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1.
Photospheric models were calculated for 90 stars with effective temperatures between 2500 K and 41600 K for five logg-values ranging from 1 to 5. Molecule formation was taken into account. In order to have an idea about possible instabilities in the different stellar layers some quantities, characteristic for convection and turbulence were calculated, such as the Rayleigh-, Reynolds-, Prandtl- and Péclet-numbers. It turned out that all the investigated stars contain unstable layers, including the hottest. Nevertheless, only stars with effective temperatures of 8300 K or less contain layers where the convective energy transport is important. For all stars the convective velocities were calculated and also the generated mechanical fluxes in the convection zones were tabulated.Under the hypothesis that this mechanical energy flux is responsible for the heating of the corona, coronal models were constructed for the Sun and for some stars with effective temperatures between 5000 K and 8320 K for logg-values of 4 or 5.For Main Sequence stars the largest fluxes are generated in F-stars; stars withT eff=7130 K and logg=4 possess also the hottest and most dense coronas with a computed temperature of 3.7·106 K and logN e =10.5.The solar corona computed in this way, on the basis of a photospheric mechanical flux of 0.14·108 erg cm–2 sec–1, has a temperature of 1.3·106 K and logN e =9.8. This density is apparently too high, but even when including in the computations all theoretical refinements proposed in the last few years by various authors it does not appear possible to obtain a solar coronal model with a smaller density.However, when taking into account the inhomogeneous structure of the chromosphere and by associating the calculated mechanical fluxes to the coarse mottles, and lower fluxes to the undisturbed regions we find a mean coronal temperature of 1.1·106 K and a mean logN e -values of 9. The computed velocity of the solar wind at a distance of 104 km above the photosphere has a value between 7 and 11 km sec–1. These latter values are in fair agreement with the observations.  相似文献   

2.
EC?11481–2303 is a peculiar, hot, high-gravity pre-white dwarf. Previous optical spectroscopy revealed that it is a sdOB star with T eff=41?790 K, log?g=5.84, and He/H = 0.014 by number. We present an on-going spectral analysis by means of non-LTE model-atmosphere techniques based on high-resolution, high-S/N optical (VLT-UVES) and ultraviolet (FUSE, IUE) observations.We are able to reproduce the optical and UV observations simultaneously with a chemically homogeneous NLTE model atmosphere with a significantly higher effective temperature and lower He abundance (T eff=55?000 K, log?g=5.8, and He/H=0.0025 by number). While C, N, and O appear less than 0.15 times solar, the iron-group abundance is strongly enhanced by at least a factor of ten.  相似文献   

3.
Instability of population I (X = 0.7, Z = 0.02) massive stars against radial oscillations during the post-main-sequence gravitational contraction of the helium core is investigated. Initial stellar masses are in the range 65M ⊙ ≤ M ZAMS ≤ 90M ⊙. In hydrodynamic computations of self-exciting stellar oscillations we assumed that energy transfer in the envelope of the pulsating star is due to radiative heat conduction and convection. The convective heat transfer was treated in the framework of the theory of time-dependent turbulent convection. During evolutionary expansion of outer layers after hydrogen exhaustion in the stellar core the star is shown to be unstable against radial oscillations while its effective temperature is T eff > 6700 K for M ZAMS = 65M ⊙ and T eff > 7200 K for M ZAMS = 90M ⊙. Pulsational instability is due to the κ-mechanism in helium ionization zones and at lower effective temperature oscillations decay because of significantly increasing convection. The upper limit of the period of radial pulsations on this stage of evolution does not exceed ≈200 day. Radial oscillations of the hypergiant resume during evolutionary contraction of outer layers when the effective temperature is T eff > 7300 K for M ZAMS = 65M ⊙ and T eff > 7600 K for M ZAMS = 90M ⊙. Initially radial oscillations are due to instability of the first overtone and transition to fundamental mode pulsations takes place at higher effective temperatures (T eff > 7700 K for M ZAMS = 65M ⊙ and T eff > 8200 K for M ZAMS = 90M ⊙). The upper limit of the period of radial oscillations of evolving blueward yellow hypergiants does not exceed ≈130 day. Thus, yellow hypergiants are stable against radial stellar pulsations during the major part of their evolutionary stage.  相似文献   

4.
This paper is devoted to spectroscopic studies of three bright Cepheids (BG Cru, R Cru, and T Cru) and continues the series of our works aimed at determining the atmospheric parameters and chemical composition of southern-hemisphere Cepheids. We have studied 12 high-resolution spectra taken with the 1.9-m telescope of the South African Astronomical Observatory and the 8-m VLT telescope of the European Southern Observatory in Chile. The atmospheric parameters and chemical composition have been determined for these stars. The averaged atmospheric parameters are: T eff = 6253 ± 30 K, log g = 2.15, V t = 4.30 km s?1 for BG Cru; T eff = 5812 ± 22 K, log g = 1.65, V t = 3.80 km s?1 for R Cru; and T eff = 5588 ± 21 K, log g = 1.70, V t = 4.30 km s?1 for T Cru. All these Cepheids exhibit a nearly solar metallicity ([Fe/H] = +0.04 dex for BG Cru, +0.06 dex for R Cru, and +0.08 dex for T Cru); the carbon, oxygen, sodium, magnesium, and aluminum abundances suggest that the objects have already passed the first dredge-up. The abundances of other elements are nearly solar. An anomalous behavior of the absorption lines of metals (neutral atoms and ions) in the atmosphere of the small-amplitude Cepheid BG Cru is pointed out. The main components in these lines split up into additional blue and red analogs that are smaller in depth and equivalent width and vary with pulsation phase. Such splitting of the absorption lines of metals (with the hydrogen lines being invariable) is known for the classical Cepheid X Sgr. The calculated nonlinear pulsation model of BG Cru with the parameters L = 2000 L ⊙, T eff = 6180 K, and M = 4.3M ⊙ shows that this small-amplitude Cepheid pulsates in the first overtone and is close to the blue boundary of the Cepheid instability strip. According to the model, the extent of the Cepheid’s atmosphere is relatively small. Therefore, no spectroscopic manifestations of shock waves through variability are possible in this Cepheid and the observed blue and red components in metal absorption lines can be explained solely by the presence of an extended circumstellar envelope around BG Cru.  相似文献   

5.
We report the discovery of a binary, HS 2233 + 3927, consisting of an sdB star with a faint companion. From its lightcurve the orbital period of 14,844 s, the mass ratio, the inclination, and other system parameters are derived. The companion does not contribute to the optical light of the system except through a strong reflection effect. The semi-amplitude of the radial velocity curve K 1= 89.6 km/s?1 and a mass function of f(m) = 0.013 M ⊙ are determined. A preliminary spectroscopic analysis of the blue spectra using NLTE model atmospheres results in Teff= 36 500 K, log g= 5.70, and log(n He/n H) =?2.15. These parameters are typical for sdB stars, the companion is probably an M dwarf.  相似文献   

6.
The existence of condensed carbon in the form of liquid droplets and graphite grains is found in white dwarf atmospheres with parametersg=108 cm s–2, H/He10–3, andT eff6000 K on the basis of model atmospheres techniques. It is shown that the condensation layers are dynamically stable and, consequently, that white dwarfs cannot supply the condensed particles to the interstellar medium. Possible observable effects are considered.  相似文献   

7.
We have investigated the effect of ionizing radiation from the UV stars (hot prewhite dwarfs) on the intergalactic medium (IGM). If the UV stars are powered only by gravitational contraction they radiate most of their energy at a typical surface temperature of 1.5×105 K which produces a very highly ionized IGM in which the elements carbon, nitrogen and oxygen are left with only one or two electrons. This results in these elements being very inefficient coolants. The gas is cooled principally by free-free emission and the collisional ionization of hydrogen and helium. For a typical UV star temperature ofT=1.5×105 K, the temperature of the ionized gas in the IGM isT g =1.2×105 K for a Hubble constantH o=75 km s–1 Mpc–1 and a hydrogen densityn H =10–6 cm–3. Heating by cosmic rays and X-rays is insignificant in the IGM except perhaps inHi clouds because when a hydrogen atom recombines in the IGM it is far more likely to be re-ionized by a UV-star photon than by of the other two types of particles due to the greater space density of UV-star photons and their appreciably larger ionization cross-sections. If the UV stars radiate a substantial fraction of their energy in a helium-burning stage in which they have surface temperatures of about 5×104 K, the temperature of the IGM could be lowered to about 5×104 K.  相似文献   

8.
We outline a method to explore the column density of the Local Interstellar Medium (LISM) using absorptions in the resonance H and K lines of Mgii. The intrinsic strengths of these lines in the temperature and density conditions prevailing in warm clouds (T eff<104 K) in the LISM allows them to be used to explore many lines of sight where lines such a NaD and Caii H and K are too weak, but where L is saturated. The number of measurable lines-of-sight is greatly enhanced by using cool stars as the background emitters, but this implies reliable separation of the LISM components from stellar chromospheric selfabsorptions. We explain how to do this, and how to use a combination of column density and radial velocity data to measure the spatial extent and the physical parameters of the single cloud in which the Sun is embedded. This proves to be an oblate spheroid, of characteristic diameter 8 pc, withT eff 104 K,n(Hi) of 0.1 cm–3 and a mass <5M , streaming in the LSR from a point 1=4°,B=+16° with velocity equal to 16 km s–1, and is surrounded by the much hotter lower density ionized gas of the local supernova bubble.  相似文献   

9.
Double-lined spectra have been obtained at 2 Å/mm for the Mn star 112 Herculis AB. The components are shown to be a B6.5V star and A2V star. Hydrogen-line-blanketed models are used to calculate atmospheric abundances. The best models appear to beT e=13500 K, logg=4.0, T =2.5 km/sec for the primary; andT e=10000K, logg=4.2, T =6 km/sec for the secondary. Both stars appear to have the same abundances. Helium, carbon, magnesium, aluminum, silicon, calcium, vanadium, and nickel appear to be considerably underabundant; phosphorus, scandium, titanium, manganese, iron, gallium, and mercury considerably overabundant; and chromium, strontium, and zirconium normal in abundance.  相似文献   

10.
Nine high- and low-resolution IEU spectra at different orbital phases during different cycles, of the hydrogen-poor single-lined spectroscopic binary KS per (HD 30353) have been studied. The near-UV spectrum is characterized by the presence of several lines of once ionized metals which show the same orbital RV shifts observed in the visual range. The MgII resonance lines present a sharp interstellar + circumstellar core and an emission peak at about 83 and 92 km s–1. The far UV spectrum is characterized by the presence of strong absorptions of the resonance lines ofNV,CIV, SiIV, SiIII.Direct determination of the IS extinction from the 2200 Å feature givesE(B-V)=0.33. A comparison of corrected logarithmic continuous energy distribution with the theoretical models by Kurucz, indicates that the companion is a hot star,T e=15000 K; logg=4. A comparison with the recent UV work ofv Sgr, shows that, KS Per is very similar tov Sgr.Based on observations by the International Ultraviolet Explorer (IUE) collected at the Villafrance Satellite Tracking Station and obtained from the IUE data bank.  相似文献   

11.
The spectral energy distributions between λ 3700 Å and λ 8100 Å of the binary systems COU1289 and COU1291 have been measured with the Carl‐Zeiss‐Jena 1 m telescope of the Special Astrophysical Observatory. Their B, V, R magnitudes and B – V colour indices were computed and compared with earlier investigations. Model atmospheres of both systems were constructed using a grid of Kurucz blanketed models, their spectral energy distributions in the continuous spectrum were computed and compared with the observational ones. The model atmosphere parameters for the components of COU1289 were derived as: T aeff = 7100 K, T beff = 6300 K, log g a = 4.22, log g b = 4.22, R a = 1.50 R⊙, R b = 1.40 R⊙, and for the components of COU1291 as: T aeff = 6400 K, T beff = 6100 K, log g a = 4.20, log g b = 4.35, R a = 1.47 R⊙, R b = 1.12 R⊙. The spectral types of both components of the system COU1289 were concluded as F1 and F7, and of the system COU1291 as F6 and F9. Finally the formation and evolution of the systems were discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

12.
Extreme ultraviolet spectra of several active regions are presented and analyzed. Spectral intensities of 3 active regions observed with the NRL Skylab XUV spectroheliograph (170–630 Å) are derived. From this data density sensitive line ratios of Mg viii, Si x, S xii, Fe ix, Fe x, Fe xi, Fe xii, Fe xiii, Fe xiv, and Fe xv are examined and typically yield, to within a factor of 2, electron pressures of 1 dyne cm–2 (n e T = 6 × 1015 cm–3 K). The differential emission measure of the brightest 35 × 35 portion of an active region is obtained between 1.4 × 104 K and 5 × 106 K from HCO OSO-VI XUV (280–1370 Å) spectra published by Dupree et al. (1973). Stigmatic EUV spectra (1170–1710 Å) obtained by the NRL High Resolution Telescope and Spectrograph (HRTS) are also presented. Doppler velocities as a function of position along the slit are derived in an active region plage and sunspot. The velocities are based on an absolute wavelength scale derived from neutral chromospheric lines and are accurate to ±2 km s–1. Downflows at 105 K are found throughout the plage with typical velocities of 10 km s–1. In the sunspot, downflows are typically 5 to 20 km s–1 over the umbra and zero over the penumbra. In addition localized 90 and 150 km s–1 downflows are found in the umbra in the same 1 × 1 resolution elements which contain the lower velocity downflows. Spectral intensities and velocities in a typical plage 1 resolution element are derived. The velocities are greatest ( 10 km s–1) at 105 K with lower velocities at higher and lower temperatures. The differential emission measure between 1.3 × 104 K and 2 × 106 K is derived and is found to be comparable to that derived from the OSO-VI data. An electron pressure of 1.4 dynes cm–2 (n e T = 1.0 × 1016 cm–3 K) is determined from pressure sensitive line ratios of Si iii, O iv, and N iv. From the data presented it is shown that convection plays a major role in determining the structure and dynamics of the active region transition zone and corona.  相似文献   

13.
Two CCD spectra of the star V1016 Ori were obtained with the echelle spectrograph of the 6-m (BTA) telescope. An analysis of these spectra allowed us to estimate the star's atmospheric parameters (T eff=29700 K, logg=4.4) and projected rotational velocity (Vsini=60 km s?1) and to determine its chemical composition. Chemical anomalies were found. The Fe abundance is nearly solar; He, C, O, Mg, Al, Si are underabundant; and Ne, S, Zn are overabundant. The “spectroscopic” radius of the primary is in satisfactory agreement with its radius determined from the light and radial-velocity curves if the small star is assumed to lie in front of the giant star during an eclipse. The paradox of the primary's anomalous radius is thus resolved. A table of line equivalent widths and a portion of the star's spectrum are given in Appendices 1 and 2.  相似文献   

14.
Two CCD spectra of the star BM Ori were obtained with the echelle spectrograph of the 6-m telescope. In one of the spectra, a large proportion of lines are distorted by emission. The emission component is blueshifted by 50 km s?1, suggesting hot-gas outflow from the atmosphere. The equivalent-width ratio of measured lines in the spectra outside and during eclipse is consistent with the assumption that ～2/3 of the primary star’s area is obscured during eclipse, as follows from light curves. Measured line equivalent widths were used to estimate atmospheric parameters of the secondary star, T eff=7300 K, log g=5.2, and microturbulence ξt=6 km s?1, and to determine its chemical composition. The C, Na, Al, Si, S, Ca, Fe, Ni, and Zn abundances are solar, within the error limits. Li, Sc, Ti, V, Cr, Mn, Co, and Y are overabundant, while Mg, Cu, and Ba are underabundant. In general, the secondary is similar in chemical composition to the star V 1016 Ori. Based on the secondary’s mass determined by solving the radial-velocity curve and on log g estimated spectroscopically from iron ionization equilibrium, we calculated its photospheric radius, R 2 = 0.5R ⊙. However, the spectroscopic log g=5.2 disagrees with log g=3.5 calculated from the luminosity and effective temperature and with log g=3.0 calculated from light and radial-velocity curves. If the secondary’s photospheric radius is indeed small; this argues for the hypothesis that the eclipsing body is a dust envelope. The radial velocities measured from the two spectra are systematically higher than those calculated from the radial-velocity curve by +34 and +24 km s?1. It is likely that the secondary’s atmosphere occasionally shrinks.  相似文献   

15.
We analyze IUE spectra of the star 1016 Ori. Together with previously obtained visible spectra, they have allowed the wavelength range from 1150 to 7000 Å to be studied. Atmospheric parameters of the star were refined: logg=4.5(1), T eff=30000(1000) K, and ξt=15(5) km s?1. We measured the equivalent widths of ～500 lines and used them to compute the chemical composition. It turned out that the He, B, Mg, P, and S abundances were nearly solar; Ne, Ti, and Cr were overabundant; and C, N, O, Al, Si, Mn, Fe, Ni, and Zn were underabundant.  相似文献   

16.
We present LTE analysis of high resolution optical spectra for B-type hot PAGB stars LS IV-04 1 and LB3116 (LSE 237). The spectra of these high Galactic latitude stars were obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph. The standard 1D LTE analysis with line-blanketed LTE model atmospheres and spectral synthesis provided fundamental atmospheric parameters of Teff= 15 000±1000 K, log g= 2.5±0.2, ξ = 5.0±1.0 km s?1, [M/H] = ?1.81 dex, and v sin i= 5 km s?1 for LSIV-04 1 and Teff= 16 000±1000 K, log g= 2.5±0.1, v sin i= 25 km s?1, and [Fe/H] = ?0.93 dex for LB 3116. Chemical abundances of ten different elements were obtained. For LS IV-04 1, its derived model temperature contradicts with previous analysis results. The upper limits for its nitrogen and oxygen abundances were reported for the first time. The magnesium, silicon and calcium were overabundant (i.e. [Mg/Fe] = 0.8 dex, [Si/Fe] = 0.5 dex, [Ca/Fe] = 0.9 dex). With its metal-poor photosphere and VLSR ≈ 96 km s?1, LSIV-04 1 is likely a population II star and most probably a PAGB star. LTE abundances of LB 3116 were reported for the first time. The spectrum of this helium rich star shows 0.9 dex enhancement in the nitrogen. The photosphere of the star is slightly deficient in Mg, Si, and S. (i.e. [Mg/Fe] = ?0.2 dex, [Si/Fe] = ?0.4 dex, [S/Fe] = ?0.2 dex). The Al is slightly enhanced. The phosphorus is overabundant, i.e. [P/Fe] ≈ 1.7 ± 0.47 dex, hence LB3116 may be the first example of a PAGB star which is rich in phosphorus. With its high radial velocity (i.e.VLSR = 73 km s?1), and the deficiencies observed in C, Mg, Si, and S indicate that LB 3116 is likely a hot PAGB star at high galactic latitude.  相似文献   

17.
The eclipsing binary α CrB, is a well-known double-lined spectroscopic binary. The system is considered unique among main-sequence systems with respect to its small mass ratio and large magnitude difference between the components. Our aim in the present paper is to compute the orbital parameters and to model the atmospheric parameters of the system. Synthetic spectral analysis of both the individual and disentangled spectra has been performed and yielded effective temperatures T eff?=?10000±250 K, surface gravities logg?=?4±0.25 and projected rotational velocities $\emph{v}$ sini?=?110±5 km/sec for the primary component, and T eff?=?6000±250 K and logg?=?4.5±0.25 for the secondary component. Evolutionary state of the system is investigated using stellar models.  相似文献   

18.
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   

19.
The physical properties in the coronal disturbance (CD) (W90, N25°) associated with an active prominence are investigated on the basis of the intensities and profiles of 5694 Å Caxv and 6702 Å Nixv lines and continuum measured in the eclipse coronal spectra of 31 July, 1981. The spectrograms have been taken with a dispersion of between 7 to 10 Å mm-1 and a solar image of 15 mm in diameter. The following characteristics of the CD have been deduced. The CD occurred cospatially with an active prominence and consisted of two discrete regions with different temperatures penetrating each other. (1) Caxv region: T e= 3.8 × 106 K, the length along the slit of the spectrograph Z 65000 km, the effective line-of-sight length L 20000 km, the average electron density , nonthermal velocities V t= (20–32) km s-1. (2)Nixv-Caxiii region: T e= 2.3 × 106 K, Z 37000 km, L 35000 km, n e 1 × 109 cm-3, V t= (23–30) km s-1. A macroscopic mass motion has been discovered within the Nixv region of the CD from the Doppler shifts of the 6702 Å Nixv line: V r= + 27 km s-1 on the lower and V r= - 12 km s-1 on the upper border of the CD. The average height of the CD was H 0.08 R . The radial velocities in the prominence found from the emission line tilts are + 12 and - 8 km s-1 on its lower and upper borders. A similar picture of the mass motion in the CD and the prominence speaks in favour of an intimate relation between them.  相似文献   

20.
A comparison between model atmosphere grids with and without metal blanketing has been performed in the low-temperature range (T eff=6000 K to 10000 K) and for different metal contents (logA=0, –1, –2;A=scaled solar abundance). ForA10–1 andT eff7000 K, the Johnson colour indicesU-B andB-V, together with the Strömgrenu-b, b-y and the bolometric correction (BC) are little affected by metal blanketing ( mag<0 . m 04). On the other hand, the trend of the physical quantities and them 1 andc 1 colour indices reflect the inadequateness of the models even withA=10–2 andT eff=9500 K, where hydrogen line blanketing is expected to dominate. This fact discourages once and for all the use of metal unblanketed atmospheres other than for comparison of colour indices or the calculation of bolometric corrections for Population II A-F spectral types.  相似文献   

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