scholarly journals Low Mass White Dwarfs in Binaries

1996 ◽  
Vol 158 ◽  
pp. 465-468
Author(s):  
T. R. Marsh ◽  
V. S. Dhillon ◽  
S. R. Duck
Keyword(s):  
Binary Stars ◽  
White Dwarfs ◽  
Close Binaries ◽  
Single Star ◽  
Star Evolution ◽  
Short Period ◽  
The Galaxy ◽  
Low Mass ◽  
Binary Evolution

The lowest mass white dwarfs that can have been produced by single star evolution in the lifetime of the Galaxy have masses of about 0.53 M⊙. There are however several white dwarfs known with significantly lower masses. Evolution in a binary provides a straightforward explanation as the star can lose its envelope before ever burning helium. The products are expected to be short-period binary stars. To test this we have looked at 15 such stars and have found that 8 of them are close binaries. Thus binary evolution does have a major role in the formation of low-mass white dwarfs. We discuss whether the non-detections could also be binary stars.

scholarly journals A Limit on the Space Density of Short-Period Binary White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 492-497
Author(s):  
Edward L. Robinson ◽  
Allen W. Shafter
Keyword(s):  
Orbital Period ◽  
Binary Stars ◽  
White Dwarfs ◽  
Main Sequence ◽  
Close Binaries ◽  
Main Sequence Stars ◽  
Space Density ◽  
Short Period ◽  
Hot Subdwarfs ◽  
Orbital Periods

We infer that detached binary white dwarfs with orbital periods of a few hours exist because we observe both their progenitors and their descendents. The binary LB 3459 has an orbital period of 6.3 hr and contains a pair of hot subdwarfs that will eventually cool to become white dwarfs (Kilkenny, Hill, and Penfold 1981). L870-2 is a pair of white dwarfs and, given enough time, its 1.55 d orbital period will decay to shorter periods (Saffer, Liebert, and Olszewski 1988). GP Com, AM CVn, V803 Cen, and PG1346+082 are interacting binary white dwarfs with orbital periods between 1051 s for AM CVn and 46.5 min for GP Com (Nather, Robinson, and Stover 1981; Solheim et al. 1984; Wood et al. 1987; O’Donoghue and Kilkenny 1988). These ultrashort period systems must be descendents of detached pairs of white dwarfs. We also expect short-period binary white dwarfs to exist for theoretical reasons. All calculations of the evolution of binary stars show that main-sequence binaries can evolve to binary white dwarfs (e.g., Iben and Tutukov 1984). Among Population I stars, 1/2 to 2/3 of all main-sequence stars are binaries and about 20% of these binaries should become double white dwarfs with short orbital periods (Abt 1983, Iben and Tutukov 1986). Thus, about 1/10 of all white dwarfs could be close binaries (Paczynski 1985). Nevertheless, no detached binary white dwarfs with extremely short periods have yet been found.

scholarly journals Asteroseismological Probing of the Thermal Evolution of White Dwarf Stars

1992 ◽  
Vol 9 ◽  
pp. 643-645
Author(s):  
G. Fontaine ◽  
F. Wesemael
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Thermal Evolution ◽  
Sequence Evolution ◽  
Helium Burning ◽  
Dwarf Stars ◽  
White Dwarf Stars ◽  
The Galaxy ◽  
Low Mass

AbstractIt is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of helium burning, mostly carbon and oxygen. The exact proportions of C and 0 are unknown because of uncertainties in the nuclear rates of helium burning.

scholarly journals Close-In Substellar Companions and the Formation of sdB-Type Close Binary Stars

2015 ◽  
Vol 2 (1) ◽  
pp. 183-187 ◽  
Author(s):  
L. Y. Zhu ◽  
S. B. Qian ◽  
E.-G. Zhao ◽  
E. Fernández Lajús ◽  
Z.-T. Han
Keyword(s):  
Binary Stars ◽  
Eclipsing Binaries ◽  
Close Binary ◽  
Close Binaries ◽  
Close Binary Stars ◽  
Cataclysmic Binaries ◽  
Low Mass ◽  
Substellar Companions ◽  
Orbital Periods

The sdB-type close binaries are believed to have experienced a common-envelope phase and may evolve into cataclysmic binaries (CVs). About 10% of all known sdB binaries are eclipsing binaries consisting of very hot subdwarf primaries and low-mass companions with short orbital periods. The eclipse profiles of these systems are very narrow and deep, which benefits the determination of high precise eclipsing times and makes the detection of small and close-in tertiary bodies possible. Since 2006 we have monitored some sdB-type eclipsing binaries to search for the close-in substellar companions by analyzing the light travel time effect. Here some progresses of the program are reviewed and the formation of sdB-type binary is discussed.

scholarly journals Case AD, AR, and AS binary evolution and their possible connections with W UMa binaries

2019 ◽  
Vol 492 (2) ◽  
pp. 2731-2738 ◽  
Author(s):  
Dengkai Jiang
Keyword(s):  
Parameter Spaces ◽  
Short Period ◽  
Contact Binaries ◽  
Low Mass ◽  
Orbital Periods ◽  
The Difference ◽  
Binary Evolution ◽  
Detached Binaries ◽  
Period Limit ◽  
The Moment

ABSTRACT Close detached binaries were theoretically predicted to evolve into contact by three subtypes of case A binary evolution, cases AD, AR, and AS, which correspond to the formation of contact during dynamic-, thermal-, and nuclear-time-scale mass transfer phases, respectively. It is unclear, however, what is the difference between contact binaries in these subtypes, and whether all of these subtypes can account for the formation of observed W Ursae Majoris (W UMa) binaries. Using Eggleton’s stellar evolution code with the non-conservative assumption, I obtained the low-mass contact binaries produced by cases AD, AR, and AS at the moment of contact and their parameter spaces. The results support that the progenitors of low-mass contact binaries are detached binaries with orbital periods shorter than $\sim 2\!-\!5\,$ d, and their borderlines depend strongly on the primary mass. In addition, the period–colour relations for cases AR and AS can be in better agreement with that for observed W UMa candidates, but case AD shows a significantly worse agreement. Moreover, cases AR and AS can produce a short-period limit (corresponding to a low-mass limit) at almost any age, e.g. from young age ($\sim 0.2\,$ Gyr) to old age ($\sim 13\,$ Gyr), agreeing with observed W UMa binaries in star clusters, but no such limit occurs for case AD at any age. These results support that cases AR and AS, as opposed to case AD, can lead to W UMa binaries (including young W UMa binaries).

scholarly journals Spectroscopy of Overluminous Cepheids in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 223-224
Author(s):  
Horace A. Smith ◽  
Leo Connolly
Keyword(s):  
Globular Cluster ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Small Magellanic Cloud ◽  
Single Star ◽  
Rr Lyrae ◽  
Short Period ◽  
The Galaxy

The Small Magellanic Cloud is known to contain types of short period Cepheid variable stars not yet discovered in either the Large Magellanic Cloud or, with the exception of a single star, in the Galaxy. These variables can be divided into two categories: anomalous Cepheids and Wesselink-Shuttleworth (WS) stars. The former, which have also been found in dwarf spheroidal systems and in the globular cluster NGC 5466, have periods of 0.4–3 days, but average 0.7–1.0 mag. brighter than RR Lyrae and BL Her stars of equal period. The stars we call WS stars have periods less than about 1.1 day and, at MV = −1 to −2, are brighter than anomalous Cepheids of equal period.

scholarly journals Gaia Data Release 2 catalogue of extremely low-mass white dwarf candidates

2019 ◽  
Vol 488 (2) ◽  
pp. 2892-2903 ◽  
Author(s):  
Ingrid Pelisoli ◽  
Joris Vos
Keyword(s):  
White Dwarf ◽  
Theoretical Models ◽  
Dwarf Stars ◽  
Single Star ◽  
Common Envelope ◽  
White Dwarf Stars ◽  
Final Sample ◽  
Data Release ◽  
Low Mass ◽  
Binary Evolution

ABSTRACT Extremely low-mass white dwarf stars (ELMs) are M < 0.3 M⊙ helium-core white dwarfs born either as a result of a common-envelope phase or after a stable Roche lobe overflow episode in a multiple system. The Universe is not old enough for ELMs to have formed through single-star evolution channels. As remnants of binary evolution, ELMs can shed light onto the poorly understood phase of common-envelope evolution and provide constraints to the physics of mass accretion. Most known ELMs will merge in less than a Hubble time, providing an important contribution to the signal to be detected by upcoming space-based gravitational wave detectors. There are currently less than 150 known ELMs; most were selected by colour, focusing on hot objects, in a magnitude-limited survey of the Northern hemisphere only. Recent theoretical models have predicted a much larger space density for ELMs than estimated observationally based on this limited sample. In order to perform meaningful comparisons with theoretical models and test their predictions, a larger well-defined sample is required. In this work, we present a catalogue of ELM candidates selected from the second data release of Gaia (DR2). We have used predictions from theoretical models and analysed the properties of the known sample to map the space spanned by ELMs in the Gaia Hertzsprung–Russell diagram. Defining a set of colour cuts and quality flags, we have obtained a final sample of 5762 ELM candidates down to Teff ≈ 5000 K.

scholarly journals SNIa Diversity: Theory and Diagnostics

1996 ◽  
Vol 145 ◽  
pp. 69-76
Author(s):  
R. Canal ◽  
P. Ruiz-Lapuente
Keyword(s):  
Physical Modeling ◽  
White Dwarfs ◽  
Extreme Case ◽  
Light Curves ◽  
The Galaxy ◽  
Hα Emission ◽  
Low Mass ◽  
Appreciable Variation

Existing evidence of photometric and spectroscopic diversity among Type la supernovae is compared with the predictions from physical modeling of the explosions. Concerning light curves, changes in the central ignition density of massive (M ≃ Mch) C+O white dwarfs alone do not give appreciable variation. Spectroscopic diversity has been found in the nebular phase, the underluminous SN 1991bg providing an extreme case. A range of 0.4-0.8 Mʘ of 56Ni synthesized in the explosions is derived from the nebular spectra of a sample of SNe la. For SN 1991bg, however, a 56Ni mass of ∼ 0.1 Mʘ only is obtained. That leads us to explore models based on the detonation of low-mass WDs for this SN. Additionally, a nebular spectrum of SN 1991bg shows narrow Hα emission at the position of the SN. If this emission is confirmed against background contamination from the galaxy, it would be first evidence of a nondegenerate, H-rich companion in a SNIa.

scholarly journals Clues to the origin and properties of magnetic white dwarfs

2019 ◽  
Vol 15 (S357) ◽  
pp. 60-74
Author(s):  
Adela Kawka
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarfs ◽  
Field Structure ◽  
Complex Structures ◽  
Surface Mapping ◽  
Time Resolved ◽  
Single Star ◽  
Rotation Rates ◽  
Star Evolution

AbstractA significant fraction of white dwarfs possess a magnetic field with strengths ranging from a few kG up to about 1000 MG. However, the incidence of magnetism varies when the white dwarf population is broken down into different spectral types providing clues on the formation of magnetic fields in white dwarfs. Several scenarios for the origin of magnetic fields have been proposed from a fossil field origin to dynamo generation at various stages of evolution. Offset dipoles are often assumed sufficient to model the field structure, however time-resolved spectropolarimetric observations have revealed more complex structures such as magnetic spots or multipoles. Surface mapping of these field structures combined with measured rotation rates help distinguish scenarios involving single star evolution from other scenarios involving binary interactions. I describe key observational properties of magnetic white dwarfs such as age, mass, and field strength, and confront proposed formation scenarios with these properties.

scholarly journals Statistical Properties of Solar-Type Close Binaries

2004 ◽  
Vol 191 ◽  
pp. 20-27
Author(s):  
J.-L. Halbwachs ◽  
M. Mayor ◽  
S. Udry ◽  
F. Arenou
Keyword(s):  
Binary Stars ◽  
Equal Mass ◽  
Open Clusters ◽  
Statistical Properties ◽  
Spectroscopic Binaries ◽  
Close Binary ◽  
Close Binaries ◽  
Multiple Systems ◽  
Short Period ◽  
Mass Ratios

AbstractTwo Coravel radial velocity surveys dedicated to F7-K field dwarfs and to open clusters are merged in order to investigate the statistical properties of binaries with periods up to 10 years. Thanks to the accurate trigonometric parallaxes provided by Hipparcos, an unbiased sample of spectroscopic binaries (SB) is selected. After correction for the uncertainties of the measurements, the following results are obtained: 1. The distribution of mass ratios exhibits a peak for equal-mass binaries (twins), which is higher for short-period binaries than for long-period binaries. 2. Apart from the twins, the distribution of mass ratios exhibits a broad peak from 0.2 to 0.6. 3. The orbital eccentricities of twins are slightly smaller than those of other binaries. 4. An excess of SB is observed with periods shorter than about 50 days in comparison with the Duquennoy and Mayor log-normal distribution of periods. These features suggest that close binary stars are generated by two different processes. A possible difference could come from the accretion onto the binary, for instance from a common envelope or from a circumbinary disk. Alternatively, twins could come from dynamic evolution of multiple systems. It is not clear whether the formation models are already sufficiently elaborated to reproduce our statistics.

scholarly journals The ESO supernovae type Ia progenitor survey (SPY)

2020 ◽  
Vol 638 ◽  
pp. A131 ◽  
Author(s):  
R. Napiwotzki ◽  
C. A. Karl ◽  
T. Lisker ◽  
S. Catalán ◽  
H. Drechsel ◽  
...  
Keyword(s):  
Radial Velocity ◽  
White Dwarfs ◽  
Binary Systems ◽  
Detection Efficiency ◽  
Close Binary ◽  
The Galaxy ◽  
Type Ia ◽  
Low Mass ◽  
Kinematic Studies ◽  
Ia Supernovae

Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY – SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA white dwarfs (displaying hydrogen-rich atmospheres), of which 46 were found to possess a cool companion. We measured radial velocities (RV) of the remaining 643 DA white dwarfs. We managed to secure observations at two or more epochs for 625 targets, supplemented by eleven objects meeting our selection criteria from literature. The data reduction and analysis methods applied to the survey data are described in detail. The sample contains 39 double degenerate binaries, only four of which were previously known. Twenty are double-lined systems, in which features from both components are visible, the other 19 are single-lined binaries. We provide absolute RVs transformed to the heliocentric system suitable for kinematic studies. Our sample is large enough to sub-divide by mass: 16 out of 44 low mass targets (≤0.45 M⊙) are detected as DDs, while just 23 of the remaining 567 targets with multiple spectra and mass > 0.45 M⊙ are double. The detected fraction amongst the low mass objects (36.4 ± 7.3%) is significantly higher than for the higher-mass, carbon-oxygen core dominated part of the sample (3.9 ± 0.8%), but it is much lower than expected from the detection efficiency for companion masses of 0.05 M⊙ or higher and a 100% binary fraction. This suggests either companion stars of with a mass below 0.05 M⊙ or some of the low mass white dwarfs are single.

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