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1.
Phase changing variations between Be and shell stars are considered from the viewpoint of the formation of shell absorption lines in the envelopes of these stars. Typical shell stars are characterized by large optical depths of the envelopes in the H line (H) in a range of 2000 to 5000, whereas the envelopes of typical Be stars are optically thinner with the values of (H)100. This infers that the envelopes of Be stars should be fully expanded as compared to those of shell stars, so as to reduce the optical thickness. Spectral formation in shell stars shows that their envelopes are well condensed near the equatorial planes forming disks or rings. In this paper a simple model of transformation from a disk envelope of shell star to a spherical envelope of Be star is considered to show the relative volume and volume emission measures of the envelopes in both phases. The phase change variations observed in Pleione and in other Be and shell stars are discussed based on this simple consideration. Some implications of the present model in the linear polarization, IR-excess, UV spectra and the radiation field of the envelope are also discussed briefly.  相似文献   

2.
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   

3.
For the interpretation of observed hydrogen emission lines in the spectrum of Cas calculations of the relative intensities of spectral lines of the Balmer, Paschen, Brackett and Pfund series are carried out, by using the theory of moving stellar envelopes.It is shown that in the spectra of Be stars, which have opaque envelopes and therefore a slow Balmer decrement, infrared hydrogen lines must be relatively strong.It is also found that the observed relative line intensities of Cas are in qualitative agreement with those calculated for the case of a simple model-envelope which consists of low and high opacity regions.  相似文献   

4.
All hot stars are observed to have X-ray emission: O stars haveL X /L bol 10–7, whilst B stars' emission drops off with spectral subtype. Dynamical instability of OB star radiatively driven winds generates shocked regions which may be responsible for the bulk of the X-rays observed. The wind-compressed disc model of Bjorkman & Cassinelli (1993) presents another site for X-ray emission. The disc formed in the equatorial plane of a fast rotating Be star from equatorward drift of wind streamlines is confined on both sides by a shock which may also generate X-rays. As the X-ray emission originating from the wind shocking is ubiquitous amongst B and Be stars then the wind-compressed disc model näively predicts that Be stars should generate more X-rays than B stars of equivalent spectral subtype.The X-ray emission from the shocks confining compression discs has been calculated and compared to a limited set of observations. The excess X-ray emission from the Be star disc shocks is found to be undetectable over the inherent wind shocking emission.  相似文献   

5.
From a long-term spectroscopic observing campaign of Be stars we have found that their emission line profiles separate into two classes, the second of which is very asymmetric. The sign of asymmetry changes on a timescale of a few years. We show that these line profiles and the well-known enigmaticV/R variations observed in some Be stars are two aspects of the same phenomenon, one-armed global oscillations in a Keplerian disk. We present model profiles and a line fit to support this hypothesis and find good overall agreement.  相似文献   

6.
Be stars show both emission and absorption profiles in the optical part of the spectrum, and these are found to vary with the time. Some of the shifts in profiles were earlier interpreted as Doppler shifts. However, some of the shifts of features in both emission and absorption line profiles may be artifacts due to superposition of an emission profile arising from an Hii region around a binary compact object, and a profile due to the Be star. This interpretation of shifts in line profiles has the advantage over the conventional Doppler-shift interpretation in so far as it does not need the oscillation of a large mass of circumstellar gas, and leads to the observed correlation between radial velocity (RV) variations and V/R variations.  相似文献   

7.
High dispersion CCD spectra are used to study the profiles of the Hα and Hβ lines of 48 stars in early spectral classes in the young diffuse binary cluster h/χ Per. In addition, moderate resolution spectra of 15 B and Be stars were taken over the interval 4400–4960 Å. One or, possibly, two new Be stars are discovered. The major parameters of the Hα line are measured for the observed B and Be stars. The spectra over 4400–4960 Å are used to estimate Teff, logg, and υsin i. No traces of emission are detected in the Hα line profiles for 28 of the stars and emission is observed in the Hα line for 20. During our observations an absorption profile of the Hα line was observed for some of the stars, such as Oo146, Oo566, Oo922, and Oo1268, although they have previously been identified as Be stars. A significant long-term variability of the Hα line is discovered for the Be stars Oo1161 and Oo2242. Oo2371 manifests a variability in its faint emission spectrum which is typical of close binary systems that include a Be star. __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008).  相似文献   

8.
This paper presents the spectrophotometric observations of five Be stars belonging to spectral type from B2.5 to B5 and luminosity class from III to V. The continuum energy distribution data of these stars are extracted from the spectrophotometric measurements over the wavelength range of λλ 3200–8000 Å. The observed data of continuum energy distribution are compared with the theoretical energy distribution curves to derive the value of effective temperatures of these stars. We have also examined the effect of circumstellar envelopes of Be stars on their continuum energy distribution. It has been found that the extended circumstellar envelope of Be stars affect the underlying continua in the near-ultraviolet and near-infrared regions. Three Be stars are found to exhibit near-ultraviolet and near-infrared flux deficiency in their continua. For one of the Be, namely star HR 1289, we report the first continuum energy distribution measurements. Another normal B star HR 1363, which was observed as comparison star, was found to exhibit near-ultraviolet and excess emission, which are signatures of a Be star, thus putting this star in the category of Be stars.  相似文献   

9.
Rapid observations of H profiles of eight Be stars have been obtained and it is found that rapid (in a time-scale of 4 to 6 minutes) and irregular variations of total emission strength of H line are present in these stars. It has been suggested that these variations may be due to the material circulation in the envelope of Be stars.  相似文献   

10.
PSR B1259-63 is the only known binary system with a radio pulsar from which the non-pulsed radio and X-ray emission was detected. The companion star in this system is a Be star SS 2883. A rapidly rotating radio pulsar is expected to produce a wind of relativistic particles. Be stars are known to produce highly asymmetric mass loss. Due to the interaction of the pulsar wind and the Be star wind the system of two shocks between the pulsar and the Be star forms. In this paper we show that the observed non-pulsed radio emission from the system is a result of the synchrotron emission of the relativistic particles in the outflow beyond the shock wave and that the non-pulsed X-ray emission is due to the inverse Compton scattering of the Be star photons on this particles. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
The continuum energy distribution data of seven Be and five normal B stars have been presented in the wavelength range 3200–8000 Å. Empirical effective temperatures of these stars have been derived by comparing the observed continuum energy distributions with the computed energy distributions given by Kurucz (1979). The effective temperatures of all observed be stars except KX And found here are in fair agreement with those of normal B stars. The Be stars KY And, EW Lac, and LQ And show normal continuum energy distributions over the whole observed wavelength range. The Be stars ES Vul and 6 Cyg show moderate near-infrared excess emission longward of 6000 Å.o And shows Balmer jump slightly in absorption and 6 Cyg shows slightly in emission. The variable nature of the Be stars has been discussed.The Be star KX And shows a peculiar type of continuum energy distribution. The continuum energy distribution of KX And has been discussed in relation to its binary nature.No excess or deficiency in the mean flux of normal B stars was detected.  相似文献   

12.
We have calculated the total flux emitted in H α , P α and Br α by the circumstellar envelope of both an early Be star, γ Cas, and a late Be star, 1 Delphini, assuming the central star is the only source of energy input into the circumstellar envelope. These estimates are based on the Be-star models of Millar & Marlborough which have self-consistent temperature distributions determined by equating the local rates of energy gain and energy loss in the envelopes. We find that an additional source of ionizing photons, as argued by Apparao, is not necessary to account for the observed emission.  相似文献   

13.
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   

14.
We have found that the range in wavelength of the line-profile variations (lpv) in the Be star Eridani increases by some 20% during its emission phases. This growth is associated with a possible increase in the equatorial velocity of the star during emission.  相似文献   

15.
I present theoretical line profiles and intensity maps from an axi-symmetric radiative wind model from a rapidly rotating Be star. The introduction of a viscosity parameter in the latitude-dependent hydrodynamic code enables us to consider the effects of the viscous force in the azimuthal component of momentum equations (Araújo et al. 1994). Both velocity field and density law derived from the hydrodynamic equations have been used for solving the statistical equilibrium equations. By adopting the Sobolev approximation, we could easily obtain a good estimate of both electronic density and hydrogen level populations throughout the envelope. The numerical calculation was performed for parameters characterisic of the Be star Cassiopeiae.  相似文献   

16.
High-resolution Coude observations of non-axisymmetric line emission from the dwarf nova SS Cygni are presented. By subtracting the constant line component, the asymmetric line emission responsible for the observed phase shift between the absorption and emission line radial velocity curves can be isolated. The extra emission is a large fraction of the total line emission and extends to large velocities (1500 km sec–1). The phase stability of the emission demands a large-scale structure which is fixed in the frame of the binary. A magnetic origin of the excitation cannot be ruled out but is implausible. A simple explanation is that the accretion stream from the companion star is able to spill over the edge of the disk, introducing emission at non-circular velocities and most likely disturbing the upper layers of the accretion disk.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables, Recent Multi-Frequency Observations and Theoretical Development, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.  相似文献   

17.
The WN5 star HD 50896 is a well known variable star but the cause of the variations is uncertain. As part of an extensive observing campaign on HD 50896, 68 spectra were obtained with the AAT and UCL echelle spectrograph over three nights in January 1991. The variations seen in the emission line profiles of He II 4686, He II 4860, N V 4945 and N V 4603, 4620, sampling different regions of the wind, are described. Gross night-to-night changes are seen in the tops of all the emission lines, with the pattern of variability being different for each line, as a consequence of the different line formation regions. The edges of the emission line profiles are seen to shift but not in a systematic way, as expected for binary motion. In terms of hourly variations which monitor the propagation of instabilities in the wind, distinct blobs are seen moving outwards through the emission line profiles of the He II lines but are absent in NV 4945. This appears to indicate that, at least for the epoch of these observations, the instabilities develop farther out in the wind than the N V formation region and may well rule out photospheric-induced wind instabilities.  相似文献   

18.
Observations of the Be star HD 50138 have been extended to the photographic infrared region up to 9500 Å. The main features noted in this wavelength range are strong lines of Oi (8446 Å), Hi (from P 9 to P 20), the Caii infrared triplet and the 8629 line attributed to Ni. The 7772 multiplet of Oi is shown to undergo important changes during the period of observations (1959–1971). Higher Balmer lines do not exhibit any emission component, but their profiles are variable and indicate the presence of satellite absorption, as already mentioned by some authors.Les observations ont été obtenues aux télescopes de 120 et 193 cm de l'observatoire de Haute-Provence (CNRS).  相似文献   

19.
Aur binaries are particularly well suited for the study of the winds of late type supergiants. The analysis technique is based on theoretical modelling of flux profiles which are formed by resonance scattering in the expanding envelope. However, the hot B star ionizes the wind and can produce a considerable H II region around the B star. In order to investigate the influence of the Strömgren sphere on the line formation we have calculated theoretical P Cyg line profiles with an H II region. The line source function is solved with the Sobolev method followed by a correct formal integration (Hempe, 1982). The ionization of metals within the H II region is described by an ionization parameter which mimics the typical ionization fraction of the relevant ions. The resulting line profiles are dependent on the geometric shape of the H II region, the velocity distribution, and the opacity parameter. The reduced absorber density within the H II region produces weakened line profiles and the specific geometry of the H II region influences the emission and the absorption component in different ways. The careful analysis of model computations suggests that the region of the line formation is not only restricted to the vicinity of the B star, hence the outer integration boundary has to be taken to a sufficiently large radius in the calculation of line profiles.  相似文献   

20.
A model for a symbiotic system is presented which is not spherically symmetrical. The system consists of a cool, mass losing giant and a hot star. The stellar wind from the cool star is radiatively ionized by the hot companion, and the resulting nebular lines are emitted mainly close to the cool star. Due to the elliptical orbit, the line fluxes change with time because of the varying separation of the stars. The line profiles vary from symmetrical to asymmetrical, depending on the angle between the line of sight and the axis of symmetry. The calculated line profiles are compared with observed UV lines of the symbiotic star HBV 475.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables, Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.  相似文献   

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