We show that the extremely low-mass white dwarf NLTT 11748 (0.17 $M_\odot$) is in a close binary with a fainter companion. We obtained a series of radial velocity measurements of the low-mass white ...dwarf using the Hα core and determined an orbital period of 5.64 h. The velocity semi-amplitude (K = 274.8 km s-1) and orbital period imply that it is a degenerate star, and that the minimum mass for the companion is 0.75 $M_\odot$ (assuming a mass of 0.167 $M_\odot$ for the primary). Our analysis of Balmer line profiles shows that a 0.75 $M_\odot$ white dwarf companion does not contribute more than 2% or 5% of the flux (V-band) for helium- or hydrogen-rich surfaces, respectively. The kinematics of the system suggest that it belongs to the Galactic halo.
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We report the discovery of two new hot, hydrogen-rich subdwarfs (sdB) in close binary systems. The hot subdwarfs, GALEX J0321+4727 and GALEX J2349+3844, were selected from a joint optical–ultraviolet ...catalogue of hot subluminous stars based on GSC2.3.2 and the Galaxy Evolution Explorer all-sky survey. Using high-dispersion spectra of the Hα core, obtained using the 2-m telescope at Ondřejov Observatory, we measured the radial velocities of the sdB primaries and determined orbital periods of 0.265 84 ± 0.000 04 d and 0.462 49 ± 0.000 07 d for GALEX J0321+4727 and GALEX J2349+3844, respectively. The time series obtained from the Northern Sky Variability Survey with an effective wavelength near the R-band show that GALEX J0321+4727 is a variable star (Δm= 0.12 mag), while no significant variations are observed in GALEX J2349+3844. The period of variations in GALEX J0321+4727 coincides with the orbital period and the variability is probably caused by a reflection effect on a late-type secondary star. Lack of photometric variations in GALEX J2349+3844 probably indicates that the companion is a white dwarf star. Using all available photometry and spectroscopy, we measured the atmospheric properties of the two sdB stars and placed limits on the mass and luminosity of the companion stars.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
New spectroscopic observations show that the double-degenerate system NLTT 16249 is in a close orbit (a = 5.6 + or - 0.3 R sub(middot in circle)) with a period of 1.17 days. The total mass of the ...system is estimated between 1.47 and 2.04 M sub(middot in circle) but it is not expected to merge within a Hubble timescale (t sub(merge) approximate 10 super(11) yr). Vennes & Kawka originally identified the system because of the peculiar composite hydrogen (DA class) and molecular (C sub(2)-DQ class and CN) spectra and the new observations establish this system as the first DA plus DQ close double degenerate. Also, the DQ component was the first of its class to show nitrogen dredged up from the core in its atmosphere. The star may be viewed as the first known DQ descendant of the born-again PG1159 stars. Alternatively, the presence of nitrogen may be the result of past interactions and truncated evolution in a close binary system.
We re-examine the properties of the high-velocity and extremely low-mass white dwarf LP 400-22 and its close companion. Based on an extended observation timeline, we determined a binary period of $P ...= 1.01016$ d, somewhat longer than the previously published period, and a mass function $f(M_2)$ = 0.180 $M_\odot$, implying a mass for the companion M2 > 0.41 $M_\odot$. We also re-appraised the mass and cooling age of the white dwarf using low-metallicity ($Z = 0.001$) evolutionary models appropriate for an old halo member, M1 = 0.19 $M_\odot$, and $t_{\mathrm{cool}}$≈1.8 Gyr, and we infer a mass of 0.85–1.0 $M_\odot$ for the progenitor of the white dwarf. We discuss the likely origin of this system.
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We report on the discovery of the shortest period binary comprising a hot subdwarf star (CD-30 11223, GALEX J1411-3053) and a massive unseen companion. Photometric data from the All Sky Automated ...Survey show ellipsoidal variations of the hot subdwarf primary and spectroscopic series revealed an orbital period of 70.5 minutes. The large velocity amplitude suggests the presence of a massive white dwarf in the system (M sub(2)/M sub(middot in circle) > 0.77) assuming a canonical mass for the hot subdwarf (0.48 M sub(middot in circle)), although a white dwarf mass as low as 0.75 M sub(middot in circle) is allowable by postulating a subdwarf mass as low as 0.44 M sub(middot in circle). The amplitude of ellipsoidal variations and a high rotation velocity imposed a high-inclination to the system (i > ~ 68degrees) and, possibly, observable secondary transits (i > ~ 74degrees). At the lowest permissible inclination and assuming a subdwarf mass of ~0.48 M sub(middot in circle), the total mass of the system reaches the Chandrasekhar mass limit at 1.35 M sub(middot in circle) and would exceed it for a subdwarf mass above 0.48 M sub(middot in circle). The system should be considered, like its sibling KPD 1930+2752, a candidate progenitor for a Type Ia supernova. The system should become semi-detached and initiate mass transfer within asymptotically =30 Myr.
On the nature of the Be star HR7409 (7Vul) Vennes, S; Kawka, A; Jonic, S ...
Monthly notices of the Royal Astronomical Society,
06/2011, Volume:
413, Issue:
4
Journal Article
Peer reviewed
HR7409 (7Vul) is a newly identified Be star, possibly part of the Gould Belt, and is the massive component of a 69-d spectroscopic binary. The binary parameters and properties of the Be star measured ...using high-dispersion spectra obtained at Ondrejov Observatory and at Rozhen Observatory imply the presence of a low-mass companion (asymptotically =0.5-0.8M). If the pair is relatively young (<50-80Myr), then the companion is a KV star, but, following another, older evolutionary scenario, the companion is a horizontal branch star or possibly a white dwarf star. In the latter scenario, a past episode of mass transfer from an evolved star on to a less massive dwarf star would be responsible for the peculiar nature of the present-day, fast-rotating Be star. PUBLICATION ABSTRACT
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On the nature of the Be star HR 7409 (7 Vul) Vennes, S.; Kawka, A.; Jonić, S. ...
Monthly notices of the Royal Astronomical Society,
June 2011, Volume:
413, Issue:
4
Journal Article
Peer reviewed
HR 7409 (7 Vul) is a newly identified Be star, possibly part of the Gould Belt, and is the massive component of a 69-d spectroscopic binary. The binary parameters and properties of the Be star ...measured using high-dispersion spectra obtained at Ondřejov Observatory and at Rozhen Observatory imply the presence of a low-mass companion (≈0.5-0.8 M⊙). If the pair is relatively young (<50-80 Myr), then the companion is a K V star, but, following another, older evolutionary scenario, the companion is a horizontal branch star or possibly a white dwarf star. In the latter scenario, a past episode of mass transfer from an evolved star on to a less massive dwarf star would be responsible for the peculiar nature of the present-day, fast-rotating Be star.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
We report the discovery of the partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically ...active dM4 stars in a circular 1.6 day orbit. Light and velocity curve modeling to our differential photometry and velocity data show that each star has a mass and radius of 0.340 plus or minus 0.014 M unk and 0.33 plus or minus 0.02 R unk. The binary Is itself part of a common proper motion pair with LP 133-374, a cool DC or possible DA white dwarf with a mass of 0.49-0.82 M unk, which would make the system at least 3 Gyr old.
We studied both components of a slightly overlooked visual binary HR 1847 spectroscopically to determine its basic physical and orbital parameters. Basic stellar parameters were determined by ...comparing synthetic spectra to the observed echelle spectra, which cover both the optical and near-IR regions. New observations of this system used the Ondřejov and Rozhen 2-m telescopes and their coudé spectrographs. Radial velocities from individual spectra were measured and then analysed with the code FOTEL to determine orbital parameters. The spectroscopic orbit of HR 1847A is presented for the first time. It is a single-lined spectroscopic binary with a B-type primary, a period of 719.79 days, and a highly eccentric orbit with e=0.7. We confirmed that HR 1847B is a Be star. Its Hα emission significantly decreased from 2003 to 2008. Both components have a spectral type B7-8 and luminosity class IV-V.
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