共查询到20条相似文献,搜索用时 31 毫秒
1.
F. Sánchez-Bajo E. García-Melendo J. M. Gómez-Forrellad 《Astrophysics and Space Science》2007,312(3-4):151-159
New ephemeris and the absolute parameters—masses, radii and luminosities—of the contact systems VW LMi and BX Dra have been
obtained, by means of the analysis of the minima data available in the literature (for the determination of the ephemeris)
and combining the previously published spectroscopic information and the results of the Wilson-Devinney method using photometric
data (for the determination of the absolute parameters). The VW LMi O−C analysis confirms the multiplicity of the system detected previously from the spectroscopic data. Masses of the VW LMi contact
system primary and secondary components are 1.67 ± 0.02M
⊙ and 0.70 ± 0.02M
⊙, respectively. The corresponding radii are 1.709 ± 0.007R
⊙ and 1.208 ± 0.006R
⊙, respectively. For the BX Dra contact system the masses are 2.19 ± 0.13M
⊙ and 0.63 ± 0.06M
⊙, and the radii, 2.13 ± 0.04R
⊙ and 1.26 ± 0.03R
⊙, for the primary and secondary, respectively. In both cases, the estimated luminosities seem to be slightly greater that
the values derived from the Hipparcos distances. 相似文献
2.
Based on high precision measurements of the distances to nearby galaxies with the Hubble telescope, we have determined the
radii of the zero velocity spheres for the local group, R0 = 0.96±0.03Mpc, and for the group of galaxies around M 81/M 82, 0.89±0.05Mpc. These yield estimates of MT = (1.29±0.14)· 1012 M⊙ and (1.03±0.17)· 1012 M⊙, respectively, for the total masses of these groups. The R0 method allows us to determine the mass ratios for the two brightest members in both groups, as well. By varying the position
of the center of mass between the two principal members of a group to obtain minimal scatter in the galaxies on a Hubble diagram,
we find mass ratios of 0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81 galaxies, in good agreement
with the observed ratios of the luminosities of these galaxies.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 5–22 (February 2006). 相似文献
3.
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
4.
We present the results of our infrared observations of WR 140 (=V1687 Cyg) in 2001–2010. Analysis of the observations has
shown that the J brightness at maximum increased near the periastron by about 0
m
.3; the M brightness increased by ∼2
m
in less than 50 days. The minimum J brightness and the minimum L and M brightnesses were observed 550–600 and 1300–1400 days after the maximum, respectively. The JHKLM brightness minimum was observed in the range of orbital phases 0.7–0.9. The parameters of the primary O5 component of the
binary have been estimated to be the following: R(O5) ≈ 24.7R
⊙, L(O5) ≈ 8 × 105
L
⊙, and M
bol(O5) ≈ −10
m
. At the infrared brightness minimum, T
g ∼ 820–880 K, R
g ≈ 2.6 × 105
R
⊙, the optical depth of the shell at 3.5 μm is ∼5.3 × 10−6, and its mass is ≈1.4 × 10−8
M
⊙. At the maximum, the corresponding parameters are ∼1300 K, 8.6 × 104
R
⊙, ∼2 × 10−4, and ∼6 × 10−8
M
⊙; the mean rate of dust inflow (condensation) into the dust structure is ∼3.3 × 10−8
M
⊙ yr−1. The mean escape velocity of the shell from the heating source is ∼103 km s−1 and the mean dispersal rate of the shell is ∼1.1 × 10−8
M
⊙ yr−1. 相似文献
5.
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
6.
The first set of supermassive black hole mass estimates, published from 1977 to 1984 by E.A. Dibai, are shown to be in excellent
agreement with recent reverberation-mapping estimates. Comparison of the masses of 17 AGNs covering a mass range from about
106 to 109
M
⊙ shows that the Dibai mass estimates agree with reverberation-mapping mass estimates to significantly better than ±0.3 dex
and were, on average, only 0.14 dex (∼40%) systematically lower than masses obtained from reverberation mapping. This surprising
agreement with the results of over a quarter of a century ago has important implication for the structure and kinematics of
AGNs and implies that type-1 AGNs are very similar. Our results give strong support to the use of the single-epoch-spectrum
(Dibai) method for investigating the co-evolution of supermassive black holes and their host galaxies.
The article was translated by the authors. 相似文献
7.
Results from two-color VR photometry of the unique cataclysmic magnetic variable star V1432 Aql and a theoretical model of
these data are presented. The accuracy is improved by using the “mean-weighted comparison star” method. The derivative of
the rotational period is dP/dt = −1.11(±0.016)·10−8. The characteristic synchronization time for the rotational and orbital motions of the white dwarf is 96.7±1.5 years, in
good agreement with theory for the acceleration of an asynchronous propeller owing to the angular momentum of accreting matter.
A third type of minimum detected in the light curve is interpreted in terms of the presence of an arc, or ring, rather than
an accretion disk. A theoretical model is developed for determining the capture radius of accreted matter by the magnetic
field of the white dwarf using the phase difference between the two types of minima associated with the axial rotation. This
parameter is estimated to be 16–28 times the radius of the white dwarf for an inclined column model. A dependence of the main
characteristics of the system on the mass of the white dwarf is derived which yields better values for the range of this quantity
than those determined by indirect methods. For the assumed masses (M1 = 0.9 M⊙ and M2 = 0.3 M⊙) the estimated accretion rate is ∼7×10−10 M⊙. It is shown that in a synchronizing polar the contribution to the change in the period by the variation in the angular momentum
of the white dwarf is negligible compared to the accretion torque. In the future multicolor monitoring is needed for studying
the spin-orbital synchronization and periodic changes in the accretion structure caused by “spinning” of the white dwarf.
__________
Translated from Astrofizika, Vol. 50, No. 1, pp. 135–159 (February 2007). 相似文献
8.
More than 635 thousand positional observations of planets and spacecraft of various types (mostly radiotechnical ones, 1961–2010)
were used to estimate possible changes in the gravitational constant, Sun’s mass, and semi-major axes of planetary orbits,
as well as the associated value of the astronomical unit. The observations were analyzed based on the EPM2010 ephemerides
constructed at the Institute of Applied Astronomy (Russian Academy of Sciences) in a post-Newtonian approximation as a result
of simultanious numerical integration of the equations of motion of nine major planets, the Sun, the Moon, asteroids, and
trans-Neptunian objects. The heliocentric gravitational constant GM
⊙ was found to vary with a rate of (GṀ
⊙/GM
⊙ = (−5.0 ± 4.1)) × 10−14 per year (at the 3σ level). The positive secular changes in the semimajor axes ȧ
i
/a
i
were found for Mercury, Venus, Mars, Jupiter, and Saturn provided by high-precision observations. These changes also correspond
to the decrease in the heliocentric gravitational constant. The changing of GM
⊙, itself is probably caused by the loss of the mass M
⊙ of the Sun due to its radiation and solar wind; these effects are partly compensated by the material falling onto the Sun.
Allowing for the maximum bounds on the possible change in the Sun’s mass M
⊙, it has been found from the change obtained in GM
⊙ that the annual change Ġ/G of the gravitational constant G falls within the interval −4.2 × 10−14 < ȧ/G < +7.5 × 10−14 with a 95% probability. The astronomical unit (AU) is connected by its definition only with the heliocentric gravitational
constant. The decrease of GM
⊙ obtained in this paper should correspond to a secular decrease in the AU. It is shown, however, that the modern level of
accuracy does not allow us to determine a change in the AU. The attained posibility of determining changes in GM
⊙ using high-accuracy observations encourages us to have a relation between GM
⊙ and the AU fixed for a certain moment in time, since it is inconvenient to have a time-dependent length for the AU. 相似文献
9.
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
10.
A catalog of massive (⩾10 M
⊙) stars in binary and multiple systems with well-known masses and luminosities has been compiled. The catalog is analyzed
using a theoretical mass-luminosity relation. This relation allows both normal main-sequence stars and stars with peculiarities:
with clear manifestations of mass transfer, mass accretion, and axial rotation, to be identified. Least-squares fitting of
the observational data in the range of stellar masses 10M
⊙ ⩽ M ≲ 50 M
⊙ yields the relation L ∼ M
2.76.
An erratum to this article is available at . 相似文献
11.
We report the results of study of the A1569 cluster (12
h
36m.3, +16°35′) and the neighboring A1589 cluster (12
h
41m.3, +18°34′), making up a pair (a supercluster) with a projected size of about 10Mpc. This study is done within the framework
of our program for investigating the galaxy clusters with bimodal velocity distributions (i.e., clusters where the velocities
of subsystems differ by more than Δcz ∼ 3000 km/s). In the A1569 cluster we have identified two subsystems: A1569A (cz = 20613 km/s) and A1569B (cz = 23783 km/s). These subsystems have the line-of-sight velocity dispersions of 484 km/s and 493 km/s, and dynamic masses
within the R
200 radius equal to 1.8 × 1014 and 2.0 × 1014
M
⊙, respectively. We directly estimate the distances to these subsystems using three methods applied to earlytype galaxies:
the Kormendy relation, photometric plane, and fundamental plane. To this end, we use the results of our observations made
with the 1-m telescope of the SAO RAS and the data adopted from the SDSS DR7 catalog. We found that A1569 consists of two
independent clusters. The A1569B cluster is located at the Hubble distance corresponding to its radial velocity. The A1569A
cluster has a peculiar velocity of −1290 ± 630 km/s, which can be explained by the effect of the more massive A1589 cluster
(with a mass of 7.9 × 1014
M
⊙) and of the supercluster where it resides. In all the four bimodal clusters that we studied within the framework of our program,
A1035, A1775, A1831, and A1569, the subsystems are independent clusters lying close to the Hubble relation between redshift
and distance. 相似文献
12.
C. V. S. R. Sarma M. B. K. Sarma N. B. Sanwal 《Journal of Astrophysics and Astronomy》1989,10(3):307-346
The extensiveUBV observations of SV Camelopardalis by Patkos (1982) have been analysed to derive the orbital elements of the system. The data
were corrected for the effect of third body (Sarma, Sarma & Abhyankar 1985) and for the ‘RS CVn’ distortion wave (Sarma, Vivekanandarao
& Sarma 1988). The cleaned data were used to obtain a preliminary solution by a modified version of Wellmann method (Sarma
& Abhyankar 1979) from which we concluded that the primary eclipse is a transit. The final orbital elements of SV Cam were
obtained by the modified version (Sarma 1988; Sarmaet al. 1987) of WINK program by Wood (1972). The colour and median brightness variation are discussed. From the spectroscopic mass
functionf(m) = 0.118 M⊙ (Hiltner 1953), the absolute dimensions of the components are found to be 0.826 Mbd & 0.592 M⊙ and 1.236 R⊙ & 0.778 R⊙ for the primary and secondary components, respectively. The age of the binary system is estimated to be 6.0 ± 1.0 × 108 years 相似文献
13.
The gravitational instability of expanding shells evolving in a homogeneous and static medium is discussed. In the low density
environment (n = 1 cm-3), the fragmentation starts in shells with diameters of a few 100 pc and fragment masses are in the range of 5 × 103 - 106
M
⊙. In the high density environment (n = 105 - 107 cm-3), shells fragment at diameters of
pc producing clumps of stellar masses. The mass spectrum in both environments is approximated by a power law dN/dm ∼ m
-2.3. This is close to the slope of the stellar IMF. To reproduce the observed mass spectrum of clouds (the spectral index close
to ∼ -2.0) we have to assume, that the cloud formation time is independent of the cloud size, similarly to the Jeans unstable
medium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
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
15.
The large amounts of dust detected in sub-millimeter galaxies and quasars at high redshift pose a challenge to galaxy formation
models and theories of cosmic dust formation. At z>6 only stars of relatively high mass (>3 M⊙) are sufficiently short-lived to be potential stellar sources of dust. This review is devoted to identifying and quantifying
the most important stellar channels of rapid dust formation. We ascertain the dust production efficiency of stars in the mass
range 3–40 M⊙ using both observed and theoretical dust yields of evolved massive stars and supernovae (SNe) and provide analytical expressions
for the dust production efficiencies in various scenarios. We also address the strong sensitivity of the total dust productivity
to the initial mass function. From simple considerations, we find that, in the early Universe, high-mass (>3 M⊙) asymptotic giant branch stars can only be dominant dust producers if SNe generate ≲3×10−3 M⊙ of dust whereas SNe prevail if they are more efficient. We address the challenges in inferring dust masses and star-formation
rates from observations of high-redshift galaxies. We conclude that significant SN dust production at high redshift is likely
required to reproduce current dust mass estimates, possibly coupled with rapid dust grain growth in the interstellar medium. 相似文献
16.
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
17.
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
18.
On the basis of the published times of minima and our own observations, we analysed the period change of the Algol-type eclipsing binary CU Pegasi. Over almost seventy years of observations, the parabolic period change has been clearly seen as dP/dt = 1.38 × 10−6 d/year. The estimated mass transfer in the system is about 1 × 10−7 MM⊙/year. 相似文献
19.
P. Amram C. Mendes de Oliveira H. Plana C. Balkowski M. Bolte 《Astrophysics and Space Science》2002,281(1-2):397-400
We present kinematics and photometric evidence for the presence of seven candidate tidal dwarf galaxies in Stephan's Quintet.
The central regions of the two most probable parent galaxies, NGC 7319 and NGC 7318B, contain little or no gas whereas the
intragroup medium and, in particular, the optical tails that seem to be associated with NGC 7318B are rich in cold and ionized
gas. Two tidal dwarf candidates may be located at the edge of a tidal tail, another located within a tail, and for the four
others there is no obvious stellar/gaseous bridge between them and the parent galaxy. Two of the candidates are associated
with H I clouds, one of which is, in addition, associated with a CO cloud. All seven regions have low continuum fluxes and
high Hα luminosity densities [F(Hα) = (1-60) × 10-14 ergs s-1 cm-2]. Their magnitudes (MB = –16.1 to –12.6), sizes (∼ 3.5 h75
-1 kpc), colors (typically B – R = 0.7), and gas velocity gradients (∼ 8 –26 h75 km s-1 kpc-1) are typical for tidal dwarf galaxies. In addition, the ratios between their star formation rates determined from Hα and
from the B-band luminosity are typical of other tidal dwarf galaxies. The masses of the tidal dwarf galaxies in Stephan's
Quintet range from ∼ 2 × 108 to 1010 M⊙, and the median value for their inferred mass-to-light ratios is 7 (M/L)⊙. At least two of the systems may survive possible ‘fallbacks’ or disruption by the parent galaxies and may already be, or
turn into, self-gravitating dwarf galaxies, new members of the group.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
20.
In this study complete BV light curves of the W Ursae Majoris binary V1073 Cygni obtained in 2005 are presented. We have used the spectroscopic data of V1073 Cyg obtained by Ahn et al. (1992) for analysis. The analysis of radial velocity and light curves was made with Wilson} program (1998) and the geometric and physical elements} of the system were derived. By searching the simultaneous} solutions of the system, we have determined the masses and radii of the components: 1.64M⊙, 2.275R⊙ for the primary component and 0.55M⊙, 1.397R⊙ for the secondary component respectively. The effective temperature of 6494 ± 53 K for the secondary component was also estimated. 相似文献