizieR/J/MNRAS/420/757
Title:
STEREO magnetic chemically peculiar stars
Short Name:
J/MNRAS/420/757
Date:
21 Oct 2021
Publisher:
CDS
Description:
About 10% of upper main-sequence stars are characterized by the presence of chemical peculiarities, often found together with a structured magnetic field. The atmospheres of most of those chemically peculiar stars present surface spots, leading to photometric variability caused by rotational modulation. The study of the light curves of those stars therefore permits a precise measurement of their rotational period, which is important to study stellar evolution and to plan further detailed observations. We analysed the light curves of 1028 chemically peculiar stars obtained with the STEREO spacecraft. We present here the results obtained for the 337 magnetic chemically peculiar stars in our sample.

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