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1.
This is a study of the stability of strange dwarfs, superdense stars with a small quark core (M
0core
/M
⨀ < 0.017) and an extended crust consisting of atomic nuclei and a degenerate electron gas where the density may be two orders
of magnitude greater than the maximum density for white dwarfs. For a given equation of state, the mass, total number of baryons,
and radius of strange dwarfs are uniquely determined by the central energy density ρ
c
and the energy density ρ
tr
of the crust at the surface of the quark core. Thus, the entire range of variation of ρ
c
and ρ
tr
must be taken into account in studying the stability of these configurations. This can be done by examining a series of configurations
with a fixed rest mass M
0 (total baryon number) of the quark core and different masses of the crust. In each series, ρ
tr
ranges from the value for white dwarfs to ρ
drip
= 4.3∙1011 g/cm3, at which free neutrons are created in the crust. According to the static criterion for stability, stability is lost in an
individual series when the mass of the strange dwarf reaches a maximum as a function of ρ
tr
.
Translated from Astrofizika, Vol. 52, No. 2, pp. 325–332 (May 2009). 相似文献
2.
This is a study of the stability of strange dwarfs, superdense stars with a small self-confining core (M
core
< 0.02 M⊙) containing strange quark matter and an extended crust consisting of atomic nuclei and degenerate electron gas. The mass
and radius of these stars are of the same orders as those of ordinary white dwarfs. It is shown that any study of their stability
must examine the dependence of the mass on two variables, which can, for convenience, be taken to be the rest mass (total
baryon mass) of the quark core and the energy density ρ
tr
of the crust at the surface of the quark core. The range of variation of these quantities over which strange dwarfs are stable
is determined. This region is referred to as the stability valley for strange dwarfs. The mass and radius from theoretical
models of strange dworfs are compared with observational data obtained through the HIPPARCOS program and the most probable
candidate strange dwarfs are identified. 相似文献
3.
Strange quark stars with a crust and strange dwarfs consisting of a compact strange quark core and an extended crust are investigated in terms of a bag model. The crust, which consists of atomic nuclei and degenerate electrons, has a limiting density of cr=drip=4.3·1011 g/cm3. A series of configurations are calculated for two sets of bag model parameters and three different values of cr (109 g/cm3 cr drip) to find the dependence of a star's mass M and radius R on the central density. Sequences of stars ranging from compact strange stars to extended strange dwarfs are constructed out of strange quark matter with a crust. The effect of the bag model parameters and limiting crust density cr on the parameters of the strange stars and strange dwarfs is examined. The strange dwarfs are compared with ordinary white dwarfs and observational differences between the two are pointed out. 相似文献
4.
Low-mass strange stars with a crust are investigated within the framework of the bag model. The crust, which consists of degenerate electrons and atomic nuclei, has a limiting boundary density
cr
, which is determined by the mass of the crust, and it cannot exceed the value
drip
= 4.3·1011 g/cm3, corresponding to the density at which neutrons drip from nuclei. For different values of
cr
in the low-mass range (M 0.1 M) we calculate several series of configurations: we find the dependence of the stellar mass M on the central density
c
for
cr
= const, with 109 g/cm3
cr
drip
, and for each series we determine the parameters of the configuration for which the condition dM/d
c
> 0 is violated. When the boundary density of the crust decreases to 109 g/cm3, the minimum mass of a strange star decreases to M
min 10-3 M, while the radius reaches 600 km. 相似文献
5.
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
6.
In the present article, a family of static spherical symmetric well behaved interior solutions is derived by considering the
metric potential g
44=B(1−Cr
2)−n
for the various values of n, such that (1+n)/(1−n) is positive integer. The solutions so obtained are utilised to construct the heavenly bodies’ like quasi-black holes such
as white dwarfs, neutron stars, quarks etc., by taking the surface density 2×1014 gm/cm3. The red shifts at the centre and on the surface are also computed for the different star models. Moreover the adiabatic
index is calculated in each case. In this process the authors come across the quarks star only. Least and maximum mass are
fond to be 3.4348M
Θ and 4.410454M
Θ along with the radii 21.0932 km and 23.7245 km respectively. 相似文献
7.
Models of strange quark stars with a crust consisting of atomic nuclei and degenerate electrons, maintained by an electrostatic
barrier at the surface of the strange quark matter, are investigated for a realistic range of parameters of the MIT bag model.
The density at which neutrons escape from nuclei, ρ = ρdrip, is taken as the maximum possible boundary density of the crust. Series of strange stars are calculated as a function of
central density. Configurations with masses of 1.44 and 1.77 M{ie330-1} and a gravitational redshift Zs = 0.23, corresponding to the best-known observational data, are investigated. The presence of a crust results in the existence
of a minimum mass for strange stars, and also helps to explain the glitch phenomenon of pulsars within the framework of the
existence of strange quark matter.
Translated from Astrofizika, Vol. 42, No. 3, pp. 439–448, July–September, 1999. 相似文献
8.
A detailed investigation of the evolution of low-mass binaries is performed for the case when the secondary fills its Roche lobe at the stage of core hydrogen exhaustion. The obtained results are compared with observational data for ultra-short periodic X-ray systems MXB 1820-30 and MXB 1916-05. In the frame of the proposed evolutionary scenario it is possible to obtain for MXB 1820-30 its periodP=11.4 min twice (see Figure 2). In the first case the parameters of the system are:M
2 0.13–0.15M
,X0.05–0.13, |P/P| (3.6–6.2) } 10–7 yr–1, M2 (4.1–9.6) } 10–9
M
yr–1, for the second:M
2 0.08–0.09M
,X= 0, |P/P| (1.3–1.5) } 10–7 yr–1, M2 (1.4–1.8) } 10–8
M
yr–1. It is suggested that MXB 1916-05 is the progenitor of the system MXB 1820-30 (M
2 = 0.1M,X 0.221,M
2 1.8 × 10–10
M
yr–1). 相似文献
9.
The integrated magnitudes of 221 Galactic open clusters have been used to derive the luminosity function. The completeness
of the data has also been discussed. In the luminosity distribution the maximum frequency of clusters occurs nearI (Mv) = −3
m
.
5, and some plausible reasons for a sharp cut-off atI (Mv) = −2m. 0 have been discussed. It is concluded that the paucity of the clusters fainter thanI (M
v) = −2
m
.0
is not purely due to selection effects. The surface density of the clusters for different magnitude intervals has. been obtained
using the completeness radius estimated from the logN- logd plots. A relation betweenI (Mv) and surface density has been obtained which yields a steeper slope than that obtained by van den Bergh & Lafontaine (1984). 相似文献
10.
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
11.
V. V. Bobylev 《Astronomy Letters》2010,36(9):634-644
We analyze the three-dimensional kinematics of about 82 000 Tycho-2 stars belonging to the red giant clump (RGC). First, based
on all of the currently available data, we have determined new, most probable components of the residual rotation vector of
the optical realization of the ICRS/HIPPARCOS system relative to an inertial frame of reference, (ω
x
, ω
y
, ω
z
) = (−0.11, 0.24, −0.52) ± (0.14, 0.10, 0.16) mas yr−1. The stellar proper motions in the form μα cos δ have then be corrected by applying the correction ω
z
= −0.52 mas yr−1. We show that, apart from their involvement in the general Galactic rotation described by the Oort constants A = 15.82 ± 0.21 km s−1 kpc−1 and B = −10.87 ± 0.15 km s−1 kpc−1, the RGC stars have kinematic peculiarities in the Galactic yz plane related to the kinematics of the warped stellar-gaseous Galactic disk. We show that the parameters of the linear Ogorodnikov-Milne
model that describe the kinematics of RGC stars in the zx plane do not differ significantly from zero. The situation in the yz plane is different. For example, the component of the solid-body rotation vector of the local solar neighborhood around the
Galactic x axis is M
32− = −2.6 ± 0.2 km s−1 kpc−1. Two parameters of the deformation tensor in this plane, namely M
23+ = 1.0 ± 0.2 km s−1 kpc−1 and M
33 − M
22 = −1.3 ± 0.4 km s−1 kpc−1, also differ significantly from zero. On the whole, the kinematics of the warped stellar-gaseous Galactic disk in the local
solar neighborhood can be described as a rotation around the Galactic x axis (close to the line of nodes of this structure) with an angular velocity −3.1 ± 0.5 km s−1 kpc−1 ≤ ΩW ≤ −4.4 ± 0.5 km s−1 kpc−1. 相似文献
12.
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
13.
The population synthesis method is used to study the possibility of explaining the appreciable fraction of the intergalactic
type-Ia supernovae (SN Ia), 20
−15
+12
%, observed in galaxy clusters (Gal-Yam et al. 2003) when close white dwarf binaries merge in the cores of globular clusters. In a typical globular cluster, the number
of merging double white dwarfs does not exceed ∼10−13 per year per average cluster star in the entire evolution time of the cluster, which is a factor of ∼3 higher than that in
a Milky-Way-type spiral galaxy. From 5 to 30% of the merging white dwarfs are dynamically expelled from the cluster with barycenter
velocities up to 150 km s−1. SN Ia explosions during the mergers of double white dwarfs in dense star clusters may account for ∼1% of the total rate
of thermonuclear supernovae in the central parts of galaxy clusters if the baryon mass fraction in such star clusters is ∼0.3%. 相似文献
14.
Measurements of the Hα flux from 30 neighboring dwarf galaxies are presented. After correction for absorption, these fluxes
are used to estimate the star formation rate (SFR). The SFR for 18 of the galaxies according to the Hα emission are compared
with estimates of the SFR from FUV magnitudes obtained with the GALEX telescope. These are in good agreement over the range
log[SFR] = [ −3, 0] M⨀
/year. 相似文献
15.
Matthew R. Edwards 《Astrophysics and Space Science》2012,339(1):13-17
Due to the Hubble redshift, photon energy, chiefly in the form of CMBR photons, is currently disappearing from the universe
at the rate of nearly 1055 erg s−1. An ongoing problem in cosmology concerns the fate of this energy. In one interpretation it is irretrievably lost, i.e., energy is not conserved on the cosmic scale. Here we consider a different possibility which retains universal energy conservation.
Treating gravitational potential energy conventionally as ‘negative’, it has earlier been proposed that the Hubble shift flips
positive energy (photons) to negative energy (gravitons) and vice versa. The lost photon energy would thus be directed towards gravitation, making gravitational energy wells more negative. Conversely, within astrophysical bodies, the flipping of gravitons
to photons would give rise to a ‘Hubble luminosity’ of magnitude −UH
0, where U is the internal gravitational potential energy of the object. Preliminary evidence of such an energy release is presented
in bodies ranging from planets, white dwarfs and neutron stars to supermassive black holes and the visible universe. 相似文献
16.
As part of our study of the larger-scale remanent magnetic field of the Moon, we have examined the effects of cratering in
an otherwise spherically symmetrical shell magnetized by a concentric dipolar magnetic fieldH
o to an intensity of magnetizationc
H
o, wherec is a constant. In our initial model, we assume that the material excavated from the craters is distributed with random orientation
and thus does not contribute to the remanent dipole momentM
g
. We further assume that the mare fill does not contribute significantly toM
g
. We choose the magnetizing dipole momentM
o and the constantc such that the magnitude of the productcH
o ≃ 3 × 10−4Г at the outer surface of the shell in the equatorial plane of the dipole. This value of the intensity of remanent magnetization
was chosen to be within the range 10−7−10−3Г’; the intensities of thermo-remanent magnetization exhibited by Apollo samples. Finally, we use the locations and diameters
of the 10 largest craters on the Moon and the depth-to-diameter ratios of Pike’s formulation to model approximately the excavation
of the magnetized shell.
The remanent dipole momentM
g
was calculated for each of three orthogonal orientations of the magnetizing dipoleM
o. The three magnitudes ofM
g
fall in the range 4 × 1018−1 × 1019Г cm3 which is close to the upper limit of 1019Г cm3 estimated forM
g
from the field measurements obtained with the Apollo subsatellites. Further, the distribution of the craters is such as to
produce a significant transverse component ofM
g
with acute angles between the spin axis andM
g
in the range 51°–77°. 相似文献
17.
A global iteration method to determine the self-consistent structure of steady plane-parallel radiative shock waves is shown
to converge to the stable solution with upstream front velocities of 15 km/s ≤ U
1≤ 60 km/s and for hydrogen gas of unperturbed temperature T= 3000 K and density ρ = 10−10gcm−3.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Questions of the equilibrium, stability, and observational manifestations of strange stars are considered, in which electrical
neutralization of the quark matter is provided by positrons, as occurs for some sets of bag parameters resulting in a stiffer
equation of state. Such models consist entirely of self-contained, strange quark matter and their maximum mass reaches 2.4–2.5
M⊙ with a radius of 13–14 km. The cooling of such strange quark stars both in the absence and in the presence of mass accretion
is investigated. It is shown that in the absence of mass accretion onto the strange star, the dependence of temperature (T,
K) on age (t, yr) depends very little on the mass of the configuration and has the form T ≈ 2.3·108r−1/5. If the star’s initial temperature is sufficiently high (T0≥2·1010K), then the total number of electron-positron pairs emitted does not depend on it and is determined only by the total mass
of the configuration. In the case of accretion, the annihilation of electrons of the infalling fatter with positrons of the
strange quark matter results in the emission of γ-rays with an energy of∼0.5 MeV, by observing which one can distinguish candidates
for strange stars. The maximum temperature of strange stars with mass accretion is calculated.
Translated from Astrofizika, Vol. 42, No. 4, pp. 617–630, October–December, 1999. 相似文献
19.
It is well known that the interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation
of the ICME and solar wind velocities at 1 AU. This can be understood in terms of an aerodynamic drag force per unit mass
of the form F
D/M=−(ρe
AC
D/M)(V
i−V
e)∣V
i−V
e∣, where A and M are the ICME cross-section and sum of the mass and virtual mass, V
i and V
e the speed of the ICME and solar wind, ρe the solar wind density, C
D a dimensionless drag coefficient, and the inverse deceleration length γ=ρe
A/M. The optimal radial parameterisation of γ and C
D beyond approximately 15 solar radii is calculated. Magnetohydrodynamic simulations show that for dense ICMEs, C
D varies slowly between the Sun and 1 AU, and is of order unity. When the ICME and solar wind densities are similar, C
D is larger (between 3 and 10), but remains approximately constant with radial distance. For tenuous ICMEs, the ICME and solar
wind velocities equalise rapidly due to the very effective drag force. For ICMEs denser that the ambient solar wind, both
approaches show that γ is approximately independent of radius, while for tenuous ICMEs, γ falls off linearly with distance.
When the ICME density is similar to or less than that in the solar wind, inclusion of virtual mass effects is essential. 相似文献
20.
A statistical study of the dependence of the star formation rate in the nuclear regions of 39 Kazarian galaxies on the integral
parameters of these galaxies is carried out on the basis of spectra from SDSS DR6. The value of SFR/kpc2 for our sample lies in the range 0.013÷2.04M
⨀ year−1kpc−2 (with the maximum value of 2.04 corresponding to the Kaz 98 (merger)). It is found that the surface density of the rate of
star formation correlates positively with the bar structure parameter and EW(Hα), and that, for spiral galaxies of early morphological types, SFR/kpc2 is greater than for the later types. It is shown that the color B-R for the galaxies and the color (u − g)
nucl
for the nuclear region correlate positively with the total absorption A(Hα) in the Ha line for the nuclear region. The average value of A(Hα) for our samples is found to be A(Hα)=1.3±0.09 magnitudes.
Translated from Astrofizika, Vol. 52, No. 2, pp. 211–224 (May 2009). 相似文献