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1.
M. M. Zakirov 《Kinematics and Physics of Celestial Bodies》2008,24(1):25-35
We made up a list of eclipsing variables from The Sixth Catalog of Orbits of Visual Binary Stars and supplemented it with physical parameters and some orbital elements of triple stars. A histogram of the angles between the orbital planes of close and wide pairs was built. These angles were shown to be no greater than 20° in two-thirds of cases, and the difference between the angles was shown to increase with semimajor axis of visual orbit. The distribution of the ratios between long and short periods has local maxima in certain intervals. The dynamical sum of the masses of triple-system components turned out to be in good agreement with the sum of the masses of close binary components estimated by precise methods and the mass of the tertiary component determined from the mass-luminosity relation. Most of tertiary components were found to have masses half as large as the sums of the masses of close pair components. Our estimates suggest that the precession periods of the orbits of close binary systems range from several thousand to several tens of million years. 相似文献
2.
Several mechanisms have been proposed for the formation of brown dwarfs, but there is as yet no consensus as to which—if any—are operative in nature. Any theory of brown dwarf formation must explain the observed statistics of brown dwarfs. These statistics are limited by selection effects, but they are becoming increasingly discriminating. In particular, it appears (a) that brown dwarfs that are secondaries to Sun-like stars tend to be on wide orbits, a≳100 AU (the Brown Dwarf Desert), and (b) that these brown dwarfs have a significantly higher chance of being in a close (a≲10 AU) binary system with another brown dwarf than do brown dwarfs in the field. This then raises the issue of whether these brown dwarfs have formed in situ, i.e. by fragmentation of a circumstellar disc; or have formed elsewhere and subsequently been captured. We present numerical simulations of the purely gravitational interaction between a close brown-dwarf binary and a Sun-like star. These simulations demonstrate that such interactions have a negligible chance (<0.001) of leading to the close brown-dwarf binary being captured by the Sun-like star. Making the interactions dissipative by invoking the hydrodynamic effects of attendant discs might alter this conclusion. However, in order to explain the above statistics, this dissipation would have to favour the capture of brown-dwarf binaries over single brown-dwarfs, and we present arguments why this is unlikely. The simplest inference is that most brown-dwarf binaries—and therefore possibly also most single brown dwarfs—form by fragmentation of circumstellar discs around Sun-like protostars, with some of them subsequently being ejected into the field. 相似文献
3.
We consider a model for the cyclic activity of young binary stars that accrete matter from the remnants of a protostellar
cloud. If the orbit of such a binary system is inclined at a small angle to the line of sight, then the streams of matter
and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer. To
study these phenomena by the SPH (smoothed particle hydrodynamics) method, we have computed grids of hydrodynamic models for
binary systems based on which we have constructed the light curves as a function of the orbital phase. The main emphasis is
on investigating the properties of the brightness oscillations. Therefore, the model parameters were varied within the following
ranges: the component mass ratio q = M
2: M
1 = 0.2–0.5 and the eccentricity = 0–0.7. The parameter that defined the binary viscosity was also varied. We adopted optical
grain characteristics typical of circumstellar dust. Our computations have shown that bimodal oscillations are excited in
binaries with eccentric orbits, provided that the binary components do not differ too much in mass. In this case, the ratios
of the periods and amplitudes of the bimodal oscillations and their shape depend strongly on the inclination of the binary
plane and its orientation relative to the observer. Our analysis shows that the computed light curves can be used in interpreting
the cyclic activity of UX Ori stars. 相似文献
4.
Sake J. Hogeveen 《Astrophysics and Space Science》1990,173(2):315-342
The selection effects that govern the observations of Visual Binary Stars are investigated, in order to obtain a realistic statistical distribution of the mass-ratioq=M
sec/M
prim. To this end a numerical simulation programme has been developed, which generates binary stars and looks at them to determine whether an observer on Earth would be able to detect them. The simulations show that for mass-ratiosq>0.35, observations are expected to reveal the realq-distributions, while for mass-ratiosq<0.35 selection effects begin to play a major part. It is found that the observed mass-ratio distribution for Main-Sequence systems, derived from theIndex Catalogue of Visual Binary Stars (IDS), can be explained by a distribution of secondary masses according to the Initial Mass Function (IMF), i.e., (M)M
–2.7.From theFourth Catalogue of Orbits of Visual Binary Stars (OVB) authors find aq-distribution that peaks strongly forq-values close toq=1. It is shown that this mass-ratio distribution may be the result of a sampling selection effect. Due to this sampling selection effect, the OVB is a considerably morebiased sample of the binary population in our Galaxy than the IDS. Numerical simulations of biased sampling show that theq-distribution, found from the OVB, is not incompatible with the distribution of secondary masses according to the IMF (forq>0.35), found from the IDS.Because of the selection effects, it is difficult to establish the realq-distribution forq<0.35. If the realq-distribution departs from (q)q
–2.7 forq0.35, about 36% of all stars are in visual binaries (i.e., if theq-distribution is assumed to be flat for 0<q<0.35); if the distribution flattens forq0.25, about 60% of the stars must be primaries of visual binaries. 相似文献
5.
The Hertzsprung-Russell diagram of the Large Magellanic Cloud compiled recently by Fitzpatrick & Garmany (1990) shows that
there are a number of supergiant stars immediately redward of the main sequence although theoretical models of massive stars
with normal hydrogen abundance predict that the region 4.5 ≤ logT
eff ≤ 4.3 should be un-populated (“gap”). Supergiants having surface enrichment of helium acquired for example from a previous
phase of accretion from a binary companion, however, evolve in a way so that the evolved models and observed data are consistent
— an observation first made by Tuchman & Wheeler (1990). We compare the available optical data on OB supergiants with computed
evolutionary tracks of massive stars of metallicity relevant to the LMC with and without helium-enriched envelopes and conclude
that a large fraction (≈ 60 per cent) of supergiant stars may occur in binaries. As these less evolved binaries will later evolve into massive X-ray
binaries, the observed number and orbital period distribution of the latter can constrain the evolutionary scenarios of the
supergiant binaries. The distributions of post main sequence binaries and closely related systems like WR + O stars are bimodal-consisting
of close and wide binaries in which the latter type is numerically dominating. When the primary star explodes as a supernova
leaving behind a neutron star, the system receives a kick and in some cases can lead to runaway O-stars. We calculate the
expected space velocity distribution for these systems. After the second supernova explosion, the binaries in most cases,
will be disrupted leading to two runaway neutron stars. In between the two explosions, the first born neutron star’s spin
evolution will be affected by accretion of mass from the companion star. We determine the steady-state spin and radio luminosity
distributions of single pulsars born from the massive stars under some simple assumptions. Due to their great distance, only
the brightest radio pulsars may be detected in a flux-limited survey of the LMC. A small but significant number of observable
single radio pulsars arising out of the disrupted massive binaries may appear in the short spin period range. Most pulsars
will have a low velocity of ejection and therefore may cluster around the OB associations in the LMC. 相似文献
6.
O. O. Vasilkova 《Astronomy Letters》2010,36(3):227-230
Dynamical behaviour of a small binary with equal components, each of mass m, is considered under attraction of a heavy body of mass M. Differential equations of the general three-body problem are integrated numerically using the code by S. J. Aarseth (Aarseth,
Zare 1974) for mass ratios m/M within 10−11–10−4 range. The direct and retrograde orbits of light bodies about each other are considered which lie either in the plane of
moving their center of mass or in the plane perpendicular to it. It is shown numerically that the critical separation between
the binary components which leads to disruption of binary is proportional to (m/M)1/3. The criterion can be used for studying (in the first approximation) the motion of double stars and binary asteroids or computing
the parameters of magnetic monopol and antimonopol pairs. 相似文献
7.
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more
than 60 000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of stars in the range 4500≲T
eff≲9000 K. Our preliminary results indicate that the majority of the sample is formed by main sequence F- and G-type stars,
with metallicity [M/H]≳−1 dex. 相似文献
8.
We present new photometric data and analyze long-term UBV observations of three candidates for protoplanetary nebulae—F supergiants with infrared excesses at high Galactic latitudes—IRAS
18095+2704, IRAS 19386+0155, and IRAS 19500-1709. All these stars exhibit quasi-periodic low-amplitude variations caused by
pulsations against the background of long-term brightness trends. For IRAS 18095+2704=V887 Her, we have found a pulsation
period of 109 days and revealed a linear brightness trend—the star brightens at constant (within the limits of the measurement
errors) yearly mean color indices. The light curve of IRAS 19386+0155=V1648 Aql in 2000–2008 is represented by a wave with
a fundamental period of 102 days whose modulation with a close period of 98 days leads to variations with a variable amplitude.
V1648 Aql also shows a systematic rise in V brightness along with a reddening. IRAS 19500–1709=V5112 Sgr exhibits irregular pulsations with periods of 39 and 47 days.
The long-term variability component of V5112 Sgr may indicate that the star is binary. 相似文献
9.
N. D. Caranicolas 《Astrophysics and Space Science》1996,246(1):15-28
We use a composite galaxy model consisting of a disk-halo, bulge, nucleus and dark-halo components in order to investigate the motion of stars in ther-z plane. It is observed that high angular momentum stars move in regular orbits. The majority of orbits are box orbits. There are also banana-like orbits. For a given value of energy, only a fraction of the low angular momentum stars — those going near the nucleus — show chaotic motion while the rest move in regular orbits. Again one observes the above two kinds of orbits. In addition to the above one can also see orbits with the characteristics of the 2/3 and 3/4 resonance. It is also shown that, in the absence of the bulge component, the area of chaotic motion in the surface of section increases, significantly. This suggests that a larger number of low angular momentum stars are in chaotic orbits in galaxies with massive nuclei and no bulge components. 相似文献
10.
The applications of the spectral analysis methods discovered by Kirchhoff for the investigation of stellar magnetic fields
are considered. The statistical properties of the mean magnetic fields for OBA stars have been investigated by analyzing data
from two catalogs of magnetic fields. It is shown that the mean effective magnetic field ℬ of a star can be used as a statistically
significant characteristic of its magnetic field. The magnetic field distribution functions F(ℬ) have been constructed for B-type and chemically peculiar (CP) stars, which exhibit a power-law dependence on ℬ. A sharp
decrease in F(ℬ) in the range of weak magnetic fields has been found. The statistical properties of the magnetic fluxes for main-sequence
stars, white dwarfs, and neutron stars are analyzed. 相似文献
11.
R. Kh Hovhannessian 《Astrophysics》1997,40(4):373-378
The distribution of B stars in the vicinity of nine southern, long-period (P > 11 days) Cepheids is studied on the basis of
U, B, V data. The parameters Q, the normal color indices (B — V)0 and (U — B)0, the color excesses E(B — V), the spectral types, and the distance moduli of these stars are determined.
Translated from Astrofizika, Vol. 40. No. 4, pp. 573–580, October-December, 1997. 相似文献
12.
Michaël De Becker 《Astronomy and Astrophysics Review》2007,14(3-4):171-216
In this paper, I present a general discussion of several astrophysical processes likely to play a role in the production of
non-thermal emission in massive stars, with emphasis on massive binaries. Even though the discussion will start in the radio
domain where the non-thermal emission was first detected, the census of physical processes involved in the non-thermal emission
from massive stars shows that many spectral domains are concerned, from the radio to the very high energies. First, the theoretical
aspects of the non-thermal emission from early-type stars will be addressed. The main topics that will be discussed are respectively
the physics of individual stellar winds and their interaction in binary systems, the acceleration of relativistic electrons,
the magnetic field of massive stars, and finally the non-thermal emission processes relevant to the case of massive stars.
Second, this general qualitative discussion will be followed by a more quantitative one, devoted to the most probable scenario
where non-thermal radio emitters are massive binaries. I will show how several stellar, wind and orbital parameters can be
combined in order to make some semi-quantitative predictions on the high-energy counterpart to the non-thermal emission detected
in the radio domain. These theoretical considerations will be followed by a census of results obtained so far, and related
to this topic. These results concern the radio, the visible, the X-ray and the γ-ray domains. Prospects for the very high energy γ-ray emission from massive stars will also be addressed. Two particularly interesting examples—one O-type and one Wolf-Rayet
binary—will be considered in details. Finally, strategies for future developments in this field will be discussed. 相似文献
13.
O. N. Sholukhova S. N. Fabrika A. V. Zharova A. F. Valeev V. P. Goranskij 《Astrophysical Bulletin》2011,66(2):123-143
We present the results of studying the spectral and photometric variability of the luminous blue variable star V532 in M33.
The photometric variations are traced from 1960 to 2010, spectral variations—from 1992 to 2009. The star has revealed an absolute
maximum of visual brightness (1992–1994, high/cold state) and an absolute minimum (2007–2008, low/hot state) with a brightness
difference of ΔB ≈ 2.3
m
. The temperature estimates in the absolute maximum and absolute minimum were found to be T ∼ 22000 K and T ∼ 42000 K, respectively. The variability of the spectrum of V532 is fully consistent with the temperature variations in its
photosphere, while both permitted and forbidden lines are formed in an extended stellar atmosphere. Broad components of the
brightest lines were found, the broadening of these components is due to electron scattering in the wind parts closest to
the photosphere. We measured the wind velocity as a difference between the emission and absorption peaks in the PCyg type
profiles. The wind velocity clearly depends on the size of the stellar photosphere or on the visual brightness, when brightness
declines, the wind velocity increases. In the absolute minimum a kinematic profile of the V532 atmosphere was detected. The
wind velocity increases and its temperature declines with distance from the star. In the low/hot state, the spectral type
of the star corresponds to WN8.5h, in the high/cold state—to WN11. We studied the evolution of V532 along with the evolution
of AGCar and the massive WR binary HD5980 in SMC. During their visual minima, all the three stars perfectly fit with the WNL
star sequence by Crowther and Smith (1997). However, when visual brightness increases, all the three stars form a separate
sequence. It is possible that this reflects a new property of LBV stars, namely, in the high/cold states they do not pertain
to the bona fide WNL stars. 相似文献
14.
The probabilities of discovering detached close binary (type DM) stars as eclipsing variables are calculated as a function
of the mass of the main component, mass ratio, major semiaxis, and angle of inclination of the orbit. The case of total limb
darkening (hypothesis “D”) is examined. This is compared with earlier results for uniformly bright stellar disks (hypothesis
“U”). Based on data from Svechnikov and Kuznetsova’s Catalog of Approximate Photometric and Absolute Elements of Eclipsing
Variables, the spatial density of stars of this type in the neighborhood of the sun is estimated to be ≈ 460 · 10
−6
pc−3.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 151–169 (February 2006). 相似文献
15.
Stars in the Pulkovo Observatory program are observed with a 65-cm refractor during many years to study their positions and movements. We present examples of two visual binary stars, for which orbits and masses of components were determined, and two astrometric stars, for which masses of their unseen companions were estimated. The first two stars are ADS 14636(61 Cygni) and ADS 7251,and the others are Gliese 623 and ADS 8035(Alpha UMa). Direct astrometric methods are used for estimation of mass-ratio and masses. 相似文献
16.
Based on archival Hubble Space Telescope ACS/WFC images, we have performed stellar photometry for more than 0.6 million stars
in the interacting galaxies NGC 5194 and NGC 5195 of the M51 system. Stars of various ages have been identified on the constructed
Hertzsprung-Russell diagram: blue and red supergiants, AGB stars, and red giants. The distance to M51 has been measured from
the position of the tip of the red giant branch, D = 9.9 ± 0.7 Mpc. We have determined the change in the metallicity of red supergiants along the galactic radius in NGC 5194.
Despite the gravitational interaction, the distribution of stars in NGC 5194 does not differ from that in isolated galaxies.
The asymmetric stellar structures of NGC5195 (the so-called “feathers”) formed through the interaction of two galaxies have
been found to consist mostly of AGB stars. 相似文献
17.
We investigate the relative motion of three stars, ADS 7446, 9346, and 9701, based on long-term observations with the Pulkovo
26-inch refractor. The relative motion of all three stars shows a perturbation that could be produced by the gravitational
influence of an invisible companion. For ADS 7446, we have determined the orbit of the photocenter with a period of 7.9 yr;
the mass of the companion is more than 0.4M
⊙. For ADS 9346, we have determined the radial velocities of the components: −14.60 km s−1 for A and −13.94 km s−1 for B. For ADS 9346 and 9701, we have determined the dynamical parallaxes, 24 and 20 mas, respectively, which are larger
than those in the Hipparcos catalog by 5 mas, and calculated the orbits by the apparent motion parameter (AMP) method. The
new orbit of ADS 9346 is: a = 5″.2, P = 2035 yr, and e = 0.46 at the system’s mass M = 2.5M
⊙. The new orbits of ADS 9701 are: (a = 2″.9, P = 829 yr, e = 0.54, M = 4.3M
⊙) and (a = 3″.8, P = 1157 yr, e = 0.53, M = 5.0M
⊙). 相似文献
18.
Yu. V. Glagolevskij 《Astrophysical Bulletin》2012,67(3):264-270
We continue our program of the study of large-scale structures of magnetic fields in chemically peculiar stars. In this paper we analyze eight stars, out of which three stars have the structure of a central dipole, three—the structure of a dipole shifted along the axis, and two—of a dipole shifted across the axis. High-precision measurements (with σ = 50 and 80 G) are available for two stars (HD62140 and HD71866, respectively). The model phase dependences agree with the measurements within the errors. This result shows that the hypothesis about the dipole structure of the magnetic fields of CP stars is well founded. 相似文献
19.
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
20.
We consider a model of cyclic brightness variations in a young star with a low-mass (q = M
2/M
1 ≤ 0.1) companion that accretes matter from the remnants of a protostellar cloud (circumbinary disk). We assume that the orbit
of the companion is circular and that its plane does not coincide with the disk plane. We have computed grids of hydrodynamic
models for such a binary by the SPH method based on which we have investigated the circumstellar extinction variations produced
by the streams of matter and density waves excited in the circumbinary disk by the orbital motion of the companion. We show
that, depending on the inclination and orientation of the binary’s line of nodes relative to the observer, the brightness
of the primary component can undergo various (in shape and depth) oscillations with a period equal to the orbital one. In
contrast to the models with coplanar circular orbits, the accretion rate onto the components of a binary with a noncoplanar
orbit depends on the orbital phase. The results of our computations can be used to study the cyclic activity of UX Ori stars
and young eclipsing binaries with anomalously long eclipses. 相似文献