- ID:
- ivo://CDS.VizieR/J/A+A/530/A2
- Title:
- New hot subdwarf stars
- Short Name:
- J/A+A/530/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent massive sky surveys in different bandwidths are providing new opportunities to modern astronomy. The Virtual Observatory (VO) provides the adequate framework to handle the huge amount of information available and filter out data according to specific requirements. Hot subdwarf stars are faint, blue objects, and are the main contributors to the far-UV excess observed in elliptical galaxies. They offer an excellent laboratory to study close and wide binary systems, and to scrutinize their interiors through asteroseismology, since some of them undergo stellar oscillations. However, their origins are still uncertain, and increasing the number of detections is crucial to undertake statistical studies. In this work, we aim at defining a strategy to find new, uncatalogued hot subdwarfs.
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- ID:
- ivo://CDS.VizieR/J/AJ/153/137
- Title:
- New NSVS 14256825 eclipse times
- Short Name:
- J/AJ/153/137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The cyclic behavior of (O-C) residuals of eclipse timings in the sdB+M eclipsing binary NSVS 14256825 was previously attributed to one or two Jovian-type circumbinary planets. We report 83 new eclipse timings that not only fill in the gaps in those already published but also extend the time span of the (O-C) diagram by three years. Based on the archival and our new data spanning over more than 17 years, we re-examined the up-to-date system (O-C). The data revealed a systematic, quasi-sinusoidal variation deviating from an older linear ephemeris by about 100 s. It also exhibits a maximum in the (O-C) near JD 2456400 that was previously unknown. We consider two most credible explanations of the (O-C) variability: the light propagation time due to the presence of an invisible companion in a distant circumbinary orbit, and magnetic cycles reshaping one of the binary components, known as the Applegate or Lanza-Rodono effect. We found that the latter mechanism is unlikely due to the insufficient energy budget of the M-dwarf secondary. In the framework of the third-body hypothesis, we obtained meaningful constraints on the Keplerian parameters of a putative companion and its mass. Our best-fitting model indicates that the observed quasi-periodic (O-C) variability can be explained by the presence of a brown dwarf with the minimal mass of 15 Jupiter masses rather than a planet, orbiting the binary in a moderately elliptical orbit (e~0.175) with a period of ~10 years. Our analysis rules out the two-planet model proposed earlier.
- ID:
- ivo://CDS.VizieR/J/A+A/551/A31
- Title:
- New spectral classification for hot subdwarfs
- Short Name:
- J/A+A/551/A31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An MK (Morgan-Keenan)-like system of spectral classification for hot subdwarfs is presented. We find that a three-dimensional spectral type, consisting of a 'spectral' class, a 'luminosity' class, and a 'helium' class, is necessary to classify the sdO (subdwarf O) and sdB (subdwarf B) stars. In addition, the helium-strong stars appear to form two parallel spectral sequences: one showing strong lines of CII, CIII, or CIV, and the other with these same lines weak or absent. We also give a preliminary calibration of the new spectral types in terms of effective temperature, surface gravity, and surface helium-to-hydrogen abundance ratio, and show the relation between the new spectral types and the natural groups defined by the PG (Palomar-Green) survey.
- ID:
- ivo://CDS.VizieR/J/ApJS/190/100
- Title:
- NIR proper motion survey using 2MASS
- Short Name:
- J/ApJS/190/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a 4030deg^2^ near-infrared proper motion survey using multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778 proper motion candidates, 647 of which are not listed in SIMBAD. After comparison to Digitized Sky Survey images, we find that 107 of our proper motion candidates lack counterparts at B, R, and I bands and are thus 2MASS-only detections. We present results of spectroscopic follow-up of 188 targets that include the infrared-only sources along with selected optical-counterpart sources with faint reduced proper motions or interesting colors. We also establish a set of near-infrared spectroscopic standards with which to anchor near-infrared classifications for our objects. Among the discoveries are six young field brown dwarfs, five "red L" dwarfs, three L-type subdwarfs, twelve M-type subdwarfs, eight "blue L" dwarfs, and several T dwarfs. We further refine the definitions of these exotic classes to aid future identification of similar objects. We examine their kinematics and find that both the "blue L" and "red L" dwarfs appear to be drawn from a relatively old population.
- ID:
- ivo://CDS.VizieR/J/A+A/513/A6
- Title:
- NOT survey of subdwarf B stars
- Short Name:
- J/A+A/513/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A search programme for pulsating subdwarf B stars was conducted with the Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The purpose of the programme was to significantly extend the number of rapidly pulsating sdB stars to better understand the properties of this new group of variable compact stars. Candidates were selected initially from the HS and HE surveys, but were supplemented with additional objects from other surveys. Short sequences of time-series photometry were made on the candidates to determine the presence of rapid pulsations.
- ID:
- ivo://CDS.VizieR/J/AJ/157/184
- Title:
- NY Virginis primary mid-eclipse times
- Short Name:
- J/AJ/157/184
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report 18 new primary minima timing observations of the short-period eclipsing binary system NY Virginis. We combined these minima with previously published primary minima to update circumbinary exoplanet models in this system based on O-C timing variations. We performed a nonlinear least-squares minimization search using a quadratic ephemeris and either one or two exoplanets. The only model with an acceptable fit includes a period derivative P=2.83x10^-12^ and two planets in eccentric orbits e=0.15, 0.15 with minimum masses of 2.7 and 5.5 Jovian masses. Analysis of the orbit stability shows that this solution is stable for at least 10^8^ years, but a small increase in eccentricity (e>=0.20) for either planet renders the orbits unstable in less than 10^6^ years. A number of model parameters are significantly degenerate, so additional observations are required to determine planetary parameters with high statistical confidence.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A95
- Title:
- Orbital solutions of eight close sdB binaries
- Short Name:
- J/A+A/562/A95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars (sdBs) with massive compact companions such as white dwarfs, neutron stars, or stellar-mass black holes. In a supplementary programme we obtained time-resolved spectroscopy of known hot subdwarf binary candidates. Here we present orbital solutions of eight close sdB binaries with orbital periods ranging from 0.1 to 10 days, which allow us to derive lower limits on the masses of their companions. Additionally, a dedicated photometric follow-up campaign was conducted to obtain light curves of the reflection-effect binary HS 2043+0615. We are able to constrain the most likely nature of the companions in all cases but one, making use of information derived from photometry and spectroscopy. Four sdBs have white dwarf companions, while another three are orbited by low-mass main sequence stars of spectral type M.
- ID:
- ivo://CDS.VizieR/J/A+A/459/557
- Title:
- Oscillation modes of PG 1325+101
- Short Name:
- J/A+A/459/557
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of 215h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (T_eff_=35000K, logg=5.8, logN(He)/N(H)=-1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55{mu}Hz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies are found: three of them at 7704.92, 9380.17 and 14511.10{mu}Hz were already present in the discovery run with small differences in frequency, probably due to 1-day aliasing effects. The peak at 7704.92{mu}Hz belongs to a triplet of almost equally spaced frequencies that could be due to rotational splitting and would imply a rotational period of about 1.6 days. Based on the results of this article, a detailed asteroseismic analysis of PG 1325+101 is presented in a separate paper (Charpinet et al., 2996A&A...459..565C, Paper II).
- ID:
- ivo://CDS.VizieR/J/A+A/493/L27
- Title:
- Parallaxes of 10 ultracool subdwarfs
- Short Name:
- J/A+A/493/L27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure absolute trigonometric parallaxes and proper motions with respect to many background galaxies for a sample of ten ultracool subdwarfs. Observations were taken in the H-band with the OMEGA2000 camera on the 3.5 m-telescope at Calar Alto, Spain during a time period of 3.5-years. For the first time, the reduction of the astrometric measurements was carried out directly with respect to background galaxies. We obtained absolute parallaxes with mean errors ranging between 1 and 3mas.
- ID:
- ivo://CDS.VizieR/J/A+A/430/223
- Title:
- Parameters of cool companions of sdB stars
- Short Name:
- J/A+A/430/223
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of a high-resolution, high-quality sample of optical spectra for 76 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey (SPY, Napiwotzki et al., 2001A&A...367..973N). Effective temperature, surface gravity, and photospheric helium abundance are determined simultaneously by fitting the profiles of hydrogen and helium lines using synthetic spectra calculated from LTE and NLTE model atmospheres. We perform a detailed comparison of our measurements with theoretical calculations, both for single star evolution and for binary population synthesis models of close binary evolution.
