Astronomick Ustav

Ondřejov, Czech Republic

Astronomick Ustav

Ondřejov, Czech Republic

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Vennes S.,Astronomick Ustav | Vennes S.,Kitt Peak National Observatory | Kawka A.,Astronomick Ustav | Kawka A.,Kitt Peak National Observatory | And 2 more authors.
Astrophysical Journal Letters | Year: 2012

New spectroscopic observations show that the double-degenerate system NLTT 16249 is in a close orbit (a = 5.6 ± 0.3 R ⊙) with a period of 1.17days. The total mass of the system is estimated between 1.47 and 2.04M ⊙ but it is not expected to merge within a Hubble timescale (t merge ≈ 1011 yr). Vennes & Kawka originally identified the system because of the peculiar composite hydrogen (DA class) and molecular (C2-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. © © 2012. The American Astronomical Society. All rights reserved.


Vennes S.,Astronomick Ustav | Kawka A.,Astronomick Ustav | O'Toole S.J.,Australian Astronomical Observatory | Nemeth P.,Astronomick Ustav | And 2 more authors.
Astrophysical Journal Letters | Year: 2012

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 70.5minutes. The large velocity amplitude suggests the presence of a massive white dwarf in the system (M 2/M ⊙ ≳ 0.77) assuming a canonical mass for the hot subdwarf (0.48 M ⊙), although a white dwarf mass as low as 0.75 M ⊙ is allowable by postulating a subdwarf mass as low as 0.44 M ⊙. The amplitude of ellipsoidal variations and a high rotation velocity imposed a high-inclination to the system (i ≳ 68°) and, possibly, observable secondary transits (i ≳ 74°). At the lowest permissible inclination and assuming a subdwarf mass of 0.48 M ⊙, the total mass of the system reaches the Chandrasekhar mass limit at 1.35 M ⊙ and would exceed it for a subdwarf mass above 0.48 M ⊙. 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 30 Myr. © 2012. The American Astronomical Society. All rights reserved.

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