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1.
Possible paths for the formation of Ap/Bp stars—massive main-sequence stars with strong magnetic fields—are analyzed based
on modern theories for the evolution of single and binary stars. Assuming that the strong magnetic fields of these stars are
the main reason for their comparatively slow axial rotation and the observed anomalies in the chemical compositions of their
atmospheres, possible origins for these high magnetic fields are considered. Analysis of several possible scenarios for the
formation of these stars leads to the conclusion that their surface magnetic fields are probably generated in the convective
envelopes of the precursor stars. These precursors may be young, single stars with masses 1.5–3 M
⊙ that formed at the peripheries of forming star clusters and ended their accretion at the Hayashi boundary, or alternatively
close binaries whose components have convective envelopes, whose merger leads to the formation of an Ap/Bp star. Arguments
are presented supporting the view that the merger of close binaries is the main channel for the formation of Ap/Bp stars,
and a detailed analysis of this scenario is presented. The initial major axes of the merging binary systems must be in the
range 6–12 R
⊙, and the masses of their components in the range 0.7–1.5 M
⊙. When the merging components possess developed convective envelopes and fairly strong initial magnetic fields, these can
generate powerful magnetic fields “inherited” by the products of the merger—Ap/Bp stars. The reason the components of the
close binaries merge is a loss of angular momentum via the magnetic stellar winds of the components. 相似文献
2.
E. I. Staritsin 《Astronomy Reports》2017,61(5):450-460
Partial mixing of material in the radiative envelopes and convective cores of rotating main sequence stars with masses of 8 and 16 M ⊙ is considered as a function of the inital angular momentum of the stars. Losses of rotational kinetic energy to the generation of shear turbulence in the radiative envelope and the subsequent mixing of material in the envelope are taken into account. With an initial equatorial rotational velocity of 100 km/s, partial mixing develops in the upper part of the layer with variable chemical composition and the lower part of the chemically homogeneous radiative envelope. When the initial equatorial rotational velocity is 150–250 km/s, the joint action of shear turbulence and semi-convection leads to partial mixing in the radiative envelope and central parts of the star. The surface abundance of helium is enhanced, with this effect increasing with the angular momentum of the star. With an initial equatorial rotational velocity of 250 km/s, the ratio of the surface abundances of helium and hydrogen grows by ~30% and ~70% toward the end of the main-sequence evolution of an 8 M ⊙ and 16 M ⊙ star, respectively. The transformation of rotational kinetic energy into the energy of partial mixing increases with the angular momentum of the star, but does not exceed ~2%?3% in the cases considered. 相似文献
3.
E. O. Vasiliev E. I. Vorobyov A. O. Razoumov Yu. A. Shchekinov 《Astronomy Reports》2012,56(7):564-571
We consider the evolution of the ionization zone around Population III stars with M * ?? 25?C200M ?? in protogalaxies with M ?? 107 M ?? at redshifts z = 12, assuming that the dark-energy profile is a modified isothermal sphere. We study the conditions for the growth of instabilities in the ionization zones. The Rayleigh-Taylor and thermal instabilities develop efficiently in the ionization zones around 25?C40M ?? stars, while this efficiency is lower for stars withM * ?? 120M ??. For more massive stars (??200M ??), the flux of ionizing photons is strong enough to considerably reduce the gas density in the ionization zone, and the typical lifetimes of stars (??2 Myr) are insufficient for the growth of instabilities. The gas in a protogalaxy with M ?? 107 M ?? with a 200M ?? central star is completely ionized by the end of the star??s lifetime; in the case of a 120M ?? central star, only one-third of the total mass of gas is ionized. Thus, ionizing photons from stars with M * ? 120M ?? cannot leave protogalaxies with M ? 107 M ??. If the masses of the central stars are 25 and 40M ??, the gas in protogalaxies of this mass remains essentially neutral. We discuss the consequences of the evolution of the ionization zones for the propagation of the envelope after the supernova explosions of the strs and the efficiency of enrichment of the intergalactic medium in heavy elements. 相似文献
4.
We investigate the physical characteristics of single, rapidly rotating white dwarfs, which could form as a result of a merger of two white dwarfs with different masses and filled Roche lobes, due to the radiation of gravitational waves. When the merging of the binary components occurs without loss of mass and angular momentum, the merger products are subject to secular instability, and the density in their cores does not exceed ～108 g/cm3. Models are constructed for rapidly rotating neutron stars, which could form after the collapse of rotating iron cores of evolved massive stars. Dynamically unstable neutron-star models are characterized by a shift of the maximum density from the rotational axis. The total momentum of such neutron stars is about half the maximum possible momentum for the evolved cores of massive stars. 相似文献
5.
Two-color photometric data obtained on the 6-m telescope of the Special Astrophysical Observatory are used to analyze the
structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 studied galaxies are classified as lenticular galaxies.
The stellar populations in the galaxies are very diverse, from old stars with ages of T > 10 billion years (IC 1541) to relatively young stars with ages of T ∼ 1–3 billion years (IC 1548, NGC 85); in one case, star formation is ongoing (UCM 0018+2216). In most of the studied galaxies,
more precisely in all of them brighter than M
B ∼ −18, two-tiered stellar disks are detected, whose radial surface-brightness profiles can be described by two exponential
segments with different characteristic scales—shorter near the center and longer at the periphery. All of the dwarf S0 galaxies
with single-tiered disks are close companions to larger galaxies. Except for this fact, no dependence of the properties of
S0 galaxies on distance from the center of the group is found. Morphological signs of a “minor merger” are found in the lenticular
galaxy NGC 85. Based on these last two results, it is concluded that the most probable mechanism for their transformation
of spiral into lenticular galaxies in groups is gravitational (minor mergers and tidal interactions). 相似文献
6.
Under certain conditions, stars close to intermediate-mass black holes (IMBHs) can form close binary systems with these objects, in which the Roche lobe can be filled by the star and intense accretion of the star’s matter onto the IMBH is possible. Recently, accreting IMBHs have been associated with hyperluminous X-ray sources (HLXs), whose X-ray luminosities can exceed 1041 erg/s. In this paper, the evolution of star—IMBH binary systems is investigated assuming that the IMBH mainly accretes the matter of its companion star, and that the presence of gas in the vicinity of the IMBH does not appreciably affect changes in the orbit of the star. The computations take into account all processes determining the evolution of ordinary binary systems, as well as the irradiation of a star by hard radiation during the accretion of its matter onto the IMBH. The absorption of external radiation in the stellar envelope was calculated applying the same formalism that is used to calculate the opacity of the stellar matter. The computations also assumed that, if the characteristic time for the mass transfer is less than the thermal time scale of the star, there is no exchange betwween the orbital angular momentum of the system and the angular momentum of the matter flowing onto the IMBH.
Numerical simulations have shown that, under these assumptions, three types of evolution are possible for such a binary system, depending on the mass of the IMBH and the star, as well as on the star’s initial distance from the IMBH. The first type ends with the destruction of the star. For low-mass main sequence (MS) stars, only this option is realized, even in the case of large initial distances from IMBH. For massive MS stars, the star is also destroyed if the mass of the IMBH is high and the initial distance of the star from the IMBH is sufficiently small.
The second type of evolution can occur for massive MS stars, which are initially located farther from the IMBH than in the first type of evolution. In this case, the massive star fills its Roche lobe during its evolutionary expansion, after which a stage of intense mass transfer begins. It is in this phase of the evolution that the star- IMBH system can manifest itself as a HLX, when its X-ray luminosity LX exceeds 1041 erg/s for a fairly long time. Numerical simulations show that the initial mass of the donor star in systems with MBH = (103?105)M⊙ must be close to ～10 M⊙ in this case. The characteristic duration of the HLX stage is 30 000–70 000 years. For smaller initial donor masses close to ～5M⊙, LX does not reach 1041 erg/s in the stage of intense mass transfer, but can exceed 1040 erg/s. The duration of this stage of evolution is 300 000–800 000 years. A characteristic feature of this second type of evolution is an increase in the orbital period of the system over time. As a result, after a period of intense mass loss, the star “retreats” inside the Roche lobe. A remnant of the star in the form of a white dwarf is left behind, and can end up fairly far from the IMBH.
The third type of evolution can occur for massive MS stars that are initially even farther from the IMBH, as well as for massive stars that are already evolved at the initial time. In this case, conservative mass exchange in the presence of intense stellar wind leads to the star moving away from the IMBH, without filling its Roche lobe at all. For massive stars with sufficiently strong stellar winds (for example, stars with masses ～50M⊙), the accretion rate of matter onto the IMBH in this case can reach values that are characteristic of HLXs. As in the case of the second type of evolution, the stellar remnant can remain at a fairly large distance from the IMBH.
相似文献7.
The statistical relation between the masses of supermassive black holes (SMBHs) in disk galaxies and the kinematic properties
of their host galaxies is analyzed. Velocity estimates for several galaxies obtained earlier at the 6-m telescope of the Special
Astrophysical Observatory of the Russian Academy of Sciences and the data for other galaxies taken from the literature are
used. The SMBH masses correlate well with the rotational velocities at a distance of R ≈ 1 kpc, V
1, which characterize the mean density of the central region of the galaxy. The SMBH masses correlate appreciably weaker with
the asymptotic velocity at large distances from the center and the angular velocity at the optical radius R
25. We have found for the first time a correlation between the SMBH mass and the total mass of the galaxy within the optical
radius R
25, M
25, which includes both baryonic and “dark” mass. The masses of the nuclear star clusters in disk galaxies (based on the catalog
of Seth et al.) are also related to the dynamical mass M
25; the correlations with the luminosity and rotational velocity of the disk are appreciably weaker. For a given value of M
25, the masses of the central cluster are, on average, an order of magnitude higher in S0-Sbc galaxies than in late-type galaxies,
or than the SMBH masses. We suggest that the growth of the SMBH occurs in the forming “classical” bulge of the galaxy over
a time < 109 yr, during a monolithic collapse of gas in the central region of the protogalaxy. The central star clusters form on a different
time scale, and their stellar masses continue to grow for a long time after the growth of the central black hole has ceased,
if this process is not hindered by activity of the nucleus. 相似文献
8.
E. P. Kurbatov 《Astronomy Reports》2010,54(7):590-598
The ejection of stars from spheroidal and disk dwarf galaxies resulting from the decay of OB associations is studied. This
has substantial observational consequences for disk galaxies with escape velocities up to 20 km/s, or dynamical masses up
to 108
M
⊙. The ejection of stars can (i) reduce the abundances of the products of Type Ia supernovae and, to a lesser degree, Type
II supernovae, in disk stars, (ii) chemically enrich the galactic halo and intergalactic medium, (iii) lead to the loss of
50% of the stellar mass in galaxies with masses ∼107
M
⊙ and the loss of all stars in systems with masses ≲105
M
⊙, (iv) increase the mass-to-luminosity ratio of the galaxy. 相似文献
9.
The physical properties of young stellar objects are studied as functions of the initial spatial distributions of the gas
surface density Σ and angular velocity Ω in pre-stellar cores using numerical hydrodynamic simulations. Two limiting cases
are considered: spatially homogeneous cores with Σ = const and Ω = const and centrally concentrated cores with radius-dependent
densities Σ ∝ r
−1 and Ω ∝ r
−1. The degree of gravitational instability and protostellar disk fragmentation is mostly determined by the initial core mass
and the ratio of the rotational to the gravitational energy, and depends only weakly on the initial spatial configuration
of pre-stellar cores, except for the earliest stages of evolution, when models with spatially homogeneous cores can be more
gravitationally unstable. The accretion of disk matter onto a protostar also depends weakly on the initial distributions of
Σ and Ω, with matter from the collapsing core falling onto the disk at a rate that is slightly higher in models with spatially
homogeneous cores. An appreciable dependence of the disk mass, disk radius, and the disk-to-protostar mass ratio on the initial
density and angular velocity profiles of the parent core is found only for class 0 young objects; this relationship is not
systematic in the later I and II stages of stellar evolution. The mass of the central protostar depends weakly on the initial
core configuration in all three evolutionary stages. 相似文献
10.
E. I. Staritsin 《Astronomy Reports》2005,49(8):634-643
We study the rotation of a chemically homogeneous star with a mass of 16M⊙, assuming that the angular-momentum distribution in its radiative envelope is determined by hydrodynamical processes—flows and turbulent diffusion. Meridional circulation and horizontal shear turbulence are the main hydrodynamical processes forming the radial distribution of the angular momentum in young massive stars in the absence of magnetic fields. The rotation of such stars is close to steady-state. The angular velocity of rotation of the convective core can be ～5–20% higher than the surface value. Under these conditions, the characteristic time for the radial transport of angular momentum by meridional flows and shear turbulence is comparable to the nuclear time scale. 相似文献
11.
We present JHKLM photometry obtained in 1984–2009 for the RCB stars UV Cas and SU Tau. No major fadings characteristic of RCB stars were detected
during the observations of UV Cas, while two events of this kind occurred for SU Tau. The observed flux and color-index variations
can be explained with a changing dust concentration in the line of sight, and possibly variations of the stellar temperature.
We use the measured fluxes, supplemented with observations in the intermediate IR, to compute spherically symmetric dust-shell
models for the stars. The mass-loss rate is estimated to be 1.7 × 10−6
M
⊙ yr−1 for UV Cas and 4.1 × 10−6
M
⊙ yr−1 for SU Tau. 相似文献
12.
We present JHKLM photometry of the carbon stars ST And and T Lyn acquired in 2000–2010. Along with brightness variations due to pulsations,
changes on timescales of 2000–3000 days are also observed. Our combined light curves can be satisfactorily represented with
light elements derived from visual observations, but the maxima are delayed relative to the calculated times. A color-index
analysis demonstrates that the dust shell of ST And is fairly weak, and is manifest only episodically, while the presence
of hot dust was always detected for T Lyn. These results confirm models of spherically symmetric stellar dust shells based
on mean-flux data, supplemented with observations in the intermediate IR from the IRAS and AKARI satellites. The visual optical
depth of the relatively cool dust shell of ST And assuming a dust temperature at the inner edge of T
1 = 510 K is very low: τ
V = 0.047. The dust shell of T Lyn is considerably hotter (T
1 = 940 K), with τ
V = 0.95. We estimate the mass-loss rate to be 1.8 × 10−7
M
⊙/year for ST And and 3.7 × 10−7
M
⊙/year for T Lyn. 相似文献
13.
J. K. W. Lee 《Contributions to Mineralogy and Petrology》2000,139(5):526-540
The elucidation of thermal histories by geochronological and isotopic means is based fundamentally on solid-state diffusion
and the concept of closure temperatures. Because diffusion is thermally activated, an analytical solution of the closure temperature
(T
c
*) can only be obtained if the diffusion coefficient D of the diffusion process is measured at two or more different temperatures. If the diffusion coefficient is known at only
one temperature, however, the true closure temperature (T
c
*) cannot be calculated analytically because there exist an infinite number of possible (apparent) closure temperatures (Tˉ
c
) which can be generated by this single datum. By introducing further empirical constraints to limit the range of possible
closure temperatures, however, mathematical analysis of a modified form of the closure temperature equation shows that it
is possible to make both qualitative and quantitative estimates of T
c
* given knowledge of only one diffusion coefficient D
M
measured at one temperature T
M
. Qualitative constraints of the true closure temperature T
c
* are obtained from the shapes of curves on a graph of the apparent T
c
(Tˉ
c
) vs. activation energy E, in which each curve is based on a single diffusion coefficient measurement D
M
at temperature T
M
. Using a realistic range of E, the concavity of the curve shows whether T
M
is less than, approximately equal to, or greater than T
c
*. Quantitative estimates are obtained by considering two dimensionless parameters [ln
êRT^
c
vs. T
c
*/T
M
] derived from these curves. When these parameters are plotted for known argon diffusion data and for a given diffusion size
and cooling rate, it is found that the resultant curves are almost identical for all of the commonly dated K–Ar minerals –
biotite, phlogopite, muscovite, hornblende and orthoclase – in spite of differences in their diffusion parameters. A common
curve for Ar diffusion can be derived by least-squares fitting of all the Ar diffusion data and provides a way of predicting
a “model” closure temperature T
cm
from a single diffusion coefficient D
M
at temperature T
M
. Preliminary diffusion data for a labradorite lead to a T
cm
of 507 ± 17 °C and a corresponding activation energy of about 65 kcal/mol, given a grain size of 200 μm and a cooling rate
of 5 °C/Ma. Curves for He diffusion in silicates (augite, quartz and sanidine) also overlap to a significant degree, both
among themselves and with the Ar model curve, suggesting that a single model curve may be a good representation of noble gas
closure temperatures in silicates. An analogous model curve for a selection of 18O data can also be constructed, but this curve differs from the Ar model curve. A single model curve for cationic species
does not appear to exist, however, suggesting that chemical bonding relationships between the ionic size/charge and crystal
structure may influence the closure temperatures of diffusing cations. An indication of the degree of overlap among the various
curves for Ar, He, 18O and cations is also obtained by considering the dimensionless parameter E/RT
c
*; for the noble gases and 18O, E/RT
c
* values for the respective minerals are very similar, whereas for cations, there is significant dispersion. Given these constraints,
this may be a potential method of estimating closure temperatures for certain diffusing species when there are limited diffusion
data.
Received: 1 July 1999 / Accepted: 24 March 2000 相似文献
14.
15.
The surface gravities and effective temperatures have been added to a compilative catalog published earlier, which includes the relative abundances of several chemical elements for 100 field RR Lyrae stars. These atmoshperic parameters and evolutionary tracks from the Dartmouth database are used to determine the masses of the stars and perform a comparative analysis of the properties of RR Lyrae stars with different chemical compositions. The masses of metal-rich ([Fe/H] > −0.5) RR Lyrae stars with thin disk kinematics are in the range (0.51−0.60)M⊙. Only stars with initial masses exceeding 1M⊙ can reach the horizontal branch during the lifetime of this subsystem. To become an RR Lyrae variable, a star must have lost approximately half of its mass during the red-giant phase. The appearance of such young, metal-rich RR Lyrae stars is possibly due to high initial helium abundances of their progenitors. According to the Dartmouth evolutionary tracks for Y = 0.4, a star with an initial mass as low as 0.8 M⊙ could evolve to become an RR Lyrae variable during this time. Such stars should have lost (0.2−0.3)M⊙ in the red-giant phase, which seems quite realistic. Populations of red giants and RR Lyrae stars with such high helium abundances have already been discovered in the bulge; some of these could easily be transported to the solar neighborhood as a consequence of perturbations due to inhomogeneities of the Galaxy’s gravitational potential.
相似文献16.
A. B. Tutukov 《Astronomy Reports》2002,46(8):691-695
The conditions for the formation of planets and brown dwarfs around single main-sequence stars are considered in two scenarios. The formation of planets and brown dwarfs requires that the initial specific angular momentum of a solar-mass protostar be (0.32)×1018 cm2/s. The accreted matter of the protostar envelope forms a compact gas ring (disk) around the young star. If the viscosity of the matter in this ring (disk) is small, increasing its mass above a certain limit results in gravitational instability and the formation of a brown dwarf. If the viscosity of the gas is sufficiently large, the bulk of the protostar envelope material will be accreted by the young star, and the gas disk will grow considerably to the size of a protoplanetary dust disk due to the conservation of angular momentum. The formation of dust in the cool part of the extended disk and its subsequent collisional coalescence ultimately results in the formation of solar-type planetary systems. 相似文献
17.
The evolution of close binary systems containing Wolf-Rayet (WR) stars and black holes (BHs) is analyzed numerically. Both the stellar wind from the donor star itself and the induced stellar wind due to irradiation of the donor with hard radiation arising during accretion onto the relativistic component are considered. The mass and angular momentum losses due to the stellar wind are also taken into account at phases when the WR star fills its Roche lobe. It is shown that, if a WR star with a mass higher than ～10M ⊙ fills its Roche lobe in an initial evolutionary phase, the donor star will eventually lose contact with the Roche lobe as the binary loses mass and angular momentum via the stellar wind, suggesting that the semi-detached binary will become detached. The star will remain a bright X-ray source, since the stellar wind that is captured by the black hole ensures a near-Eddington accretion rate. If the initial mass of the helium donor is below ～5M ⊙, the donor may only temporarily detach from its Roche lobe. Induced stellar wind plays a significant role in the evolution of binaries containing helium donors with initial masses of ～2M ⊙. We compute the evolution of three observed WR-BH binaries: Cyg X-3, IC 10 X-1, and NGC 300 X-1, as well as the evolution of the SS 433 binary system, which is a progenitor of such systems, under the assumption that this binary will avoid a common-envelope stage in its further evolution, as it does in its current evolutionary phase. 相似文献
18.
Based on the theory of thermal conductivity, in this paper we derived a formula to estimate the prolongation period （AtL） of cooling-crystallization process of a granitic melt caused by latent heat of crystallization as follows：△tL=QL×△tcol/（TM-TC）×CP where TM is initial temperature of the granite melt, Tc crystallization temperature of the granite melt, Cp specific heat, △tcol cooling period of a granite melt from its initial temperature （TM） to its crystallization temperature （Tc）, QL latent heat of the granite melt.
The cooling period of the melt for the Fanshan granodiorite from its initial temperature （900℃） to crystallization temperature （600℃） could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference （ECTD） in granite batholith. 相似文献
The cooling period of the melt for the Fanshan granodiorite from its initial temperature （900℃） to crystallization temperature （600℃） could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference （ECTD） in granite batholith. 相似文献
19.
Data from the revised Geneva-Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences
of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of
the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative
metallicity gradient in the thin disk, are responsible for the observed negative correlation between the metallicities and
angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do
not depend on either age or metallicity. The velocity components of the Sun relative to the Local Standard of Rest derived
using data for stars born at the solar Galactocentric distance are (U
⊙, V
⊙, W
⊙)
LSR
= (5.1 ± 0.4, 7.9 ± 0.5, 7.7 ± 0.2) km/s. The two coordinates of the apex of the solar motion remain equal to 〈l
⊙〉 = 70° ± 7° and 〈b
⊙〉 = 41° ± 2°, within the errors. The indices for the power-law age dependences of them ajor, middle, and minor semi-axes become
0.26±0.04, 0.32±0.03, and 0.07±0.03, respectively. As a result, with age, the velocity ellipsoid for thin-disk stars born
at the solar Galactocentric distance increases only in the plane of the disk, remaining virtually constant in the perpendicular
direction. Its shape remains far from equilibrium, and the direction of the major axis does not change with age: the ellipsoid
vertex deviation remains constant and equal to zero within the errors (〈L〉 = 0.7° ± 0.6°, 〈B〉 = 1.9° ± 1.1°). Such a small increase in the velocity dispersion perpendicular to the Galactic plane with age can probably
be explained by “heating” of the stellar system purely by spiral density waves, without a contribution from giant molecular
clouds. 相似文献
20.
We consider the formation of massive stars under the assumption that a young star accretes material from the protostellar cloud through its accretion disk while losing gas in the polar directions via its stellar wind. The mass of the star reaches its maximum when the intensity of the gradually strengthening stellar wind of the young star becomes equal to the accretion rate. We show that the maximum mass of the forming stars increases with the temperature of gas in the protostellar cloud T 0, since the rate at which the protostellar matter is accreted increases with T 0. Numerical modeling indicates that the maximum mass of the forming stars increases to ～900 M ⊙ for T 0 ～ 300 K. Such high temperatures of the protostellar gas can be reached either in dense star-formation regions or in the vicinity of bright active galactic nuclei. It is also shown that, the lower the abundance of heavy elements in the initial stellar material Z, the larger the maximum mass of the star, since the mass-loss rate due to the stellar wind decreases with decreasing Z. This suggests that supermassive stars with masses up to 106 M ⊙ could be formed at early stages in the evolution of the Universe, in young galaxies that are almost devoid of heavy elements. Under the current conditions, for T 0 = (30–100) K, the maximum mass of a star can reach ～100M ⊙, as is confirmed by observations. Another opportunity for the most massive stars to increase their masses emerges in connection with the formation and early stages of evolution of the most massive close binary systems: the most massive stars can be produced either by coalescence of the binary components or via mass transfer in such systems. 相似文献