The population of hot subdwarf stars studied with Gaia I. The catalogue of known hot subdwarf stars

In preparation for the upcoming all-sky data releases of the Gaia mission we compiled a catalogue of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalogue contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colours, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques we removed outliers and misclassified objects. By matching this catalogue with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalogue of hot subdwarf stars based on Gaia data.Comment: 11 pages, A&A accepte

Pulse Timing Discovery of a Three-Day Companion to the Hot Subdwarf BPM 36430

Hot subdwarf B stars are core-helium burning objects that have undergone envelope stripping, likely by a binary companion. Using high-speed photometry from the Transiting Exoplanet Survey Satellite, we have discovered the hot subdwarf BPM 36430 is a hybrid sdBV_rs pulsator exhibiting several low-amplitude g-modes and a strong p-mode pulsation. The latter shows a clear, periodic variation in its pulse arrival times. Fits to this phase oscillation imply BPM 36430 orbits a barycenter approximately 10 light-seconds away once every 3.1 d. Using the CHIRON echelle spectrograph on the CTIO 1.5-m telescope, we confirm the reflex motion by detecting a radial velocity variation with semi-amplitude, period, and phase in agreement with the pulse timings. We conclude that a white dwarf companion with minimum mass of 0.42 Msun orbits BPM 36430. Our study represents only the second time a companion orbiting a pulsating hot subdwarf or white dwarf has been detected from pulse timings and confirmed with radial velocities.Comment: 7 pages, 5 figures, 4 tables. Accepted for publication in the Astrophysical Journa

Spectroscopic twin to the hypervelocity sdO star US 708 and three fast sdB stars from the Hyper-MUCHFUSS project

Important tracers for the dark matter halo of the Galaxy are hypervelocity stars (HVSs), which are faster than the local escape velocity of the Galaxy and their slower counterparts, the high-velocity stars in the Galactic halo. Such HVSs are believed to be ejected from the Galactic centre (GC) through tidal disruption of a binary by the super-massive black hole (Hills mechanism). The Hyper-MUCHFUSS survey aims at finding high-velocity potentially unbound hot subdwarf stars. We present the spectroscopic and kinematical analyses of a He-sdO as well as three candidates among the sdB stars using optical Keck/ESI and VLT (X-shooter, FORS) spectroscopy. Proper motions are determined by combining positions from early-epoch photographic plates with those derived from modern digital sky surveys. The Galactic rest frame velocities range from 203 km s^(-1) to 660 km s^(-1), indicating that most likely all four stars are gravitationally bound to the Galaxy. With T_(eff) = 47 000 K and a surface gravity of log g = 5.7, SDSS J205030.39−061957.8 (J2050) is a spectroscopic twin of the hypervelocity He-sdO US 708. As for the latter, the GC is excluded as a place of origin based on the kinematic analysis. Hence, the Hills mechanism can be excluded for J2050. The ejection velocity is much more moderate (385 ± 79 km s^(-1)) than that of US 708 (998 ± 68 km s^(-1)). The binary thermonuclear supernova scenario suggested for US 708 would explain the observed properties of J2050 very well without pushing the model parameters to their extreme limits, as required for US 708. Accordingly, the star would be the surviving donor of a type Ia supernova. Three sdB stars also showed extreme kinematics; one could be a HVS ejected from the GC, whereas the other two could be ejected from the Galactic disk through the binary supernova mechanism. Alternatively, they might be extreme halo stars

Spectral Analysis of Binary Pre-white Dwarf Systems

Short period double degenerate white dwarf (WD) binaries with periodsof less than ∼1 day are considered to be one of the likely progenitors of type Ia super-novae. These binaries have undergone a period of common envelope evolution. If thecore ignites helium before the envelope is ejected, then a hot subdwarf remains priorto contracting into a WD. Here we present a comparison of two very rare systems thatcontain two hot subdwarfs in short period orbits. We provide a quantitative spectro-scopic analysis of the systems using synthetic spectra from state-of-the-art non-LTEmodels to constrain the atmospheric parameters of the stars. We also use these modelsto determine the radial velocities, and thus calculate dynamical masses for the stars ineach system.Fil: Finch, N. L.. University of Leicester; Reino UnidoFil: Braker, I. P.. University of Leicester; Reino UnidoFil: Reindl, N.. University of Leicester; Reino UnidoFil: Barstow, M. A.. University of Leicester; Reino UnidoFil: Casewell, S. L.. University of Leicester; Reino UnidoFil: Burleigh, M.. University of Leicester; Reino UnidoFil: Kupfer, T.. University of California; Estados UnidosFil: Kilkenny, D.. University of the Western Cape; SudáfricaFil: Geier, S.. Universitat Potsdam; AlemaniaFil: Schaffenroth, V.. Universitat Potsdam; AlemaniaFil: Schaffenroth, V.. Universitat Potsdam; AlemaniaFil: Miller Bertolami, Marcelo Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Taubenberger, S.. Gobierno de la República Federal de Alemania. Max Planck Institut für Astrophysik; AlemaniaFil: Freudenthal, J.. No especifíca;Radiative Signatures from the Cosmos: A Conference in Honor of Ivan HubenyParisFranciaUniversidad de Pari

The first massive compact companion in a wide orbit around a hot subdwarf star

We report the discovery of the first hot subdwarf B (sdB) star with a massive compact companion in a wide ($P=892.5\pm60.2\,{\rm d}$) binary system. It was discovered based on an astrometric binary solution provided by the Gaia mission Data Release 3. We performed detailed analyses of the spectral energy distribution (SED) as well as spectroscopic follow-up observations and confirm the nature of the visible component as a sdB star. The companion is invisible despite of its high mass of $M_{\rm comp}=1.50_{-0.45}^{+0.37}\,M_{\rm \odot}$. A main sequence star of this mass would significantly contribute to the SED and can be excluded. The companion must be a compact object, either a massive white dwarf or a neutron star. Stable Roche lobe overflow to the companion likely led to the stripping of a red giant and the formation of the sdB, the hot and exposed helium core of the giant. Based on very preliminary data, we estimate that $\sim9\%$ of the sdBs might be formed through this new channel. This binary might also be the prototype for a new progenitor class of supernovae type Ia, which has been predicted by theory.Comment: 11 pages, accepted for publication in A&

Substellar companions and the formation of hot subdwarf stars

"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."We give a brief review over the observational evidence for close substellar companions to hot subdwarf stars. The formation of these core helium-burning objects requires huge mass loss of their red giant progenitors. It has been suggested that besides stellar companions substellar objects in close orbits may be able to trigger this mass loss. Such objects can be easily detected around hot subdwarf stars by medium or high resolution spectroscopy with an RV accuracy at the km s(-1)-level. Eclipsing systems of Vir type stick out of transit surveys because of their characteristic light curves. The best evidence that substellar objects in close orbits around sdBs exist and that they are able to trigger the required mass loss is provided by the eclipsing system SDSS J0820+0008, which was found in the course of the MUCHFUSS project. Furthermore, several candidate systems have been discovered.Final Accepted Versio

The EREBOS project -- Investigating the effect of substellar and low-mass stellar companions on late stellar evolution

Eclipsing post-common envelope binaries are highly important for resolving the poorly understood, very short-lived common envelope phase. Most hot subdwarfs (sdO/Bs) are the bare He-burning cores of red giants which have lost almost all of their hydrogen envelopes. This mass loss is often triggered by common envelope interactions with close stellar or even sub-stellar companions. In the recently published catalog of eclipsing binaries in the Galactic Bulge and in the ATLAS survey, we discovered 161 new eclipsing systems showing a reflection effect by visual inspection of the light curves and using a machine-learning algorithm. The EREBOS (Eclipsing Reflection Effect Binaries from Optical Surveys) project aims at analyzing all newly discovered eclipsing binaries with reflection effect based on a spectroscopic and photometric follow up. To constrain the nature of the primary we derived the absolute magnitude and the reduced proper motion of all our targets with the help of the parallaxes and proper motions measured by the Gaia mission and compared those to the Gaia white dwarf catalogue. For a sub-set of our targets with observed spectra the nature could be derived by measuring the atmospheric parameter of the primary confirming that less than 10\% of our systems are not sdO/Bs with cool companions but white dwarfs or central stars of planetary nebula. This large sample of eclipsing hot subdwarfs with cool companions allowed us to derive a significant period distribution for hot subdwarfs with cool companions for the first time showing that the period distribution is much broader than previously thought and ideally suited to find the lowest mass companions to hot subdwarf stars. In the future several new photometric surveys will be carried out, which will increase the sample of this project even more giving the potential to test many aspects of common envelope theory and binary evolution.Comment: accepted in A&A, 29 pages, 18 figure

EC 10246-2707: a new eclipsing sdB + M dwarf binary⋆

We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246-2707, and present multi-colour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.118 507 993 6 ± 0.000 000 000 9 days, or about three hours. Analysis of our time- series spectroscopy reveals a velocity semi-amplitude of K1 = 71.6 ± 1.7 km s−1 for the sdB and best-fitting atmospheric parameters of Teff = 28900 ± 500 K, log g = 5.64 ± 0.06, and log N(He)/N(H) = -2.5 ± 0.2. Although we cannot claim a unique solution from modeling the light curve, the best–fitting model has an sdB mass of 0.45 M⊙ and a cool companion mass of 0.12 M⊙. These results are roughly consistent with a canonical–mass sdB and M dwarf separated by a ∼ 0.84 R⊙. We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to < 0.08%. Using 15 years of eclipse timings, we construct an O-C diagram but find no statistically significant period changes; we rule out | ˙P | > 7.2×10−12. If EC 10246- 2707 evolves into a cataclysmic variable, its period should fall below the famous CV period gap.Web of Scienc

Discovery of the Closest Hot Subdwarf Binary with White Dwarf Companion

Contains fulltext : 117396.pdf (preprint version ) (Open Access