Two candidate brown dwarf companions around core helium-burning stars

Schaffenroth, V.; Classen, L.; Nagel, Kurt; Geier, S.; Koen, C.; Heber, U.; Edelmann, H.

doi:10.1051/0004-6361/201424616

Cited by 28 publications

(39 citation statements)

References 38 publications

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“…The ASAS and NSVS light curves do not show significant variations when folded on the orbital period, i.e., 12 mmag, while the predicted semi-amplitude of variations due to a substellar object (R 2 ≈ 0.1 R , see a review by Chabrier et al 2009) would be ≈ 20 mmag. Variations of the order of 10 mmag have been observed in brown dwarf plus hot subdwarf binaries (see, e.g., Schaffenroth et al 2014c) and such variations would be detectable in GALEX J0805−1058 in quality photometric time series. We conclude that the apparent lack of variations is a consequence of the small radius of a substellar secondary.…”

Section: Close Binariesmentioning

confidence: 97%

New binaries among UV-selected, hot subdwarf stars and population properties★

Kawka

Vennes

O'Toole

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We have measured the orbital parameters of seven close binaries, including six new objects, in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from ∼ 0.17 to 3 d. One new system, GALEX J2205−3141, shows reflection on a M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low mass white dwarf (GALEX J0805−1058) paired with an unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses ranging from 0.03 to 0.39 M . Photometric time series suggest that, apart from GALEX J0805−1058 and J2205−3141, the companions are most likely white dwarfs. We update the binary population statistics: Close to 40 per cent of hot subdwarfs have a companion. Also, we found that the secondary mass distribution shows a low-mass peak attributed to late-type dwarfs, and a higher-mass peak and tail distribution attributed to white dwarfs and a few spectroscopic composites. Also, we found that the population kinematics imply an old age and include a few likely halo population members.

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Section: Close Binariesmentioning

confidence: 97%

New binaries among UV-selected, hot subdwarf stars and population properties★

Kawka

Vennes

O'Toole

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…CPD-64481 and PHL 457 (Schaffenroth et al 2014), were missed due to low amplitude (sub-1%) variability and a close source that was blended in the Evryscope pixels. A list of known, solved HSD binaries showing reflection effects can be found in Kupfer et al (2015).…”

Section: Reflection Effect or Partially Eclipsing Binariesmentioning

confidence: 99%

Hot Subdwarf All Southern Sky Fast Transit Survey with the Evryscope

Ratzloff

Barlow

Németh

et al. 2020

ApJ

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We have conducted a survey of candidate hot subdwarf stars in the southern sky searching for fast transits, eclipses, and sinusoidal like variability in the Evryscope light curves. The survey aims to detect transit signals from Neptune size planets to gas-giants, and eclipses from M-dwarfs and brown dwarfs. The other variability signals are primarily expected to be from compact binaries and reflection effect binaries. Due to the small size of hot subdwarfs (R ≈ 0.2R ), transit and eclipse signals are expected to last only ≈twenty minutes, but with large signal depths (up to completely eclipsing if the orientation is edge on). With its 2-minute cadence and continuous observing Evryscope is well placed to recover these fast transits and eclipses. The very large field of view (8150 sq. deg.) is critical to obtain enough hot subdwarf targets, despite their rarity. We identified ≈11,000 potential hot subdwarfs from the 9.3M Evryscope light curves for sources brighter than m g = 15. With our machine learning spectral classifier, we flagged high-confidence targets and estimate the total hot subdwarfs in the survey to be ≈1400. The light curve search detected three planet transit candidates, shown to have stellar companions from follow-up analysis. We discovered several new compact binaries (including two with unseen degenerate companions, and several others with potentially rare secondaries), two eclipsing binaries with M-dwarf companions, as well as new reflection effect binaries and others with sinusoidal like variability. The hot subdwarf discoveries identified here are spectroscopically confirmed and we verified the Evryscope discovery light curve with TESS light curves when available. Four of the discoveries are in the process of being published in separate followup papers, and we discuss the followup potential of several of the other discoveries.

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“…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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Two candidate brown dwarf companions around core helium-burning stars

Cited by 28 publications

References 38 publications

New binaries among UV-selected, hot subdwarf stars and population properties★

New binaries among UV-selected, hot subdwarf stars and population properties★

Hot Subdwarf All Southern Sky Fast Transit Survey with the Evryscope

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

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