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L. Yungelson

Publications and source records attributed to L. Yungelson.

At least 19 recordsLinked to original sources
arXiv2024

Elusive hot stripped helium stars in the Galaxy I. Evolutionary stellar models in the gap between subdwarfs and Wolf-Rayet stars

Stellar evolution theory predicts the existence of He-core remnants of the primary components of intermediate-mass close binaries that lost most of their H/He envelopes due to the mass exchange. They are expected to be observed as (1-7) solar mass hot He-rich stars located in the HRD between sdO/B and WR-stars. Several thousands of such stars are expected to exist in the Galaxy, but none of them have been identified so far. We aim to provide comprehensive predictions of the numbers and fundamental properties of He-stars and their companions in the Galaxy. This is a necessary first step to guide observations, to enable a comparison between evolutionary models and observed populations, and to determine the feedback of He-stars in the Galaxy. We expanded the previously considered space of parameters describing progenitors of He-stars and applied a population synthesis based on a grid of models computed by the code MESA. The estimated number of Galactic binaries hosting (1-7) solar mass He-stars is about 20000; it declines to about 3000 for mass exceeding two solar ones. The decisive factor that defines the number of He-stars is runaway mass loss after Roche lobe overflow by primary components, resulting in formation of common envelopes and merger of components. He-stars are much less numerous than expected, since a fraction of close binaries with primary masses below (5-7) solar ones produce subdwarfs with masses below solar. Overwhelming majority of He-stars reside in binaries with an early-type companions and can be identified neither by the UV excess nor by emission features. The large periods of a significant fraction of binaries hosting stripped stars (exceeding several hundred days) also hamper their discovery. (Abridged).

astro-ph.SR↗
arXiv2019

The ESO supernovae type Ia progenitor survey (SPY)

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 (displaying hydrogen-rich atmospheres), of which 46 turned out 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. 20 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 Msun) are detected as DDs, while just 23 of the remaining 567 with multiple spectra and mass >0.45 Msun are double. Although 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%), it is lower than the detection efficiency based upon companion star masses >= 0.05 Msun. This suggests either companion stars of mass < 0.05 Msun, or that some of the low mass white dwarfs are single.

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arXiv2017

Visual binary stars: data to investigate formation of binaries

Statistics of orbital parameters of binary stars as well as statistics of their physical characteristics bear traces of star formation history. However, statistical investigations of binaries are complicated by lacking or incomplete observational data and by a number of observational selection effects. Visual binaries are the most numerous observed binaries, the number of pairs exceeds 130000. The most complete list of presently known visual binary stars was compiled by cross-matching objects and combining data of the three largest catalogues of visual binaries. It was supplemented by the data on parallaxes, multicolor photometry, spectral characteristics of the stars of this list taken from other catalogues. This allowed us to compensate partly for the lack of observational data for these objects. Combined data allowed us to check validity of observational values and to investigate statistics of the orbital and physical parameters of visual binaries. Corrections for incompleteness of observational data are discussed. Obtained datasets and modern distributions of binary parameters will be used to reconstruct the initial distributions and parameters of the function of star formation for binary systems.

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arXiv2016

Statistical analysis of a comprehensive list of visual binaries

Visual binary stars are the most abundant class of observed binaries. The most comprehensive list of data on visual binaries compiled recently by cross-matching the largest catalogues of visual binaries allowed a statistical investigation of observational parameters of these systems. The dataset was cleaned by correcting uncertainties and misclassifications, and supplemented with available parallax data. The refined dataset is free from technical biases and contains 3676 presumably physical visual pairs of luminosity class V with known angular separations, magnitudes of the components, spectral types, and parallaxes. We also compiled a restricted sample of 998 pairs free from observational biases due to the probability of binary discovery. Certain distributions of observational and physical parameters of stars of our dataset are discussed.

astro-ph.SR↗
arXiv2011

Wind accretion in symbiotic X-ray binaries

The properties of wind accretion in symbiotic X-ray binaries (SyXBs) consisting of red-giant and magnetized neutron star (NS) are discussed. The spin-up/spin-down torques applied to NS are derived based on a hydrodynamic theory of quasi-spherical accretion onto magnetized NSs. In this model, a settling subsonic accretion proceeds through a hot shell formed around the NS magnetosphere. The accretion rate onto the NS is determined by the ability of the plasma to enter the magnetosphere.Due to large Reynolds numbers in the shell, the interaction of the rotating magnetosphere with plasma initiates a subsonic turbulence. The convective motions are capable of carrying the angular momentum through the shell. We carry out a population synthesis of SyXBs in the Galaxy with account for the spin evolution of magnetized NS. The Galactic number of SyXBs with bright (M_v<1) low-mass red-giant companion is found to be from \sim 40 to 120, and their birthrate is \sim 5\times 10^{-5}-10^{-4} per year. According to our model, among known SyXBs, Sct X-1 and IRXS J180431.1-273932 are wind-fed accretors. GX 1+4 lies in the transition from the wind-fed SyXBs to SyXBs in which the giants overflow their Roche lobe. The model successfully reproduces very long NS spins (such as in IGR J16358-4724 and 4U 1954+31) without the need to invoke very strong magnetic fields.

astro-ph.HE↗
arXiv2011

Type Ia Supernovae and Supersoft X-ray Sources

The rates of SN Ia for double-degenerate and single-degenerate scenario are computed for the models of spiral and elliptical galaxies. The number of nuclearly burning white dwarfs (NBWD) is traced. The data favours double-degenerate scenario and suggests lower number of NBWD per unit mass in ellipticals and their lower average mass as one of the reasons for the difference in the number of supersoft X-ray sources observed in the galaxies of different types.

astro-ph.SR↗
arXiv2009

The chemical composition of TS 01, the most oxygen-deficient planetary nebula. AGB nucleosynthesis in a metal-poor binary star

The planetary nebula TS 01 (also called PN G 135.9+55.9 or SBS 1150+599A), with its record-holding low oxygen abundance and its double degenerate close binary core (period 3.9 h), is an exceptional object located in the Galactic halo. We have secured observational data in a complete wavelength range in order to pin down the abundances of half a dozen elements in the nebula. The abundances are obtained via detailed photoionization modelling taking into account all the observational constraints (including geometry and aperture effects) using the pseudo-3D photoionization code Cloudy_3D. The spectral energy distribution of the ionizing radiation is taken from appropriate model atmospheres. Both stellar components contribute to the ionization: the ``cool'' one provides the bulk of hydrogen ionization, and the ``hot'' one is responsible for the presence of the most highly charged ions, which explains why previous attempts to model the nebula experienced difficulties. The nebular abundances of C, N, O, and Ne are found to be respectively, 1/3.5, 1/4.2, 1/70, and 1/11 of the Solar value, with uncertainties of a factor 2. Thus the extreme O deficiency of this object is confirmed. The abundances of S and Ar are less than 1/30 of Solar. Standard models of stellar evolution and nucleosynthesis cannot explain the abundance pattern observed in the nebula. To obtain an extreme oxygen deficiency in a star whose progenitor has an initial mass of about 1 msun requires an additional mixing process, which can be induced by stellar rotation and/or by the presence of the close companion. We have computed a stellar model with initial mass of 1 msun, appropriate metallicity, and initial rotation of 100 kms, and find that rotation greatly improves the agreement between the predicted and observed abundances.

astro-ph.GA↗
arXiv2008

Evolutionary models of short-period soft X-ray transients: comparison with observations

We consider evolutionary models for the population of short-period (<10 hr) low-mass black-hole binaries (LMBHBs) and compare them with observations of soft X-ray transients (SXTs). We show that assuming strongly reduced magnetic braking (as suggested by us before for low-mass semidetached binaries) the calculated masses and effective temperatures of secondaries are encouragingly close to the observed masses and effective temperatures (as inferred from their spectra) of donor stars in short-period LMBHBs. Theoretical mass-transfer rates in SXTs are consistent with the observed ones if one assumes that accretion discs in these systems are truncated (``leaky''). We find that the population of short-period SXTs is formed mainly by systems which had unevolved or slightly evolved main-sequence donors ($M_2 \lesssim 1.2M_\odot$) with a hydrogen abundance in the center $X_c > 0.35$ at the Roche-lobe overflow (RLOF). Longer period (0.5 - 1) day) SXTs might descend from systems with initial donor masses of about 1 $M_\odot$ and $X_c < 0.35$. Thus, one can explain the origin of short period LMBHB without invoking donors with cores almost totally depleted of hydrogen. Our models suggest that, unless the currently accepted empirical estimates of mass-loss rates by winds for massive O-stars and Wolf-Rayet stars are significantly over-evaluated, a very high efficiency of common-envelope ejection is necessary to form short-period LMBHBs.

astro-ph↗
arXiv2008

Evolution of low-mass binaries with black-hole components

We consider evolutionary models for the population of short-period (<10 hr) low-mass black-hole binaries (LMBHB) and compare them with observations of soft X-ray transients (SXT). Evolution of LMBHB is determined by nuclear evolution of the donors and/or orbital angular momentum loss due to magnetic braking by the stellar wind of the donors and gravitational wave radiation. We show that the absence of observed stable luminous LMBHB implies that upon RLOF by the low-mass donor angular momentum losses are substantially reduced with respect to the Verbunt and Zwaan "standard" prescription for magnetic braking. Under this assumption masses and effective temperatures of the model secondaries of LMBHB are in a satisfactory agreement with the masses and effective temperatures (as inferred from their spectra) of the observed donors in LMBHB. Theoretical mass-transfer rates in SXTs are consistent with the observed ones if one assumes that accretion discs in these systems are truncated ("leaky"). We find that the population of short-period SXT is formed mainly by systems which had unevolved or slightly evolved (X_c > 0.35) donors at the RLOF. Longer period (0.5 - 1 day) SXT might descend from systems with initial donor mass about 1 solar and X_c < 0.35. It is unnecessary to invoke donors with almost hydrogen-depleted cores to explain the origin of LMBHB. Our models suggest that a very high efficiency of common-envelopes ejection is necessary to form LMBHB, unless currently commonly accepted empirical estimates of mass-loss rates by winds for pre-WR and WR-stars are significantly over-evaluated.

astro-ph↗
arXiv2007

An object that defies stereotypes. X-ray observations of SBS 1150+599A -- the binary nucleus of PN G135.9+55.9

We present X-ray observations of the close binary nucleus of the planetary nebula PN G135.9+55.9 obtained with the XMM satellite. The nebula is the most oxygen-poor PN known to date and is located in the Galactic halo. It is known to harbor a close binary nucleus of which only one component can be observed in optical-UV range. New X-ray observations show that the invisible component is a very hot compact star. This finding allows us to reconstruct the immediate past of the object and predict its future. The parameters of the binary components we determine strongly suggest that the precursor was a symbiotic supersoft X-ray source that finished its life by Roche lobe overflow. PN G135.9+55.9 is an excelent candidate for a future type Ia supernova.

astro-ph↗
arXiv2007

A 33 hour period for the Wolf-Rayet/black hole X-ray binary candidate NGC 300 X-1

Context. NGC 300 X-1 is the second extragalactic candidate, after IC 10 X-1, in the rare class of Wolf-Rayet/compact object X-ray binary systems exemplified in the Galaxy by Cyg X-3. From a theoretical point of view, accretion onto a black hole in a detached system is possible for large orbital periods only if the mass of the relativistic object is high or the velocity of the accreted wind is low. Aims. We analysed a 2 week SWIFT XRT light curve of NGC 300 X-1 and searched for periodicities. Methods. Period searches were made using Lomb-Scargle periodogram analysis. We evaluated the confidence level using Monte Carlo simulations. Results. A period of 32.8+-0.4h (3 sigma error) was found for NGC 300 X-1 with a confidence level >99%. Furthermore, we confirm the high irregular variability during the high flux level, as already observed in the XMM-Newton observations of the source. A folded XMM-Newton light curve is shown, with a profile that is in agreement with SWIFT. The mean absorbed X-ray luminosity in the SWIFT observations was 1.5x10^38 erg/s, close to the value derived from the XMM-Newton data. Conclusions. While Cyg X-3 has a short period of 4.8 h, the period of NGC 300 X-1 is very close to that of IC 10 X-1 (34.8+-0.9 h). These are likely orbital periods. Possibility of formation of accretion disk for such high orbital periods strongly depends on the terminal velocity of the Wolf-Rayet star wind and black-hole mass. While low masses are possible for wind velocities < 1000 km/s, these increase to several tens of solar masses for velocities > 1600 km/s and no accretion disk may form for terminal velocities larger than 1900 km/s.

astro-ph↗
arXiv2006

Evolution of Ultramassive Stars

We show that even most massive initial solar composition stars hardly form black holes with mass exceeding about 100 solar mass.

astro-ph↗
arXiv2005

A model for the population of helium stars in the Galaxy I. Low-mass stars

By means of population synthesis we model the Galactic ensemble of helium stars. It is assumed that all helium stars are formed in binaries. Under this assumption, single helium stars are produced by the mergers of helium remnants of components of close binaries (mainly, by merging helium white dwarfs) and by disruption of binaries with helium components in supernovae explosions. The estimate of the total birthrate of helium stars in the Galaxy is 0.043 yr$^{-1}$, their total number is estimated as $4 \times 10^6$. The rate of binarity in the total sample is 76%. We construct a subsample of low-mass ($M_{\rm He} \lesssim 2 \ms$) helium stars limited by observational selection effects: stellar magnitude ($V_{\rm He} \leq 16$), ratio of stellar magnitudes of components in binaries ($V_{\rm He}\leq V_{\rm comp}$), lower limit of the semiamplitude of radial velocity that is necessary for discovery of binarity ($K_{min}=30$ km/s). The parameters of this ``observable'' sample are in satisfactory agreement with the parameters of the observed ensemble of sdB stars. In particular, in the selection-limited sample binarity rate is 58%. We analyze the relations between orbital periods and masses of helium stars and their companions in systems with different combinations of components. We expect that overwhelming majority ($\sim 90$%) of unobserved components in binary sdB stars are white dwarfs, predominantly, carbon-oxygen ones.

astro-ph↗
arXiv2004

Double degenerates and progenitors of supernovae type Ia

We report on systematic radial velocity surveys for white dwarf - white dwarf binaries (double degenerates - DDs) including SPY (ESO Supernovae Ia progenitor survey) recently carried out at the VLT. A large sample of DD will allow us to put strong constrains on the phases of close binary evolution of the progenitor systems and to perform an observational test of the DD scenario for supernovae of type Ia. We explain how parameters of the binaries can be derived from various methods. Results for a sample of DDs are presented and discussed.

astro-ph↗
arXiv2004

AM CVn systems as optical, X-ray and GWR sources

We discuss the model for the Galactic sample of the AM CVn systems with orbital periods P less than 1500 s, that can be detected in the optical and/or X-ray bands and may be resolved by the gravitational waves detector LISA. At P=3 to 10 min all detectable systems are X-ray sources. At P greater than 10 min most systems are only detectable in the V-band. About 30% of the X-ray sources is also detectable in the V-band. About 10,000 AM CVn systems might be resolved by LISA; this is comparable to the number of detached double white dwarfs that can be resolved. Several hundreds of AM CVn LISA sources might be also detectable in the V- and/or X-ray bands.

astro-ph↗
arXiv2002

Search for double degenerate progenitors of supernovae type Ia with SPY

We report on a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (SN Ia Progenitor surveY - SPY). About 560 white dwarfs were checked for radial velocity variations until now. Ninety new DDs have been discovered, including short period systems with masses close to the Chandrasekhar mass.

astro-ph↗
arXiv2002

Search for progenitors of supnernovae type Ia with SPY

We have started a large survey for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY). About 400 white dwarfs were checked for radial velocity variations during the first 15 months of this project, twice the number of white dwarfs investigated during the last 20 years. We give an overview of the SPY project and present first results Fifty four new DDs have been discovered, seven of them double lined (only 18 and 6 objects of these groups were known before, respectively). The final sample is expected to contain 150 to 200 DDs. Eight new pre-cataclysmic binaries were also detected. SPY is the first DD survey which encompasses also non-DA white dwarfs. SPY produces an immense, unique sample of very high resolution white dwarf spectra, which provides a lot of spin-off opportunities. We describe our projects to exploit the SPY sample for the determination of basic parameters, kinematics, and rotational velocities of white dwarfs. A catalogue with a first subset of our white dwarf data has already been published by Koester et al. 2001.

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