共查询到20条相似文献，搜索用时 937 毫秒
1.
O. Cardona 《Astrophysics》2011,54(1):75-86
A new method for finding the line widths of atomic lines produced by thermal energy fluctuations in a gaseous system is developed
assuming that the atomic linear density change in the energy of the levels is equal to the linear density of the energy fluctuations
per degree of freedom. A formula is derived for the atomic line widths that depends on temperature, the cubic root of the
total number density of particles in the system, and on the sum of the squares of the principal quantum numbers of the states
that participate in the transitions that produce the lines. The calculated widths agree well with the published experimental
and theoretical values. This formula will be useful for directly diagnosing the physical state of stellar atmospheres and
plasmas. 相似文献
2.
Janet E. Drew 《Astrophysics and Space Science》1994,216(1-2):45-54
New high-quality high spectral resolution observations of the HI line emission from massive young stellar objects are described and discussed. It is proposed that two distinct physical components contribute to the observed emission. One of these is an optically-thick high-velocity stellar wind, the other a more slowly moving optically-thin volume of gas that may, in the case of S106IR at least, be caused by mass loading of the stellar wind. This decomposition is shown to resolve a long-standing problem regarding the relative widths of high and low opacity lines. 相似文献
3.
Roberto Cid Fernandes Jr Thaisa Storchi-Bergmann & Henrique R. Schmitt 《Monthly notices of the Royal Astronomical Society》1998,297(2):579-616
We present the results of a long-slit spectroscopic study of 38 active and four normal galaxies. Stellar absorption features, continuum colours and their radial variations are analysed in an effort to characterize the stellar population in these galaxies and detect the presence of a featureless continuum underlying the starlight spectral component. Spatial variations of the equivalent widths of conspicuous absorption lines and continuum colours are detected in most galaxies. Star-forming rings, in particular, leave clear fingerprints in the equivalent widths and colour profiles. We find that the stellar populations in the inner regions of active galaxies present a variety of characteristics, and cannot be represented by a single starlight template. Dilution of the stellar lines by an underlying featureless continuum is detected in most broad-lined objects, but little or no dilution is found for most of the 20 type 2 Seyferts in the sample. Colour gradients are also ubiquitous. In particular, all but one of the observed Seyfert 2s are redder at the nucleus than in its immediate vicinity. Possible consequences of these findings are briefly outlined. 相似文献
4.
X. Kong 《Astrophysics and Space Science》2003,284(2):905-908
We have observed the largest optical spectra sample of 97 blue compact galaxies. Stellar population properties of 74 star-forming BCGs of them were derived by comparing the equivalent widths of strong absorption features and continuum colors, using a method of empirical population synthesis based on star cluster sample. The results indicate that blue compact galaxies are typically age-composite stellar system, the continuum flux fractions at 5870Å due to old stellar components and young stellar components are both important for most of the galaxies. The stellar populations of blue compact galaxies present a variety of characteristics, and the contribution from different age and metallicity components is different. The star formation episodes are usually short, some galaxies maybe undergoing their first global episode of star formation, while for the most sample galaxies, older stars contribute to at most half the optical emission. Our results suggest that BCGs are old galaxies, in which star formation occurs in short intense burst separated by long quiescent phases. 相似文献
5.
A number of strong infrared forbidden lines have been observed in several evolved Wolf–Rayet (WR) star winds, and these are important for deriving metal abundances and testing stellar evolution models. In addition, because these optically thin lines form at large radius in the wind, their resolved profiles carry an imprint of the asymptotic structure of the wind flow. This work presents model forbidden line profile shapes formed in axisymmetric winds. It is well known that an optically thin emission line formed in a spherical wind expanding at constant velocity yields a flat-topped emission profile shape. Simulated forbidden lines are produced for a model stellar wind with an axisymmetric density distribution that treats the latitudinal ionization self-consistently and examines the influence of the ion stage on the profile shape. The resulting line profiles are symmetric about line centre. Within a given atomic species, profile shapes can vary between centrally peaked, doubly peaked, and approximately flat-topped in appearance depending on the ion stage (relative to the dominant ion) and viewing inclination. Although application to WR star winds is emphasized, the concepts are also relevant to other classes of hot stars such as luminous blue variables and Be/B[e] stars. 相似文献
6.
María Luisa García Vargas Angeles I. Díaz Elena Terlevich Roberto Terlevich 《Astrophysics and Space Science》1993,205(1):85-89
In the frame of the Starburst Model for AGN, we show that the evolution of a massive stellar cluster in a high metallicity environment can reproduce the observed equivalent widths of Ca II triplet lines in absorption in Starburst and active galactic nuclei. In the case of Starburst galaxies, this strength, together with the emission-line ratio [O II]/[O III], can be used to determine the age of the cluster. The strength of the Ca II lines is mainly governed by the age of the stellar cluster through the presence of red supergiant stars. 相似文献
7.
Mitsugu Makita 《Solar physics》1968,3(4):557-562
The equivalent widths of the TiO lines in the α system have been measured on a high dispersion (11 mm/Å) spectrogram of large sunspot. The lines were so weak that the measurement was made by methods giving maximum and minimum equivalent widths, depending on the adopted continuum. The rotational temperature obtained in this way was about 3000 °K. The result is unaffected by stray light because there are no TiO lines in the undisturbed spectrum. The calculation of equivalent widths using several sunspot models (all of which can satisfy the observed data) shows that the logarithmic optical depth at the effective layer of molecular line formation is about -1.6. 相似文献
8.
Reinhard W. Hanuschik 《Astrophysics and Space Science》1989,161(1):61-73
I re-investigate empirical correlations between line widths of photospheric absorption lines — as a measure of the stellar projected rotational velocityv sini- and of circumstellar emission lines in Be stars. The degree of this correlation is a measure for the kinematic, i.e., rotational, contribution to the total emission line broadening.From the literature and from additional data, I have collected a sample of photoelectric measurements of Balmer and Feii emission lines of the 115 brightest Be stars in the sky, most of them observed several times during the past decade. I investigate the following emission line widths parameters: full width at half maximum, total width at the base, and double-peak separation. I find from the FWHM that the basic origin of emission line broadening in Be stars is undoubtedly rotational, the correlations withv sini being best for weaker emission lines while H shows considerable scatter. Total width at the base is uncorrelated withv sini except for the Feii lines. Peak separation is found to be a function both ofv sini and of equivalent width. The latter dependence can straightforwardly be understood by the fact that within Huang's disk model peak separation, normalized tov sini, is governed by the outer envelope radius.I conclude that observational evidence leaves no doubt that Be star envelopes as visible in optical emission lines are rotationally supported and have axisymmetric geometry.Partly based on observations obtained at the European Southern Observatory, La Silla, Chile. 相似文献
9.
The influence of a bubble-like structure around a starburst within the H II regions on the shape of the ionizing spectrum and the generation of the observed emission lines was studied using multicomponent photoionization modeling. The distributions of density and other physical parameters in such bubble-like structures were determined by Weaver et al. in 1977. The first two components represent the region of the stellar wind from the central starburst region. The gas density and electron temperature distributions in these components were described by the solution of the system of equations of continuity and energy transfer with account for the heat conductivity. The third component represents a thin layer of gas with a high density that emerges due to the passage of a normal shock wave of the stellar wind. The fourth component represents a “typical” H II region. The ionizing radiation spectra were set from the calculated evolutionary models whose free parameters determine the physical conditions within the “bubble.” The influence of the stellar wind bubble on the shape of the ionizing radiation spectrum and the generation of fluxes in important emission lines was analyzed. 相似文献
10.
11.
Results from a spectrophotometric study of 21 galaxies with UV excess are presented. The half widths (FWHM) and equivalent widths of observed spectrum lines of these galaxies, as well as the relative intensities of the emission lines observed in the spectrum of the galaxy Kaz243, are determined. It is conjectured that the latter galaxy has the properties of an Sy2 type galaxy. The electron densities and masses of the gaseous components are found for 15 galaxies, along with the masses of 8 galaxies for which the ratio M/L has been calculated. It is shown that the spectral structures of these galaxies do not depend on whether they are members of physical systems or are isolated. 相似文献
12.
Varshni maintained that the emission lines observed in QSOs can be satisfactorily explained as being due to laser action in certain atomic species in the expanding envelope of a star and having no appreciable redshift. In order to test this hypothesis we have examined the conditions conducive to laser action in the stellar atmosphere and compared all the emission lines of 633 QSOs discovered till August 1976 (as listed by Burbidgeet al.) with the laser transitions found in the laboratory till April 1976 (as listed by Willett and Becket al.). It was found that 88% of the QSO lines agreed to within 10 Å with the laser lines and 94% agreed to within 20 Å. The main reason Greenstein and Schmidt failed to fit the spectral lines of 3C 48 and 3C 273 with known emission lines is that laser transitions in hydrogen do not occur in stellar atmospheres. The spectra are explained on the basis of the new theory and the broadening of lines explained. 相似文献
13.
类星体SDSS J151653.22+190048.2 (简称J1516+1900)在紫外-光学-近红外波段展现出奇特的光谱性质:其光学Hα、Hβ和近红外的Paα、Paβ等发射线的半高全宽(full width at half maximum intensity, FWHM)均超过5000 km/s,等值宽度接近类星体平均值;而紫外波段光谱的常见发射线Lyβ、OVI、Lyα、NV、Si IV和CIV等,由FWHM1700 km/s的中等宽度成分主导.这种现象很可能是由于紫外发射线的宽线成分经尘埃消光,强度严重削弱,从而使得中等宽度成分凸显出来;在光学和近红外波段,尘埃消光减弱,发射线由宽线成分主导,潜在的中等宽度成分不容易被看到.根据中等宽度成分的线宽和J1516+1900中央超大质量黑洞的质量MBH5.75×108M⊙,在维里化假设下,估计中等宽度发射区到中央黑洞的距离约为1.6 pc.另一方面,利用J1516+1900丰富的观测谱线,结合光致电离模型计算,可以限定J1516+1900的中等宽度发射线区气体密度1012cm-3、电离参数10-0.65.据此估计该发射线区到中心黑洞距离0.016 pc,只有维里化距离的1%.这一矛盾结果预示着中等宽度发射区可能具有较为复杂的物理结构,未来需要观测更多类似J1516+1900的部分遮蔽类星体并进行系统的分类和研究. 相似文献
14.
Simple theoretical arguments indicate that cooled interstellar gas in bright elliptical galaxies forms into a young stellar population having a bottom-heavy but optically luminous initial mass function extending to approximately 2 M middle dot in circle. When the colors and spectral features of this young population are combined with those of the underlying old stellar population, the apparent ages are significantly reduced, similar to the relatively young apparent ages observed in many elliptical galaxies. Galactic mergers are not required to resupply young stars. The sensitivity of continuous star formation to LB and LX&solm0;LB is likely to account for the observed spread in apparent ages among elliptical galaxies. Local star formation is accompanied by enhanced stellar Hbeta equivalent widths, stronger optical emission lines, more thermal X-ray emission, and lower apparent temperatures in the hot gas. The young stars should cause M&solm0;L to vary with galactic radius, perturbing the fundamental plane of the old stars alone. 相似文献
15.
V. S. Tamazian N. D. Melikian A. A. Karapetian R. Sh. Natsvlishvili 《Astrophysics》2005,48(3):279-290
Results are presented from a study of 27 spectra of the flare star HU Del obtained during 2000–2002 on the 2.6 meter telescope at the Byurakan Observatory. Two flares were detected, along with a weak correlation between the equivalent widths of the Hα and Hβ emission lines. At the time of the photometric maximum of a flare the equivalent widths of both these lines are minimal and reach their maximum only significantly afterward. A strong increase in the Hβ line intensity is observed which appears to be the consequence of a photometrically undetected, short-duration flare. A possible relationship between the binary (multiple) character and the physical activity of this star is examined briefly in terms of current theoretical models.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 335–348 (August 2005). 相似文献
16.
Results from a spectrophotometric study of the galaxy Kaz 701 are presented. Spectra of this galaxy were obtained on the 2.6-m
telescope at the Byurakan Observatory with the SCORPIO spectral camera. In the spectra of Kaz 701, strong Hα, [OIII] λλ5007,
4959, and Hβ emission were observed, and the [SII]λλ6731, 6717 lines were observed with moderate intensities, while the [NII]λ6584
line was scarcely noticeable in the spectra obtained in 2004, but was much more intense in the spectra of 2009. The lines
observed in the spectrum of this galaxy are typical of type Sy2 galaxies. A component was observed in the red wings of both
the Hα and Hβ lines in the data of 2004, but, although these lines were stronger, these components were absent in the spectra
taken in 2009. The relative intensities, equivalent widths, and half widths of these lines are given. These data, obtained
in different observation periods (2004 and 2009), differ greatly; that is, the emission is variable. 相似文献
17.
H. Lehmann 《Astronomische Nachrichten》1982,303(4):263-268
A computer controlled measuring procedure is presented ascertaining intensity courses. The procedure is capable for measurement and storage of the transmittance of photographic spectrograms and for the determination of residual intensities derived from a mean local continum. Residual intensity courses obtained from several spectrograms can be superimposed and correlated with wavelength scale. The method was applied to eight weakly or not reddened early type stars in order to obtain data on atomic lines in the central part of the diffuse interstellar line at 4430 Å. The results show the general influence of the stellar portion on the central depth and equivalent width of the whole diffuse feature. 相似文献
18.
We observed the spectrum of 44i Boo in 1981 March and in 1983 March. We found that the equivalent widths of the CaII K and CaI 4227 A lines showed periodic variations with different phases, and that the profile of the Hα line also varied in step. A preliminary analysis is made based on our observations and the recent IUE data and a simple model atmosphere with stellar activity of 44i Boo (B) is proposed. 相似文献
19.
V. L. Khokhlova D. V. Vasilchenko V. V. Stepanov I. I. Romanyuk 《Astronomy Letters》2000,26(3):177-191
We present the results of our analysis of magnetic-field configuration and abundance anomalies on the surface of the rapidly rotating, chemically peculiar helium-strong variable B2 V star HD 37776 with unresolved Zeeman components of spectral lines. Simultaneous inversion of the observed Stokes I and V profiles, which realizes the method of Doppler-Zeeman mapping [1], has been applied for the first time. Spectroscopic observations were carried out with the Main stellar spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a Zeeman analyzer and a CCD array, which allowed spectra in right-and left-hand circularly polarized light to be taken simultaneously at a signal-to-noise ratio S/N≥200 [2]. The profile width of winged spectral lines (reaching 5 Å) is determined by Zeeman line splitting; however, the observed Zeeman components are blurred and unresolved because of the rapid stellar rotation. When solving the inverse problem, we sought for the magnetic-field configuration in the form of a combination of arbitrarily oriented dipole, quadrupole, and octupole placed at the stellar center. The observed Stokes I and V profiles for eight spectral lines of He, O II, Al III, Si III, and Fe III averaged over the visible stellar surface were used as input data. We constructed a model of the magnetic field from the condition of coincidence of magnetic maps obtained from different lines of different chemical elements and from the condition of a minimum profile residual. This model is a combination of centered coaxial dipole and quadrupole with the dominant quadrupole component at 30°<i<50°, β=40°, and a maximum surface field strength H s=60 kG. A comparison of our abundance maps with the field configuration shows that the He concentration is at a maximum in the regions of maximum radial field, while the maximum concentrations of O, Al, Si, and Fe coincide with the regions of maximum tangential field. 相似文献
20.
A helium model atom that includes 55 He I levels and the He II ground level in a detailed consideration has been constructed to investigate the departures from local thermodynamic equilibrium (LTE) in the formation of helium lines in stars with effective temperatures from 9300 to 20 000 K. For eight stars with effective temperatures from 9380 to 17 500 K the helium abundance has been determined from He I lines. The neutral helium lines in B stars cannot be described under LTE conditions using the common helium abundance. Furthermore, the profiles of several lines cannot be described in terms of the LTE approach at all. In contrast, a satisfactory coincidence of the theoretical and observed profiles for the entire set of helium lines observed in a wide spectral range can be achieved using virtually the same helium abundance by taking into account the departures from LTE. The LTE and non-LTE helium abundances can differ by up to a factor of 2–3, depending on the stellar parameters. The higher the stellar temperature, the stronger the departures from LTE. As a rule, the lines in the blue spectral region are less affected by non- LTE effects. In the atmospheres of six stars the helium abundance corresponds, within the error limits, to the present-day solar value. A helium underabundance is observed in the atmospheres of Sirius and HD 72660 classified as hot Am stars. 相似文献