共查询到20条相似文献，搜索用时 31 毫秒
1.
D. L. Terrett 《Astrophysics and Space Science》1980,70(2):393-399
The effective temperature of the short period cepheid SU Cas has been determined from a comparison of its spectral scans with appropriate model atmospheres. Using this temperature and an independent Wesselink radius determination, the luminosity of the star has been redetermined. The pulsation mass and the evolutionary mass of the star have been discussed. The evolutionary to pulsation mass ratio comes out to be greater than unity. 相似文献
2.
BU Tauri (Pleione) an interesting star in the Pleiades cluster, has been observed spectrophotometrically. The energy distribution
curves of the star have been discussed vis a vis model atmospheres for normal stars in the appropriate range of temperature
and effective gravity. The changes in the energy distribution curve noticed during our observations and previous observations
taken from the literature have been pointed out. On the basis of the measured Há emission equivalent width, a rough estimate
of the dimensions of the extended envelope of the star has been made. 相似文献
3.
An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the chemically peculiar (CP) star HD 25823 model parameters were determined from H profile and photometric data. Its pattern of abundance shows that the heavier elements in HD 25823 are overabundant. 相似文献
4.
The brightest star in either Magellanic cloud has been analyzed by the method of model atmospheres using observational data secured at Cerro Tololo. The results from abundance studies are in general accord with the conclusions by Przybylski. We find solar abundances for Fe, Sc, Mg, Si and, probably, Ca. The V, Cr, Si, Ti data suggest lower abundances but the evidence is not conclusive. 相似文献
5.
An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the chemically peculiar (CP) star HD 26385. Model parameters were determined from H-profile and photometric data. Its pattern of abundance shows that HD 26385 is typically Ap Si-star. 相似文献
6.
We present a study of atmospheric thermal structure of nine MIII giants located in the zone of a star formation region in the stellar Galactic bar. Vibrational temperatures of the layers of formation of δ, π and ε TiO molecular band systems have been determined spectroscopically. These temperatures have been associated to optical depths by use of an appropriate model atmospheres and in view of several T eff calibration scales. Significant temperature gradient in the upper atmospheric layers has been established. 相似文献
7.
An abundance analysis using photographic region spectrograms and fully line-blanketed model atmospheres has been performed for the metallic-lined (Am) star HD 73730. Model parameters were determined from the Balmer line profiles and Strömgren index (c
1). The values of effective temperature and gravity were confirmed ionization equilibrium of Fe and Cr. Its abundance pattern gives that HD 73730 shows mild Am-like characteristics. 相似文献
8.
The absolute energy distributions of the cepheid Gem at several phases of the light cycle have been given. By matching these with suitable model atmospheres, the effective temperatures of the star at these phases have been determined. The radius and effective gravity variations as well as the mass have been derived. 相似文献
9.
A moment method with three stream division of the radiation field was suggested by Wilson, Wan and Sen (1980) for solving radiative transfer problems in stationary, non-grey extended shells surrounding a central star. Use was made of the generalised Eddington relations as the closure conditions of the moment equations. In the present paper the same method has been utilised to study the radiative transfer problems in a non-grey, expanding gaseous spherical shells surrounding a central star. The transfer equation has been set in comoving frame in spherical geometry. The radiation and material quantities, angles and frequencies have been expressed in comoving frame. The mean intensity, flux and K-integrals have been calculated for extensive atmospheres in the presence of different velocity fields. 相似文献
10.
G. Israelian A. Herrero F. Musaev A. Kaufer A. Galeev G. Galazutdinov E. Santolaya-Rey 《Monthly notices of the Royal Astronomical Society》2000,316(2):407-417
We report spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations of photospheric absorption lines with a possible quasi-period of ∼6.4 d have been detected in high-resolution echelle spectra. Night-to-night variations in the position and strength of the central emission reversal of the H α profile occurring over ill-defined time-scales have been observed. The fundamental parameters of the star are derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, the latter including the mass-loss rate. The derived helium abundance is moderately enhanced with respect to solar, and the stellar masses are lower than those predicted by the evolutionary models. The binary nature of this star is not suggested either from Hipparcos photometry or from radial velocity curves. 相似文献
11.
Brown dwarfs are the coolest class of stellar objects known to date. Our present perception is that brown dwarfs follow the principles of star formation, and that brown dwarfs share many characteristics with planets. Being the darkest and lowest mass stars known makes brown dwarfs also the coolest stars known. This has profound implication for their spectral fingerprints. Brown dwarfs cover a range of effective temperatures which cause brown dwarfs atmospheres to be a sequence that gradually changes from a M-dwarf-like spectrum into a planet-like spectrum. This further implies that below an effective temperature of \(\lesssim \)2,800 K, clouds form already in atmospheres of objects marking the boundary between M-Dwarfs and brown dwarfs. Recent developments have sparked the interest in plasma processes in such very cool atmospheres: sporadic and quiescent radio emission has been observed in combination with decaying X-ray activity indicators across the fully convective boundary. 相似文献
12.
Ya. V. Pavlenko 《Kinematics and Physics of Celestial Bodies》2010,26(2):51-61
A numerical technique for determining absorption line formation depths in the atmospheres of late-type stars and substellar-mass
subdwarfs is proposed. The technique is based on estimating individual absorptions contributed by certain layers of the stellar
model atmosphere to the resulting equivalent width of a spectral line. In particular, the proposed technique can be used when
considering lithium absorption lines formed at the background of molecular bands. The technique is applied to the formation
of lithium lines in stellar atmospheres, specifically, in the atmosphere of the Sun (spectral type G2V) and those of the red
giant star in the binary system RS Oph (M2III), the giant carbon star WZ Cas (C6), and the brown dwarf LP944-20 (M9V). 相似文献
13.
S. Geier U. Heber H. Edelmann L. Morales-Rueda R. Napiwotzki 《Astrophysics and Space Science》2010,329(1-2):127-131
The formation of sdBs as well as the chemical composition of their atmospheres is still puzzling. While helium and other light elements are depleted relative to solar values, heavy elements are highly enriched. Diffusion processes in the hot, radiative atmosphere of these stars are the most likely explanation. Although several attempts have been made, it has not yet been possible to model all the observed features of sdB atmospheres. A drawback of most prior studies was the small sample size. We present a detailed abundance analysis of 139 sdBs. A general trend of enrichment was found with increasing temperature for most of the heavier elements. The lighter elements like carbon, oxygen and nitrogen are depleted and less affected by temperature. Although there is considerable scatter from one star to the other, the general abundance patterns in most sdBs are similar. An interplay between gravitational settling, radiative levitation and weak winds is most likely responsible. About 3% of the analysed stars show an enrichment in carbon and helium, which cannot be explained in the framework of diffusion alone. Nuclear processed material must have been transported to the surface somehow. 相似文献
14.
N. Lehner P. L. Dufton D. L. Lambert R. S. I. Ryans F. P. Keenan 《Monthly notices of the Royal Astronomical Society》2000,314(1):199-208
Very-high-resolution ( R ∼160 000) spectroscopic observations are presented for the early B-type star, HD 83206. Because it has very sharp metal lines, this star affords an opportunity to test theories of model atmospheres and line formation. Non-LTE model atmosphere calculations have been used to estimate the atmospheric parameters and absolute metal abundances (C, N, O, Mg and Si); an LTE analysis was also undertaken to investigate the validity of this simpler approach and to estimate an iron abundance. For the non-LTE calculations, there is excellent agreement with observations of the Balmer lines H α and H δ and the lines of Si ii and Si iii for atmospheric parameters of T eff ≃21 700±600 K and log g ≃4.00±0.15 dex. The agreement is less convincing for the LTE calculations, and a higher gravity is deduced. Careful comparison of the metal line profiles with non-LTE calculations implies that the projected rotational and microturbulent velocities have maximum values of ≃5 and ≃2 km s−1 , respectively. The latter value is smaller than has often been adopted in LTE model atmosphere analyses of main-sequence stars. Non-LTE absolute metal abundances are estimated, and a comparison with those for normal B-type stars (deduced using similar non-LTE techniques) shows no significant differences. A comparison of the abundances deduced using non-LTE and LTE calculations implies systematic differences of 0.1–0.2 dex, showing the importance of using a non-LTE approach when accurate absolute abundances are required. Its location in the Hertzsprung–Russell diagram and normal metal abundance lead us to conclude that HD 83206 is probably a main-sequence B-type star. As such, it is among the sharpest-lined young B-type star discovered to date. 相似文献
15.
A. P. Linnell † 《Monthly notices of the Royal Astronomical Society》2002,332(1):21-28
A new composite model eliminates discrepancies between synthetic spectra for the L2000 model of β Lyrae and spectrophotometric scans and charge-coupled device (CCD) spectra of that binary star. The source of the discrepancies is the use of synthetic spectra from standard model atmospheres to represent the radiation characteristics of the accretion disc rim. Substitution of a composite synthetic spectrum to represent the accretion disc rim eliminates the discrepancies and produces accordance with both scan data, including their temporal variation, and CCD spectra. 相似文献
16.
We present numerical models based on realistic treatment of the intensity spectrum (from model atmospheres), and demonstrate that they are consistent with Kurtz and Medupe's recent formula in showing that limb darkening is too small an effect to explain the observed sharp decline of pulsation light amplitude with wavelength in rapidly oscillating Ap stars. Kurtz and Medupe's formula is shown to be a special form of Watson's earlier general formula for non-radial light variations of a star pulsating in any mode ( l m ). Using a technique suggested by Kurtz and Medupe we derive temperature semi-amplitude as a function of depth in the atmospheres of α Cir and HR 3831, assuming that we can neglect non-adiabatic effects. 相似文献
17.
The causes of variability of line profiles in the spectra of O supergiants are analyzed. It is suggested that the main cause
of the variability is the motion in the atmosphere of dense clumps of matter (inhomogeneities or clouds) along the Une of
sight between star and observer. The profiles of C IV and Si IV UV resonance lines in the spectra of bright OB supergiants
are calculated for spherically symmetric atmospheres and for atmospheres with inhomogeneity along the line of sight. The dependence
of the line profiles on the distance of the inhomogeneity from the center of the star is investigated. It is shown that the
formation and evolution with time of discrete absorption components (DACs) in the profiles of C IV and Si IV UV resonance
lines can be explained within the framework of the proposed model of variability of line profiles. The parameters of the inhomogeneities
moving in the atmosphere to produce DACs are estimated.
Translated from Astrofizika, Vol. 41, No. 3, pp. 423–441, July–September, 1998. 相似文献
18.
AA Dor is one of only seven known eclipsing binaries consisting of a hot subdwarf star and a low-mass companion. Although AA Dor has been studied in many investigations, a controversy about the nature of its companion persists. Is it a brown dwarf or a low-mass main sequence star? We reanalyse high resolution spectra using metal enhanced LTE model atmospheres. The optical spectra are polluted by reflected light from the companion. Using spectra taken during secondary eclipse, we derive atmospheric parameters consistent with results from the light curve. For the first time we achieve a self-consistent solution that matches all available observations, i.e. the light and radial velocity curves, as well as the atmospheric parameters. The resulting masses $M_{1}=0.510^{+0.125}_{-0.108}\ \mathrm{M}_{\odot}$ and $M_{2}=0.085^{+0.031}_{-0.023}\ \mathrm{M}_{\odot}$ are consistent with the canonical mass of an sdB star and a low-mass main sequence star. However, a brown dwarf companion cannot be excluded. 相似文献
19.
I. S. Savanov 《Astrophysics》1996,39(2):107-111
The abundances of 12 elements in the atmosphere of the "F str 4077" star HD 177645 have been determined from new spectroscopic observations with the CCD camera and the model atmosphere method. The overabundance of nitrogen found for this star indicates its possible relation to barium dwarfs with anomalies in the chemical composition of their atmospheres due to mass transfer from the more evolved companion in a binary system. As an object related to Ba stars and CH subgiants, HD 177645 with an effective temperature Teff=7150K may also have anomalies in the chemical composition characteristic of diffusion processes in chemically peculiar stars of the upper main sequence, as may be indicated by the overabundance of sulfur in its atmosphere.Translated fromAstrofizika, Vol. 39, No. 2, pp. 201–209, April–June, 1996. 相似文献
20.
An analytic solution has been found in the Roche approximation for the axially symmetric structure of a hydrostatically equilibrium atmosphere of a neutron star produced by collapse. A hydrodynamic (quasione-dimensional) model for the collapse of a rotating iron core in a massive star gives rise to a heterogeneous rotating protoneutron star with an extended atmosphere composed of matter from the outer part of the iron core with differential rotation (Imshennik and Nadyozhin, 1992). The equation of state of a completely degenerate iron gas with an arbitrary degree of relativity is taken for the atmospheric matter. We construct a family of toroidal model atmospheres with total masses M≈ 0.1?2M ⊙ and total angular momenta J≈(1?5.5)×49 erg s, which are acceptable for the outer part of the collapsed iron core, in accordance with the hydrodynamic model, as a function of constant parameters ω0 and r 0 of the specified differential rotation law Ω=ω0exp[?(rsinθ)2/r 0 2 ] in spherical coordinates. The assumed rotation law is also qualitatively consistent with the hydrodynamic model for the collapse of an iron core. 相似文献