TY  - JOUR
A1  - Baran, Andrzej S.
A1  - Telting, J. H.
A1  - Jeffery, C. Simon
A1  - Ostensen, R. H.
A1  - Vos, Joris
A1  - Reed, M. D.
A1  - Vŭcković, Maja
T1  - K2 observations of the sdBV plus dM/bd binaries PHL457 and EQPsc
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present an analysis of two pulsating subdwarf B stars PHL 457 and EQ Psc observed during the K2 mission. The K2 light curves of both stars show variation consistent with irradiation of a cooler companion by the hot subdwarf. They also show higher frequency oscillations consistent with pulsation. Using new spectroscopic data, we measured the radial velocity, effective temperature, surface gravity, and helium abundance of both hot subdwarfs as a function of orbital phase. We confirm the previously published spectroscopic orbit of PHL 457, and present the first spectroscopic orbit of EQ Psc. The orbital periods are 0.313 and 0.801 d, respectively. For EQPsc, we find a strong correlation between T-eff and orbital phase, due to contribution of light from the irradiated companion. We calculated amplitude spectra, identified significant pulsation frequencies, and searched for multiplets and asymptotic period spacings. By means of multiplets and period spacing, we identified the degrees of several pulsation modes in each star. The g-mode multiplets indicate subsynchronous core rotation with periods of 4.6 d (PHL 457) and 9.4 d (EQ Psc). We made spectral energy disctribution (SED) fits of PHL 457 and EQ Psc using available broad-band photometry and Gaia data. While the SED of PHL 457 shows no evidence of a cool companion, the SED for EQPsc clearly shows an infrared (IR) access consistent with a secondary with a temperature of about 6800K and a radius of 0.23 R-circle dot. This is the first detection of an IR access in any sdB + dM binary.
KW  - binaries: general
KW  - stars: individual (PHL 457, EQ Psc)
KW  - stars: oscillations (including pulsations)
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz2209
SN  - 0035-8711
SN  - 1365-2966
VL  - 489
IS  - 2
SP  - 1556
EP  - 1571
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Pelisoli, Ingrid Domingos
A1  - Vos, Joris
T1  - Gaia Data Release 2 catalogue of extremely low-mass white dwarf candidates
JF  - Monthly notices of the Royal Astronomical Society
N2  - Extremely low-mass white dwarf stars (ELMs) are M < 0.3 M-circle dot helium-core white dwarfs born either as a result of a common-envelope phase or after a stable Roche lobe overflow episode in a multiple system. The Universe is not old enough for ELMs to have formed through single-star evolution channels. As remnants of binary evolution, ELMs can shed light onto the poorly understood phase of common-envelope evolution and provide constraints to the physics of mass accretion. Most known ELMs will merge in less than a Hubble time, providing an important contribution to the signal to be detected by upcoming space-based gravitational wave detectors. There are currently less than 150 known ELMs; most were selected by colour, focusing on hot objects, in a magnitude-limited survey of the Northern hemisphere only. Recent theoretical models have predicted a much larger space density for ELMs than estimated observationally based on this limited sample. In order to perform meaningful comparisons with theoretical models and test their predictions, a larger well-defined sample is required. In this work, we present a catalogue of ELM candidates selected from the second data release of Gaia (DR2). We have used predictions from theoretical models and analysed the properties of the known sample to map the space spanned by ELMs in the Gaia Hertzsprung-Russell diagram. Defining a set of colour cuts and quality flags, we have obtained a final sample of 5762 ELM candidates down to T-eff approximate to 5000 K.
KW  - catalogues
KW  - surveys
KW  - binaries: close
KW  - white dwarfs
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz1876
SN  - 0035-8711
SN  - 1365-2966
VL  - 488
IS  - 2
SP  - 2892
EP  - 2903
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Vos, Joris
A1  - Vuckovic, Maja
A1  - Chen, X.
A1  - Han, Zh
A1  - Boudreaux, Thomas
A1  - Barlow, Brad N.
A1  - Ostensen, R.
A1  - Nemeth, Péter
T1  - Using wide hot subdwarf binaries to constrain Roche-lobe overflow models
JF  - Contributions of the Astronomical Observatory Skalnaté Pleso
N2  - Hot subdwarf B (sdB) stars are evolved core helium burning stars that have lost most of their hydrogen envelope due to binary interaction on the red giant branch. As sdB stars in wide binary systems can only be created by stable Roche lobe overflow, they are a great test sample to constrain the theoretical models for stable mass loss on the red giant branch. We present here the findings of a long term monitoring program of wide sdB+MS binaries. We found two main features in the orbital parameters. The majority of the systems have eccentric orbits with systems on longer orbital period having a higher eccentricity. As these systems have undergone mass loss near the tip of the RGB, tidal circularisation theory predicts them to be circularized. Our observations suggest that efficient eccentricity pumping mechanisms are active during the mass loss phase. Secondly we find a strong correlation between the mass ratio and the orbital period. Using binary evolution models, this relation is used to derive both an upper and lower limit on the initial mass ratio at which RLOF will be stable. These limits depend on the core mass of the sdB progenitor.
KW  - stars: subdwarfs
KW  - stars: binaries: spectroscopic
KW  - stars: fundamental parameters
KW  - stars: evolution
Y1  - 2019
SN  - 1335-1842
SN  - 1336-0337
VL  - 49
IS  - 2
SP  - 264
EP  - 270
PB  - Astronomický Ústav SAV
CY  - Tatranská Lomnica
ER  -