TY  - JOUR
A1  - Baran, Andrzej S.
A1  - Ostensen, R. H.
A1  - Telting, J. H.
A1  - Vos, Joris
A1  - Kilkenny, D.
A1  - Vuckovic, Maja
A1  - Reed, M. D.
A1  - Silvotti, R.
A1  - Jeffery, C. Simon
A1  - Parsons, Steven G.
A1  - Dhillon, V. S.
A1  - Marsh, T. R.
T1  - Pulsations and eclipse-time analysis of HW Vir
JF  - Monthly notices of the Royal Astronomical Society
N2  - We analysed recent K2 data of the short-period eclipsing binary system HW Vir, which consists of a hot subdwarf-B type primary with an M-dwarf companion. We determined the mid-times of eclipses, calculated O-C diagrams, and an average shift of the secondary minimum. Our results show that the orbital period is stable within the errors over the course of the 70 days of observations. Interestingly, the offset from mid-orbital phase between the primary and the secondary eclipses is found to be 1.62 s. If the shift is explained solely by light-travel time, the mass of the sdB primary must be 0.26 M-circle dot, which is too low for the star to be core-helium burning. However, we argue that this result is unlikely to be correct and that a number of effects caused by the relative sizes of the stars conspire to reduce the effective light-travel time measurement. After removing the flux variation caused by the orbit, we calculated the amplitude spectrum to search for pulsations. The spectrum clearly shows periodic signal from close to the orbital frequency up to 4600 mu Hz, with the majority of peaks found below 2600 mu Hz. The amplitudes are below 0.1 part-per-thousand, too low to be detected with ground-based photometry. Thus, the high-precision data from the Kepler spacecraft has revealed that the primary of the HW Vir system is a pulsating sdBV star. We argue that the pulsation spectrum of the primary in HW Vir differs from that in other sdB stars due to its relatively fast rotation that is (nearly) phase-locked with the orbit.
KW  - binaries: eclipsing
KW  - stars: oscillations
KW  - subdwarfs
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/sty2473
SN  - 0035-8711
SN  - 1365-2966
VL  - 481
IS  - 2
SP  - 2721
EP  - 2735
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Reindl, Nicole
A1  - Bainbridge, M.
A1  - Przybilla, Norbert
A1  - Geier, Stephan Alfred
A1  - Prvak, M.
A1  - Krticka, Jiri
A1  - Ostensen, R. H.
A1  - Telting, J.
A1  - Werner, K.
T1  - Unravelling the baffling mystery of the ultrahot wind phenomenon in white dwarfs
JF  - Monthly notices of the Royal Astronomical Society
N2  - The presence of ultrahigh excitation (UHE) absorption lines (e.g. OVIII) in the optical spectra of several of the hottest white dwarfs poses a decades-long mystery and is something that has never been observed in any other astrophysical object. The occurrence of such features requires a dense environment with temperatures near 10(6) K, by far exceeding the stellar effective temperature. Here we report the discovery of a new hot wind white dwarf, GALEXJ014636.8+323615. Astonishingly, we found for the first time rapid changes of the equivalent widths of the UHE features, which are correlated to the rotational period of the star (P=0.242035 d). We explain this with the presence of a wind-fed circumstellar magnetosphere in which magnetically confined wind shocks heat up the material to the high temperatures required for the creation of the UHE lines. The photometric and spectroscopic variability of GALEXJ014636.8+323615 can then be understood as consequence of the obliquity of the magnetic axis with respect to the rotation axis of the white dwarf. This is the first time a wind-fed circumstellar magnetosphere around an apparently isolated white dwarf has been discovered and finally offers a plausible explanation of the ultrahot wind phenomenon.
KW  - stars: AGB and post-AGB
KW  - stars: evolution
KW  - stars: magnetic field
Y1  - 2018
U6  - https://doi.org/10.1093/mnrasl/sly191
SN  - 0035-8711
SN  - 1365-2966
VL  - 482
IS  - 1
SP  - L93
EP  - L98
PB  - Oxford Univ. Press
CY  - Oxford
ER  -