- ID:
- ivo://CDS.VizieR/J/AJ/157/211
- Title:
- Unresolved binaries in TESS with speckle imaging
- Short Name:
- J/AJ/157/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Transiting Exoplanet Survey Satellite (TESS) is conducting a two-year wide-field survey searching for transiting exoplanets around nearby bright stars that will be ideal for follow-up characterization. To facilitate studies of planet compositions and atmospheric properties, accurate and precise planetary radii need to be derived from the transit light curves. Since 40%-50% of exoplanet host stars are in multiple star systems, however, the observed transit depth may be diluted by the flux of a companion star, causing the radius of the planet to be underestimated. High angular resolution imaging can detect companion stars that are not resolved in the TESS Input Catalog, or by seeing-limited photometry, to validate exoplanet candidates and derive accurate planetary radii. We examine the population of stellar companions that will be detectable around TESS planet candidate host stars, and those that will remain undetected, by applying the detection limits of speckle imaging to the simulated host star populations of Sullivan et al. (2015, J/ApJ/809/77) and Barclay et al. (2018, J/ApJS/239/2). By detecting companions with contrasts of {Delta}m~<7-9 and separations of ~0.02"-1.2", speckle imaging can detect companion stars as faint as early M stars around A-F stars and stars as faint as mid-M around G-M stars, as well as up to 99% of the expected binary star distribution for systems located within a few hundred parsecs.
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- ID:
- ivo://CDS.VizieR/J/ApJS/235/16
- Title:
- UV emission of stars in LAMOST. I. Catalogs
- Short Name:
- J/ApJS/235/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the ultraviolet magnitudes for over three million stars in the LAMOST survey, in which 2,202,116 stars are detected by GALEX. For 889,235 undetected stars, we develop a method to estimate their upper limit magnitudes. The distribution of (FUV-NUV) shows that the color declines with increasing effective temperature for stars hotter than 7000K in our sample, while the trend disappears for the cooler stars due to upper atmosphere emission from the regions higher than their photospheres. For stars with valid stellar parameters, we calculate the UV excesses with synthetic model spectra, and find that the (FUV - NUV) versus R'_FUV_ can be fitted with a linear relation and late-type dwarfs tend to have high UV excesses. There are 87,178 and 1,498,103 stars detected more than once in the visit exposures of GALEX in the FUV and NUV, respectively. We make use of the quantified photometric errors to determine statistical properties of the UV variation, including intrinsic variability and the structure function on the timescale of days. The overall occurrence of possible false positives is below 1.3% in our sample. UV absolute magnitudes are calculated for stars with valid parallaxes, which could serve as a possible reference frame in the NUV. We conclude that the colors related to UV provide good criteria to distinguish between M giants and M dwarfs, and the variability of RR Lyrae stars in our sample is stronger than that of other A and F stars.
- ID:
- ivo://CDS.VizieR/J/A+A/378/556
- Title:
- UVES/VLT spectra of white dwarfs
- Short Name:
- J/A+A/378/556
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have started a large survey for radial velocity variations in white dwarfs (PI R. Napiwotzki) with the aim of finding close double degenerates, which could be precursor systems for SNe Ia. The UVES spectrograph at the ESO VLT is used to obtain high resolution spectra with good S/N. During this project 1500 white dwarfs will be observed. This unique data set will also allow to derive atmospheric parameters and masses for the largest sample of white dwarfs ever analyzed in a homogeneous way. In this paper we present a catalog of objects and report results for the first sample of about 200 white dwarfs, many of which are spectroscopic confirmations of candidates from the Hamburg ESO Quasar Survey (HE, Cat. <J/A+AS/115/235>), Montreal-Cambridge-Tololo Survey (MCT), and Edinburgh-Cape Survey (EC, Cat. <J/MNRAS/287/867>) surveys. Among the peculiar spectra we identify two new magnetic DA, one previously known magnetic DA, several DA with emission cores, in some cases due to a late-type companion, and two new DBA.
- ID:
- ivo://CDS.VizieR/J/A+A/505/441
- Title:
- UVES/VLT spectra of white dwarfs
- Short Name:
- J/A+A/505/441
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ESO Supernova Ia Progenitor Survey (SPY) took high-resolution spectra of more than 1000 white dwarfs and pre-white dwarfs. About two thirds of the stars observed are hydrogen-dominated DA white dwarfs. Here we present a catalog and detailed spectroscopic analysis of the DA stars in the SPY. Atmospheric parameters effective temperature and surface gravity are determined for normal DAs. Double-degenerate binaries, DAs with magnetic fields or dM companions, are classified and discussed.
- ID:
- ivo://CDS.VizieR/J/A+A/470/1079
- Title:
- UVES/VLT spectroscopy of white dwarfs
- Short Name:
- J/A+A/470/1079
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic analysis of the stars with helium-dominated spectra in the ESO Supernova Ia Progenitor Survey (SPY). Atmospheric parameters, masses, and abundances of trace hydrogen are determined and discussed in the context of spectral evolution of white dwarfs. The spectra are compared with theoretical model atmospheres using a {chi}^2^ fitting technique, leading to determinations of effective temperature, surface gravity, and hydrogen abundance. Our final sample contains 71 objects, of which 6 are new detections and 14 are reclassified from DB to DBA because of the presence of H lines. One is a cool DO with weak HeII lines, 2 are composite DB+dM. 55% of the DB sample show hydrogen and are thus DBA, a significantly higher fraction than found before.
- ID:
- ivo://CDS.VizieR/J/ApJ/709/1042
- Title:
- Variability in C-rich proto-PNe.
- Short Name:
- J/ApJ/709/1042
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out long-term (14 years) V and R photometric monitoring of 12 carbon-rich proto-planetary nebulae. The light and color curves display variability in all of them. The light curves are complex and suggest multiple periods, changing periods, and/or changing amplitudes, which are attributed to pulsation. A dominant period has been determined for each and found to be in the range of ~150 days for the coolest (G8) to 35-40 days for the warmest (F3). A clear, linear inverse relationship has been found in the sample between the pulsation period and the effective temperature and also an inverse relationship between the amplitude of light variation and the effective temperature. These are consistent with the expectation for a pulsating post-asymptotic giant branch (post-AGB) star evolving toward higher temperature at constant luminosity. The published spectral energy distributions and mid-infrared images show these objects to have cool (200K), detached dust shells and published models imply that intensive mass loss ended 400-2000 years ago.
- ID:
- ivo://CDS.VizieR/J/A+A/534/A125
- Title:
- Variability of A- and F-stars from Kepler
- Short Name:
- J/A+A/534/A125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kepler spacecraft is providing time series of photometric data with micromagnitude precision for hundreds of A-F type stars. We present a first general characterization of the pulsational behaviour of A-F type stars as observed in the Kepler light curves of a sample of 750 candidate A-F type stars, and observationally investigate the relation between {gamma} Doradus ({gamma} Dor), {delta} Scuti ({delta} Sct), and hybrid stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/73
- Title:
- Variability of RSGs in M31 from the iPTF survey
- Short Name:
- J/ApJ/859/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Most massive stars end their lives as red supergiants (RSGs), a short-lived evolutionary phase when they are known to pulsate with varying amplitudes. The RSG period-luminosity (PL) relation has been measured in the Milky Way, the Magellanic Clouds and M33 for about 120 stars in total. Using over 1500 epochs of R-band monitoring from the Palomar Transient Factory survey over a five-year period, we study the variability of 255 spectroscopically cataloged RSGs in M31. We find that all RGSs brighter than M_K_~-10mag (log(L/L_{sun}_)>4.8) are variable at {Delta}m_R_>0.05mag. Our period analysis finds 63 with significant pulsation periods. Using the periods found and the known values of M_K_ for these stars, we derive the RSG PL relation in M31 and show that it is consistent with those derived earlier in other galaxies of different metallicities. We also detect, for the first time, a sequence of likely first-overtone pulsations. Comparison to stellar evolution models from MESA confirms the first-overtone hypothesis and indicates that the variable stars in this sample have 12M_{sun}_<M<24M_{sun}_. As these RSGs are the immediate progenitors to Type II-P core-collapse supernovae (SNe), we also explore the implication of their variability in the initial-mass estimates for SN progenitors based on archival images of the progenitors. We find that this effect is small compared to the present measurement errors.
- ID:
- ivo://CDS.VizieR/J/AJ/155/39
- Title:
- Variability properties of TIC sources with KELT
- Short Name:
- J/AJ/155/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kilodegree Extremely Little Telescope (KELT) has been surveying more than 70% of the celestial sphere for nearly a decade. While the primary science goal of the survey is the discovery of transiting, large-radii planets around bright host stars, the survey has collected more than 10^6^ images, with a typical cadence between 10-30 minutes, for more than four million sources with apparent visual magnitudes in the approximate range 7<V<13. Here, we provide a catalog of 52741 objects showing significant large-amplitude fluctuations likely caused by stellar variability, as well as 62229 objects identified with likely stellar rotation periods. The detected variability ranges in rms-amplitude from ~3 mmag to ~2.3 mag, and the detected periods range from ~0.1 to >~2000 days. We provide variability upper limits for all other ~4000000 sources. These upper limits are principally a function of stellar brightness, but we achieve typical 1{sigma} sensitivity on 30 min timescales down to ~5 mmag at V~8, and down to ~43 mmag at V~13. We have matched our catalog to the TESS Input catalog and the AAVSO Variable Star Index to precipitate the follow-up and classification of each source. The catalog is maintained as a living database on the Filtergraph visualization portal at the URL https://filtergraph.com/kelt_vars.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/5
- Title:
- Variable stars and cand. planets from K2
- Short Name:
- J/ApJS/239/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We produce light curves for all ~34000 targets observed with K2 in Campaign 17 (C17), identifying 34 planet candidates, 184 eclipsing binaries, and 222 other periodic variables. The forward-facing direction of the C17 field means follow-up can begin immediately now that the campaign has concluded and interesting targets have been identified. The C17 field has a large overlap with C6, so this latest campaign also offers an infrequent opportunity to study a large number of targets already observed in a previous K2 campaign. The timing of the C17 data release, shortly before science operations begin with the Transiting Exoplanet Survey Satellite (TESS), also lets us exercise some of the tools and methods developed for identification and dissemination of planet candidates from TESS. We find excellent agreement between these results and those identified using only K2-based tools. Among our planet candidates are several planet candidates with sizes <4R_{Earth}_ and orbiting stars with Kp<~10 (indicating good RV targets of the sort TESS hopes to find) and a Jupiter-sized single-transit event around a star already hosting a 6 day planet candidate.
