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 of stellar evolution. Most hot subdwarfs (sdO/Bs) are the bare helium-burning cores of red giants that have lost almost all of their hydrogen envelope. This mass loss is often triggered by common-envelope interactions with close stellar or even substellar 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 Asteroid Terrestrial-impact Last Alert System (ATLAS) survey, we discovered 125 new eclipsing systems showing a reflection effect seen by visual inspection of the light curves and using a machine-learning algorithm, in addition to the 36 systems previously discovered by the Optical Gravitational Lesing Experiment (OGLE) team. The Eclipsing Reflection Effect Binaries from Optical Surveys (EREBOS) 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 substellar 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 catalog. It was possible to derive the nature of a subset of our targets, for which observed spectra are available, by measuring the atmospheric parameter of the primary, confirming that less than 10% of our systems are not sdO/Bs with cool companions but are 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 is ideally suited to finding 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 further increase the sample of this project, providing the potential to test many aspects of common-envelope theory and binary evolution.

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When nature tries to trick us

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833693 ◽

2018 ◽

Vol 619 ◽

pp. A84 ◽

Cited By ~ 6

Author(s):

Henri M. J. Boffin ◽

David Jones ◽

Roger Wesson ◽

Yuri Beletsky ◽

Brent Miszalski ◽

...

Keyword(s):

Planetary Nebula ◽

Binary Star ◽

Central Star ◽

Equal Mass ◽

Type I ◽

Eclipsing Binary ◽

Common Envelope ◽

Bright Object ◽

F Stars ◽

Central Stars

Bipolar planetary nebulae (PNe) are thought to result from binary star interactions and, indeed, tens of binary central stars of PNe have been found, in particular using photometric time-series that allow for the detection of post-common envelope systems. Using photometry at the NTT in La Silla we have studied the bright object close to the centre of PN M 3-2 and found it to be an eclipsing binary with an orbital period of 1.88 days. However, the components of the binary appear to be two A or F stars, of almost equal mass, and are therefore too cold to be the source of ionisation of the nebula. Using deep images of the central star obtained in good seeing conditions, we confirm a previous result that the central star is more likely much fainter, located 2″ away from the bright star. The eclipsing binary is thus a chance alignment on top of the planetary nebula. We also studied the nebular abundance and confirm it to be a Type I PN.

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The MUCHFUSS photometric campaign

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629789 ◽

2018 ◽

Vol 614 ◽

pp. A77 ◽

Cited By ~ 4

Author(s):

V. Schaffenroth ◽

S. Geier ◽

U. Heber ◽

R. Gerber ◽

D. Schneider ◽

...

Keyword(s):

Brown Dwarfs ◽

Close Binary ◽

Red Giants ◽

Reflection Effect ◽

Common Envelope ◽

Sdb Stars ◽

Solar Type ◽

Low Mass ◽

Substellar Companions ◽

Almost All

Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which have lost almost all of their hydrogen envelope. 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 (0.116 M⊙). Three more reflection effect binaries found in the course of the campaign have already been published; two of them are eclipsing systems, and 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 may 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 suggest that common envelope interactions with substellar objects are preferentially followed by a hot subdwarf phase.

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Eclipsing binaries in the OGLE variable star catalogue: long-period evolved systems

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1476 ◽

2020 ◽

Vol 496 (1) ◽

pp. 550-563

Author(s):

Barış Hoyman ◽

Sara Bulut ◽

Orkun Özdarcan ◽

Ömür Çakırlı

Keyword(s):

Stellar Evolution ◽

Binary Stars ◽

Eclipsing Binaries ◽

Parameter Determination ◽

Atmospheric Parameter ◽

Physical Parameters ◽

Giant Stars ◽

Red Giant ◽

Type Giant ◽

Stellar Masses

ABSTRACT Red giant stars are proving to be an exceptional source of information for testing models of stellar evolution, as photometric and spectroscopic analysis has opened up a window into their interiors, providing an exciting chance to develop highly constrained stellar models. In this study, we present a determination of precise fundamental physical parameters belonging to five detached, double-lined, eclipsing binary stars in the Large and Small Magellanic Clouds containing G- or early K-type giant stars with extended envelopes. We also derived the distances to the systems by using a temperature–colour relation and compared these distances with the measurements provided in the literature. The measured stellar masses are in the range 1.8–3.0 M⊙ and comparison with the PAdova and TRieste Stellar Evolution Code (PARSEC) isochrones gives ages between 0.4 and 1.1 Gyr. The derived uncertainties for individual masses and radii of components are better than 3 and 7 per cent, respectively, for these systems. Additionally, we performed atmospheric parameter determination and [M/H] analysis for each, where we disentangled the spectra.

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35. Stellar Constitution

Transactions of the International Astronomical Union ◽

10.1017/s0251107x00006544 ◽

1985 ◽

Vol 19 (1) ◽

pp. 479-502

Author(s):

A. N. Cox ◽

D. Sugimoto ◽

P. H. Bodenheimer ◽

C. S. Chiosi ◽

D. J. Faulkner ◽

...

Keyword(s):

Stellar Evolution ◽

Planetary Nebula ◽

Massive Stars ◽

Structure Stability ◽

Current Interest ◽

Late Type ◽

Dwarf Stars ◽

Entire Field ◽

Stellar Formation ◽

Central Stars

This report of Commission 35, as in past reports, consists of some details of only a few selected topics. This is necessary because a survey of the entire field of stellar formation, structure, stability, evolution, pulsation, and explosions for the three year period from mid-1981 to mid-1984 would be excessively long. Our topics here, in order from the most massive stellar classes to the least are: Massive Stars (R.M. Humphreys), Rotation in Late Type Stars (W. Benz), Helioseismology (J. Christensen-Dalsgaard), Planetary Nebula Central Stars (E.M. Sion), Pulsations in Hot Degenerate Dwarf Stars (A.N. Cox and S.D. Kawaler), and White Dwarfs (V. Weidemann). There is some overlap in the reviewing of these last three reports because the topics are very closely related. Concentration in this dying stage of stellar evolution seems appropriate because of the great current interest in these matters.

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Planetary nebulae with Wolf–Rayet-type central stars – I. The case of the high-excitation NGC 2371

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1542 ◽

2020 ◽

Vol 496 (1) ◽

pp. 959-973

Author(s):

V M A Gómez-González ◽

J A Toalá ◽

M A Guerrero ◽

H Todt ◽

L Sabin ◽

...

Keyword(s):

Stellar Evolution ◽

Planetary Nebula ◽

Symmetry Axis ◽

High Excitation ◽

Central Cavity ◽

Isaac Newton ◽

Double Structure ◽

High Ionization ◽

Isaac Newton Telescope ◽

Central Stars

ABSTRACT We present the analysis of the planetary nebula (PN) NGC 2371 around the [Wolf–Rayet] (WR) star WD 0722+295. Our Isaac Newton Telescope intermediate dispersion spectrograph spectra, in conjunction with archival optical and ultraviolet images, unveil in unprecedented detail the high ionization of NGC 2371. The nebula has an apparent multipolar morphology, with two pairs of lobes protruding from a barrel-like central cavity, a pair of dense low ionization knots misaligned with the symmetry axis embedded within the central cavity, and a high-excitation halo mainly detected in He ii. The abundances from the barrel-like central cavity and dense knots agree with abundance determinations for other PNe with [WR]-type central stars of PNe. We suggest that the densest knots inside NGC 2371 are the oldest structures, remnant of a dense equatorial structure, while the main nebular shell and outer lobes resulted from a latter ejection that ended the stellar evolution. The analysis of position–velocity diagrams produced from our high-quality spectra suggests that NGC 2371 has a bipolar shape with each lobe presenting a double structure protruding from a barrel-like central region. The analysis of the spectra of WD 0722+295 results in similar stellar parameters as previously reported. We corroborate that the spectral subtype corresponds with a [WO1] type.

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Proto-Planetary Nebulae

Symposium - International Astronomical Union ◽

10.1017/s0074180900208255 ◽

2003 ◽

Vol 209 ◽

pp. 113-120 ◽

Cited By ~ 3

Author(s):

Bruce J. Hrivnak

Keyword(s):

Stellar Evolution ◽

Planetary Nebula ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Central Stars

The study of proto-planetary nebulae (PPNs) leads to a better understanding of both the preceding asymptotic giant branch and the succeeding planetary nebula phases of stellar evolution. Recent results are reviewed, emphasizing the properties of the central stars and the shape and chemistry of the nebulae. The study of PPNs is seen to be important in its own right.

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Surveying Planetary Nebulae Central Stars for Close Binaries: Constraining Evolution of Central Stars Based on Binary Parameters

Galaxies ◽

10.3390/galaxies6030085 ◽

2018 ◽

Vol 6 (3) ◽

pp. 85 ◽

Cited By ~ 2

Author(s):

Todd Hillwig

Keyword(s):

Binary Stars ◽

Planetary Nebula ◽

Planetary Nebulae ◽

Close Binary ◽

Close Binaries ◽

Common Envelope ◽

Close Binary Stars ◽

Red Giant ◽

The Relationship ◽

Central Stars

The increase in discovered close binary central stars of planetary nebulae is leading to a sufficiently large sample to begin to make broader conclusions about the effect of close binary stars on common envelope evolution and planetary nebula formation. Herein I review some of the recent results and conclusions specifically relating close binary central stars to nebular shaping, common envelope evolution off the red giant branch, and the total binary fraction and double degenerate fraction of central stars. Finally, I use parameters of known binary central stars to explore the relationship between the proto-planetary nebula and planetary nebula stages, demonstrating that the known proto-planetary nebulae are not the precursors of planetary nebulae with close binary central stars.

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12. The Nuclei of Planetary Nebulae as Progenitors of White Dwarfs

Symposium - International Astronomical Union ◽

10.1017/s0074180900097114 ◽

1971 ◽

Vol 42 ◽

pp. 77-78

Author(s):

C. R. O'Dell

Keyword(s):

Stellar Evolution ◽

Planetary Nebula ◽

White Dwarfs ◽

Rapid Change ◽

Planetary Nebulae ◽

Review Article ◽

The Past ◽

The Subject ◽

Central Stars

Stellar evolution is characterized by fast and slow phases. Usually the periods of rapid change are difficult to follow observationally; but, this does not seem to be the case when passing through the planetary nebula stage. Because of their high intrinsic luminosities and easy identification, it is possible to identify and study these objects and their central stars rather completely. It is quite relevant to discuss these objects at a symposium on white dwarfs since the central stars may be in the immediate progenitor stage before white dwarfs. The actual picture of the evolution of the nuclei has changed rather little in the past few years and is the subject of an earlier review article (O'Dell, 1968) to which the reader is referred.

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Late Stages of Stellar Evolution

Symposium - International Astronomical Union ◽

10.1017/s0074180900228039 ◽

1995 ◽

Vol 166 ◽

pp. 173-180

Author(s):

P. Thejll

Keyword(s):

Stellar Evolution ◽

White Dwarfs ◽

Planetary Nebulae ◽

High Accuracy ◽

Current Understanding ◽

Large Numbers ◽

Hot Subdwarfs ◽

Late Stages ◽

Central Stars

A review is given of the use of high-accuracy astrometry on research on white dwarfs and the hot subdwarfs and central stars of planetary nebulae (CSPN). Predictions are made about the expected impact of HIPPARCOS, and the possible impacts of GAIA and ROEMER. Discovery of large numbers of new white dwarfs is expected, and, for the more distant hot subdwarfs and CSPN, important refinements of our current understanding of these objects. For white dwarfs independent values of mass and radius may be accurate enough to allow new understanding of the internal composition.

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Planetary Nebula Evolution Traced by Distance-Independent Parameters

Symposium - International Astronomical Union ◽

10.1017/s0074180900172134 ◽

1993 ◽

Vol 155 ◽

pp. 480-480

Author(s):

C.Y. Zhang ◽

S. Kwok

Keyword(s):

Physical Properties ◽

Mass Distribution ◽

Planetary Nebula ◽

Strong Support ◽

Planetary Nebulae ◽

Central Star ◽

Evolution Model ◽

The Core ◽

Independent Parameters ◽

Central Stars

Making use of the results from recent infrared and radio surveys of planetary nebulae, we have selected 431 nebulae to form a sample where a number of distance-independent parameters (e.g., Tb, Td, I60μm and IRE) can be constructed. In addition, we also made use of other distance-independent parameters ne and T∗ where recent measurements are available. We have investigated the relationships among these parameters in the context of a coupled evolution model of the nebula and the central star. We find that most of the observed data in fact lie within the area covered by the model tracks, therefore lending strong support to the correctness of the model. Most interestingly, we find that the evolutionary tracks for nebulae with central stars of different core masses can be separated in a Tb-T∗ plane. This implies that the core masses and ages of the central stars can be determined completely independent of distance assumptions. The core masses and ages have been obtained for 302 central stars with previously determined central-star temperatures. We find that the mass distribution of the central stars strongly peaks at 0.6 M⊙, with 66% of the sample having masses <0.64 MM⊙. The luminosities of the central stars are then derived from their positions in the HR diagram according to their core masses and central star temperatures. If this method of mass (and luminosity) determination turns out to be accurate, we can bypass the extremely unreliable estimates for distances, and will be able to derive other physical properties of planetary nebulae.

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