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

2019 ◽  
Vol 626 ◽  
pp. A128 ◽  
Author(s):  
A. Escorza ◽  
D. Karinkuzhi ◽  
A. Jorissen ◽  
L. Siess ◽  
H. Van Winckel ◽  
...  
Keyword(s):  
Radial Velocity ◽  
White Dwarf ◽  
Main Sequence ◽  
Mass Function ◽  
Orbital Evolution ◽  
Asymptotic Giant Branch ◽  
Second Phase ◽  
Evolutionary Models ◽  
Orbital Inclination ◽  
Orbital Parameters

Barium (Ba) dwarfs and CH subgiants are the less evolved analogues of Ba and CH giants. They are F- to G-type main-sequence stars polluted with heavy elements by their binary companions when the companion was on the asymptotic giant branch (AGB). This companion is now a white dwarf that in most cases cannot be directly detected. We present a large systematic study of 60 objects classified as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL and CORALIE, we determine the orbital parameters of 27 systems. We also derive their masses by comparing their location in the Hertzsprung–Russell diagram with evolutionary models. We confirm that Ba dwarfs and CH subgiants are not at different evolutionary stages, and that they have similar metallicities, despite their different names. Additionally, Ba giants appear significantly more massive than their main-sequence analogues. This is likely due to observational biases against the detection of hotter main-sequence post-mass-transfer objects. Combining our spectroscopic orbits with the HIPPARCOS astrometric data, we derive the orbital inclination and the mass of the WD companion for four systems. Since this cannot be done for all systems in our sample yet (but should be possible with upcoming Gaia data releases), we also analyse the mass-function distribution of our binaries. We can model this distribution with very narrow mass distributions for the two components and random orbital orientations on the sky. Finally, based on BINSTAR evolutionary models, we suggest that the orbital evolution of low-mass Ba systems can be affected by a second phase of interactions along the red giant branch of the Ba star, which impact the eccentricities and periods of the giants.

scholarly journals Fluorescence and Chromospheric Activity of V471 Tau

2002 ◽  
Vol 187 ◽  
pp. 167-172
Author(s):  
T.R. Vaccaro ◽  
R.E. Wilson
Keyword(s):  
Light Curve ◽  
Radial Velocity ◽  
Orbital Period ◽  
White Dwarf ◽  
Binary Star ◽  
Star Model ◽  
Orbital Inclination ◽  
Orbital Parameters ◽  
Maximum Emission ◽  
Chromospheric Activity

AbstractThe red dwarf + white dwarf eclipsing binary V471 Tau shows a variable Hα feature that varies from absorption during eclipse to maximum emission during white dwarf transit. In 1998 we obtained simultaneous BVRI photometry and Hα spectroscopy, with thorough phase coverage of the 12.5 hour orbital period. A binary star model was used with our light curve, radial velocity, and Hα data to refine stellar and orbital parameters. Combined absorption-emission profiles were generated by the model and fit to the observations, yielding a red star radius of 0.94R⊙. Orbital inclination 78° is required with this size and other known parameters. The model includes three spots 1,000 K cooler than the surrounding photosphere. The variable Hα profile was modeled as a chromospheric fluorescing region (essentially on the surface of the red star) centered at the substellar point. Additional emission seen outside our modeled profiles may be large co-rotating prominences that complicate the picture.

scholarly journals Binary evolution along the red giant branch with BINSTAR: The barium star perspective

2020 ◽  
Vol 639 ◽  
pp. A24 ◽  
Author(s):  
A. Escorza ◽  
L. Siess ◽  
H. Van Winckel ◽  
A. Jorissen
Keyword(s):  
White Dwarf ◽  
Binary Systems ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
Binary Interaction ◽  
Second Phase ◽  
Capture Process ◽  
Short Period ◽  
Binary Evolution ◽  
Red Giant

Barium (Ba), CH, and extrinsic or Tc-poor S-type stars are evolved low- and intermediate-mass stars that show enhancement of slow-neutron-capture-process elements on their surface, an indication of mass accretion from a former asymptotic giant branch companion, which is now a white dwarf (WD). Ba and CH stars can be found in the main-sequence (MS), the sub-giant, and the giant phase, while extrinsic S-type stars populate the giant branches only. As these polluted stars evolve, they might be involved in a second phase of interaction with their now white dwarf companion. In this paper, we consider systems composed of a main-sequence Ba star and a WD companion when the former evolves along the red giant branch (RGB). We want to determine if the orbital properties of the known population of Ba, CH, and S giants can be inferred from the evolution of their suspected dwarf progenitors. For this purpose, we used the BINSTAR binary evolution code and model MS+WD binary systems, considering different binary interaction mechanisms, such as a tidally enhanced wind mass loss, and a reduced circularisation efficiency. To explore their impact on the second RGB ascent, we compared the modelled orbits with the observed period and eccentricity distributions of Ba and related giants. We show that, independently of the considered mechanism, there is a strong period cut-off below which core-He burning stars should not be found in binary systems with a WD companion. This limit is shorter for more massive RGB stars and for more metal-poor systems. However, we still find a few low-mass short-period giant systems that are difficult to explain with our models, as well as two systems with very high eccentricities.

scholarly journals Classical Novae – Before and After Outburst

1988 ◽  
Vol 108 ◽  
pp. 226-231
Author(s):  
Mario Livio
Keyword(s):  
White Dwarf ◽  
Main Sequence ◽  
Orbital Parameters ◽  
Classical Novae ◽  
Classical Nova ◽  
Before And After ◽  
Low Mass ◽  
Orbital Periods ◽  
Thermonuclear Runaway ◽  
Nova Outburst

Classical nova (CN) and dwarf nova (DN) systems have the same binary components (a low-mass main sequence star and a white dwarf) and the same orbital periods. An important question that therefore arises is: are these systems really different ? (and if so, what is the fundamental difference ?) or, are these the same systems, metamorphosing from one class to the other ?The first thing to note in this respect is that the white dwarfs in DN systems are believed to accrete continuously (both at quiescence and during eruptions). At the same time, both analytic (e.g. Fujimoto 1982) and numerical calculations show, that when sufficient mass accumulates on the white dwarf, a thermonuclear runaway (TNR) is obtained and a nova outburst ensues (see e.g. reviews by Gallagher and Starrfield 1978, Truran 1982). It is thus only natural, to ask the question, is the fact that we have not seen a DN undergo a CN outburst (in about 50 years of almost complete coverage) consistent with observations of DN systems ? In an attempt to answer this question, we have calculated the probability for a nova outburst not to occur (in 50 years) in 86 DN systems (for which at least some of the orbital parameters are known).

scholarly journals Two new double-lined spectroscopic binary white dwarfs

2020 ◽  
Vol 493 (2) ◽  
pp. 2805-2816 ◽  
Author(s):  
Mukremin Kilic ◽  
A Bédard ◽  
P Bergeron ◽  
Alekzander Kosakowski
Keyword(s):  
Radial Velocity ◽  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Mass Ratio ◽  
Orbital Parameters ◽  
Long Period ◽  
Spectroscopic Binary ◽  
Velocity Variations ◽  
Period System

ABSTRACT We present radial velocity observations of four binary white dwarf candidates identified through their overluminosity. We identify two new double-lined spectroscopic binary systems, WD 0311–649 and WD 1606+422, and constrain their orbital parameters. WD 0311–649 is a 17.7 h period system with a mass ratio of 1.44 ± 0.06 and WD 1606+422 is a 20.1 h period system with a mass ratio of 1.33 ± 0.03. An additional object, WD 1447–190, is a 43 h period single-lined white dwarf binary, whereas WD 1418–088 does not show any significant velocity variations over time-scales ranging from minutes to decades. We present an overview of the 14 overluminous white dwarfs that were identified by Bédard et al., and find the fraction of double- and single-lined systems to be both 31 per cent. However, an additional 31 per cent of these overluminous white dwarfs do not show any significant radial velocity variations. We demonstrate that these must be in long-period binaries that may be resolved by Gaia astrometry. We also discuss the overabundance of single low-mass white dwarfs identified in the SPY survey, and suggest that some of those systems are also likely long-period binary systems of more massive white dwarfs.

scholarly journals The eccentric behaviour of windy binary stars

2019 ◽  
Vol 629 ◽  
pp. A103 ◽  
Author(s):  
M. I. Saladino ◽  
O. R. Pols
Keyword(s):  
Mass Transfer ◽  
Binary Stars ◽  
Numerical Models ◽  
Orbital Evolution ◽  
Small Sample ◽  
Asymptotic Giant Branch ◽  
Tidal Effects ◽  
Orbital Parameters ◽  
Orbital Periods ◽  
The Impact

Carbon-enhanced metal-poor stars, CH stars, barium stars, and extrinsic S stars, among other classes of chemically peculiar stars, are thought to be the products of the interaction of low- and intermediate-mass binaries, which occurred when the most evolved star was in the asymptotic giant branch (AGB) phase. Binary evolution models predict that because of the large sizes of AGB stars, if the initial orbital periods of such systems are shorter than a few thousand days, their orbits should have circularised due to tidal effects. However, observations of the progeny of AGB binary stars show that many of these objects have substantial eccentricities, up to e ≈ 0.9. In this work we explore the impact of wind mass transfer on the orbital parameters of AGB binary stars by performing numerical simulations in which the AGB wind is modelled using a hydrodynamical code and the dynamics of the stars is evolved using an N-body code. We find that in most models the effect of wind mass transfer contributes to the circularisation of the orbit, but on longer timescales than tidal circularisation if e ≲ 0.4. For relatively low initial wind velocities and pseudo-synchronisation of the donor star, we find a structure resembling wind Roche-lobe overflow as the stars approach periastron. In this case, the interaction between the gas and the star is stronger than when the initial wind velocity is high and the orbit shrinks while the eccentricity decreases. In one of our models wind interaction is found to pump the eccentricity of the orbit on a similar timescale as tidal circularisation. However, since the orbit of this model is shrinking tidal effects will become stronger during the evolution of the system. Although our study is based on a small sample of models, it offers some insight into the orbital evolution of eccentric binary stars interacting via winds. A larger grid of numerical models for different binary parameters is needed to test if a regime exists where hydrodynamical eccentricity pumping can effectively counteract tidal circularisation, and if this can explain the puzzling eccentricities of the descendants of AGB binaries.

scholarly journals Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades

2021 ◽  
Vol 163 (1) ◽  
pp. 34
Author(s):  
Philip S. Muirhead ◽  
Jason Nordhaus ◽  
Maria R. Drout
Keyword(s):  
White Dwarf ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Main Sequence Star ◽  
Velocity Measurements ◽  
Single Star ◽  
Orbital Parameters ◽  
Common Envelope ◽  
Star Evolution ◽  
First Time

Abstract V471 Tau is a post-common-envelope binary consisting of an eclipsing DA white dwarf and a K-type main-sequence star in the Hyades star cluster. We analyzed publicly available photometry and spectroscopy of V471 Tau to revise the stellar and orbital parameters of the system. We used archival K2 photometry, archival Hubble Space Telescope spectroscopy, and published radial-velocity measurements of the K-type star. Employing Gaussian processes to fit for rotational modulation of the system flux by the main-sequence star, we recovered the transits of the white dwarf in front of the main-sequence star for the first time. The transits are shallower than would be expected from purely geometric occultations owing to gravitational microlensing during transit, which places an additional constraint on the white-dwarf mass. Our revised mass and radius for the main-sequence star is consistent with single-star evolutionary models given the age and metallicity of the Hyades. However, as noted previously in the literature, the white dwarf is too massive and too hot to be the result of single-star evolution given the age of the Hyades, and may be the product of a merger scenario. We independently estimate the conditions of the system at the time of common envelope that would result in the measured orbital parameters today.

Star-Disc Interactions and Binary Formation

1992 ◽  
Vol 135 ◽  
pp. 176-184
Author(s):  
Cathie Clarke
Keyword(s):  
Mass Exchange ◽  
Main Sequence ◽  
Orbital Evolution ◽  
Body System ◽  
Tidal Effects ◽  
Orbital Parameters ◽  
Binary Formation

By the time a binary arrives on the main sequence, its dynamics have essentially become those of a simple two-body system, so that its orbital parameters are constants of the motion thereafter. This statement of course needs to be modified under several circumstances, such as where tidal effects, mass exchange or interactions with field stars come into play. For the majority of binaries, however, orbital evolution is all but over by the main sequence. Therefore, in order to explain the distribution of binary orbital parameters one has to look to earlier times (prior to 107 years) when the more complicated dynamics can drive the orbital evolution that establishes these parameters.

scholarly journals First stellar spectroscopy in Leo P

2019 ◽  
Vol 622 ◽  
pp. A129 ◽  
Author(s):  
C. J. Evans ◽  
N. Castro ◽  
O. A. Gonzalez ◽  
M. Garcia ◽  
N. Bastian ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Evolutionary Models ◽  
Low Oxygen ◽  
Stellar Spectroscopy ◽  
Giant Branch Stars

We present the first stellar spectroscopy in the low-luminosity (MV ∼ −9.3 mag), dwarf galaxy Leo P. Its significantly low oxygen abundance (3% solar) and relative proximity (∼1.6 Mpc) make it a unique galaxy in which to investigate the properties of massive stars with near-primordial compositions akin to those in the early Universe. From our VLT-MUSE spectroscopy we find the first direct evidence for an O-type star in the prominent H II region, providing an important test case to investigate the potential environmental dependence of the upper end of the initial mass function in the dwarf galaxy regime. We classify 14 further sources as massive stars (and 17 more as candidate massive stars), most likely B-type objects. From comparisons with published evolutionary models we argue that the absolute visual magnitudes of massive stars in very metal-poor systems such as Leo P and I Zw 18 may be fainter by ∼0.5 mag compared to Galactic stars. We also present spectroscopy of two carbon stars identified previously as candidate asymptotic-giant-branch stars. Two of three further candidate asymptotic-giant-branch stars display Ca II absorption, confirming them as cool, evolved stars; we also recover Ca II absorption in the stacked data of the next brightest 16 stars in the upper red giant branch. These discoveries will provide targets for future observations to investigate the physical properties of these objects and to calibrate evolutionary models of luminous stars at such low metallicity. The MUSE data also reveal two 100 pc-scale ring structures in Hα emission, with the H II region located on the northern edge of the southern ring. Lastly, we report serendipitous observations of 20 galaxies, with redshifts ranging from z = 0.39, to a close pair of star-forming galaxies at z = 2.5.

HD 226766: a hierarchical SB3 system with two twin Am stars

2019 ◽  
Vol 487 (1) ◽  
pp. 919-927 ◽  
Author(s):  
G Catanzaro ◽  
M Gangi ◽  
M Giarrusso ◽  
M Munari ◽  
F Leone
Keyword(s):  
Chemical Composition ◽  
Main Sequence ◽  
Point Of View ◽  
Eccentric Orbit ◽  
Orbital Inclination ◽  
Orbital Parameters ◽  
Component C ◽  
Effective Temperatures ◽  
Chemical Anomalies ◽  
The Masses

ABSTRACT In this paper, we present a detailed revision of the orbital parameters and the first quantitative abundance analysis of the spectroscopic triple system HD 226766. By means of a simultaneous fit of the radial velocities of all the three components, we derived precise orbital parameters for the system, in particular inner pair has P(d)  =  31.9187 ± 0.0001, e  =  0.28 ± 0.01, and MA/MB  = 1.03 ± 0.03, while the C component orbits around the inner pair with a period of P(d)  =  1615 ± 59 in a very eccentric orbit (e  =  0.54 ± 0.11). From the fit of the Hβ and Hα profiles, we determined the effective temperatures and surface gravities of each component of the inner pair: Teff  =  8600 ± 500 K and log g  =  3.8 ± 0.2 for HD 226766 A and Teff  =  8500 ± 400 K and log g  =  4.0 ± 0.2 for HD 226766 B. In the hypothesis that component C is a main sequence star (log g  =  4.0) we derived Teff  =  8000 ± 500 K. Rotational velocities have been estimated by modeling the profiles of metallic lines: v sin i  =  13 ± 1 km s−1 for inner pair and v sin i  =  150 ± 20 km s−1 for the C component. We find that the inner pair is heterogeneous from the point of view of the chemical composition: both stars are very similar and show chemical anomalies typical of Am stars. With some hypothesis about the masses of the components, we estimated the orbital inclination angle for the inner binary, i = (47 ± 1)○, and for the outer orbit, i = (54 ± 19)○.

scholarly journals Red Spectroscopy of IP Pegasi

1987 ◽  
Vol 93 ◽  
pp. 145-149
Author(s):  
J.S. Martin ◽  
D.H.P. Jones ◽  
R.C Smith
Keyword(s):  
Radial Velocity ◽  
Cross Correlation ◽  
Main Sequence ◽  
Mass Function ◽  
Velocity Curve ◽  
Absorption Lines ◽  
Radial Velocity Curve ◽  
Time Resolved ◽  
Time Resolved Spectroscopy ◽  
Dwarf Nova

AbstractTime resolved spectroscopy of the dwarf nova IP Pegasi in the range λλ 7670–8320Å shows absorption lines originating from the cool secondary. A radial velocity curve for this component has been derived by cross-correlation with a normal M star. The curve has semi-amplitude K2 = 288.3 ± 4 km s−1, and is slightly distorted. This distortion is equivalent to an orbit with an apparent eccentricity of 0.075 ± 0.024. The mass function of the primary is 0.394 ± 0.016M⊙. From this we derive constraints on the component masses of 0.62 < M1 < 1.14M⊙ and 0.17 < M2 < 0.71M⊙. The red star has a radius in the range 0.32 < R2 < 0.51R⊙ and is probably on the main sequence.

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