共查询到20条相似文献，搜索用时 32 毫秒
1.
We present theoretical calculations of the observed coronal emission line profiles of Fexiv (5303 Å) and Fex (6374 Å) ions, which are observed at the time of total solar eclipse. Baumbach's relation (Allen, 1973) of electron density has been employed to compute the full width at half maximum FWHM. We have employed several other electron density distributions and found that the calculated differences in the FWHM are within 0.5% of one another. We have used the ion densities N
i/NE given by Jordan (1969). To explain the observed FWHM, we have assumed that the corona is expanding spherically symmetrically with a velocity of one or two mean thermal units and no turbulence is included. With these highly simplified assumptions, we have reproduced qualitatively the profiles and FWHM's of the above lines. However, to explain quantities of FWHM's, we should take into account the inhomogeneities in the structure of the corona. It is thus shown, that turbulence is not necessary to explain the observed FWHM. 相似文献
2.
S. V. Chalov 《Astrophysics and Space Science》1990,164(2):183-191
The kinematic turbulent dynamo equations are studied in the presence of a large-scale velocity field. The two length-scales approach is employed and solutions of the equations are found in the limit of small bulk motion and shear, and for large Reynolds numberR
m
. The regeneration term is calculated up to second-order in 1/R
m
using cyclonic convective turbulent velocity field. 相似文献
3.
The partial frequency redistribution function for zero natural line width with dipole scattering (RI) has been considered in obtaining the simultaneous solution of the statistical equilibrium and line transfer equations in
the comoving frame of the expanding gas. We have considered a non-LTE two level atom in an expanding spherical medium whose
outer radii are 3, 10 and 20 times the stellar radius with a total optical depthT ≃ 2 × 103. In all the cases, we have calculated the population ratio of the two levels N2/N1 and compared these results with those obtained by using different expansion velocities and geometrical extensions. Initially,
the upper level population (N2) is set equal to zero. The converged simultaneous solution shows that the upper level population is enhanced considerably
from the initial value. Variation in velocity gradients seem to have little effect on the ratio N2/N1 when the geometrical thickness of the medium is 3 or 10 times the stellar radius. However, when the thickness is increased
to 20 times the central radius, the velocity gradients change the ratio N2/N1 considerably in the region where log T ≤ 2. The effect of variation of geometrical thickness is to reduce the N2/N1 ratio atτ = 0. 相似文献
4.
A. Peraiah 《Journal of Astrophysics and Astronomy》1980,1(1):17-23
Spectral lines formed in a rotating and expanding atmosphere have been computed in the frame of the observer at infinity.
Two kinds of velocity laws are employed: (i) a uniform radial velocity of the gas and (ii) velocity increasing with radius
(i.e. velocity gradients). The atmosphere has been assumed to be rotating with constant velocity. We have considered maximum radial
and rotational velocities to be 10 and 3 mean thermal units respectively in an atmosphere whose geometrical thickness is 10
times the stellar radius. The total radial optical depth at line centre is taken to be about 100. In all cases, Doppler profile
and a source function which is varying as 1/r
2 have been used.
Generally, the lines are broadened when rotation is introduced. However, when radial motion is also present, broadening becomes
asymmetric and the red emission and blue absorption are enhanced. 相似文献
5.
The distribution of monthly counts of grouped solar flares N
f
has been studied for the time period 1967–1985 and they have been compared to other solar activity index R
z
, F
2800, and F
3750 i.e. intensities of solar radio flux at 2800 MH
z
and 3750 MH
z
. Seasonal variations have been found in the monthly distribution of solar flares.We have also studied the variation of the correlation coefficient for every year between N
F
and R
z
for the time period 1967–1985. The distribution of monthly counts of grouped solar flares N
f
has also been compared to the number at high velocity solar-wind streamers for the same period. 相似文献
6.
T. N. Chakrabarty 《Journal of Astrophysics and Astronomy》2004,25(1-2):93-101
Radial dipole matrix elements having astrophysical importance have been computed for highly excited states of hydrogen atom.
Computation is based on Heisenberg’s form of correspondence principle for Coulomb potential. Particular attention has been
paid to the choice of classical analogue(n
c) of principal quantum number (n). The computed radial matrix elements are in good agreement with quantum mechanical results. Further, radial matrix elements
for few transitions involving highn neighboring states of hydrogen atom are presented. 相似文献
7.
We have obtained a simultaneous solution of the statistical equilibrium equation for a non-LTE two-level atom and the radiative transfer equation in the comoving frames by employing the angle-averaged partial frequency redistribution.R
i
with isotropic scattering. In the first iteration we have set the population density of the upper level equal to zero and allow it to be populated in the subsequent iterations. The solution converges within two to four iterations. The process of iteration is terminated when the ratios of population densities in two successive iterations at each radial point, attain an accuracy of 1%. The effects of partial frequency redistribution is to increase the population density of the upper level. Radial gas motions do not seem to have significant effects, although in highly extend geometries, velocity gradients change the population densities considerably. 相似文献
8.
Angle-averaged partial frequency redistributionR II has been employed in obtaining a simultaneous solution of radiative transfer equation in the comoving frame and the statistical equilibrium equation for a non-LTE two level atom. We have obtained the ratios of population densities of the upper and lower levels of the resonance line of PV by utilizing the data given in Bernacca and Bianchi (1979). Line source functions are also obtained for different types of variations of density and velocity of the expanding gases. We have considered the atmosphere to be 11 times as thick as the stellar radius. The first iteration was started by putting the density of the upper level (N 2) equal to zero. However, the convergent solution shows a substantial increase inN 2 although it is still much less than the equilibrium value. The line source function and the ratio of the densities of the particles in the upper and lower levels fall sharply from a maximum at τ=τmax to minimum at τ=0. We have studied the scattering integral \(\int {_{ - \infty }^{ + \infty } J_x \phi _x } dx\) and found that this quantity also varies quite similar to the ratioN 2/N 1 and the line source functionS L. 相似文献
9.
Cemal Aydin 《Astrophysics and Space Science》1979,64(2):481-507
Twenty-five coudé spectrograms (22 with dispersion 12 Å mm–1 and three 7 Å mm–1) of 6 Cassiopeiae (A3 Ia) have been studied. The observations were made at the Haute Provence Observatory. The results of the analysis suggest a correlation between the variations of the equivalent widths, the microturbulence and the radial velocity. The radial velocity and turbulent velocity present a rapid variation with time, even in intervals as short as about an hour. The hydrogen lines are slightly asymmetric but the strongest Feii lines are clearly asymmetric. We found that the amount of asymmetry of the strongest Feii lines (I>6) correlates with the loggf value, with the estimated laboratory intensityI, and with the equivalent widthW
.The observations have been made at the Astronomical Observatory of Haute Provence (CNRS). This work has been supported by TUBITAK (Scientific and Technical Research Council of Turkey), and partially by CNR (Consiglio Nazionale delle Ricerche) of Italy. 相似文献
10.
We have investigated the effects of increasing optical depths on spectral lines formed in a rotating and expanding spherical
shell. We have assumed a shell whose outer radius is 3 times the inner radius, with the radial optical depths equal to 10,
50, 100, 500. We have employed a constant velocity with no velocity gradients in the shell. The shell is assumed to be rotating
with velocities varying as 1/ρ, whereρ is the perpendicular distance from the axis of rotation, implying the conservation of angular momentum. Two expansion (radial)
velocities are treated: (1)V = 0 (static case) and (2)V = 10 mean thermal units. The maximum rotational velocities areV
rot = 0, 5, 10 and 20. In the shell where there are no radial motions, we obtain symmetric lines with emission in the wings forV
rot = 0 and 5 while forV
rot ≥ 10 we obtain symmetric absorption lines. In the case of an expanding shell, we obtain lines with central emission. 相似文献
11.
Ralf Koppmann 《Astrophysics and Space Science》1985,110(2):321-330
Radial velocities of both components of Zeta Aurigae have been measured on 39 grating spectra obtained in the interval February 1970-November 1981.The evaluation of the orbital elements of the primary component confirmed, the elements observed so far. The velocity variation of the secondary component has been determined according to the method described by Popper (1961) yieldingK
B=30.57±5.97 (m.e.) km s–1. The masses of the components were found to beM
K sin3
i=6.4±1.7 andM
B sin3
i=4.5±0.9 solar masses. With the elements obtained a radial velocity curve of the B-star has been calculated. Comparison of the radial velocities derived from the hydrogen lines of the B-star with the calculated radial velocity curve shows systematic deviations which indicate that these lines originate partly in an expanding circumstellar envelope of the system. The main constituent of the envelope must be neutral hydrogen of high density. Variations of the radial velocities indicate density variations due to condensations inside this envelope. 相似文献
12.
We have studied the kinematic properties of the candidates for hot subdwarfs (HSDs) selected by Geier et al. from theGaiaDR2 catalogue. We have used a total of 12 515 stars with relative trigonometric parallax errors less than 30%. The HSDs are shown to have different kinematics, depending on their positions on the celestial sphere. For example, the sample of low-latitude (|b| < 20°) HSDs rotates around the Galactic center with a linear velocity V0 = 221 ± 5 km s?1. This suggests that they belong to the Galactic thin disk. At the same time, they lag behind the local standard of rest by ΔV☉ ~ 16 km s?1 due to the asymmetric drift. The high-latitude (|b| ≥ 20°) HSDs rotate with a considerably lower velocity, V☉ = 168 ± 6 km s?1. Their lagging behind the local standard of rest is already ΔV☉ ～ 40 km s?1. Based on the entire sample of 12 515 HSDs, we have found a positive rotation around the x axis significantly differing from zero with an angular velocity ω1 = 1.36±0.24 km s?1 kpc?1. We have studied the samples of HSDs that are complete within r < 1.5 kpc. Based on them, we have traced the evolution of the parameters of the residual velocity ellipsoid as a function of both latitude |b| and coordinate |z|. The following vertical disk scale heights have been found: h = 180 ± 6 and 290 ± 10 pc from the low- and high-latitude HSDs, respectively. A new estimate of the local stellar density Σout = 53 ± 4 M☉ kpc?2 has been obtained for zout = 0.56 kpc from the high-latitude HSDs.
相似文献13.
We have studied the structure of hot accretion flow bathed in a general large-scale magnetic field. We have considered magnetic parameters , where are the Alfvén sound speeds in three direction of cylindrical coordinate (r,φ,z). The dominant mechanism of energy dissipation is assumed to be the magnetic diffusivity due to turbulence and viscosity in the accretion flow. Also, we adopt a more realistic model for kinematic viscosity (ν=αc s H), with both c s and H as a function of magnetic field. As a result in our model, the kinematic viscosity and magnetic diffusivity (η=η 0 c s H) are not constant. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. It is found that the existence of magnetic resistivity will increase the radial infall velocity as well as sound speed and vertical thickness of the disk. However the rotational velocity of the disk decreases by the increase of magnetic resistivity. Moreover, we study the effect of three components of global magnetic field on the structure of the disk. We found out that the radial velocity and sound speed are Sub-Keplerian for all values of magnetic field parameters, but the rotational velocity can be Super-Keplerian by the increase of toroidal magnetic field. Also, Our numerical results show that all components of magnetic field can be important and have a considerable effect on velocities and vertical thickness of the disk. 相似文献
14.
V. V. Bobylev 《Astronomy Letters》2010,36(11):816-822
Based on currently available kinematic data, we have searched for stars outside the Hipparcos list that either closely encountered
in the past or will encounter in the future the Solar system within several parsecs. For the first time, we have identified
two single stars, GJ 3379 (G 099-049) and GJ 3323 (LHS 1723), as candidate for a close encounter with the solar orbit. The
star GJ 3379 could encounter the Sunmore closely to aminimumdistance d
min = 1.32±0.03 pc at time t
min = −163 ± 3 thousand years. We have found two potential candidates for a close encounter that have only photometrical distances:
the white dwarf SSSPM J1549-3544 without any data on its radial velocity and the L-dwarf SDSS J1416+1348. The probabilities
of their penetration into the Oort cloud region are 0.09 (at a model radial velocity <V
r
< = 50 km s−1) and 0.05, respectively. 相似文献
15.
SOHO/LASCO data were used to obtain the latitudinal and radial distributions of the brightness of the K- and F-corona in the
period of 1996 – 2007, and their solar-cycle variations were studied. Then an inversion method was employed to obtain the
radial distributions of the electron density N
e(R,θ) for various latitude values on the coronal images. Our values of N
e(R,θ) are in good agreement with the findings of other authors. We found that in an edge-on streamer belt the electron density,
like the K-corona brightness, varies with distance more slowly in the near-equatorial rays than in near-polar regions. We
have developed a method for assessing the maximum values of the electron density at the center of the face-on streamer belt
in its bright rays and depressions between them. Not all bright rays observed in the face-on streamer belt are found to be
associated with an increased electron density in them. Mechanisms for forming such rays have been suggested. 相似文献
16.
Krishna Raj Choubey 《Astrophysics and Space Science》1984,104(1):157-161
In this paper the unsteady flow in the Ekman layer of a visco-elastic non-Newtonian fluid near a flat plate is discussed. Laplace transform technique has been employed to show the basic differential equations. Expressions for velocity profile, the skin friction have been calculated. It is shown that the time to attain the steady state increases with the elastic parameter. It is shown that normally the ultimate steady state is reached through a decay of inertial oscillations whose frequency decreases with increase in the elastic parameter. In the present study we examine the following unsteady problem in non-Newtonian fluid. Consider an infinite plate coinciding with the platez=0 and rotating in unison with elasticoviscous liquid occupying the regionz>0 with a uniform angular velocity about thez-axis for timet<-0. At timet>0, the plate starts moving with a uniform velocityU
o along thex-axis relative to the rotating frame of reference. The horizontal homogeneity of the problem demands that conditions depend onz andt only. The equation of continuity together with the no slip condition at the plate then shows that thez-component of the velocity vanishes everywhere. 相似文献
17.
M. Narasimha Rao Saleh Mohamed Alladin K. S. V. S. Narasimhan 《Celestial Mechanics and Dynamical Astronomy》1994,58(1):65-80
A simple, semi-analytic method is developed for obtaining the orbits of galaxies undergoing fast collisions in which the galaxies are represented by Plummer models. The results are found to agree fairly well with those of N-body simulations.A simple formula for obtaining the angle of deflection is deduced. The maximum angle of deflection is 180° forV
p/V
esc(p)=1.00, about 36° forV
p/V
esc(p)=1.50, and about 18° forV
p/V
esc(p)=2.00, whereV
p is the velocity at closest approachp, andV
esc(p) is the parabolic velocity of escape atp. The angle of deflection of a pair of colliding elliptical galaxies without halos is about twice that for a pair of galaxies with halos for the same relative velocity at infinite separation. 相似文献
18.
Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes,
proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to
the Galactic center R
0, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives.
For R
0 = 8 kpc, we have found the circular velocity of the Sun to be V
0 = 243 ± 16 km s−1, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s−1 kpc−1 and B = −13.5 ± 1.4 km s−1 kpc−1. Our simulation of the influence of a spiral density wave has shown that the peculiar velocity of the Sun with respect to
the local standard of rest and the component (V
⊙)LSR depend significantly on the Sun’s phase in the spiral wave. 相似文献
19.
We have mapped 16 molecular clouds toward a new OB association in the Pup-CMa region to derive their physical properties.
The observations were carried out in the 12CO (J = 1 – 0) line with the Southern millimetre-wave Telescope at Cerro Tololo, Chile. Distances have been determined kinematically
using the rotation curve of Brand with R⊙ = 8.5 kpc and V⊙ = 220 km/s. Masses have been derived adopting a CO luminosity to H2 conversion factor X = 3.8 . 1020 molecules cm-2 (K km/s)-1. The observed mean radial velocity of the clouds is comparable with the mean radial velocity of stars composing an OB association
in Pup-CMa; it is in favor of the close connection of clouds with these stars.
__________
Published in Astrofizika, Vol. 48, No. 4, pp. 491–501 (October–December, 2005). 相似文献
20.
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