- 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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Search Results
- 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/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/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.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A15
- Title:
- Parameters of EHB stars in {omega} Cen
- Short Name:
- J/A+A/618/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. While several evolutionary scenarios have been proposed to explain the characteristics of this peculiar population of evolved stars, their observational verification has been limited by the availability of spectroscopic data for a statistically significant sample of such objects in any single GGC. In this first paper, we focus on {omega} Centauri, a peculiar, massive GGC that hosts multiple stellar populations. We use non-LTE model atmospheres to derive atmospheric parameters (Teff, log g and N(He)/N(H)) and spectroscopic masses for 152 EHB stars in the cluster. We also search for close binaries among these stars based on radial velocity variations. The majority of our sample consists of sdOB stars that have roughly solar or super-solar atmospheric helium abundances. It is these objects that constitute the blue hook at V>18.5mag in the {omega} Cen colour-magnitude diagram.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A109
- Title:
- Parameters of HB stars in {omega} Cen
- Short Name:
- J/A+A/547/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the reddening, surface helium abundance and spectroscopic mass of 115 blue horizontal branch (HB) and blue hook (BH) stars in {omega} Centauri (NGC5139), spanning the cluster HB from the blue edge of the instability strip (T_eff_=8000K) to BH objects with T_eff_~50000K.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A28
- Title:
- Priority targets for the MUCHFUSS project
- Short Name:
- J/A+A/530/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding sdBs with compact companions like supermassive white dwarfs (M>1.0M_{sun}_), neutron stars or black holes. The existence of such systems is predicted by binary evolution theory and recent discoveries indicate that they are likely to exist in our Galaxy. A determination of the orbital parameters is sufficient to put a lower limit on the companion mass by calculating the binary mass function. If this lower limit exceeds the Chandrasekhar mass and no sign of a companion is visible in the spectra, the existence of a massive compact companion is proven without the need for any additional assumptions. We identified about 1100 hot subdwarf stars from the SDSS by colour selection and visual inspection of their spectra. Stars with high velocities have been reobserved and individual SDSS spectra have been analysed. In total 127 radial velocity variable subdwarfs have been discovered. Binaries with high RV shifts and binaries with moderate shifts within short timespans have the highest probability of hosting massive compact companions. Atmospheric parameters of 69 hot subdwarfs in these binary systems have been determined by means of a quantitative spectral analysis. The atmospheric parameter distribution of the selected sample does not differ from previously studied samples of hot subdwarfs. The systems are considered the best candidates to search for massive compact companions by follow-up time resolved spectroscopy.
