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1.
We present multi-colour CCD observations of the low-temperature contact binaries, V453 Mon and V523 Cas. Their light curves
are modelled to determine a new set of stellar and orbital parameters. Analysis of mid-eclipse times yields a new linear ephemeris
for both systems. A period decrease (dP/dt=2.3×10−7 days/yr) in V453 Mon is discovered. V523 Cas, however, is detected to show a period increase (dP/dt=9.8×10−8 days/yr) because of the mass transfer of a rate of 1.1×10−7 M⊙ yr−1, from a less massive donor. Using these findings we can determine the physical parameters of the components of V523 Cas to
be M
1=0.76 (3)M
⊙, M
2=0.39 (2)M
⊙, R
1=0.74 (2)R
⊙, R
2=0.55 (2)R
⊙, L
1=0.19 (3)L
⊙, L
2=0.14 (3)L
⊙, and the distance of system as 46(9) pc. 相似文献
2.
Yu. A. Fadeyev 《Astronomy Letters》2010,36(5):362-369
Hydrodynamic calculations of nonlinear radial oscillations of LBV stars with effective temperatures 1.5 × 104 K ⩽ T
eff ⩽ 3 × 104 K and luminosities 1.2 × 106
L
⊙ ⩽ L ⩽ 1.9 × 106
L
⊙ have been performed. Models for the evolutionary sequences of Population I stars (X = 0.7, Z = 0.02) with initial masses 70M
⊙ ⩽ M
ZAMS ⩽ 90M
⊙ at the initial helium burning stage have been used as the initial conditions. The radial oscillations develop on a dynamical
time scale and are nonlinear traveling waves propagating from the core boundary to the stellar surface. The amplitude of the
velocity variations for the outer layers is several hundred km s−1, while the bolometric magnitude variations are within ΔM
bol ⩽ 0·
m
2. The onset of oscillations is not related to the κ-mechanism and is attributable to the instability of a self-gravitating envelope gas whose adiabatic index is close to its
critical value of Γ1 = 4/3 due to the dominant contribution of radiation in the internal energy and pressure. The interval of magnitude variation
periods (6 days ≤ II ≤ 31 days) encompasses all currently available estimates of the microvariability periods for LBV stars,
suggesting that this type of nonstationarity is pulsational in origin. 相似文献
3.
Two CCD epochs of light minimum and a complete R light curve of SS Ari are presented. The light curve obtained in 2007 was
analyzed with the 2003 version of the W-D code. It is shown that SS Ari is a shallow contact binary system with a mass ratio
q=3.25 and a degree of contact factor f=9.4%(±0.8%). A period investigation based on all available data shows that there may exist two distinct solutions about the
assumed third body. One, assuming eccentric orbit of the third body and constant orbital period of the eclipsing pair, results
in a massive third body with M
3=1.73M
⊙ and P
3=87.0 yr. On the contrary, assuming continuous period changes of the eclipsing pair the orbital period of tertiary is 37.75
yr and its mass is about 0.278M
⊙. Both of the cases suggest the presence of an unseen third component in the system. 相似文献
4.
A compact structure of a low-mass Type I presupernovae is assumed to be an essential feature of the hydrodynamical problem
dealing with the supernova Type I (SNI) envelope outbursts. This structure is characterized by a degenerate carbon-oxygen
core, which suffers a thermonuclear explosion of carbon fuel (M
0≃1.40M
⊙), and by a compact lowmass envelope (M
e
≲0.1M
⊙) with external radiusR
e≃109 cm. The parameters, of this hydrostatic envelope are specified and then, for a relatively small explosion energy, ofW
0≃(2–10)×1049 erg, hydrodynamic problem of the envelope ejection is solved numerically. This energy comes from neutrino-induced detonative
carbon burning. The resulting structure of the SNI atmosphere expanding with the velocity gradient can be employed for an
interpretation of the observed SNI spectra. In accordance with our previous papers, the SNI light curves are considered to
occur due to an additional slow (with time-scale 106–107 s) release of the bulk of the SNI energy,W≃1051, erg. The slow energy release does not, however, affect the structure of the outermost expanding layers of the envelope which
are responsible for the SNI spectra.
A short (Δt≃10−2 s) burst of soft (2–10 keV) X-rays with total radiated energy of about 1040 erg is found to appear 10–20 days before the SNI optical maximum. 相似文献
5.
Yu. A. Fadeyev 《Astronomy Letters》2011,37(6):403-413
Instability of population I (X = 0.7, Z = 0.02) massive stars against radial oscillations during the post-main-sequence gravitational contraction of the helium core
is investigated. Initial stellar masses are in the range 65M
⊙ ≤ M
ZAMS ≤ 90M
⊙. In hydrodynamic computations of self-exciting stellar oscillations we assumed that energy transfer in the envelope of the
pulsating star is due to radiative heat conduction and convection. The convective heat transfer was treated in the framework
of the theory of time-dependent turbulent convection. During evolutionary expansion of outer layers after hydrogen exhaustion
in the stellar core the star is shown to be unstable against radial oscillations while its effective temperature is T
eff > 6700 K for M
ZAMS = 65M
⊙ and T
eff > 7200 K for M
ZAMS = 90M
⊙. Pulsational instability is due to the κ-mechanism in helium ionization zones and at lower effective temperature oscillations decay because of significantly increasing
convection. The upper limit of the period of radial pulsations on this stage of evolution does not exceed ≈200 day. Radial
oscillations of the hypergiant resume during evolutionary contraction of outer layers when the effective temperature is T
eff > 7300 K for M
ZAMS = 65M
⊙ and T
eff > 7600 K for M
ZAMS = 90M
⊙. Initially radial oscillations are due to instability of the first overtone and transition to fundamental mode pulsations
takes place at higher effective temperatures (T
eff > 7700 K for M
ZAMS = 65M
⊙ and T
eff > 8200 K for M
ZAMS = 90M
⊙). The upper limit of the period of radial oscillations of evolving blueward yellow hypergiants does not exceed ≈130 day.
Thus, yellow hypergiants are stable against radial stellar pulsations during the major part of their evolutionary stage. 相似文献
6.
L. V. Glazunova 《Astronomy Letters》2011,37(6):414-419
Based on two high-dispersion spectra of the close binary BW Boo, we have detected lines of the secondary component whose contribution
to the combined spectrum does not exceed 2%. We have determined the rotation velocities of the components and spectroscopic
orbital elements. Numerous lines of neutral and ionized iron have been used to determine the effective temperature and surface
gravity for the primary component. The photometric light curves for this binary have been solved for the first time. Its primary
component is an A2Vm star with a mass of 2 ± 0.1M
⊙ and a radius of 1.9 ± 0.4R
⊙. Its rotation velocity is 2 km s−1, which is a factor of 18 lower than the pseudo-synchronous velocity for this component. The G6 secondary component, a T Tau
star, has a rotation velocity of 17 km s−1, amass of 1.1M
⊙, and a radius of 1 R
⊙. The age of the binary has been estimated to be 107 yr. 相似文献
7.
Yu. A. Fadeyev 《Astronomy Letters》2011,37(1):11-19
The evolution of Population I stars (X = 0.7, Z = 0.02) with initial masses 40M
⊙ ≤ M
ZAMS ≤ 120M
⊙ until core hydrogen exhaustion has been computed. Models of evolutionary sequences have been used as the initial conditions
in solving the equations of radiation hydrodynamics that describe the spherically symmetric motion of a self-gravitating gas.
Stars with initial masses M
ZAMS ≥ 50M
⊙ are shown to become unstable against radial oscillations during the main-sequence evolution. The instability growth rate
and the limit-cycle oscillation amplitude increase as the star evolves and as its initial mass increases. The pulsational
instability is attributable to the iron Z-bump κ mechanism (T ∼ 2 × 105 K). Convection that transfers from 20 to 50% of the total energy flux and, thus, reduces the efficiency of the κ mechanism emerges in the same layers. The periods of the radial oscillations of main-sequence stars lie within the range
from 0.09 to 8 days. The boundaries of the instability region of radial pulsations in the Hertzsprung-Russell diagram have
been determined and observational criteria for revealing pulsating variable main-sequence stars have been proposed. 相似文献
8.
We propose a model for the bolometric light curve of a type-Ia supernova (SN Ia) that explodes in a dense circumstellar (CS) envelope. Our modeling of the light curves for SN 2002ic and SN 1997cy shows that the densities of the CS envelopes around both supernovae at a radius of ~7×1015 cm are similar, while the characteristic ejection time for this envelope around SN 1997cy does not exceed 600 yr. We analyze two possible evolutionary scenarios that could lead to the explosion of a SN Ia inside a dense C S hydrogen envelope: accretion onto a CO white dwarf in a symbiotic binary and the evolution of a single star with an initial mass of about 8M⊙. If the hypothesis of a SN Ia explosion in a dense CS envelope is correct for SN 2002ic and SN 1997cy, then we must assume that the the rapid loss of the red-supergiant envelope in several hundred years and the subsequent explosion of the CO white dwarf are synchronized by some physical mechanism. This mechanism may be related to the contraction of the white dwarf as it approaches the Chandrasekhar limit. We show that the formation of a (super-)Chandrasekhar mass due to the merger of a CO white dwarf and the CO core of a red supergiant followed by a supernovae explosion is unlikely, since this mechanism does not provide the required synchronization of the rapid mass loss and the explosion. 相似文献
9.
Ken’ichi Nomoto Keiichi Maeda Masaomi Tanaka Tomoharu Suzuki 《Astrophysics and Space Science》2011,336(1):129-137
The connection between long Gamma Ray Bursts (GRBs) and Supernovae (SNe) have been established through the well observed cases.
These events can be explained as the prompt collapse to a black hole (BH) of the core of a massive star (M≳40M
⊙). The energies of these GRB-SNe were much larger than those of typical SNe, thus these SNe are called Hypernovae (HNe). The
case of SN 2006aj/GRB060218 appears different: the GRB was weak and soft, being called an X-Ray Flash (XRF); the SN is dimmer
and has very weak oxygen lines. The explosion energy of SN 2006aj was smaller, as was the ejected mass. In our model, the
progenitor star had a smaller mass than other GRB-SNe (M∼20M
⊙), suggesting that a neutron star (NS) rather than a BH was formed. If the nascent NS was strongly magnetized as a magnetar
and rapidly spinning, it may launch a weak GRB or an XRF. The peculiar light curve of Type Ib SN 2005bf may also be powered
by a magnetar. The blue-shifted nebular emission lines of 2005bf indicate the unipolar explosion possibly related to standing
accretion shock instability (SASI) associated with a newly born NS. 相似文献
10.
Atsuma Yamasaki 《Astrophysics and Space Science》2005,296(1-4):277-280
New BV light curves of the A-type W UMa star AQ Psc (P = 0.476d) have been observed and are described. A few times of minimum light are obtained and the ephemeris is improved.
The light curves are analyzed for the binary parameters with a light curve synthesis method. Combining the results with Lu
and Rucinski’s spectroscopic mass ratio we determined the masses and radii of the components: M
1 = 1.69M
⊙, M
2 = 0.38M
⊙, R
1 = 1.77R
⊙, and R
2 = 0.89R
⊙. 相似文献
11.
V. M. Chechetkin S. S. Gershtein V. S. Imshennik L. N. Ivanova M. Yu. Khlopov 《Astrophysics and Space Science》1980,67(1):61-97
The present work studies the hydrodynamic process of thermonuclear explosion of hydrostatic equilibrium, degenerate carbon-oxygen
cores withM
C=1.40M
⊙ with different values of central densityϱ
c
within the interval 2 × 109 <ϱ
c
< 3 × 1010 g cm−3. The initial temperature distribution has been determined by the preceding thermal stage of explosion. The calculations successively
include the kinetics of thermonuclear burning, the kinetics of β-processes, and neutrino energy losses. By considering the
neutrino mechanism of heating and carbon ignition we obtained in our numerical hydrodynamic calculations two characteristic
versions of the development of an explosion: (a) at 2 × 109 <ϱ
c
< 9 × 109 g cm−3 there is disruption of the whole star with either complete or partial burning of the carbon and a 1050–1051 erg kinetic energy; and (b) at 9 × 109 <ϱ
c
< 3 × 1010 g cm−3 the stellar core collapses into a neutron star with partial outburst of the outer envelope with a smaller kinetic energy
of 1049–1050 erg. The paper proposes and details a hypothesis (the scenario of supernovae and the formation of neutron stars) on the first
version of explosion, corresponding to SNII, and on the second, supplemented by some mechanism of slow energy release into
the envelope expelled from the newly formed neutron star, corresponding to SNI. On the basis of the proposed hypothesis a
satisfactory agreement with the observed masses and energies of the supernovae envelope, their light curves and spectra, as
well as with the data on their chemical composition has been obtained. For this agreement we must assume that type I pre-supernovae
are almost bare compact carbon-oxygen stellar cores, and that type II presupernovae are red supergiants. It is most probable
that the evolution of type I pre-supernovae occurs in close binaries while the evolution of type II pre-supernovae seems to
be very similar to the evolution of a single star. 相似文献
12.
The initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime ofEXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984#1 (PW Vul), and two observations of Nova Vulpeculae 1984#2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is 2 to 3 years, which leads to the conclusion that the burned envelope massM
burn should be of the order of
. The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9M
, core luminosity of 2×104
L
, and envelope mass of 10–6
M
, can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have 1.1M
core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind withM5×10–7
M
yr–1 appears to be necessary. The few observations of Nova Vulpeculae 1984 #1 and Nova Vulpeculae 1984#2, during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F. R. G., 16–19 June, 1986. 相似文献
13.
Mark Cropper Silvia Zane Roberto Turolla Luca Zampieri Matteo Chieregato Jeremy Drake Aldo Treves 《Astrophysics and Space Science》2007,308(1-4):161-166
We report XMM-Newton observations of the isolated neutron star RBS1774 and confirm its membership as an XDINS. The X-ray spectrum is best fit
with an absorbed blackbody with temperature kT=101 eV and absorption edge at 0.7 keV. No power law component is required. An absorption feature in the RGS data at 0.4 keV
is not evident in the EPIC data, but it is not possible to resolve this inconsistency. The star is not seen in the UV OM data
to m
AB
∼21. There is a sinusoidal variation in the X-ray flux at a period of 9.437 s with an amplitude of 4%. The age as determined
from cooling and magnetic field decay arguments is 105–106 yr for a neutron star mass of 1.35–1.5 M⊙.
相似文献
14.
The ionizing star BD+60°2522 is known as the central star of Bubble Nebulae NGC 7635—wind-blown bubble created by the interaction
of the stellar wind of BD+60°2522 (O6.5 IIIef, V=8.7 mag, mass loss rate 10−5.76
M
⊙/year) with the ambient interstellar medium. From the evolutionary calculations for the star with mass loss and overshooting,
we find that the initial mass of the star is 60M
⊙, its present age is 2.5×106 years, and the present mass is 45M
⊙. 相似文献
15.
We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as
massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates
were selected from the Massey et al. catalog based on the following criteria: emission in H
α
, V<18./m 5 and 0.m 35 < (B - V) < 1.m 2. The spectra of both stars reveal a broad and strong H
α
emission with extended wings (770 and 1000 kms−1). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L⊙) = 6.0–6.2 with the value of interstellar extinction A
V
= 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero
Age Main Sequence is M∼ 60–80 M⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts
to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable
variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L⊙) = 6.3 − 6.6, the value of interstellar extinction is A
V
= 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two
thermal components with the temperatures Twarm ∼ 1000K and Tcold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines
indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and
broad H
α emissions allow classifying the studied objects as LBV candidates. 相似文献
16.
We present observations and light curve analysis of the eclipsing binary R CMa in the narrow band filters v and b. Observations were made during 1993 at Biruni Observatory and the light curves have been analyzed using the Wilson-Devinney
light curve interpretation program. Assuming a semi-detached configuration for R CMa, the parameters i, Ω1, L
1, T
2 and A
2 were adjusted for the best fit between the synthesized light curves and observations. Both light curves were fitted well
with a lower value of bolometric albedo than what would be expected for a normal cool star with a convective envelope. The
masses of the primary and secondary components and the absolute dimensions of the stars have been calculated using the derived
relative dimensions from Wilson-Devinney codes and the spectroscopic observations. 相似文献
17.
Zhe Chen Jiang Zhang YanPing Chen WenYuan Cui Bo Zhang 《Astrophysics and Space Science》2006,306(1-2):33-39
The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metal-poor stars on the left-side [{Ba/Mg}]--[{Mg/H}] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass M
ms ≤ 18 M
⊙ are infertile sources and the SNe II with 20 M
⊙ ≤ M
ms ≤ 40 M
⊙ are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20 M
⊙ ≤ M
ms ≤ 40 M
⊙
with compared to the all massive stars is about∼ 18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced. 相似文献
18.
Cross correlations between observed and synthetic spectra are used to discover yet another satellite of BM Ori with the following
characteristics: effective temperature Teff = 4000 K, radius R = 16R⊙, mass M = 1.8M⊙, spectral type K7 III, absolute bolometric stellar magnitude Mb = + 4m·0, axial rotation velocity V sini = 85 km/s, and relative luminosity 0.005 near the V band.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 111–120 (February 2006). 相似文献
19.
Main results of computations of evolution for massive close binaries (10M
+9.4M
, 16M
+15M
, 32M
+30M
, 64M
+60M
) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars — mass exchange — Wolf-Rayet star or blue supergiant plus main sequence star — explosion of the initially more massive star appearing as a supernova event — collapsed or neutron star plus Main-Sequence star, that may be observed as a runaway star — mass exchange leading to X-rays emission — collapsed or neutron star plus WR-star or blue supergiant — second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars.Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries. 相似文献
20.
Synthetic light curve solutions for the W UMa-system VW Cep have been determined by applying the most new version of Wilson
(1998)approach to B-observations of 1996 and VRI-observations of 1999. From a consideration of the possible evolution of this
system, it is found that the system is a partial eclipsing contact one, and its primary to be a nearly Main-Sequence F5 star
of mass 0.85 M
⊙ and the secondary to be a dwarf of spectral type G0 of mass 0.34 M
⊙.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献