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1.
Ronald E. Taam 《Astrophysics and Space Science》1979,66(2):467-474
We have studied the thermonuclear runaways which develop on white dwarfs of 1.205M
and 1.358M
accreting hydrogen rich material at 10–10
M
yr–1. It is found that ignition of this material occurs at densities in excess of about 104 gm cm–3 and that the critical accumulated mass required to initiate the runaway is 0.7(1.5)×10–4
M
for a 1.358(1.205)M
white dwarf. 相似文献
2.
Shiv S. Kumar 《Astrophysics and Space Science》1972,17(1):219-222
It is suggested that the minimum mass of a star at the time of its formation is approximately 0.01M
. Making use of this fact and the stellar mass functionF(M) M
–, it is found that the hidden mass (or the missing mass) in the solar neighborhood may be explained by the presence of a large number of invisible stars of very low mass (0.01M
M<0.07M
). 相似文献
3.
M. D. T. Naylor 《Astrophysics and Space Science》1972,18(1):59-84
Internal models have been obtained for uniformly rotating synchronous close binary systems using a modified double approximation scheme. We have considered primaries of 10M
, 5M
, and 2M
with mass ratios of 0.0 to 1.0 in steps of 0.1, and some results are given for a 1M
primary with a mass ratio of 1.0. A maximum luminosity reduction of 2.3% was found for a 10M
primary with a mass ratio of 1.0 and 7.7% for a mass ratio of 0.0. The corresponding values for 5M
are 2.0% and 7.0%, and for 2M
they are 1.6% and 5.3%, respectively. These values were not found to be sensitive to small changes in composition. The maximum equatorial velocity varies from 399 km s–1 for 2M
to 567 km s–1 for 10M
when the mass ratio is zero, but these velocities decrease by 200–300 km s–1 if the mass ratio is unity. The effect of gravity darkening on the apparent position of the primary in the theoretical H-R diagram was investigated. It was determined that an unresolved close binary of unit mass ratio can lie up to 0.9 magnitudes (depending on inclination) above the main sequence, whereas if the effects of distortion are ignored this number is at most 0.75 magnitudes. There seems to be some observational support for the larger value. Two models of the secondaries are given and their dimensions are compared with their critical Roche lobes. 相似文献
4.
In this paper we calculate the number of close binaries formed during the evolution process of a globular cluster core. The globular cluster core is assumed to contain a massive black hole at its center. We show that the central black hole can drive binaries formation in the core and the rate of binaries formation depends on the mass of the black hole at its center. When the massM of the black hole is between 102
M
and 3×103
M
, there will be a few binaries formed. When the mass of the black hole is 4×103
M
M6×103
M
, the number of binary star formation will suddenly increase with a jump to the maximum value 58. When the mass of the black hole is 7×103
M
M9×103
M
, the number of binary star will immediately decrease. Whether cluster X-ray is produced mainly by the central black hole or by binaries in the core depends on the mass of the central black hole. Therefore, two cases arise: namely, black hole accretion domination and binaries radiation domination. We do think that we cannot exclude the possibility of the existence of a central black hole even when binary radiation characteristics have been observed in globular cluster X-ray sources. 相似文献
5.
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
6.
C12 stars in the range 1.04–1.55M
are evolved to simulate the core evolution of the possible precursors of planetary nebulae. The nuclear shell burning in stars above 1.2M
advances to within about 0.2M
of the surface, where the intense radiation interacts with the surface matter and causes mass loss. Comparison between our theoretical results and observations suggests that this may be a mechanism by which planetary nebulae are formed.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968. 相似文献
7.
Zhi-Yao Yu 《Astrophysics and Space Science》1993,210(1-2):167-168
The life-time of the star on AGB is approximately 6 × 104 yr. We divide it into front half and back half of AGB (including to optical Mira variable and OH/IR star) according to their evolution character. The observations show that the star has non-pulsation, but constant mass loss rate ( 5 × 10–7
M
yr–1) on front half of AGB. Its circumstellar envelope is formed. When the star has pulsation on back half of AGB, its mass loss rate is relative with time, and increases gradually. In this time the star is on the stage of optical Mira variable. When the mass loss rate reaches the value of 3 × 10–6
M
yr–1, the star evoluted from the stage of optical variable into the stage of radio bright OH/IR star. On the end of AGB the mass loss rate reaches 10–4
M
yr–1. (Band and Habing 1983, Hermen and Habing 1985). 相似文献
8.
Time resolved spectroscopy of the dwarf nova IP Pegasi in the range 7670–8320Å shows absorption lines originating from the cool secondary. A radial velocity curve for this component has been derived by cross-correlation with a normal M star. The curve has semi-amplitude K2=288.3±4 km s–1, and is slightly distorted. This distortion is equivalent to an orbit with an apparent eccentricity of 0.075±0.024. The mass function of the primary is 0.394±0.016M. From this we derive constraints on the component masses of 0.621<1.14M and 0.172<0.71M. The red star has a radius in the range 0.322<0.51R and is probably on the main sequence.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
9.
K. R. Radhakrishnan M. B. K. Sarma K. D. Abhyankar 《Astrophysics and Space Science》1984,99(1-2):229-236
UBV light curves and spectrograms of R CMa obtained with the 48-inch telescope of Japal-Rangapur Observatory during 1980–82 have been used for deriving the eclipse and orbital elements as well as the absolute dimensions of the components. The primary is found to be a Main-Sequence F2V star of mass 1.52M
and the secondary a subgiant star of spectral type G8 and mass 0.20M
which fills its Roche lobe, in agreement with Kopal and Shapley (1956) results, Kopal (1959), or Sahade's (1963) results. From a consideration of the possible evolution of this system it is concluded that a large fraction of the original mass of the secondary is lost from the system. A study of the period changes indicates the possible presence of a third component of mass of about 0.5M
which is most likely to be anM dwarf.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983. 相似文献
10.
V. P. Utrobin 《Astrophysics and Space Science》1978,55(2):441-457
The study of supernova (SN) models with slow energy pumping is continued. At maximum luminosity the main characteristics of a SN are shown to be independent of the initial structure of the model (Table I, Figure 1). However, they depend on the massM
e of the envelope, and on the intensity of energy pumpingL
, with an increase ofM
e leading qualitatively to the same changes in the SN parameters as a decrease inL
(Table I, Figures 2 and 3). A simple relationship connecting the important SN parameters is obtained (Equation (6)). From the inflection of the color indexB-V curve, the possibility of deriving the characteristic time of energy pumping with intensityL
1044 erg s–1 is pointed out. The comparison of the extragalactic type I SN observations with the results of calculations leads to the estimate ofM
e 0.3–0.7M.An investigation of the galactic type I SN remnants is carried out (Table III). The estimate ofM
e 0.2–0.3M
is obtained for the remnants of supernovae SN 1006, SN 1572, and SN 1604. It completely fits the results for the extragalactic type I SNs. The total initial mass of SN 1604 presupernova was shown to be at least about 7M
.It was established that the Crab nebula resulted from the outburst of a peculiar SN. The unique properties of such SNs, including SN 1054, are due to the low intensity of energy pumping (L
1042 erg s–1). The mass of the envelope of the Crab nebula is evaluated to beM
e 0.7M
. SN 1054 was shown to have m
max
v
=–4
m
.
0 at maximum luminosity. 相似文献
11.
High resolution OVRO CO 1–0 observations of the inner 30 in the LINER galaxy NGC 5218 reveal the presence of a double centrally peaked molecular concentration with extensions out to a radius of 12. The molecular mass detected is 2.4 × 109 M and the gas surface density is high, 3000 M pc square in the inner 500 pc. The SFR is 2–3 M yr–1 and the SFE is 13, which are low or moderate values for that gas surface density. We interpret the inner feature as a rotating molecular ring with a radius of 200 pc. We furthermore suggest that the LINER activity in NGC 5218 is not caused by an aging starburst, but by a buried AGN. 相似文献
12.
High dispersion time-resolved spectrograms of the dwarf nova SS Cygni, obtained with the Echelle-Mepsicron system, show double peaked emission lines with a complex profile. The intensity of the H line appears to be modulated by the orbital period. Radial velocity measurements of the wings of H and of the absorption line system of the late-type star yield semiamplitude values of Kem=101±6 km s–1 and Kab=151±7 km s–1, respectively. Radial velocity measurements of the blue and red peaks and of the central absorption of H reveal a synchronous movement with the broad wings, although there is some evidence of a narrow component probably associated with a hot spot in the disk or a chromospheric emission line from the secondary star. The H modulation, the double profile and recently discovered UBV light variations support an inclination angle i 50°. The masses of the primary are Mp=0.60 M and Ms=0.40 M, respectively. A detailed analysis of the absorption lines reveals a spectral type of K2V.Paper presented at the IAU Colloquium No. 93 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.
T. Iijima 《Astrophysics and Space Science》1988,150(2):235-250
Results of high-dispersion spectroscopy (10 Å mm–1) of the symbiotic star AX Per carried out in the years from 1979 to 1987 are reported. The emission line [FeVII] 6086 consists of a narrow and a broad component; the radial velocity of the narrow one varies according to the photometric period 681.6 days. This variation (K=30.6±1.5 km s–1) seems to be due to the orbital motion of the hot star. The radial velocity of absorption lines varies with an inverse phase dependence and a much smaller amplitude (K=5.6±2 km s–1), which may reflect the orbital motion of the red giant. The variation of the radial velocity of the emission lines of FeII, ect. (K=6.7±1.5 km s–1) might be due to the rotation of the red giant. The profile of H emission line suddenly changed around the phase of the photometric minimum, which could be explained as a result of an eclipse of the emitting region by the red giant. On the other hand, some problems remain open in the behaviour of the radial velocities of H and HeI 5876.The observed results support a binary model of AX Per consisting of a rather massive (3M
) M-type giant and a Main-Sequence star (0.6M
). AX Per seems to be in an early stage of the Case C mass transfer, and the estimated very high mass accretion rate (10–4
M
yr–1) is consistent with the theoretical models. The narrow component of the emission line of [FeVII] 6086 might be emitted in radiatively driven polar jets on the hot star of which luminosity is close to the Eddington limit.A new identification as ZrII at 6106.47 Å is proposed for the emission line at 6106 Å. 相似文献
14.
Mariko Kato 《Astrophysics and Space Science》1986,119(1):57-59
Structures of Newtonian super-massive stars are calculated with the opacity for Comptor effectK
0/(1 + T), whereK
0=0.21(1 +X and =2.2×10–9K–1. The track of the Main-Sequence is turned right in the upper part of the HR diagram. Mass loss will occur in a Main-Sequence stage for a star with mass larger than a critical mass. The cause of mass loss and the expansion of the radius is continuum radiation pressure. The critical mass for mass loss is 1.02×106
M
for a Population I star, and 1.23×105
M
for Population III star. Mass loss rates expected in these stars are 3.3×10–3 and 4.0×10–3
M
yr–1, respectively.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
15.
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
16.
Dilhan Eryurt-Ezer 《Astrophysics and Space Science》1981,79(2):265-287
The theoretical evolution of a first-generation star of 3M
after the core helium-exhaustion phase has been investigated. The star displays the character of a double shell burning model. Shell hydrogenburning produces energy mostly by the p-p chain reaction. CN-cycle reaction is only operating in the inner edge regions where sufficient amount of carbon is formed by the 3-reactions. Hence, the shell burning time of the star is longer than that of normal stars, thus lengthening the total evolutionary lifetime of the first-generation stars.Prior to carbon-burning phase, the mass of the complete hydrogen-exhausted region is 1.14M
and that of complete helium-exhausted region is 0.83M
. A carbon-oxygen core of about 0.87M
has developed within the star in which the ratio of carbon to oxygen is about 0.85, but decreases down to a value of 0.50 near the boundary of the core. 相似文献
17.
We studied grain formation process and flow structure around cool luminous mass-loss stars. The nucleation and growth theory of Yamamoto and Hasegawa was extended to the case of expanding gas flow.The envelope was assumed to be steady, spherically symmetric, in thermal and radiative equilibrium, optically thin, and driven by radiation pressure on grains. For oxygen rich stars, Mg-silicate was found to be the first condensate which can drive the gas effectively. The following stellar parameters were chosen; stellar massM
*=1M
, effective temperatureT
*=3000K, stellar luminosityL
* from 7.5×103 to 2.0×104
L
, and mass-loss rate |M| from 1.0×10–6 to 1.0×10–4
M
yr–1.Main results of calculations are as follows; (1) grain condensation temperatureT
c9801080 K; (2) total gas pressure at the condensation pointP
t6×10–116×10–9 atm; (3) scale parameterA
c1036×104; and (4) final grain sizer
f=400Å1m. For the smaller |M| or the largerL
*, these values are the smaller. We recognized two types of flow solutions (1) Dust driven flow for large |M|, which reaches the sonic point near the condensation point; and (2) Modified Parker flow for small |M| for which grain sizer
f is almost independent of |M|.A comparison with observational results ofL
* and gas terminal velocityV
suggests that Mg-silicate grains are of submicron size, which are effective for interstellar extinction in visible and infrared. Fe-grains condense in the rarefied outflow with a size probably smaller than 100Å, which may contribute for interstellar ultraviolet extinction. The envelope has three-layer structure inner dense region with small outflow velocity, grain formation layer and outer rarefied region with fast outflow velocity.No flow solutions exist forM
* greater than a critical stellar massM
*cr for a given stellar luminosityL
* and mass-loss rate |M|.For example, critical stellar massM
*cr=1.8M
forL
*=104
L
,T
*=3000 K, and |M|=10-5
M
yr-1. 相似文献
18.
M. Jura 《Astronomy and Astrophysics Review》1991,2(3-4):227-247
Summary In the solar neighborhood, approximately half of all intermediate mass main sequence stars with initially between 1 and about 5 Mbecome carbon stars with luminosities near 104 L for typically less than 106 years. These high luminosity carbon stars lose mass at rates nearly always in excess of 10–7 M yr–1 and sometimes in excess of 10–5 M yr–1. Locally, close to half of the mass returned into the interstellar medium by intermediate mass stars before they become white dwarfs is during the carbon star phase. A much greater fraction of lower metallicity stars become carbon-rich before they evolve into planetary nebulae than do higher metallicity stars; therefore, carbon stars are much more importan t in the outer than in the inner Galaxy. 相似文献
19.
The evolution of a binary system with components of 10M
and 8M
is computed through a case B of mass exchange. It is found that after the end of core helium burning, a second stage of mass transfer from the primary occurs. Carbon ignition is prohibited by the large neutrino losses in the degenerated core. The primary remnant, a 1.12M
star, ends as a white dwarf. A comparison with the 10M
single evolution is made.This research is supported by the National Foundation of Collective Fundamental Research of Belgium (F.K.F.O.) under No. 10303. 相似文献
20.
Hiroyasu Ando 《Astrophysics and Space Science》1980,71(1):249-256
Preliminary study of the eclipsing binary AB Cas is presented here by using the photometric observational data. The primary component is one of the Sct variables with period of 0d.054, and whether the oscillation is of a radial mode or of a non-radial one is discussed. Two colour indices (B-V andU-B) data and the light curve analysis suggest that this binary system is a typical Algol type binary system, in which the primary component is near the ZAMS with about 2.3M
and the secondary one is a subgiant star with about 0.5M
. 相似文献