Photometry of four binary subdwarf B stars and the nature of their unseen companion stars

Maxted, P. F. L.; Marsh, T. R.; Heber, U.; Morales-Rueda, L.; North, Rachel; Lawson, W. A.

doi:10.1046/j.1365-8711.2002.05406.x

Cited by 93 publications

(69 citation statements)

References 27 publications

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“…Maxted et al (2002) reported the detection of a significant reflection effect, but no eclipses in the light curve. Taking these informations into account, one can constrain the inclination angle to be lower than 73…”

Section: Late Main Sequence Stars and A Potential Brown Dwarfmentioning

confidence: 98%

“…No signatures of a main-sequence companion within the given mass range are visible in the flux distribution or in the spectrum f . These informations are taken from (1) Bloemen et al (2010), (2) Charpinet et al (2008), (3) Drechsel et al (2001), (4) Edelmann (2008), (5) Farihi et al (2005), (6) Geier et al (2007), (7) Geier et al (2010a), (8) Geier et al (2008a), (9) Koen (2007), (10) Koen (2009), (11) Lisker et al (2005), (12) Maxted et al (2002), (13) Maxted et al (2004), (14) Østensen (priv. comm.…”

Section: White Dwarfsmentioning

confidence: 99%

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Hot subdwarf stars in close-up view

Geier¹,

Heber²,

Podsiadlowski

et al. 2010

A&A

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162

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The origin of hot subdwarf B stars (sdBs) is still unclear. About half of the known sdBs are in close binary systems for which common envelope ejection is the most likely formation channel. Little is known about this dynamic phase of binary evolution. Since most of the known sdB systems are single-lined spectroscopic binaries, it is difficult to derive masses and unravel the companions' nature, which is the aim of this paper. Due to the tidal influence of the companion in close binary systems, the rotation of the primary becomes synchronised to its orbital motion. In this case it is possible to constrain the mass of the companion, if the primary mass, its projected rotational velocity as well as its surface gravity are known. For the first time we measured the projected rotational velocities of a large sdB binary sample from high resolution spectra. We analysed a sample of 51 sdB stars in close binaries, 40 of which have known orbital parameters comprising half of all such systems known today. Synchronisation in sdB binaries is discussed both from the theoretical and the observational point of view. The masses and the nature of the unseen companions could be constrained in 31 cases. We found orbital synchronisation most likely to be established in binaries with orbital periods shorter than 1.2 d. Only in five cases it was impossible to decide whether the sdB's companion is a white dwarf or an M dwarf. The companions to seven sdBs could be clearly identified as late M stars. One binary may have a brown dwarf companion. The unseen companions of nine sdBs are white dwarfs with typical masses. The mass of one white dwarf companion is very low. In eight cases (including the well known system KPD1930+2752) the companion mass exceeds 0.9 M , four of which even exceed the Chandrasekhar limit indicating that they may be neutron stars. Even stellar mass black holes are possible for the most massive companions. The distribution of the inclinations of the systems with low mass companions appears to be consistent with expectations, whereas a lack of high inclinations becomes obvious for the massive systems. We show that the formation of such systems can be explained with common envelope evolution and present an appropriate formation channel including two phases of unstable mass transfer and one supernova explosion. The sample also contains a candidate post-RGB star, which rotates fast despite its long orbital period. The post-RGB stars are expected to spin-up caused by their ongoing contraction. The age of the sdB is another important factor. If the EHB star is too young, the synchronisation process might not be finished yet. Estimating the ages of the target stars from their positions on the EHB band, we found PG 2345+318, which is known not to be synchronised, to lie near the zero-age extreme horizontal branch as are the massive candidates PG 1232−136, PG 1432+159 and PG 1101+249. These star may possibly be too young to have reached synchronisation. The derived large fraction of putative massive sdB binary systems ...

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Section: Late Main Sequence Stars and A Potential Brown Dwarfmentioning

confidence: 98%

Section: White Dwarfsmentioning

confidence: 99%

Hot subdwarf stars in close-up view

Geier¹,

Heber²,

Podsiadlowski

et al. 2010

A&A

Self Cite

162

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show abstract

“…Due to the early spectral type of the primary star, the gravity darkening (Van Grootel et al 2013a;Drechsel et al 2001;Geier et al 2011d;Maxted et al 2002;Klepp & Rauch 2011;Østensen et al 2008Wood & Saffer 1999;Almeida et al 2012;Barlow et al 2013). The open dots represent other sdB binaries from the literature.…”

Section: Photometric Analysismentioning

confidence: 99%

Binaries discovered by the MUCHFUSS project

Schaffenroth

Geier

Heber

et al. 2014

A&A

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Hot subdwarf B stars (sdBs) are core helium-burning stars located on the extreme horizontal branch. About half of the known sdB stars are found in close binaries. Their short orbital periods of 1.2 h to a few days suggest that they are post common-envelope systems. Eclipsing hot subdwarf binaries are rare but are important in determining the fundamental stellar parameters. Low-mass companions are identified by the reflection effect. In most cases, the companion is a main sequence star near the stellar mass limit. Here, we report the discovery of an eclipsing hot subdwarf binary SDSS J162256.66+473051.1 (J1622) with very short orbital period (0.0697 d), which has been found in the course of the MUCHFUSS project. The lightcurve shows grazing eclipses and a prominent reflection effect. An analysis of the light-and radial velocity (RV) curves indicated a mass ratio of q = 0.1325, an RV semi-amplitude K = 47.2 km s −1 , and an inclination of i = 72.33 • . We show that a companion mass of 0.064 M , which is well below the hydrogenburning limit, is the most plausible solution, which implies a mass close to the canonical mass (0.47 M ) of the sdB star. Therefore, the companion is a brown dwarf, which has not only survived the engulfment by the red-giant envelope but also triggered its ejection and enabled the sdB star to form. The rotation of J1622 is expected to be tidally locked to the orbit. However, J1622 rotates too slowly (v rot = 74.5 ± 7 km s −1 ) to be synchronized, challenging tidal interaction models.

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“…The binary scenario is supported by the finding of numerous low-mass WDs in binary systems in the field, with * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained by the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. the companion being another WD, a neutron star, or a subdwarf B star (Marsh et al 1995;Maxted et al 2002). However, single He-core WDs have also been observed (Marsh et al 1995;Kilic et al 2007), raising the possibility that severe mass loss on the first ascent of the giant branch can prevent ignition of helium burning.…”

Section: Introductionmentioning

confidence: 99%

First Detection of the White Dwarf Cooling Sequence of the Galactic Bulge

Calamida¹,

Sahu²,

Anderson³

et al. 2014

ApJ

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We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3 × 3 ), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F 606W and F 814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr −1 (≈4 km s −1 ) at F 606W ≈ 25.5 mag, and better than ≈0.5 mas yr −1 (≈20 km s −1 ) at F 606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.

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Photometry of four binary subdwarf B stars and the nature of their unseen companion stars

Cited by 93 publications

References 27 publications

Hot subdwarf stars in close-up view

Hot subdwarf stars in close-up view

Binaries discovered by the MUCHFUSS project

First Detection of the White Dwarf Cooling Sequence of the Galactic Bulge

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