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  - GEN
A1  - Finch, Nicolle L.
A1  - Braker, I. P.
A1  - Reindl, Nicole
A1  - Barstow, Martin A.
A1  - Casewell, Sarah L.
A1  - Burleigh, M.
A1  - Kupfer, Thomas
A1  - Kilkenny, D.
A1  - Geier, Stephan
A1  - Schaffenroth, Veronika
A1  - Bertolami Miller, Marcelo Miguel
A1  - Taubenberger, Stefan
A1  - Freudenthal, Joseph
T1  - Spectral Analysis of Binary Pre-white Dwarf Systems
T2  - Radiative signatures from the cosmos
N2  - Short period double degenerate white dwarf (WD) binaries with periods of less than similar to 1 day are considered to be one of the likely progenitors of type Ia supernovae. These binaries have undergone a period of common envelope evolution. If the core ignites helium before the envelope is ejected, then a hot subdwarf remains prior to contracting into a WD. Here we present a comparison of two very rare systems that contain two hot subdwarfs in short period orbits. We provide a quantitative spectroscopic analysis of the systems using synthetic spectra from state-of-the-art non-LTE models to constrain the atmospheric parameters of the stars. We also use these models to determine the radial velocities, and thus calculate dynamical masses for the stars in each system.
Y1  - 2019
SN  - 978-1-58381-925-8
SN  - 1050-3390
VL  - 519
SP  - 231
EP  - 238
PB  - Astronomical soc pacific
CY  - San Fransisco
ER  -