Ondřejov, Czech Republic
Ondřejov, Czech Republic

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Vennes S.,Astronomickyustav AV CR | Kawka A.,Astronomickyustav AV CR | Jonic S.,University of Belgrade | Pirkovic I.,University of Belgrade | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

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 Ondřejov Observatory and at Rozhen Observatory imply the presence of a low-mass companion (≈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. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Vennes S.,Astronomickyustav AV CR | Kawka A.,Astronomickyustav AV CR | Nemeth P.,Astronomickyustav AV CR | Nemeth P.,Florida Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present a detailed model atmosphere analysis of high-dispersion and high signal-to-noise ratio spectra of the heavily polluted DAZ white dwarf GALEX J1931+0117. The spectra obtained with the Very Large Telescope (VLT)-Kueyen/UV-Visual Echelle Spectrograph show several well-resolved Siii spectral lines enabling a study of pressure effects on line profiles. We observed large Stark shifts in silicon lines in agreement with theoretical predictions and laboratory measurements. Taking into account Stark shifts in the calculation of synthetic spectra, we reduced the scatter in individual line radial velocity measurements from ∼3 to ≲1kms-1. We present revised abundances of O, Mg, Si, Ca and Fe based on a critical review of line-broadening parameters and oscillator strengths. The new measurements are generally in agreement with our previous analysis with the exception of magnesium with a revised abundance of a factor of 2 lower than previously estimated. The magnesium, silicon and iron abundances exceed solar abundances, but the oxygen and calcium abundances are below solar. Also, we compared the observed line profiles to synthetic spectra computed with variable accretion rates and vertical abundance distributions assuming diffusive steady state. The inferred accretion rates vary from for calcium to 2 × 109gs-1 for oxygen. We find that the accretion flow must be oxygen rich while being deficient in calcium relative to solar abundances. The lack of radial velocity variations between two measurement epochs suggests that GALEX J1931+0117 is probably not in a close binary and that the source of the accreted material resides in a debris disc. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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