arXiv subjects

L. R. Yungelson

Publications and source records attributed to L. R. Yungelson.

At least 19 recordsLinked to original sources

arXiv2026

Stripped helium stars in UV

The model of Galactic population of stripped helium stars, the remnants of $5 \lesssim M/M_\odot \lesssim 24$ primary components of close binaries after RLOF is presented. These stars emit in the UV range of the spectrum and may be observed by detectors aboard planned "Spektr-UV" (WSO-UV) space telescope. For the current star formation rate in the Galaxy 2$\mathrm {M_\odot yr^{-1}}$, the estimate of the number of 1 to 7 $M_\odot$ objects with $T_{\rm eff} \gtrsim$25,000\,K ranges from 14700 to 28500. The number of 2 to 7 $M_\odot$ objects is 3200 to 5500. The main evolutionary factor influencing the estimate is possible formation of common envelopes and merger of components in them. Detection of candidate stripped helium stars by UV-excess is hampered by the dominance of main-sequence companions to stripped helium stars in the combined spectra of binaries. This effect of observational selection may reduce the number of candidate stripped helium stars potentially detectable by photometry to $\lesssim 1000$.

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arXiv2026

Elusive helium stars in the gap between subdwarfs and Wolf-Rayet stars III. Formation of the Galactic population of stripped helium stars

Population synthesis based on the grid of pre-computed evolutionary sequences for close binaries is applied to the problem of formation of the Galactic population of stripped helium stars, the remnants of $5 \lessapprox M/M_\odot \lessapprox 24$ primary components of close binaries after RLOF. Stellar rotation is taken into account. For the current star formation rate in the Galaxy $2\,M_\odot yr^{-1}$, the estimate of the number of 1 to $7\,M_\odot$ objects with $T_{eff} \gtrapprox $25000K ranges from 14700 to 28500, while for the number of objects with masses from $2\,M_\odot$ to $7\,M_\odot$ it is 3200 to 5500, depending on the assumptions about formation of common envelopes and their outcomes. Other factors influencing the estimate are adopted star formation rate, distributions of close binaries over initial masses of primary components, mass ratios of components, orbital periods. Observational selection may severely limit the number of detectable objects. Angular velocities of rotation of companions to stripped helium stars are 60 to 80 per cent of the critical one. Using the models of initially homogeneous helium stars as approximations for the remnants after mass loss results in the underestimate of pre-supernovae masses.

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arXiv2026

Will a Supernova explode in CD-30°11223?

Context: Accretion of He-rich matter onto a low mass carbon-oxygen white dwarf in a binary system with a He-rich donor may lead to an explosive event of Supernova Ia proportion, though with low peak luminosity and peculiar nucleosynthesis. Recently such a statement has been questioned, suggesting that, if the effects of rotation are accounted for in the evolution of the accretor, the latter does not explode, but it becomes a white dwarf with a massive He-buffer. Aims: We investigate the expected evolution of the currently detached binary CD-30°11223 harboring a 0.74 Msun carbon-oxygen white dwarf and a 0.47 Msun donor with a He-burning core and a very thin H-envelope (Delta M_H=6e-4 Msun). Methods: We use stellar the evolution code FuNS to compute the evolution of CD-30°11223. With respect to our earlier study of the system PTF J2238+743015.1, we include also the transport of angular momentum due to magnetic instabilities in the accretor interiors (``magnetic model''). Results: During the H-accretion phase, the effects of rotation in the accretor are negligible. In the ``magnetic model'', the angular momentum deposited by the accreted matter is very efficiently redistributed along the whole WD due to magnetic instabilities, so that the angular velocity of the accreted layers remains very low. During the He-accretion phase, the accretor experiences two very strong He-flashes which result in the ejection from the binary system of a large part of the matter previously accreted. The system ends its life as a carbon-oxygen core capped by a massive He/C/O-envelope (Delta M_{env} ~ 0.194 Msun) and an extremely low-mass companion, remnant of the donor. Conclusions: The system CD-30°11223 cannot be regarded as the potential progenitor of Supernova Ia. Such a conclusion applies also to all detached binary systems having similar masses of components and orbital periods.

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arXiv2025

Elusive helium stars in the gap between subdwarfs and Wolf-Rayet stars~II. Nonlinear pulsations of stripped helium stars

It is shown for the first time that the stripped helium stars with masses 2 to 7 solar mass which are formed in close binary systems in the so-called case B of mass-exchange and retained low-mass hydrogen-helium envelopes, experience nonlinear radial pulsations. Pulsations are excited by the kappa-mechanism due to helium ionization. The region of pulsation instability extends over Hertzsprung-Russel diagram from the red giants branch to the region of effective temperatures from about 30,000 K to about 50,000 K. Variations of stellar luminosity should be observed mostly in the ultraviolet. The amplitudes of pulsations of the studied models reach 0.8 stellar magnitude and increase, as the stellar radii decrease. Pulsation periods of stars with effective temperatures exceeding 10,000 K range from 0.17 to 8.5 day and decrease with decreasing radii. The stars have substantially larger effective temperatures than their companions, which could be Be-stars. They are components of relatively wide binaries with orbital periods up to several years. The number of pulsating moderate-mass stripped helium stars in the Galaxy is about 1000.

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arXiv2022

X-ray luminosity function of accreting neutron stars and black holes

We model X-ray luminosity functions (XLF) of accreting neutron stars and black holes in $10^{35} \leq L_X \leq 10^{41}$ erg/s range in star-forming galaxies and galaxies with the initial star formation burst. XLFs are obtained by combining a fast generation of compact object+normal star population using the binary population synthesis code BSE and calculation of the subsequent detailed binary evolution by the MESA code. XLFs in the galaxies of both types is broadly reproduced using the standard assumptions of the binary star evolution.

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arXiv2021

Populations of ultraluminous X-ray sources in galaxies: origin and evolution

Employing hybrid population synthesis, a model of the population of ultraluminous X-ray sources (ULX) in the binary systems with a black hole (BH) accretors is computed. It is compared to the model of the population of ULX with magnetized neutron stars (NS) that can be observed as pulsating ULX (Kuranov et al. 2020). A model of formation of BH is considered, in which their mass is determined by the mass of stellar CO core immediately before the collapse, as well as "delayed" and "rapid" collapse models (Fryer et al. 2012). Possible transiency of ULX due to accretion disks instability is taken into account The parameters and evolution of ULX are computed for the galaxies with constant star formation rate (SFR) and for the ones formed by an instantaneous star formation burst. The maximum number of ULX with BH ($\sim 10$) is reached in the galaxies with stationary $ SFR=10$\msun/yr in $\sim 1$ Gyr after beginning of star formation. ULX which are observed after the end of star formation, are binaries, in which BH and/or NS formed before the completion of star formation, while long-living donors with the mass $\sim$\msun\ continue RLOF or even fill their Roche lobes later. In several Gyr after completion of star formation the number of ULX in the galaxies with mass $M_G=10^{10}$\,\msun\ becomes less than 1 per 10 galaxies, most of them are ULX with NS. In ULX with NS, regardless of the adopted SFR model, dominate persistent sources with the donor overflowing Roche lobe. The number of transient sources is by more than an order of magnitude lower. Wind-accreting ULX are by an order of magnitude more rare than the sources with accretion via RLOF.

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arXiv2021

Population synthesis of ultraluminous X-ray sources with magnetised neutron stars

A model of population of ultraluminous X-ray sources with magnetised neutron stars (NULX) in a spiral galaxy with the star formation history similar to that in the thin disc of Milky Way is computed using a hybrid approach. First, applying analytical approximations (code BSE) we construct the ensemble of close binaries (CBS) which can be potential precursors of NULX. Next, evolution with accretion onto magnetised neutron stars (NS) is computed by the evolutionary code MESA. Accretion rate onto NS and X-ray luminosity are calculated for the models of sub- and supercritical discs and for the discs with advection. During accretion onto magnetised NS, super-Eddington luminosity $L_\mathrm{X}>10^{38}$ erg~s$^{-1}$ is attained already at the subcritical stage, when the energy release at the inner boundary of the disc defined by the NS magnetosphere is sub-Eddington. It is shown that standard evolution of CBS with an account of the peculiarities specific for accretion onto magnetised NS allows us to explain quantitatively observed characteristics of NULX (X-ray luminosities, NS spin periods, orbital periods and masses of visual components) without additional model assumptions on the collimation of X-ray emission from NS with high observed super-Eddington luminosity. In a model galaxy with star formation rate 3--5 $M_\odot {\rm yr^{-1}}$ there can exist several NULX. Discovery of a powerful wind from NULX with $L_{\mathrm X} \sim 10^{41}$ erg~s$^{-1}$ would be a signature of super-Eddington accretion onto magnetised NS.

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arXiv2020

Galactic population of black holes in detached binaries with low-mass stripped helium stars: the case of LB-1 (LS~V+22~25)

We model the Galactic population of detached binaries that harbor black holes with (0.5-1.7) solar mass companions -- the remnants of case B mass-exchange that rapidly cross Hertzsprung gap after the termination of the Roche-lobe overflow or as He-shell burning stars. Several such binaries can be currently present in the Galaxy. The range of black hole masses in them is about 4 to 10 solar ones, the orbital periods are tens to hundreds day. The unique BH-binary LB-1 fits well into this extremely rare class of double stars.

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arXiv2019

Comprehensive models of novae at metallicity $Z = 0.02$ and $Z = 10^{-4}$

Novae are the observational manifestations of thermonuclear runaways on the surface of accreting white dwarfs (WDs). Although novae are an ubiquitous phenomenon, their properties at low metallicity are not well understood. Using the publicly-available stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA), we model the evolution of accreting carbon-oxygen WDs and consider models which accrete matter with metallicity Z=0.02 or $10^{-4}$. We consider both models without mixing and with matter enriched by CO-elements assuming that mixing occurs in the process of accretion (with mixing fraction 0.25). We present and contrast ignition mass, ejected mass, recurrence period and maximum luminosity of novae for different WD masses and accretion rates for these metallicities and mixing cases. We find that models with Z = 0.02 have ignition masses and recurrence periods smaller than models with low Z, while the ejected mass and maximum luminosity are larger. Retention efficiency during novae outbursts decreases with increasing metallicity. In our implementation, inclusion of mixing at the H/He interface reduces accreted mass, ejected mass and recurrence period as compared to the no-mixing case, while the maximum luminosity becomes larger. Retention efficiency is significantly reduced, becoming negative in most of our models. For ease of use, we provide a tabular summary of our results.

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arXiv2019

Thermonuclear oubursts of AM CVn stars

We consider initial stage of the evolution of AM CVn type stars with white dwarf donors, which is accompanied by thermonuclear explosions in the layer of accreted He. It is shown that the accretion never results in detonation of He and accretors in AM CVn stars finish their evolution as massive WDs. We found, for the first time, that in the outbursts the synthesis of n-rich isotopes, initiated by the ${\mathrm{^{22}{Ne}(α,n)^{25}Mg}}$ reaction becomes possible.

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arXiv2019

He-accreting WD: Nucleosynthesis in the extreme binary system (1.02+0.30) M$_\odot$

We investigate the evolutionary properties of AM~CVn stars with massive white dwarf donors and accretors. As a representative of them we consider a binary initially composed by a 0.30 M$_\odot$, He WD and a 1.02 M$_\odot$, CO WD. We evaluate the time-dependent mass transfer rate from the donor and compute the evolution of the accretor, accounting for the effects of mass exchange on the evolution of orbital parameters. We model the thermal response of the accreting CO WD with the FUN evolutionary code coupled to a full nuclear network, from H to Bi, including more than 700 isotopes linked by about 1000 nuclear processes. We find that accretors in these systems evolve through the stages of steady He-burning and mild and strong He-flashes and become at the end CO WDs capped by a massive ($\sim 0.1$ M$_\odot$) He-rich buffer. During He-flashes (both mild and strong) the temperature in the He-shell increases above $3\times 10^8$ K, so that the ${^{22}Ne}(α,n){^{25}Mg}$ reaction becomes efficient and $n$-rich isotopes can be produced. During the RLOF episodes triggered by strong non-dynamical He-flashes matter enriched in $α$-elements and $n$-rich isotopes is ejected, polluting the interstellar medium. Our results strongly suggest that massive AM CVn systems with WD donors do not experience a final very strong dynamical He-flash driving an explosive event like SN .Ia. Though the ejected matter is highly enriched in heavy isotopes, the relative contribution of massive AM CVn systems to the Galactic chemical evolution is, most probably, negligible due to their expected paucity.

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arXiv2017

A young contracting white dwarf in the peculiar binary HD 49798/RX J0648.0--4418?

HD 49798/RX J0648.0--4418 is a peculiar X-ray binary with a hot subdwarf (sdO) mass donor. The nature of the accreting compact object is not known, but its spin period $P=13.2$~s and $\dot P =-2.15 \times 10^{-15}$s~s$^{-1}$, prove that it can be only either a white dwarf or a neutron star. The spin-up has been very stable for more than 20 years. We demonstrate that the continuous stable spin-up of the compact companion of HD 49798 can be best explained by contraction of a young white dwarf with an age $\sim 2$~Myrs. This allows us to interpret all the basic parameters of the system in the framework of an accreting white dwarf. We present examples of binary evolution which result in such systems. If correct, this is the first direct evidence for a white dwarf contraction on early evolutionary stages.

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arXiv2017

Hidden population of Algols

We present results of Monte Carlo simulation aiming at the estimate of the frequency of semi-detached Algol-type binaries among the stars observed as single ones. When account is made for various detection biases (mostly due to inclination of orbits), the fraction of Algols among Galactic disk stars appears to be 0.1--0.2\%. However, this number should be regarded as a lower limit only, since there are still unaccounted selection effects and other types of photometrically unresolved binaries. Hidden binarity appears to be an important phenomenon that should be taken into account when considering stellar statistics and construction of fundamental relations between stellar parameters.

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arXiv2016

Merging white dwarfs and SN Ia

Using population synthesis, we study a double-degenerate (DD) scenario for SNe Ia, aiming to estimate the maximum possible contribution to the rate of SNe from this scenario and the dependence of the delay-time distribution (DTD) on it. We make an extreme assumption that all mergers of super-Chandrasekhar pairs of CO white dwarfs (WDs) and mergers of CO WDs more massive than 0.47 $M_\odot$ with hybrid or helium WDs more massive than 0.37$M_\odot$ produce SNe Ia. The models are parametrized by the product of the common envelope efficiency and the parameter of binding energy of stellar envelopes $α_{ce}λ$, which we vary between 0.25 and 2. The best agreement with observations is obtained for $α_{ce}λ$=2. A substantial contribution to the rate of SNe Ia is provided by the pairs with a hybrid WD. The estimated Galactic rate of SNe Ia is $6.5 10^{-3}$ per yr (for the mass of the bulge and thin disk equal to $7.2 10^{10} M_\odot$), which is comparable to the observational estimate $(5.4\pm0.12) 10^{-3}$ per yr. The model DTD for 1 to 8 Gyr range satisfactorily fits DTD for SNe Ia in the field galaxies (Maoz et al. 2012). For this epoch, model DTD is a power low with an index -1.64. At earlier and later epochs our DTD has a deficit of events, as in other studies. Marginal agreement with observational DTD is achieved even if only CO+CO WD with $M_1\geq0.8\,M_\odot$ and $M_2\geq0.6\,M_\odot$ produce SNe Ia. A better agreement of observed and model DTD may be obtained if tidal effects are weaker than assumed and/or metallicity of population is much lower than solar.

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arXiv2016

Modelling nova populations in galaxies

Theoretical modelling of the evolution of classical and recurrent novae plays an important role in studies of binary evolution, nucleosynthesis and accretion physics. However, from a theoretical perspective the observed statistical properties of novae remain poorly understood. In this paper, we have produced model populations of novae using a hybrid binary population synthesis approach for differing star formation histories (SFHs): a starburst case (elliptical-like galaxies), a constant star formation rate case (spiral-like galaxies) and a composite case (in line with the inferred SFH for M31). We found that the nova rate at 10\;Gyr in an elliptical-like galaxy is $\sim 10-20$ times smaller than a spiral-like galaxy with the same mass. The majority of novae in elliptical-like galaxies at the present epoch are characterized by low mass white dwarfs (WDs), long decay times, relatively faint absolute magnitudes and long recurrence periods. In contrast, the majority of novae in spiral-like galaxies at 10\;Gyr have massive WDs, short decay times, are relatively bright and have short recurrence periods. The mass loss time distribution for novae in our M31-like galaxy is in agreement with observational data for Andromeda. However, it is possible that we underestimate the number of bright novae in our model. This may arise in part due to the present uncertainties in the appropriate bolometric correction for novae.

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arXiv2015

Population synthesis of accreting white dwarfs: II. X-ray and UV emission

Accreting white dwarfs (WDs) with non-degenerate companions are expected to emit in soft X-rays and the UV, if accreted H-rich material burns stably. They are an important component of the unresolved emission of elliptical galaxies, and their combined ionizing luminosity may significantly influence the optical line emission from warm ISM. In an earlier paper we modeled populations of accreting WDs, first generating WD with main-sequence, Hertzsprung gap and red giant companions with the population synthesis code \textsc{BSE}, and then following their evolution with a grid of evolutionary tracks computed with \textsc{MESA}. Now we use these results to estimate the soft X-ray (0.3-0.7keV), H- and He II-ionizing luminosities of nuclear burning WDs and the number of super-soft X-ray sources for galaxies with different star formation histories. For the starburst case, these quantities peak at $\sim 1$ Gyr and decline by $\sim 1-3$ orders of magnitude by the age of 10 Gyr. For stellar ages of $\sim$~10 Gyr, predictions of our model are consistent with soft X-ray luminosities observed by Chandra in nearby elliptical galaxies and He II 4686$Å/\rm{H}β$ line ratio measured in stacked SDSS spectra of retired galaxies, the latter characterising the strength and hardness of the UV radiation field. However, the soft X-ray luminosity and He~II~4686$Å/\rm{H}β$ ratio are significantly overpredicted for stellar ages of $\lesssim 4-8$ Gyr. We discuss various possibilities to resolve this discrepancy and tentatively conclude that it may be resolved by a modification of the typically used criteria of dynamically unstable mass loss for giant stars.

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arXiv2014

He-Accreting WDs: accretion regimes and final outcomes

The behaviour of carbon-oxygen white dwarfs (WDs) subject to direct helium accretion is extensively studied. We aim to analyze the thermal response of the accreting WD to mass deposition at different time scales. The analysis has been performed for initial WDs masses and accretion rates in the range (0.60 - 1.02) Msun and 1.e-9 - 1.e-5 Msun/yr, respectively. Thermal regimes in the parameters space M_{WD} - dot{M}_{He}, leading to formation of red-giant-like structure, steady burning of He, mild, strong and dynamical flashes have been identified and the transition between those regimes has been studied in detail. In particular, the physical properties of WDs experiencing the He-flash accretion regime have been investigated in order to determine the mass retention efficiency as a function of the accretor total mass and accretion rate. We also discuss to what extent the building-up of a He-rich layer via H-burning could be described according to the behaviour of models accreting He-rich matter directly. Polynomial fits to the obtained results are provided for use in binary population synthesis computations. Several applications for close binary systems with He-rich donors and CO WD accretors are considered and the relevance of the results for the interpretation of He-novae is discussed.

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arXiv2014

Next generation population synthesis of accreting white dwarfs: I. Hybrid calculations using BSE + MESA

Accreting, nuclear-burning white dwarfs have been deemed to be candidate progenitors of type Ia supernovae, and to account for supersoft X-ray sources, novae, etc. depending on their accretion rates. We have carried out a binary population synthesis study of their populations using two algorithms. In the first, we use the binary population synthesis code \textsf{BSE} as a baseline for the "rapid" approach commonly used in such studies. In the second, we employ a "hybrid" approach, in which we use \textsf{BSE} to generate a population of white dwarfs (WD) with non-degenerate companions on the verge of filling their Roche lobes. We then follow their mass transfer phase using the detailed stellar evolution code \textsf{MESA}. We investigate the evolution of the number of rapidly accreting white dwarfs (RAWDs) and stably nuclear-burning white dwarfs (SNBWDs), and estimate the type Ia supernovae (SNe Ia) rate produced by "single-degenerate" systems (SD). We find significant differences between the two algorithms in the predicted numbers of SNBWDs at early times, and also in the delay time distribution (DTD) of SD SNe Ia. Such differences in the treatment of mass transfer may partially account for differences in the SNe Ia rate and DTD found by different groups. Adopting 100\% efficiency for helium burning, the rate of SNe Ia produced by the SD-channel in a Milky-way-like galaxy in our calculations is $2.0\times10^{-4}\rm{yr}^{-1}$, more than an order of magnitude below the observationally inferred value. In agreement with previous studies, our calculated SD DTD is inconsistent with observations.

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