The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project

Geier, S.; Kupfer, Thomas; Heber, U.; Schaffenroth, V.; Barlow, B. N.; Østensen, R. H.; O’Toole, S. J.; Ziegerer, E.; Heuser, C.; Maxted, P. F. L.; Gänsicke, B. T.; Marsh, T. R.; Napiwotzki, R.; Brünner, P.; Schindewolf, M.; Niederhofer, Florian

doi:10.1051/0004-6361/201525666

Cited by 55 publications

(67 citation statements)

References 66 publications

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“…Individual observations and RV measurements of the five stars are listed in Geier et al (2015). The RVs were measured by fitting a set of mathematical functions (Gaussians, Lorentzians, and polynomials) to the spectral lines using the FITSB2 routine (Napiwotzki et al 2004).…”

Section: Observations and Detection Of Radial Velocity Variationsmentioning

confidence: 99%

“…To verify the close binary nature of the stars, we tried to derive orbital periods and RV semiamplitudes of the objects with more than ten epochs as described in Geier et al (2015). Unfortunately, in both cases the RV datasets were insufficient to put any meaningful constraints on the orbital parameters.…”

Section: Observations and Detection Of Radial Velocity Variationsmentioning

confidence: 99%

“…Those stars, whose SDSS sub-spectra revealed high RV variations, were selected as candidates for follow-up spectroscopy to derive the RV curves and the binary mass functions of the systems. In this way, more than 100 RV-variable subdwarfs have been found (Geier et al 2015).…”

Section: Introductionmentioning

confidence: 96%

“…By eye, the spectra of O(H), O(He), and PG 1159 stars may look very similar to those of the less luminous sdO, He-sdO, and C-strong lined He-sdO stars, respectively. Thus, the sample of Geier et al (2015) Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

“…also contains a small fraction of hot post-AGB candidates, namely SDSS J075732.18+184329.3 (hereafter J0757), SDSS J093521.39+482432.4 (J0935), SDSS J100019.98-003413.3 (J1000), SDSS J155610.40+254640.3 (J1556), and SDSS J204623.12-065926.8 (J2046). Previous analysis of these stars indicates very high effective temperatures Geier et al 2015). Because of the rareness of such objects as well as their importance for our understanding of the late, hot stages of stellar evolution we decided to subject these five stars to a more comprehensive analysis and discussion of their evolutionary status.…”

Section: Introductionmentioning

confidence: 99%

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Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Reindl¹,

Geier

Kupfer

et al. 2016

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In the course of the MUCHFUSS project we recently discovered four radial velocity (RV) variable, hot (T eff ≈ 80 000−110 000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV variable O(He) star, the only second known RV variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of a far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The "missing" PNe around the O(H)-type stars seems strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non-ejection of a PN, the occurrence of a late thermal pulse, or the re-accretion of the PN in the previous post-AGB evolution offer possible explanations for those stars not harbouring a PN (anymore). In the case of the O(He) star J0757, we speculate that it might have been previously part of a compact He transferring binary system. In this scenario, the mass transfer must have stopped after a certain time, leaving behind a low-mass close companion that may be responsible for the extreme RV shift of 107.0 ± 22.0 km s −1 that was measured within only 31 min.

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Section: Observations and Detection Of Radial Velocity Variationsmentioning

confidence: 99%

Section: Observations and Detection Of Radial Velocity Variationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Reindl¹,

Geier

Kupfer

et al. 2016

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Hot subdwarfs: Small stars marking important events in stellar evolution: Ludwig Biermann Award Lecture 2014

Geier¹

2015

Astron Nachr

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Hot subdwarfs are considered to be the compact helium cores of red giants which lost almost their entire hydrogen envelope. What causes this enormous mass loss is still unclear. Binary interactions are invoked, and a significant fraction of the hot subdwarf population is indeed found in close binaries. In a large project we search for close binary sdBs with the most and the least massive companions. Significantly enhancing the known sample of close binary sdBs we performed the first comprehensive study of this population. Triggered by the discovery of two sdB binaries with close brown dwarf companions in the course of this project, we were able to show that the interaction of stars with substellar companions is an important channel to form sdB stars. Finally, we discovered a unique and very compact binary system consisting of an sdB and a massive white dwarf which qualifies as a progenitor candidate for a supernova of type Ia. In addition to that, we could connect those explosions to the class of hypervelocity hot subdwarf stars which we consider as the surviving companions of such events. Being the stripped cores of red giants, hot subdwarfs turned out to be important markers of peculiar events in stellar evolution ranging all the way from star-planet interactions to the progenitors of stellar explosions used to measure the expansion of our Universe.

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The MUCHFUSS photometric campaign

Schaffenroth

Geier

Heber

et al. 2018

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Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which lost almost all of their hydrogen envelopes. This mass loss is often triggered by common envelope interactions with close stellar or even substellar companions. Cool companions like late-type stars or brown dwarfs are detectable via characteristic light curve variations like reflection effects and often also eclipses. To search for such objects we obtained multi-band light curves of 26 close sdO/B binary candidates from the MUCHFUSS project with the BUSCA instrument. We discovered a new eclipsing reflection effect system (P = 0.168938 d) with a low-mass M dwarf companion (0.116M ). Three more reflection effect binaries found in the course of the campaign were already published, two of them are eclipsing systems, in one system only showing the reflection effect but no eclipses the sdB primary is found to be pulsating. Amongst the targets without reflection effect a new long-period sdB pulsator was discovered and irregular light variations were found in two sdO stars. The found light variations allowed us to constrain the fraction of reflection effect binaries and the substellar companion fraction around sdB stars. The minimum fraction of reflection effect systems amongst the close sdB binaries might be greater than 15% and the fraction of close substellar companions in sdB binaries might be as high as 8.0%. This would result in a close substellar companion fraction to sdB stars of about 3%. This fraction is much higher than the fraction of brown dwarfs around possible progenitor systems, which are solar-type stars with substellar companions around 1 AU, as well as close binary white dwarfs with brown dwarf companions. This might be a hint that common envelope interactions with substellar objects are preferentially followed by a hot subdwarf phase.

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The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project

Cited by 55 publications

References 66 publications

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Radial velocity variable, hot post-AGB stars from the MUCHFUSS project

Hot subdwarfs: Small stars marking important events in stellar evolution: Ludwig Biermann Award Lecture 2014

The MUCHFUSS photometric campaign

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