- ID:
- ivo://CDS.VizieR/J/ApJ/686/1280
- Title:
- Discovery of hot subdwarf companion to FY CMa
- Short Name:
- J/ApJ/686/1280
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The rapid rotation of Be stars may be caused in some cases by past mass and angular momentum accretion in an interacting binary in which the mass donor is currently viewed as a small, hot subdwarf stripped of its outer envelope. Here we report on the spectroscopic detection of such a subdwarf in the Be binary system FY Canis Majoris from the analysis of data acquired by the IUE spacecraft and KPNO Coude Feed Telescope over the course of 16 and 21yr, respectively. We present a double-lined spectroscopic orbit for the binary based on radial velocities from the IUE spectra and use the orbital solutions with a Doppler tomography algorithm to reconstruct the components' UV spectra. The subdwarf is hot (T_eff_=45+/-5kK) and has a mass of about 1.3M_{sun}_ and a radius of about 0.6R_{sun}_. It contributes about 4% as much flux as the Be star does in the FUV. We also present observations of the H{alpha} and HeI{lambda}6678 emission features that are formed in the circumstellar disk of the Be star.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/117/227
- Title:
- Dwarf effective temperatures
- Short Name:
- J/A+AS/117/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have applied the InfraRed Flux Method (IRFM) to a sample of 475 dwarfs and subdwarfs in order to derive their effective temperatures with a mean accuracy of about 1.5%. We have used the new homogeneous grid of theoretical model atmosphere flux distributions developed by Kurucz (1991, 1993) for the application of the IRFM. The atmospheric parameters of the stars cover, roughly, the ranges: 3500K<=T_eff_<=8000K; -3.5<=[Fe/H]<=+0.5; 3.5<=log(g)<=5. The monochromatic infrared fluxes at the continuum, and the bolometric fluxes are derived using recent results, which satisfy the accuracy requirements of the work.
- ID:
- ivo://CDS.VizieR/J/A+AS/107/365
- Title:
- Dwarfs and subdwarfs IR photometry
- Short Name:
- J/A+AS/107/365
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a long term programme of broad band JHK photometry, for a sample of 360 late type stars, made at the Observatorio del Teide (Tenerife, Spain) are presented.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/181
- Title:
- EC 01541-1409 pulsations frequencies
- Short Name:
- J/MNRAS/421/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present follow-up observations of the pulsating subdwarf B (sdB) star EC 01541-1409 as part of our efforts to resolve pulsation spectra for use in asteroseismological analyses. This paper reports on data obtained from a single-site campaign, during 2008, and a multisite campaign, during 2009. From limited 2008 data, we were able to clearly resolve and pre-whiten 24 periods. A subsequent multisite campaign spanning nearly 2 months found over 30 individual periodicities most of which were unstable in amplitude and/or phase. Pulsation amplitudes were found to the detection limit, meaning that further observations would likely reveal more periodicities.
- ID:
- ivo://CDS.VizieR/J/MNRAS/475/2480
- Title:
- Extremely-low mass white dwarf star
- Short Name:
- J/MNRAS/475/2480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The so-called sdA stars are defined by having H-rich spectra and surface gravities similar to hot subdwarf stars, but effective temperature below the zero-age horizontal branch. Their evolutionary history is an enigma: their surface gravity is too high for main-sequence stars, but too low for single evolution white dwarfs. They are most likely byproducts of binary evolution, including blue-stragglers, extremely-low mass white dwarf stars (ELMs) and their precursors (pre-ELMs). A small number of ELMs with similar properties to sdAs is known. Other possibilities include metal-poor A/F dwarfs, second generation stars, or even stars accreted from dwarf galaxies. In this work, we analyse colours, proper motions, and spacial velocities of a sample of sdAs from the Sloan Digital Sky Survey to assess their nature and evolutionary origin. We define a probability of belonging to the main sequence and a probability of being a (pre-)ELM based on these properties. We find that 7 per cent of the sdAs are more likely to be (pre-)ELMs than main-sequence stars. However, the spacial velocity distribution suggests that over 35 per cent of them cannot be explained as single metal-poor A/F stars.
- ID:
- ivo://CDS.VizieR/J/A+A/250/370
- Title:
- Far-UV excess object survey
- Short Name:
- J/A+A/250/370
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Optical spectra have been obtained for a selection of objects included in a catalog of far ultraviolet bright, high galactic latitude objects detected with a balloon-borne survey telescope. The observed objects provide a sample of subdwarf O and B stars, white dwarfs, and binary systems including a hot sub-luminous member. Model atmospheres analysis of the sub-dwarf sample is used to determine the temperature, gravity, and helium to hydrogen ratio of the individual objects. A smooth distribution of objects is found on the gravity versus temperature diagram near the theoretical location of the extended horizontal branch. A break between the helium rich and helium poor objects occurs at 40000K. Suspected binary objects were found and analyzed to determine the temperature and gravity of the hot subluminous member in each system. The number of subdwarf stars contained in binaries is determined to be from 65% to 100%. The number versus ultraviolet magnitude distribution of the subdwarf B sample is modeled to obtain a midplane density of 3.3x10^-6^pc^-3^ and a population scale height of 240pc. The proportion of white dwarfs that experience the subdwarf phase of evolution is found to be 0.94%.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A35
- Title:
- FBS 0117+396 pulsating sdB star photometry
- Short Name:
- J/A+A/559/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to discover subdwarf-B stars with massive compact companions such as overmassive white dwarfs (M>1.0M_{sun}_), neutron stars or black holes. From the 127 subdwarfs with substantial radial-velocity variations discovered in the initial survey, a number of interesting objects have been selected for extensive follow-up. After an initial photometry run with BUSCA revealed that FBS0117+396 is photometrically variable both on long and short timescales, we chose it as an auxiliary target during a 6-night multi-color photometry run with Ultracam. Spectroscopy was obtained at a number of observatories in order to determine the binary period and obtain a radial-velocity amplitude. After establishing an orbital period of P=0.252d, and removing the signal associated with the irradiated hemisphere of the M-dwarf companion, we were able to detect ten pulsation periods in the Fourier spectrum of the light curve. Two pulsation modes are found to have short periods of 337 and 379s, and at least eight modes are found with periods between 45-min and 2.5h. This establishes that FBS0117+396 is an sdB+dM reflection binary, in which the primary is a hybrid pulsator, and the first one found with this particular melange of flavours.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/25
- Title:
- FUSE spectra analysis of hot subdwarf stars
- Short Name:
- J/ApJ/764/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- When the neutral interstellar medium is exposed to extreme-ultraviolet and soft X-ray radiation, the argon atoms in it are far more susceptible to being ionized than the hydrogen atoms. We make use of this fact to determine the level of ionization in the nearby warm neutral medium. By analyzing Far-Ultraviolet Spectroscopic Explorer observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred parsecs away from the Sun, we can compare column densities of Ar I to those of O I, where the relative ionization of oxygen can be used as a proxy for that of hydrogen. The measured deficiency [ArI/OI]=-0.427+/-0.11dex below the expectation for a fully neutral medium implies that the electron density n(e){approx}0.04/cm3 if n(H)=0.5/cm3. This amount of ionization is considerably larger than what we expect from primary photoionizations resulting from cosmic rays, the diffuse X-ray background, and X-ray emitting sources within the medium, along with the additional ionizations caused by energetic secondary photoelectrons, Auger electrons, and photons from helium recombinations. We favor an explanation that bursts of radiation created by previous, nearby supernova remnants that have faded by now may have elevated the ionization, and the gas has not yet recombined to a quiescent level. A different alternative is that the low-energy portion of the soft X-ray background is poorly shielded by the H I because it is frothy and has internal pockets of very hot, X-ray emitting gases.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A38
- Title:
- Gaia catalogue of hot subluminous stars
- Short Name:
- J/A+A/621/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on data from the ESA Gaia Data Release 2 (DR2) and several ground-based, multi-band photometry surveys we have compiled an all-sky catalogue of 39800 hot subluminous star candidates selected in Gaia DR2 by means of colour, absolute magnitude, and reduced proper motion cuts. We expect the majority of the candidates to be hot subdwarf stars of spectral type B and O, followed by blue horizontal branch stars of late B-type (HBB), hot post-AGB stars, and central stars of planetary nebulae. The contamination by cooler stars should be about 10%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/2180
- Title:
- GALEX survey subdwarf atmospheric parameters
- Short Name:
- J/MNRAS/427/2180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an update of our low-resolution spectroscopic follow-up and model atmosphere analysis of hot subdwarf stars from the Galaxy Evolution Explorer (GALEX) survey. Targets were selected on the basis of colour indices calculated from the GALEX GR6 N_UV_, Guide Star Catalogue (GSC2.3.2) Vand the Two Micron All Sky Survey (2MASS) J and H photometry. High signal-to-noise ratio spectra were obtained at the European Southern Observatory (ESO) and the Kitt Peak National Observatory (KPNO) over the course of three years. Detailed H, He and CNO abundance analysis helped us improve our T_eff_, logg and He abundance determination and to constrain CNO abundances. We processed 191 observations of 180 targets and found 124 sdB and 42 sdO stars in this sample while some blue horizontal branch stars were also found in this programme. With quantitative binary decomposition of 29 composite spectra we investigated the incidence of A, F and G type companions. The incidence of late G and K type companions and their effects on subdwarf atmospheric parameters were also examined.
