scholarly journals Theoretical and Observational Tests for the Mass Transfer Scenario of Ba II stars

1989 ◽  
Vol 106 ◽  
pp. 223-223
Author(s):  
H.M.J. Boffin
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
Mass Function ◽  
Spectroscopic Binaries ◽  
Red Giants ◽  
Orbital Periods ◽  
Red Giant ◽  
Necessary And Sufficient ◽  
Process Elements ◽  
Spectral Survey

Ba II stars are red giants showing an enhancement of carbon and s-process elements. The elucidation of their nature seems to require a mass transfer, either by wind or Roche lobe overflow, during their past evolution. Were it really the case, all Ba II stars would be binaries with a white dwarf as companion. To better understand the exact role of their binarity, more orbits are definitely needed. They can be obtained by monitoring the radial velocity variations of those stars. However, a quicker way to find new Ba II stars with orbital elements would be to search for their existence among known spectroscopic binaries. This would also crucially test whether mass transfer is a necessary and sufficient condition to explain Ba II stars. If it is indeed the case, then all spectroscopic binaries, made of a giant and a white dwarf, in a reasonable range of periods, would exhibit the Ba II pecularity. However, the discovery of a peculiar giant+main sequence binary system would imply a revision of our ideas about Ba II stars. To this end have we begun a systematic spectral survey of spectroscopic binaries with orbital periods in the range characteristic of known Ba II stars and containing a red giant. The realization that some stars of the catalogue we compiled were already identified as semibariium stars encourages us to pursue our investigation. Coude spectra were taken with the 152 cm telescope, at a dispersion of 12 Å mm−1 . Until now, 2 stars out of a sample of 31 present a slight enhancement of s-process elements (their anomaly being in the range Ba 0.3 to 0.5), and 2 more appear to be good candidates. The study of a larger sample is currently in progress. A discussion of the nature of the companion to the 2 newly discovered semibarium stars is presented on grounds of their mass function and photometric indices.

scholarly journals The Gaia-ESO Survey: detection and characterisation of single-line spectroscopic binaries

2020 ◽  
Vol 635 ◽  
pp. A155 ◽  
Author(s):  
T. Merle ◽  
M. Van der Swaelmen ◽  
S. Van Eck ◽  
A. Jorissen ◽  
R. J. Jackson ◽  
...  
Keyword(s):  
Confidence Level ◽  
Detection Efficiency ◽  
Signal To Noise Ratio ◽  
Mass Function ◽  
Spectroscopic Binaries ◽  
Homogeneous Sample ◽  
Giant Stars ◽  
Formation And Evolution ◽  
Orbital Periods ◽  
Red Giant

Context. Multiple stellar systems play a fundamental role in the formation and evolution of stellar populations in galaxies. Recent and ongoing large ground-based multi-object spectroscopic surveys significantly increase the sample of spectroscopic binaries (SBs) allowing analyses of their statistical properties. Aims. We investigate the repeated spectral observations of the Gaia-ESO Survey internal data release 5 (GES iDR5) to identify and characterise SBs with one visible component (SB1s) in fields covering mainly the discs, the bulge, the CoRot fields, and some stellar clusters and associations. Methods. A statistical χ2-test is performed on spectra of the iDR5 subsample of approximately 43 500 stars characterised by at least two observations and a signal-to-noise ratio larger than three. In the GES iDR5, most stars have four observations generally split into two epochs. A careful estimation of the radial velocity (RV) uncertainties is performed. Our sample of RV variables is cleaned from contamination by pulsation- and/or convection-induced variables using Gaia DR2 parallaxes and photometry. Monte-Carlo simulations using the SB9 catalogue of spectroscopic orbits allow to estimate our detection efficiency and to correct the SB1 rate to evaluate the GES SB1 binary fraction and its relation to effective temperature and metallicity. Results. We find 641 (resp., 803) FGK SB1 candidates at the 5σ (resp., 3σ) level. The maximum RV differences range from 2.2 km s−1 at the 5σ confidence level (1.6 km s−1 at 3σ) to 133 km s−1 (in both cases). Among them a quarter of the primaries are giant stars and can be located as far as 10 kpc. The orbital-period distribution is estimated from the RV standard-deviation distribution and reveals that the detected SB1s probe binaries with log P[d] ⪅ 4. We show that SB1s with dwarf primaries tend to have shorter orbital periods than SB1s with giant primaries. This is consistent with binary interactions removing shorter period systems as the primary ascends the red giant branch. For two systems, tentative orbital solutions with periods of 4 and 6 d are provided. After correcting for detection efficiency, selection biases, and the present-day mass function, we estimate the global GES SB1 fraction to be in the range 7–14% with a typical uncertainty of 4%. A small increase of the SB1 frequency is observed from K- towards F-type stars, in agreement with previous studies. The GES SB1 frequency decreases with metallicity at a rate of (−9 ± 3)% dex−1 in the metallicity range −2.7 ≤ [Fe/H] ≤ +0.6. This anticorrelation is obtained with a confidence level higher than 93% on a homogeneous sample covering spectral types FGK and a large range of metallicities. When the present-day mass function is accounted for, this rate turns to (−4 ± 2)% dex−1 with a confidence level higher than 88%. In addition we provide the variation of the SB1 fraction with metallicity separately for F, G, and K spectral types, as well as for dwarf and giant primaries.

scholarly journals A Statistical Study of Spectroscopic Binaries Containing A Late-Type Giant Star

1989 ◽  
Vol 106 ◽  
pp. 222-222
Author(s):  
H.M.J. Boffin
Keyword(s):  
Mass Transfer ◽  
Statistical Study ◽  
Asymptotic Giant Branch ◽  
Spectroscopic Binaries ◽  
Red Giants ◽  
Late Type ◽  
Giant Star ◽  
Companion Star ◽  
Observational Fact ◽  
Type Giant

Binarity seems to be a feature shared by various classes of Peculiar Red Giants (PRG). This observational fact has led to the general agreement that those stars result from a mass transfer originating from an asymptotic giant branch companion star.

scholarly journals Systematic search for stellar pulsators in the eclipsing binaries observed by Kepler

2019 ◽  
Vol 630 ◽  
pp. A106 ◽  
Author(s):  
Patrick Gaulme ◽  
Joyce A. Guzik
Keyword(s):  
Stellar Evolution ◽  
Percent Level ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Systematic Search ◽  
Red Giants ◽  
Low Mass Stars ◽  
Orbital Periods ◽  
Red Giant ◽  
Stellar Properties

Eclipsing binaries (EBs) are unique targets for measuring precise stellar properties and can be used to constrain stellar evolution models. In particular, it is possible to measure masses and radii of both components of a double-lined spectroscopic EB at the percent level. Since the advent of high-precision photometric space missions (MOST, CoRoT, Kepler, BRITE, TESS), the use of stellar pulsation properties to infer stellar interiors and dynamics constitutes a revolution for studies of low-mass stars. The Kepler mission has led to the discovery of thousands of classical pulsators such as δ Scuti and solar-like oscillators (main sequence and evolved), but also almost 3000 EBs with orbital periods shorter than 1100 days. We report the first systematic search for stellar pulsators in the entire Kepler EB catalog. The focus is mainly aimed at discovering δ Scuti, γ Doradus, red giant, and tidally excited pulsators. We developed a data inspection tool (DIT) that automatically produces a series of plots from the Kepler light curves that allows us to visually identify whether stellar oscillations are present in a given time series. We applied the DIT to the whole Kepler EB database and identified 303 systems whose light curves display oscillations, including 163 new discoveries. A total of 149 stars are flagged as δ Scuti (100 from this paper), 115 as γ Doradus (69 new), 85 as red giants (27 new), and 59 as tidally excited oscillators (29 new). There is some overlap among these groups, as some display several types of oscillations. Despite the likelihood that many of these systems are false positives, for example, when an EB light curve is blended with a pulsator, this catalog gathers a vast sample of systems that are valuable for a better understanding of stellar evolution.

scholarly journals A Gentle Process for the Formation of Algols

1989 ◽  
Vol 107 ◽  
pp. 369-369
Author(s):  
C. A. Tout ◽  
P. P. Eggleton
Keyword(s):  
Mass Transfer ◽  
Magnetic Fields ◽  
Mass Loss ◽  
White Dwarf ◽  
Binary Systems ◽  
Roche Lobe ◽  
Close Binary ◽  
Red Giants ◽  
Convective Envelope ◽  
Mass Ratios

AbstractThis work is concerned with binary systems that we call ‘moderately close’. These are systems in which the primary (by which we mean the initially more massive star) fills its Roche lobe when it is on the giant branch with a deep convective envelope but before helium ignition (late case B). We find that if the mass ratio q(= M1/M2) < qCrit = 0.7 when the primary fills its Roche lobe positive feedback will lead to a rapid hydrodynamic phase of mass transfer which will probably lead to common envelope evolution and thence to either coalescence or possibly to a close binary in a planetary nebula. Although most Algols have probably filled their Roche lobes before evolving off the main-sequence we find that some could not have and are therefore ‘moderately close’. Since rapid overflow is unlikely to lead to an Algol-like system there must be some way of avoiding it. The most likely possibility is that the primary can lose sufficient mass to reduce q below qcrit before overflow begins. Ordinary mass loss rates are insufficient but evidence that enhanced mass loss does take place is provided by RS CVn systems that have inverted mass ratios but have not yet begun mass transfer. We postulate that the cause of enhanced mass loss lies in the heating of the corona by by magnetic fields maintained by an α-ω dynamo which is enhanced by tidal effects associated with corotation. In order to model the the effects of enhanced mass loss we ignore the details and adopt an empirical approach calibrating a simple formula with the RS CVn system Z Her. Using further empirical relations (deduced from detailed stellar models) that describe the evolution of red giants we have investigated the effect on a large number of systems of various initial mass ratios and periods. These are notable in that some systems can now enter a much gentler Algol-like overflow phase and others are prevented from transferring mass altogether. We have also investigated the effects of enhanced angular momentum loss induced by corotation of the wind in the strong magnetic fields and consider this in relation to observed period changes. We find that a typical ‘moderately close’ Algol-like system evolves through an RS CVn like system and then possibly a symbiotic state before becoming an Algol and then goes on through a red giant-white dwarf state which may become symbiotic before ending up as a double white dwarf system in either a close or wide orbit depending on how much mass is lost before the secondary fills its Roche lobe.

scholarly journals Rotation in sdB stars as revealed by stellar oscillations

2018 ◽  
Vol 27 (1) ◽  
pp. 112-119 ◽  
Author(s):  
Stephane Charpinet ◽  
Noemi Giammichele ◽  
Weikai Zong ◽  
Valérie Van Grootel ◽  
Pierre Brassard ◽  
...  
Keyword(s):  
Internal Rotation ◽  
White Dwarf ◽  
Rotation Rate ◽  
Slow Rotation ◽  
Red Giants ◽  
Stellar Oscillations ◽  
Sdb Stars ◽  
White Dwarf Stars ◽  
Red Clump ◽  
Red Giant

Abstract An interesting opportunity offered by the detection of stellar oscillations is the possibility to infer the internal rotation rate of a star through the so-called rotational splittings. Such seismic measurements remained rather scarce for hot B subdwarf (sdB) stars until the advent of space observations with the Kepler spacecraft. Nowadays, however, a number of rotation measurements have become available, offering a glimpse on the global rotational properties of sdB stars. Here, we briefly discuss what asteroseismology starts to reveal on the rotation rate of these stars. We also make connections with the internal rotation of red-giant and white-dwarf stars. In particular, we show that the very slow rotation rates derived for single sdB stars, and their similarities with the dynamical properties of the cores of red-clump stars, strongly suggest that they evolved from red-giants rather than merger events.We also point out that no more angular momentum seems to be lost by stellar cores throughout the helium burning phase until the cooling white-dwarf stage, indicating that all the braking occurs before, most likely during red-giant branch evolution.

scholarly journals Binary S and MS Stars

1992 ◽  
Vol 151 ◽  
pp. 157-166
Author(s):  
Hollis R. Johnson
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
Infrared Radiation ◽  
Large Fraction ◽  
Circumstellar Dust ◽  
Agb Stars ◽  
Hot Gas ◽  
Popular View ◽  
Process Elements ◽  
Gas Cloud

We assemble and discuss evidence for binarity in S and MS stars - stars that are enriched in s-process elements. A popular view is that Tc-deficient S and MS stars are not thermally pulsing AGB stars but are mass-transfer binaries. We describe several methods used to test this hypothesis through a search for the putative white-dwarf companion: (1) periodic radial velocity variations, (2) direct observation of the hot companions with IUE, (3) evidence of a hot gas cloud (hotter than a chromosphere) in the system, and (4) evidence of circumstellar dust as revealed through infrared radiation. Results of these methods are compared. All evidence supports the idea that Tc-deficient S and MS stars are mass-transfer binaries, and a large fraction appear to be interactive.

scholarly journals Barium and related stars, and their white-dwarf companions

2019 ◽  
Vol 626 ◽  
pp. A127 ◽  
Author(s):  
A. Jorissen ◽  
H. M. J. Boffin ◽  
D. Karinkuzhi ◽  
S. Van Eck ◽  
A. Escorza ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Mass Distribution ◽  
White Dwarf ◽  
Binary Systems ◽  
Asymptotic Giant Branch ◽  
Spectroscopic Binaries ◽  
High Mass ◽  
Initial Mass ◽  
Mass Ratio ◽  
Orbital Elements

Context. Barium and S stars without technetium are red giants and are suspected of being members of binary systems due to their overabundances in heavy elements. These elements are produced by the s-process of nucleosynthesis, despite the stars not being evolved enough to be able to activate the s-process in their interiors. A companion formerly on the asymptotic giant branch (now a white dwarf) is supposed to be responsible for the barium- and S-star enrichment in s-process elements through mass transfer. Aims. This paper provides both long-period and revised orbits for barium and S stars, adding to previously published orbits. The sample of barium stars with strong anomalies (i.e., those classified as Ba3, Ba4, or Ba5 in the Warner scale) comprises all known stars of that kind, and in that sense forms a complete sample that allows us to investigate several orbital properties of these post-mass-transfer binaries in an unbiased way. Methods. Orbital elements are derived from radial velocities collected from a long-term radial-velocity monitoring campaign performed with the HERMES spectrograph mounted on the Mercator 1.2 m telescope. These new measurements were combined with older, CORAVEL measurements. With the aim of investigating possible correlations between orbital properties and abundances, we also collected a set of abundances for barium stars with orbital elements that is as homogeneous as possible. When unavailable in the literature, abundances were derived from high-resolution HERMES spectra. Results. We find orbital motion for all barium and extrinsic S stars monitored (except for the mild barium star HD 95345). We obtain the longest period known so far for a spectroscopic binary involving an S star, namely 57 Peg with a period of the order of 100−500 yr. We present the mass distribution for the barium stars, which ranges from 1 to 3 M⊙, with a tail extending up to 5 M⊙ in the case of mild barium stars. This high-mass tail is mostly comprised of high-metallicity objects ([Fe/H] ≥ −0.1). The distribution of the companion masses was extracted from the barium-star mass distribution combined with the finding that Q ≡ f(MBa,MWD)/sin3 i = MWD3/(MBa + MWD)2 is peaked at 0.057 ± 0.009 and 0.036 ± 0.027 M⊙ for strong and mild barium stars, respectively (f(MBa, MWD) is the mass function obtained from the orbital elements of spectroscopic binaries with one observable spectrum). Mass functions are compatible with WD companions whose masses range from 0.5 to 1 M⊙. Strong barium stars have a tendency to be found in systems with shorter periods than mild barium stars, although this correlation is rather lose, with metallicity and WD mass also playing a role. Using the initial–final mass relationship established for field WDs, we derived the distribution of the mass ratio q′=MAGB, ini/MBa (where MAGB, ini is the WD progenitor initial mass, i.e., the mass of the former primary component of the system) which is a proxy for the initial mass ratio (the less mass the barium star has accreted, the better the proxy). It appears that the distribution of q′ is highly nonuniform, and significantly different for mild and strong barium stars, the latter being characterized by values mostly in excess of 1.4, whereas mild barium stars occupy the range 1−1.4. Conclusions. The orbital properties presented in this paper pave the way for a comparison with binary-evolution and nucleosynthesis models, which should account for the various significant correlations found between abundances and dynamical parameters (e.g. between MBa on one hand and MWD, [Fe/H], and [s/Fe] on the other hand, between q′ and [s/Fe], between P and e, and between P and [s/Fe] altogether).

scholarly journals The formation of long-period eccentric binaries with a helium white dwarf companion

2019 ◽  
Vol 82 ◽  
pp. 107-118
Author(s):  
L. Siess
Keyword(s):  
Mass Transfer ◽  
Mass Loss ◽  
White Dwarf ◽  
Binary Star ◽  
Roche Lobe ◽  
High Eccentricity ◽  
Evolutionary Path ◽  
Orbital Parameters ◽  
Long Period ◽  
Red Giant

The recent discovery of long-period eccentric binaries hosting a He-white dwarf has been a challenge for binary-star modelling. Based on accurate determinations of the stellar and orbital parameters for IP Eri, a K0 + He-WD system, we propose an evolutionary path that is able to explain the observational properties of this system and, in particular, to account for its high eccentricity (0.25). Our scenario invokes an enhanced-wind mass loss on the first red giant branch in order to avoid mass transfer by Roche-lobe overflow, where tides systematically circularize the orbit.

scholarly journals Influence of the initial orbital period and accretion efficiency on the low-mass binary evolution

2021 ◽  
pp. 25-30
Author(s):  
J. Petrovic
Keyword(s):  
Mass Transfer ◽  
Orbital Period ◽  
White Dwarf ◽  
Binary Systems ◽  
Evolutionary Models ◽  
Stable Case ◽  
Long Period ◽  
Low Mass ◽  
Orbital Periods ◽  
Binary Evolution

This paper presents detailed evolutionary models of low-mass binary systems (1.25 + 1 M?) with initial orbital periods of 10, 50 and 100 days and accretion efficiency of 10%, 20%, 50%, and a conservative assumption. All models are calculated with the MESA (Modules for Experiments in Stellar Astrophysics) evolutionary code. We show that such binary systems can evolve via a stable Case B mass transfer into long period helium white dwarf systems.

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