- ID:
- ivo://CDS.VizieR/J/PASP/115/22
- Title:
- Stellar parameters for 134 cool subdwarfs
- Short Name:
- J/PASP/115/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a search for cool subdwarfs are presented. Kinematic (U, V, and W) and stellar parameters (Teff, logg, [Fe/H], and Vturb) are derived for 134 candidate subdwarfs based on high-resolution spectra. The observed stars span 4200K<Teff<6400K and -2.70<[Fe/H]<0.25 including only eight giants (logg<4.0). Of the sample, 100 stars have MgH bands present in their spectra. The targets were selected by their large reduced proper motion, by the offset from the solar-metallicity main sequence, or from the literature. We confirm the claims made by Ryan (1989, Cat. <J/AJ/98/1693>) that the NLTT catalog is a rich source of subdwarfs and verify the success of the reduced proper-motion constraint in identifying metal-poor stars.
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- ID:
- ivo://CDS.VizieR/J/A+A/400/939
- Title:
- Stellar parameters of 115 HQS sdB stars
- Short Name:
- J/A+A/400/939
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a spectral analysis of a large sample of subdwarf B stars selected from follow-up observations of candidates from the Hamburg Quasar Survey. Table 4 summarizes the results (effective temperatures, gravities, and helium abundances) of our analysis. Additionally, the equatorial and galactical coordinates, the B magnitudes and extinctions, the derived radial velocities, the absolute visual magnitudes, the distances from earth and from the galactic plane, and the references are given for all programme stars.
- ID:
- ivo://CDS.VizieR/J/AJ/128/426
- Title:
- Subdwarfs in the SDSS
- Short Name:
- J/AJ/128/426
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic analysis of nearly 8000 late-type dwarfs in the Sloan Digital Sky Survey. Using the H{alpha} emission line as an activity indicator, we investigate the fraction of active stars as a function of spectral type and find a peak near type M8, confirming previous results.
- ID:
- ivo://CDS.VizieR/J/AJ/154/191
- Title:
- The solar neighborhood. XLII. New nearby subdwarfs
- Short Name:
- J/AJ/154/191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Parallaxes, proper motions, and optical photometry are presented for 51 systems consisting of 37 cool subdwarf and 14 additional high proper motion systems. Thirty-seven systems have parallaxes reported for the first time, 15 of which have proper motions of at least 1"/yr. The sample includes 22 newly identified cool subdwarfs within 100 pc, of which three are within 25 pc, and an additional five subdwarfs from 100 to 160 pc. Two systems-LSR 1610-0040 AB and LHS 440 AB-are close binaries exhibiting clear astrometric perturbations that will ultimately provide important masses for cool subdwarfs. We use the accurate parallaxes and proper motions provided here, combined with additional data from our program and others, to determine that effectively all nearby stars with tangential velocities greater than 200 km/s are subdwarfs. We compare a sample of 167 confirmed cool subdwarfs to nearby main sequence dwarfs and Pleiades members on an observational Hertzsprung-Russell diagram using M_V_ versus (V-K_s_) to map trends of age and metallicity. We find that subdwarfs are clearly separated for spectral types K5-M5, indicating that the low metallicities of subdwarfs set them apart in the H-R diagram for (V-K_s_)=3-6. We then apply the tangential velocity cutoff and the subdwarf region of the H-R diagram to stars with parallaxes from Gaia Data Release 1 and the MEarth Project to identify a total of 29 new nearby subdwarf candidates that fall clearly below the main sequence.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A85
- Title:
- Time-series photometry of V391 Peg
- Short Name:
- J/A+A/611/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- V391 Peg (alias HS 2201+2610) is a subdwarf B (sdB) pulsating star that shows both p- and g-modes. By studying the arrival times of the p-mode maxima and minima through the O-C method, the presence of a planet was inferred with an orbital period of 3.2yr and a minimum mass of 3.2M_Jup_ (Silvotti et al., 2007Natur.449..189S). In this article we present an updated O-C analysis using a larger data set of 1066 hours of photometric time series (~2.5x larger in terms of the number of data points), which covers the period between 1999 and 2012 (compared with 1999-2006 of the previous analysis). Up to the end of 2008, the new O-C diagram of the main pulsation frequency (f1) is compatible with (and improves) the previous two-component solution representing the long-term variation of the pulsation period (parabolic component) and the giant planet (sine wave component). Since 2009, the O-C trend of f1 changes, and the time derivative of the pulsation period (dP/dt) passes from positive to negative; the reason of this change of regime is not clear and could be related to nonlinear interactions between different pulsation modes. With the new data, the O-C diagram of the secondary pulsation frequency (f2) continues to show two components (parabola and sine wave), like in the previous analysis. Various solutions are proposed to fit the O-C diagrams of f1 and f2 , but in all of them, the sinusoidal components of f1 and f2 differ or at least agree less well than before. The nice agreement found previously was a coincidence due to various small effects that are carefully analysed. Now, with a larger dataset, the presence of a planet is more uncertain and would require confirmation with an independent method. The new data allow us to improve the measurement of dP/dt for f1 and f2: using only the data up to the end of 2008, we obtain dP/dt1=(1.34+/-0.04)x10^-12^ and dP/dt2=(1.62+/-0.22)x10^-12^. The long-term variation of the two main pulsation periods (and the change of sign of dP/dt_1_) is visible also in direct measurements made over several years. The absence of peaks near f1 in the Fourier transform and the secondary peak close to f2 confirm a previous identification as l=0 and l=1, respectively, and suggest a stellar rotation period of about 40 days. The new data allow constraining the main g-mode pulsation periods of the star.
- ID:
- ivo://CDS.VizieR/J/AJ/98/1693
- Title:
- UBVRI photometry of NLTT stars
- Short Name:
- J/AJ/98/1693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBVRI photometry is presented for a sample of 1656 southern stars, including 1211, that were previously not measured, drawn from the NLTT (Luyten, 1979; catalogue I/98) proper-motion catalog; the catalog is shown to be a rich source of subdwarfs. The normalized UV excess, d(U-B)0.6, photometric parallax, and interstellar reddening are calculated for each star when possible. Residuals between the photometry and the magnitudes published in the NLTT catalog indicate that the latter have a large scatter (~0.6mag) and therefore the values tabulated in the NLTT catalog must be regarded as approximate only. The erratum (Astron. J. 99, 1336) which deals with position angles of proper motions (pmPA) has been taken into account.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A22
- Title:
- UVES spectra of Feige 46 and LSIV -14 116
- Short Name:
- J/A+A/643/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hot subdwarf stars of spectral types O and B represent a poorly understood phase in the evolution of low-mass stars, in particular of close compact binaries. A variety of phenomena are observed, which make them important tools for several astronomical disciplines. For instance, the richness of oscillations of many subdwarfs are important for asteroseismology. Furthermore, hot subdwarfs are among the most chemically peculiar stars known. Two intermediate He-rich hot subdwarf stars, LSIV -14 116 and Feige 46, are particularly interesting, because they show extreme enrichments of heavy elements such as Ge, Sr, Y, and Zr, strikingly similar in both stars. In addition, both stars show light oscillations at periods incompatible with standard pulsation theory and form the class of V366 Aqr variables. We investigate whether the similar chemical compositions extend to more complete abundance patterns in both stars and validate the pulsations in Feige 46 using its recent TESS light curve. High-resolution optical and near-ultraviolet spectroscopy are combined with non-local-thermodynamical-equilibrium model atmospheres and synthetic spectra calculated with Tlusty and Synspec to determine detailed metal abundance patterns in both stars consistently. Many previously unidentified lines are identified for the first time with transitions originating from GaIII, GeIII-IV, SeIII, KrIII, SrII-III, YIII, ZrIII-IV, and SnIV, most of which have not been observed so far in any star. The abundance patterns of 19 metals in both stars are almost identical, light metals being only slightly more abundant in Feige 46 while Zr, Sn, and Pb are slightly less enhanced compared to LSIV -14 116. Both abundance patterns are distinctively different from those of normal He-poor hot subdwarfs of similar temperature. The extreme enrichment in heavy metals of more than 4 dex compared to the Sun is likely the result of strong atmospheric diffusion processes that operate similarly in both stars while their similar patterns of C, N, O, and Ne abundances might provide clues to their as yet unclear evolutionary history. Finally, we find that the periods of the pulsation modes in Feige 46 are stable to better than dP/dt~=10^-8^s/s. This is is not compatible with dP/dt predicted for pulsations driven by the epsilon-mechanism and excited by helium-shell flashes in a star which is evolving, for example, onto the extended horizontal branch.
- ID:
- ivo://CDS.VizieR/J/MNRAS/426/1235
- Title:
- UVEX sources spectroscopic follow-up
- Short Name:
- J/MNRAS/426/1235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the first spectroscopic follow-up of 132 optically blue ultraviolet (UV)-excess sources selected from the UV-Excess Survey of the Northern Galactic Plane (UVEX). The UV-excess spectra are classified into different populations and grids of model spectra are fitted to determine spectral types, temperatures, surface gravities and reddening. From this initial spectroscopic follow-up 95 per cent of the UV-excess candidates turn out to be genuine UV-excess sources such as white dwarfs, white dwarf binaries, subdwarf types O and B, emission-line stars and quasi stellar objects. The remaining sources are classified as slightly reddened main-sequence stars with spectral types later than A0V. The fraction of DA white dwarfs is 47 per cent with reddening smaller than E(B-V)<=0.7mag. Relations between the different populations and their UVEX photometry, Galactic latitude and reddening are shown. A larger fraction of UVEX white dwarfs is found at magnitudes fainter than g>17 and Galactic latitude smaller than |b|<4 compared to main-sequence stars, blue horizontal branch stars and subdwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A190
- Title:
- Wide companions to M and L subdwarfs
- Short Name:
- J/A+A/650/A190
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The aim of the project is to identify wide common proper motion companions to a sample of spectroscopically confirmed M and L metal-poor dwarfs (also known as subdwarfs) to investigate the impact of metallicity on the binary fraction of low-mass metal-poor binaries and to improve the determination of their metallicity from the higher-mass binary. We made use of Virtual Observatory tools and large-scale public surveys to look in Gaia for common proper motion companions to a well-defined sample of ultracool subdwarfs with spectral types later than M5 and metallicities below or equal to ~0.5dex. We collected low-resolution optical spectroscopy for our best system, which is a binary composed of one sdM1.5 subdwarf and one sdM5.5 subdwarf located at ~1360au, and for another two likely systems separated by more than 115000au. We confirm one wide companion to an M subdwarf, and infer a multiplicity for M subdwarfs (sdMs) of 1.0_-1.0_^+2.0^% for projected physical separations of up to 743000au. We also find four M-L systems, three of which are new detections. No colder companion was identified in any of the 219 M and L subdwarfs of the sample, mainly because of limitations on the detection of faint sources with Gaia. We infer a frequency of wide systems for sdM5-9.5 of 0.60_-0.60_^+1.17^% for projected physical separations larger than 1360au (up to 142400au). This study shows a multiplicity rate of 1.0_-1.0_^+2.0^% in sdMs, and 1.9_-1.9_^+3.7^% in extreme M subdwarfs. We did not find any companion for the ultra M subdwarfs of our sample, establishing an upper limit of 5.3% on binarity for these objects.
