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1.
Two spectra of the star BM Ori were obtained with the 2.6-m Crimean Astrophysical Observatory telescope near its maximum eclipse phase. The light detector was a CCD array. The wavelength range 5305–5373 Å was chosen in such a way that it contained no strong primary lines. Optimum filtration of the spectra yielded a signal-to-noise ratio of ~300. Eighteen secondary lines are seen in the spectrum. Atmospheric parameters of the secondary star were determined: T eff=5740 K and logg=3.0; the secondary was classified by these parameters as being of spectral type G2 III. The best agreement between observed and synthetic spectra is achieved for metallicity [M/H]=?0.5 and microturbulence ξt=0 km s?1. The projected rotational velocity is Vsini=60 km s?, in agreement with the synchronous velocity in the hypothesis that assumes a total eclipse by the secondary star. Atmospheric elemental abundances in the secondary are estimated. Nickel, chromium, and iron exhibit an underabundance of ~1 dex. 相似文献
2.
R. & R. Griffin 《Journal of Astrophysics and Astronomy》1986,7(3):195-223
Composite-spectrum binary stars generally consist of a late-type giant and a main-sequence star of type A or B. Their spectra
are therefore rather confusing; but by a technique of digital subtraction of the spectra of appropriate single late-type giants,
composite spectra can be split into their individual components. In favourable cases the radial velocities of both components
can be measured and the mass ratio determined. The procedures are illustrated by reference to HR 6902, a fifth-magnitude composite-spectrum
binary. Its components are shown to have spectral types of G9 II and B8 V, with a mass ratio of 1.31, and its orbit is determined.
There is some evidence that the system shows eclipses. If it does, the masses of the components are 3.9 and 3.0M⊙ respectively, and HR 6902 becomes the sixth known member of the important class ofζ Aur binaries. 相似文献
3.
Alberto Carramiñana 《Astrophysics and Space Science》2007,309(1-4):373-378
The Cygnus region of the Milky Way is prolific in star formation and presents extended diffuse γ-ray emission with a few γ-ray point sources. Among them is 3EG J2020+4017, the brightest of the unidentified EGRET sources, positionally coincident
with the supernova remnant G78.2+2.1. Even though the EGRET and multi-wavelength data have not provided a conclusive identification
for this γ-ray loud, but otherwise faint object, the evidence favors a pulsar like source. The EGRET photon data lack the signal-to-noise
ratio required for a period search, but will serve as a valuable timing baseline extension in the case that GLAST confirms the pulsar nature of the γ-Cygni source.
Work sponsored by CONACyT grant SEP-2003-C02-42611. 相似文献
4.
A. Peraiah 《Journal of Astrophysics and Astronomy》1980,1(2):101-111
A direct iteration has been performed to obtain a simultaneous solution of the equations of line transfer in an expanding
spherically symmetric atmosphere in the comoving frame with statistical equilibrium for a non-LTE, two-level atom. The solution
converges in three or four iterations to an accuracy of 1 per cent of the ratio of the population densities of the two levels.
As initial values, the upper level population was set equal to zero or to the LTE densities. The final solution on convergence
indicates enhanced population of these levels over the initial values assumed, Large velocity gradients enhance this effect
whereas large geometrical sizes of the atmospheres tend to reduce it. 相似文献
5.
The peculiar galaxy NGC 4650 A (α=12h 42m. 1; = δ—40° 26′; 1950·0) has been studied by means of direct and spectral observations with the ESO 3·6-m telescope. It is
interpreted as a prolate, elliptical galaxy surrounded by a warped ring of H II regions, dust and stars. The distance is 47
Mpc (H
0=55 km s−1 Mpc−1). The ring is seen nearly edge-on (inclination 85°) and it rotates. It has a diameter of about 21 kpc and is bluer than the
elliptical galaxy for which the (M/L
v) ratio is ∼12 in solar units. The observed configuration may be the result of interaction with the nearby galaxy, NGC 4650. 相似文献
6.
Asantha Cooray 《Monthly notices of the Royal Astronomical Society》2005,363(3):1049-1056
The brightness temperature fluctuations in the 21-cm background related to the neutral hydrogen distribution provide a probe of the physics related to the era of reionization, when the intergalactic medium changed from being completely neutral to partially ionized. We formulate statistics of 21-cm brightness temperature anisotropies in terms of the angular power spectrum, the bispectrum, and the trispectrum. Using the trispectrum, we estimate the covariance related to the power spectrum measurements and show that correlations resulting from non-Gaussianities are below a per cent, at most. While all-sky observations of the 21-cm background at arcminute-scale resolution can be used to measure the bispectrum with a cumulative signal-to-noise ratio of the order of a few tens, in the presence of foregrounds and instrumental noise related to first-generation interferometers, the measurement is unlikely to be feasible. For most purposes, non-Gaussianities in 21-cm fluctuations can be ignored and the distribution can be described with Gaussian statistics. Because 21-cm fluctuations are significantly contaminated by foregrounds, such as galactic synchrotron or low-frequency radio point sources, the lack of significant non-Gaussianity in the signal suggests that any significant detection of non-Gaussianity could be the result of foregrounds. Similarly, in addition to the frequency information that is now proposed to separate 21-cm fluctuations from foregrounds, if the non-Gaussian structure of foregrounds is known a priori, this additional information could potentially be used to reduce the confusion further. 相似文献
7.
We have treated formation of spectral lines in a commoving frame where photoionization is predominant over collisional processes.
We have assumed that the radiation field for causing photoionization is a function of Planck function. We have also considered
the situation in which the continuum contributes to the radiation in the line. In all the models the quantityB/A (ratio of outer to inner radii) is kept equal to 10 and the total optical depth is taken to be 103. The velocity is assumed to be varying according to the lawdV/dτ ∼ < 1/τ whereτ is the optical depth (τ > 0) in the given shell. The velocities at the innermost radius (r =A) are set equal to 0 and at the outermost radius (r =B), the maximum velocities are taken to be 0, 1, 3 and 10 Doppler units. The calculated line profiles are those seen by an observer
at infinity.P Cygni-type profiles are observed in the case of a medium with no continuum absorption. For a medium with continuum absorption
double peaked asymmetric profiles are noticed when the velocities are small; the two emission peaks merge into a single asymmetric
peak for larger velocities. 相似文献
8.
S. Sukumar 《Journal of Astrophysics and Astronomy》1987,8(4):281-294
The refraction of radio waves as they traverse through the terrestrial ionosphere and troposphere introduces a differential
phase path which results for a radio interferometer in variations of the visibility phase. Though refraction due to troposphere
is significant for synthesis radio telescopes operating at 1.0 GHz and above, ionospheric refraction is dominant at lower
frequencies. This problem is important in the case of Ooty Synthesis Radio Telescope (OSRT) operating at 326.5 MHz, due to
its proximity to the magnetic equator. This paper deals with the nature of phase variations suffered by OSRT due to refraction
and explains the methodology evolved to alleviate them. 相似文献
9.
An examination of the existing period searches for 2CG195 + 4 leads to the conclusion that the 59 second periodicity is highly
significant only for the 1981 March 17–18 detection of Bignami, Caraveo & Paul (1984). The statistical significance is increased
substantially if the pulsation period is half the previously reported value. The period derivative is not well determined.
Here we propose that 2CG 195 + 4 is a neutron star powered by accretion from a low (≲ 1M
⊙) mass main-sequence companion. A distance of a few hundred pc would imply that the neutron star is a fast rotator and is
spinning down. 相似文献
10.
The conditions for the source functions of a multiplet to be equal are studied for plasmas with and without magnetic fields.
It is found that source function equality holds—in addition to the case of collisional predominance—only when the redistribution
functions are all identical and no interlocking with other lines occurs. When magnetic fields are present, the assumption
of source function equality leads to a violation of the invariance conditions of the scattering matrix and should therefore
not be made. 相似文献
11.
The Hα observations of a flare-associated surge prominence on 1980 October 30 have been described. Morphology and dynamics
of the surge prominence have been presented. From our observations and analysis we have estimated the magnetic field associated
with surge material to be about 35 gauss which is in good agreement with the earlier result of Tandberg-Hanssen & Malville
(1974). It has been determined that coronal pressure is not acting as a resistive force on the outward expansion of the surge
into the corona. The kinetic energy of the surge was about 1028 erg, which is 2 orders less than required for the mass to escape the chromosphere. It appears that the flare-associated surge
prominence was perhaps a result of kink instability in the flaring region. 相似文献
12.
We have computed a combined spectroscopic-interferometric orbit for the nearby binary Gliese 600 discovered by us. The orbital period is 2.78 years, and the semimajor axis is 100 mas (0.1″). Its M0 V components are almost identical and have a mass of 0.5M ⊙. The mass ratio is uncertain because of the low radialvelocity semiamplitude (7 km s?1) associated with the low orbital inclination (37°). The orbital parallax of the binary (52±11 mas) matches its dynamical and photometric parallaxes but differs significantly from the Hipparcos parallax (44.3±1.6) mas; the latter was probably distorted by the orbital motion that was not taken into account. 相似文献
13.
Takashi Tsuji 《Journal of Astrophysics and Astronomy》1981,2(1):95-113
It is shown that the infrared flux method for determining stellar effective temperatures (Blackwell and Shallis 1977; Blackwell,
Petford and Shallis 1980) can be applied to cool carbon stars. Although the spectra of cool carbon stars are highly line blanketed,
the spectral region between 3 and 4 μm (L-band in the infrared photometry system) is found to be relatively free from strong
line absorption. The ratioR
L of bolometric flux toL flux can then be used as a measure of effective temperature. On the basis of the predicted line-blanketed flux based on model
atmospheres, with an empirical correction for the effect of 3 μm absorption due to polyatomic species (HCN, C2H2), it is shown thatR
L is roughly proportional to T3
eff. The high sensitivity ofR
L to Teff makes it a very good measure of effective temperature, and the usual difficulty due to differential line blanketing effect
in the analyses of photometric indices of cool carbon stars can be minimized.
It is found that the majority of N-type carbon stars with small variability (SRb and Lb variables) are confined to the effective
temperature range between 2400 and 3200 K, in contrast to M-giant stars (M0 III - M6 III, including SRb and Lb variables)
that are confined to the effective temperature range between 3200 and 3900 K. The effective temperatures based on the infrared
flux method show good agreement with those derived directly from angular diameter measurements of 5 carbon stars. On the basis
of the new effective temperature scale for carbon stars, it is shown that the well known C-classification does not represent
a temperature sequence. On the other hand, colour temperatures based on various photometric indices all show good correlations
with our derived effective temperatures.
An erratum to this article is available at . 相似文献
14.
S. A. Lamzin 《Astronomy Letters》2000,26(9):589-599
The ultraviolet spectra of the stars RY Tau and HD 115043 from the Hubble Space Telescope are analyzed. RY Tau belongs to the classical T Tauri stars, while HD 115043 is a young (t~3×108 years), chromospherically active star. The most intense emission lines were identified, and their fluxes were measured. Low-resolution spectra of RY Tau and HD 115043 in the wavelength range 1160–1760 Å exhibit almost the same set of emission lines. However, first, the luminosity of RY Tau in these lines is approximately a factor of 300 higher than that of HD 115043, and, second, the relative line intensities differ greatly. The intensity ratio of the C IV λ1550, Si IV λ1400, and NV λ1240 doublet components is close to 1: 2 in the spectra of both stars. Judging by the continuum energy distribution, the spectral type of RY Tau is later than that of HD 115043. Synchronous flux variability in the C IV λ1550 and He II λ1640 lines in a time of ~20 min was detected in RY Tau. The flux rise in these lines was accompanied by a redshift of the intensity peak in the profiles by~50 km s?1. Intermediate-resolution spectra are used to study line profiles in the spectrum of RY Tau. In particular, the profiles of (optically thin) Si III]λ1892 and C III]λ1909 lines were found to be asymmetric and about 300 km s?1 in width. The (optically thick) C IV λ1550 doublet lines have similar profiles. The Mg II λ2800 doublet lines are also asymmetric, but their shape is different: they consist of a broad (?750 km s?1 at the base) emission component on which an interstellar absorption line shifted from the line symmetry center by about 20 km s?1 is superimposed. The intensity ratio of the Mg II λ2800 doublet components is?1.4. Whether there are molecular hydrogen lines in the spectrum of RY Tau is still an open question. It is shown that the emission lines in the ultraviolet spectrum of RY Tau cannot originate in a hydrostatically equilibrium chromosphere. It is argued that quasi-steady accretion of circumstellar matter is responsible for the emission. 相似文献
15.
Partha S. Pal Harinder P. Singh Kwing L. Chan M. P. Srivastava 《Astrophysics and Space Science》2007,307(4):399-407
We examine the behaviour of penetrative turbulent compressible convection under the influence of rotation by means of three
dimensional numerical simulations. We estimate the extent of penetration below a stellar-type rotating convection zone in
an f-plane configuration. Several models have been computed with a stable-unstable-stable configuration by varying the rotation
rate (Ω), the inclination of the rotation vector and the stability of the lower stable layer. The spatial and temporal average of
kinetic energy flux (Fk) is computed for several turnover times after the fluid has thermally relaxed and is used to estimate the amount of penetration
below the convectively unstable layer. Our numerical experiments show that with the increase in rotational velocity, the downward
penetration decreases. A similar behaviour is observed when the stability of the lower stable layer is increased in a rotating
configuration. Furthermore, the relative stability parameter S shows an S
−1/4 dependence on the penetration distance implying the existence of a thermal adjustment region in the lower stable layer rather
than a nearly adiabatic penetration region. 相似文献
16.
Partha S. Pal Harinder P. Singh Kwing L. Chan M. P. Srivastava 《Astrophysics and Space Science》2008,314(1-3):231-239
We perform Large eddy simulations of turbulent compressible convection in stellar-type convection zones by solving the Naviér-Stokes
equations in three dimensions. We estimate the extent of penetration into the stable layer above a stellar-type convection
zone by varying the rotation rate (Ω), the inclination of the rotation vector (θ) and the relative stability (S) of the upper stable layer The computational domain is a rectangular box in an f-plane configuration and is divided into two regions of unstable and stable stratification with the stable layer placed above
the convectively unstable layer. Several models have been computed and the penetration distance into the stable layer above
the convection zone is estimated by determining the position where time averaged kinetic energy flux has the first zero in
the upper stable layer. The vertical grid spacing in all the model is non-uniform, and is less in the upper region so that
the flows are better resolved in the region of interest. We find that the penetration distance increases as the rotation rate
increases for the case when the rotation vector is aligned with the vertical axis. However, with the increase in the stability
of the upper stable layer, the upward penetration distance decreases. Since we are not able to afford computations with finer
resolution for all the models, we compute a number of models to see the effect of increased resolution on the upward penetration.
In addition, we estimate the upper limit on the upward convective penetration from stellar convective cores. 相似文献
17.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1988,9(3):127-136
Photoelectric radial-velocity measurements show that HD 106947 is a double-lined spectroscopic binary. The components have
spectral types of about F6 V and G5 V and are in a 59-day orbit of moderate eccentricity. The system is a member of the Coma
Cluster. 相似文献
18.
A. F. Heavens 《Monthly notices of the Royal Astronomical Society》1998,299(3):805-808
The bispectrum of the microwave background sky is a possible discriminator between inflationary and defect models of structure formation in the Universe. The bispectrum, which is the analogue of the temperature three-point correlation function in harmonic space, is zero for most inflationary models, but non-zero for non-Gaussian models. The expected departures from zero are small, and easily masked by noise, so it is important to be able to estimate the bispectrum coefficients as accurately as possible, and to know the errors and correlations between the estimates so that they may be used in combination as a diagnostic to rule out non-Gaussian models. This paper presents a method for estimating in an unbiased way the bispectrum from a microwave background map in the near-Gaussian limit. The method is optimal, in the sense that no other method can have smaller error bars, and, in addition, the covariances between the bispectrum estimates are calculated explicitly. The method deals automatically with partial sky coverage and arbitrary noise correlations without modification. A preliminary application to the Cosmic Background Explorer 4-yr data set shows no evidence for non-Gaussian behaviour. 相似文献
19.
In this paper we give a detailed general relativistic formulation of the study of structure and stability of charged fluid
disks around compact objects like black holes neglecting the self-gravitation of the disk itself. Having presented the general
equations for equilibrium as well as for perturbations we solve explicitly the cases of rigidly and differentially rotating
thin disks, with constant charge density and zero pressure, confined to the equatorial plane of the black hole. By using normal
mode analysis we have analysed the stability of such disks under purely radial perturbations and find that the disks are generally
stable.
On leave of absence from Government College, Jagadalpur 494005 相似文献
20.
BV photometry of HD 116204 obtained on 57 nights during 1983–84, 1984–85 and 1986–87 observing season is presented. A photometric
period of 21.9 ± 0.2 d and a mean (B-V)= 1.196 ± 0.010 are obtained. It is suggested that the binary HD 116204 has a mass ratio close to unity. Attempts are needed
to detect the spectrum of secondary. 相似文献