An eclipsing post common-envelope system consisting of a pulsating hot subdwarf B star and a brown dwarf companion

Schaffenroth, V.; Barlow, B. N.; Drechsel, H.; Dunlap, B. H.

doi:10.1051/0004-6361/201525701

Cited by 49 publications

(45 citation statements)

References 43 publications

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“…The confirmed dM-star/brown-dwarf companions in HW Vir systems have a mass distribution concentrated around 0.1 M (Kupfer et al 2015). In the lower part of the mass distribution, there are a few cases with confirmed brown dwarfs: SDSS J162256+473051, SDSS J082053.53+000843.4, and V2008-1753, which have secondary masses 0.060M (Schaffenroth et al 2014), 0.068M (Geier et al 2011), and 0.047 M (Schaffenroth et al 2015), respectively. Thus, the secondary star of HS 2231+2441, considering both solutions, has one of the lowest masses, ∼0.036 and ∼0.046 M , for a companion object in HW Vir systems known so far.…”

Section: Masses Of the Hs 2231+2441 Componentsmentioning

confidence: 98%

HS 2231+2441: an HW Vir system composed of a low-mass white dwarf and a brown dwarf★

Almeida

Damineli

Rodrigues

et al. 2017

Monthly Notices of the Royal Astronomical Society

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HW Vir systems are rare evolved eclipsing binaries composed by a hot compact star and a low-mass main-sequence star in a close orbit. These systems provide a direct way to measure the fundamental properties, e.g. masses and radii, of their components, hence they are crucial to study the formation of sdB stars and low-mass white dwarfs, the common-envelope phase, and the pre-phase of cataclysmic variables. Here we present a detailed study of HS 2231+2441, an HW Vir type system, by analysing BVR C I C photometry and phase-resolved optical spectroscopy. The spectra of this system, which are dominated by the primary component features, were fitted using NLTE models providing effective temperature T eff = 28500±500 K, surface gravity log g = 5.40 ± 0.05 cm s −2 , and helium abundance log(n(He)/n(H)) = −2.52 ± 0.07. Geometrical orbit and physical parameters were derived by modelling simultaneously the photometric and spectroscopic data using the Wilson-Devinney code. We derive two possible solutions for HS 2231+2441 that provide component's masses: M 1 = 0.19 M and M 2 = 0.036 M or M 1 = 0.288 M and M 2 = 0.046 M . Considering the possible evolutionary channels to form a compact hot star, the primary of HS 2231+2441 probably evolved through the red-giant branch scenario and does not have a helium-burning core, which is consistent with a low-mass white dwarf. Both solutions are consistent with a brown dwarf as the secondary.

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Section: Masses Of the Hs 2231+2441 Componentsmentioning

confidence: 98%

HS 2231+2441: an HW Vir system composed of a low-mass white dwarf and a brown dwarf★

Almeida

Damineli

Rodrigues

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…The short period system J082053+000843 (0.096 d) is also eclipsing, and the companion has a mass in the range 0.045 -0.067 M (Geier et al 2011). Schaffenroth et al (2015) discovered another, specially interesting eclipsing hot subdwarf, showing pulsations, with a brown dwarf companion with a mass of 0.069 M (V2008-1753, 0.065 d). Additionally, two sdB systems with candidate brown dwarf companions have been detected (periods ∼ 0.3 d, Schaffenroth et al 2014a), but since they do not eclipse, only minimum companion masses -both below the hydrogen burning limit -can be derived (0.048 and 0.027 M ).…”

Section: Introductionmentioning

confidence: 99%

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

Schaffenroth

Barlow

Geier

et al. 2019

A&A

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Eclipsing post-common envelope binaries are highly important for resolving the poorly understood, very short-lived common envelope phase of stellar evolution. Most hot subdwarfs (sdO/Bs) are the bare helium-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. Cool companions to hot subdwarf stars such as late-type stars and brown dwarfs are detectable from characteristic light curve variations -reflection effects and often eclipses. In the recently published catalog of eclipsing binaries in the Galactic Bulge and in the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey, we discovered 125 new eclipsing systems showing a reflection effect by visual inspection of the light curves and using a machine-learning algorithm, in addition to the 36 systems discovered before by the OGLE (Optical Gravitational Lesing Experiment) team. The EREBOS (Eclipsing Reflection Effect Binaries from Optical Surveys) project aims at analyzing all newly discovered eclipsing binaries of the HW Vir type (hot subdwarf + close, cool companion) based on a spectroscopic and photometric follow up to derive the mass distribution of the companions, constrain the fraction of sub-stellar companions and determine the minimum mass needed to strip off the red-giant envelope. 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 candidate 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. The comparison with related binary populations shows that the period distribution of HW Vir systems is very similar to WD+dM systems and central stars of planetary nebula with cool companions. 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.

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“…However, most of the hot subdwarf binary systems with known orbital periods are single-lined spectroscopic binaries, making it impossible to reliably determine the absolute masses of their components. Among the PCEBs, 15 eclipsing binary systems have been found to date, which are comprised of a hot subdwarf primary (sdO or sdB star) and a low mass secondary, either a late dM or a brown dwarf (BD) (for the most recent discoveries see Schaffenroth et al 2013;Barlow et al 2013;Schaffenroth et al 2014Schaffenroth et al , 2015. Such eclipsing systems are known as HW-Vir-type binaries after the prototype.…”

Section: Introductionmentioning

confidence: 99%

Looking on the bright side: The story of AA Doradus as revealed by its cool companion

Vučković

Østensen

Németh

et al. 2016

A&A

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The effects of irradiation on the secondary stars of close binary systems are crucial for reliably determining the system parameters and for understanding the close binary evolution. They affect the stellar structure of the irradiated star and are reflected in the appearance of characteristic features in the spectroscopic and photometric data of these systems. We aim to study the light that originates from the irradiated side of the low-mass component of a close binary eclipsing system, which comprises a hot subdwarf primary and a low mass companion, to precisely interpret their high precision photometric and spectroscopic data, and accurately determine their system and surface parameters. We reanalyse the archival high-resolution time-resolved VLT/UVES spectra of AA Dor system, where irradiation features have already been detected. After removing the predominant contribution of the hot subdwarf primary, the residual spectra reveal more than 100 emission lines from the heated side of the secondary, which show maximum intensity close to the phases around the secondary eclipse. We analyse the residual spectrum to model the irradiation of the low-mass secondary. We perform a detailed analysis of 22 narrow emission lines of the irradiated secondary, mainly of O ii, with a few significant C ii lines. Their phase profiles constrain the emission region of the heated side to a radius ≥95% of the radius of the secondary, while the shape of their velocity profiles reveals two distinct asymmetry features, one at the quadrature and the other at the secondary eclipse. In addition, we identify weaker emission signatures originating from more than 70 lines, including lines from He i, N ii, Si iii, Ca ii, and Mg ii. From the emission lines of the heated side of the secondary star, we determine the radial velocity semi-amplitude of the centre-of-light and correct it to the centre-of-mass of the secondary which, in turn, gives accurate masses of both components of the AA Dor system. The resulting masses M 1 = 0.46 ± 0.01 M and M 2 = 0.079 ± 0.002 M are in perfect accordance with those of a canonical hot subdwarf primary and a low mass that is just at the substellar limit for the companion. We also compute a first generation atmosphere model of the low mass secondary, which includes irradiation effects and matches the observed spectrum well. We find an indication of an extended atmosphere of the irradiated secondary star.

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An eclipsing post common-envelope system consisting of a pulsating hot subdwarf B star and a brown dwarf companion

Cited by 49 publications

References 43 publications

HS 2231+2441: an HW Vir system composed of a low-mass white dwarf and a brown dwarf★

HS 2231+2441: an HW Vir system composed of a low-mass white dwarf and a brown dwarf★

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

Looking on the bright side: The story of AA Doradus as revealed by its cool companion

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