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Ostensen R.H.,Catholic University of Leuven | Reed M.D.,Missouri State University | Baran A.S.,University Pedagogiczny akowie | Telting J.H.,Nordic Optical Telescope
Astronomy and Astrophysics | Year: 2014

The subdwarf-B star KIC≠2991276 was monitored with the Kepler spacecraft for nearly three years. Two pulsation modes with periods of 122 and 132≠s are clearly detected in the Fourier spectrum, as well as a few weaker modes with periods ranging from 118 to 216≠s. Unlike the other subdwarf-B pulsators with similar high-quality Kepler lightcurves, the modes in KIC≠2991276 do not display long-term coherency. Rather, their pulsation amplitudes vary substantially in amplitude and phase on timescales of about a month, sometimes disappearing completely. Thus, while the pulsations are seen to have amplitudes of up to 1.4% in individual months, the amplitude spectrum of the full lightcurve shows a broad, messy peak with an amplitude of only 0.23%. Such stochastic oscillations are normal in the Sun and other cool stars with solar-like pulsations and have been suspected for V361-Hya pulsators, but thanks to the exceptional coverage of Kepler data, this is the first unambiguous case established for a hot subdwarf. © 2014 ESO. Source

Several 19th century documents concerning Polish mineral deposits, their exploitation and potential importance/or the French armaments industry were found in the Defence Historical Service Archives of the French Army, housed at the Vincennes Castle near Paris. These are military intelligence reports written prior to the 1812 campaign. Some of these reports contain chapters dealing with natural resources of Lithuania, which was to become one of the major theatres of military operations in war against Russia. These describe deposits of iron, coal and some other minerals of military relevance. The archives also include a report on copper deposits at Miedziana Góra in the Holy Cross Mts. Some reports contain also information on mineral resources of the present-day Ukraine. Source

Ostensen R.H.,Catholic University of Leuven | Telting J.H.,Nordic Optical Telescope | Reed M.D.,Missouri State University | Baran A.S.,University Pedagogiczny akowie | And 3 more authors.
Astronomy and Astrophysics | Year: 2014

The subdwarf-B pulsator, KIC≠10553698A, is one of 16 such objects observed with a one-minute sampling rate for most of the duration of the Kepler mission. Like most of these stars, it displays a rich g-mode pulsation spectrum with several clear multiplets that maintain regular frequency splitting. We identify these pulsation modes as components of rotationally split multiplets in a star rotating with a period of ~41 d. From 162 clearly significant periodicities, we are able to identify 156 as likely components of = 1 or = 2 multiplets. For the first time we are able to detect = 1 modes that interpose in the asymptotic period sequences and that provide a clear indication of mode trapping in a stratified envelope, as predicted by theoretical models. A clear signal is also present in the Kepler photometry at 3.387 d. Spectroscopic observations reveal a radial-velocity amplitude of 64.8 km s-1. We find that the radial-velocity variations and the photometric signal have phase and amplitude that are perfectly consistent with a Doppler-beaming effect and conclude that the unseen companion, KIC 10553698B, must be a white dwarf most likely with a mass close to 0.6 M. © 2014 ESO. Source

Telting J.H.,Nordic Optical Telescope | Baran A.S.,University Pedagogiczny akowie | Nemeth P.,Catholic University of Leuven | Ostensen R.H.,Catholic University of Leuven | And 6 more authors.
Astronomy and Astrophysics | Year: 2014

The recently discovered subdwarf B (sdB) pulsator KIC7668647 is one of the 18 pulsating sdB stars detected in the Kepler field. It features a rich g-mode frequency spectrum, with a few low-amplitude p-modes at short periods. This makes it a promising target for a seismic study aiming to constrain the internal structure of this star, and of sdB stars in general. We use new ground-based low-resolution spectroscopy, and the near-continuous 2.88year Kepler light curve, to reveal that KIC7668647 consists of a subdwarf B star with an unseen white-dwarf companion with an orbital period of 14.2d. An orbit with a radial-velocity amplitude of 39kms-1 is consistently determined from the spectra, from the orbital Doppler beaming seen by Kepler at 163ppm, and from measuring the orbital light-travel delay of 27s by timing of the many pulsations seen in the Kepler light curve. The white dwarf has a minimum mass of 0.40M. We use our high signal-to-noise average spectra to study the atmospheric parameters of the sdB star, and find that nitrogen and iron have abundances close to solar values, while helium, carbon, oxygen and silicon are underabundant relative to the solar mixture. We use the full Kepler Q06-Q17 light curve to extract 132 significant pulsation frequencies. Period-spacing relations and multiplet splittings allow us to identify the modal degree l for the majority of the modes. Using theg-mode multiplet splittings we constrain the internal rotation period at the base of the envelope to 46-48d as a first seismic result for this star. The few p-mode splittings may point at a slightly longer rotation period further out in the envelope of the star. From mode-visibility considerations we derive that the inclination of the rotation axis of the sdB in KIC7668647 must be around ∼60. Furthermore, we find strong evidence for a few multiplets indicative of degree 3 ≤ l ≤ 8, which is another novelty in sdB-star observations made possible by Kepler. © ESO, 2004. Source

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