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1.
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2.
The results of hydrodynamical calculations of radially pulsating helium stars with masses 0.5M⊙≤M≤0.9M⊙, bolometric luminosities 600L⊙≤5×103L⊙, and effective temperatures 1.5×104 K≤Teff≤3.5×104 K are presented. The pulsation instability of these stars is due to the effects of ionization of iron-group elements in layers with temperatures T～2×105 K. The calculations were carried out using opacities for the relative mass abundances of hydrogen and heavy elements X=0 and Z=0.01, 0.015, and 0.02. Approximate formulas for the pulsation constant Q over the entire range of pulsation instability of the hot helium stars in terms of the mass M, radius R, effective temperature Teff, and heavy-element abundance Z are derived. The instability of BX Cir to radial pulsations with the observed period Π=0.1066 d occurs only for a mass M≥0.55M⊙, effective temperature Teff≥23000 K, and heavy-element abundance Z≥0.015. The allowed mass of BX Cir is in the range 0.55M⊙≤M≤0.8M⊙, which corresponds to luminosities 800L⊙≤M≤1400L⊙ and mean radii 1.7R⊙?R?2.1R⊙.  相似文献   

3.
An analysis of high-resolution CCD spectra of the giant 25 Mon, which shows signs of metallicity, and the normal giant HR 7389 is presented. The derived effective temperatures, gravitational accelerations, and microturbulence velocities are Teff = 6700 K, log g = 3.24, and ξ t = 3.1 km/s for 25 Mon and Teff = 6630 K, log g = 3.71, and ξ t = 2.6 km/s for HR 7389. The abundances (log ε) of nine elements are determined: carbon, nitrogen, oxygen, sodium, silicon, calcium, iron, nickel, and barium. The derived excess carbon abundances are 0.23 dex for 25 Mon and 0.16 dex for HR 7389. 25 Mon displays a modest (0.08 dex) oxygen excess, with the oxygen excess for HR 7389 being somewhat higher (0.15 dex). The nitrogen abundance is probably no lower than the solar value for both stars. The abundances of iron, sodium, calcium (for HR 7389), barium, and nickel exceed the solar values by 0.22–0.40 dex for both stars. The highest excess (0.62 dex) is exhibited by the calcium abundance for 25 Mon. Silicon displays a nearly solar abundance in both stars—small deficits of ?0.03 dex and ?0.07 dex for 25 Mon and HR 7389, respectively. No fundamental differences in the elemental abundances were found in the atmospheres of 25 Mon and HR 7389. Based on their Teff and log g values, as well as theoretical calculations, A. Claret estimated the masses, radii, luminosities, and ages of 25 Mon (M/M⊙ = 2.45, log(R/R⊙) = 0.79, log(L/L⊙) = 1.85, t = 5.3 × 108 yr) and HR 7389 (M/M⊙ = 2.36, log(R/R⊙) = 0.50, log(L/L⊙) = 1.24, t = 4.6 × 108 yr), and also of the stars 20 Peg (M/M⊙ = 2.36, log(R/R⊙) = 0.73, log(L/L⊙) = 1.79, t = 4.9 × 108 yr) and 30 LMi (M/M⊙ = 2.47, log(R/R⊙) = 0.73, log(L/L⊙) = 1.88, t = 4.8 × 108 yr) studied by the author earlier.  相似文献   

4.
We have used spectrograms taken with a dispersion of 8–12 Å per mm and Kurucz model atmospheres to study the supergiant 89 Her (F2Ibe).We find the effective temperature and gravity T eff = 6300 ± 150 K and log g = 0.5 ± 0.2. We have analyzed the microturbulence in the star’s atmosphere based on FeI, FeII, and TiII lines, deriving ξ t = 7.0 ± 0.5 km/s for the FeI and TiII lines and ξ t = 8.0 ± 0.5 km/s for the FeII lines. Abundances were determined for 23 elements. The elemental abundances in the atmosphere of 89 Her show deficiencies compared to the solar chemical composition, except for sodium, which is overabundant relative to the Sun.  相似文献   

5.
Results of a study of the shell of Nova V2659 Cyg based on spectrophotometric observations carried out over a year and a half after its eruption are presented. The physical conditions in the nova shell have been studied. The electron temperature (9000 K) and density (5 × 106 cm?3) in the nebular stage have been estimated, together with the abundances of helium, oxygen, nitrogen, neon, argon, and iron. The abundances of nitrogen, oxygen, neon, and argon are enhanced relative to the solar values. The relative abundances are [N/H] = 2.26 ± 0.25 dex, [O/H] = 1.66 ± 0.35 dex, [Ne/H] = 0.78 ± 0.25 dex, and [Ar/H] = 0.32 ± 0.38 dex. The estimated mass of oxygen and total mass of the emitting shell are ≈1 × 10?4M⊙ and ≈3 × 10?4M⊙, respectively. In the period of chaotic brightness oscillations, the maximum velocity of the shell expansion derived from the radial velocities of the absorption components of the HI and FeII line profiles increased by ≈400 km/s 41 days after the maximum, and by ≈200 km/s 101 days after the maximum, reaching 1600 km/s in both cases.  相似文献   

6.
We model the Galactic ensemble of helium stars using population synthesis techniques, assuming that all helium stars are formed in binaries. In this picture, single helium stars are produced by mergers of helium remnants of the components of close binaries (mainly, the merging of helium white dwarfs) or in the disruption of binaries with helium components during supernova explosions. The estimated total birthrate of helium stars in the Galaxy is 0.043 yr?1; the total number is 4 × 106; and the binarity rate is 76%. We construct a subsample of low-mass (MHe ? 2M⊙) helium stars defined by observational selection effects: the limiting magnitude (VHe ≤ 16), ratio of the magnitudes of the components in binaries (VHe ≤ Vcomp), and lower limit for the semiamplitude of the radial velocity required for detecting binarity (Kmin = 30 km s?1). The parameters of this subsample are in satisfactory agreement with observations of helium subdwarfs. In particular, the binarity rate in the selection-limited sample is 58%. We analyze the relations between the orbital periods and masses of helium subdwarfs and their companions in systems with various combinations of components. We predict that the overwhelming majority (～97%) of unobserved companions to helium stars will be white dwarfs, predominantly, carbon-oxygen white dwarfs.  相似文献   

7.
An analysis of monitoring observations for the pulsar PSR B0655+64, which is located in a binary system, at 111 MHz during 2002–2015 are presented. The Keplerian parameters of the pulsar have been refived: the longitude of periastron ω = 276.°5785 ± 0.°0005 and the orbital semi-major axis is ap sin i = 4.124976± 0.000003 s. The parameters of the perturbed motion have been determined: the motion of periastron ω = 0.°315 ± 0.°005/ year, and the derivative of the period of the binary system ? = (-1.66 ± 0.11) × 10-14 s/s = (-0.524 ± 0.038) µs/year. The estimated time scale for the decay of the PSR 0655+64 system is (1.7 ± 0.1) × 1011 yrs.  相似文献   

8.
Based on high-resolution observations (R = 60 000 and 75 000), we have studied the optical spectral variability of the star BD + 48°1220, identified with the IR source IRAS 05040+4820. We have measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths from 4500 Å to 6760 Å, as well as the corresponding radial velocities. We use model atmospheres to determine the effective temperature T eff = 7900 K, surface gravity log g = 0.0, microturbulence velocity ξ t = 6.0, and the abundances for 16 elements. The star’s metallicity differs little from the solar value: [Fe/H] = ?0.10 dex. The main peculiarity of the chemical composition of the star is a large helium excess, derived from the Hel λ 5876 Å absorption, [He/H] = +1.04, and the equally large oxygen excess, [O/Fe] = +0.72 dex. The carbon excess is small, [C/Fe] = +0.09 dex, and the ratio [C/O] < 1. We obtained an altered relation for the light-metal abundances: [Na/Fe] = +0.87 dex with [Mg/Fe] = ?0.31 dex. The barium abundance is low, [Ba/Fe] = ?0.84 dex. It is concluded that the selective separation of elements onto dust grains of the envelope is probably efficient. The radial velocity of the star measured from photospheric absorption lines over three years of observations varies in the interval V ⊙ = ?(7–15) km/s. Time-variable differential line shifts have been revealed. The entire set of available data (the luminosity M v ≈ ?5 m , velocity V lsr ≈ ?20 km/s, metallicity [Fe/H] = ?0.10, and peculiarities of the optical spectrum and chemical composition) confirms the status of BD + 48°1220 as a post-AGB star with He and O excesses belonging to the Galactic disk.  相似文献   

9.
Optimized photoionization models of selected HII regions in Blue Compact Dwarf Galaxies are calculated with the aim of determining their chemical composition. The stability of the optimized-photoionization calculations and means of deriving the most accurate chemical abundances are checked. Initialization of the free physical parameters using different data sets, deviations from spherical geometry, and the introduction of gas-density fluctuations in an HII region do not affect the accuracy of the derived chemical compositions. The chemical abundances found for 12 HII regions using the optimized-photoionization models are used to derive the primordial helium abundance Y p and its enrichment dY/dZ. The obtained values of Y p and dY/dZ are close to values found previously using ionization-correction factors.  相似文献   

10.
Synthetic CaAlSiO4F, the Al-F analog of titanite, has been investigated using single-crystal synchrotron diffraction experiments at Beamline X06DA (Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland) and Raman spectroscopy. The presented structural model with 40 parameters was refined against 506 unique reflections to a final R o b s of 0.026 (space group A2/a, a = 6.9120(11), b = 8.5010(10), c = 6.435(2) Å, β = 114.670(11)°, and Z = 4) and exhibits less distorted coordination polyhedra than earlier models from powder data. Vibrational spectra were calculated in harmonic approximation at the Γ point from fully relaxed energy optimisations of the crystal structure, using 3D-periodic density functional theory with Gaussian basis sets and the software CRYSTAL06. The lattice parameters of the fully relaxed structure were in good agreement with the experimental values, with the calculated values 0.8 ± 0.4 % too large; the monoclinic angle was calculated 0.4° too large. The agreement of the calculated Raman frequencies with the observed ones was very good, with standard deviation ±3 cm?1 and maximum deviations of ±7 cm?1. Furthermore, a detailed discussion of the atomic displacements associated with each Raman mode is given.  相似文献   

11.
We have obtained high-accuracy photoelectric measurements of ES Lac, an eclipsing binary with an elliptical orbit (B9III + B9III; P = 4.459d, e = 0.198) in 1985–2004 at the Sternberg Astronomical Institute’s Tien Shan High-Altitude Observatory. Our detailed analysis of the 19-year uniform series of measurements has yielded the first photometric elements for this system, as well as a self-consistent set of physical and geometrical parameters for the binary. The virtually identical components (M 1 = M 2 = 3.0 M ⊙; R 1 = R 2 = 4.12 R ⊙) are appreciably separated from the main sequence, and are located on the giant branch: their age is t = (3.5 ± 0.2) × 108 yrs. An analysis of our observations together with previously published times of minima has enabled a considerable refinement of the period of the apsidal motion, U = 355 ± 20 years, and a first determination of the apsidal parameter reflecting the radial density distributions for the components stars: k 2 obs = 0.00213(18). This value is in a good agreement with the value expected theoretically for current evolutionary models of such stars: k 2 th = 0.00257(15).  相似文献   

12.
The results of infrared observations of the two Be stars X Per and V725 Tau, which are the optical components of X-ray binary systems, obtained in 1994–2016 are presented. The observations cover Be-star phases as well as shell phases. The data analysis shows that the radiation observed from the binaries at 1.25, 3.5, and 5 μm can be explained as the combined radiation from the optical components and variable sources (shells/disks) that emit as blackbodies (BBs). Emission from a source with the color temperature T c ~1000?1500 K was detected for X Per at λ ≥ 3.5 μm. The highest IR-brightness variation amplitudes for X Per were 0.9?1.2 m (JHK magnitudes) and ~1.45 m (LM magnitudes); for V725 Tau, they were 1.1?1.4 m and ~1.7 m (L magnitudes). The parameters of the optical components and interstellar extinction during the Be phases were estimated: the color excesswasE(B?V) = 0.65±0.08 m and 0.77 ± 0.03 m for X Per and V725 Tau, respectively. Light from the variable sources (disks/shells) was distinguished and their color temperatures, radii, and luminosities estimated for different observation epochs in a BB model. The variations of the binaries’ IR brightness and colors are shown to be due to changing parameters of the variable sources. The mean color temperature of the cool source (disk/shell) and the mean radius and mean luminosity of X Per are 9500± 2630 K, (35 ± 10) R⊙, and (9100± 540) L⊙. For V725 Tau, these parameters are 6200 ± 940 K, (27 ± 6) R⊙, and (980 ± 420) L⊙. The 1.25–5 μm radiation from X Per at different epochs can be represented as a sum of contributions from at least three sources: the optical component and two objects emitting as BBs. To reproduce the 1.25–3.5 μm radiation from V725 Tau, two components are sufficient: the optical component and a single variable BB object. For both binary systems, orbital variations of the IR brightness can be noted near the Be-star phase. The amplitudes of the J-band variations of X Per and V725 Tau are about 0.3 m and 0.1 m , respectively.  相似文献   

13.
We obtained speckle interferometric and spectroscopic observations of the system 41 Dra during its periastron passage in 2001. The components’ lines are resolved in the spectral interval 3700–9200 Å. The observed wavelength dependence of the brightness difference between the components is used to estimate the B-V indices separately for each of the components: B-V = 0.511 for component a and B-V = 0.502 for component b. We derived improved effective temperatures of the components from their B-V values and hydrogen-line profiles. The observations can be described with the parameters for the components T eff a = 6370 K, log ga = 4.05 and T eff b = 6410 K, log gb = 4.20. The iron, carbon, nitrogen, and oxygen abundances in the atmospheres of the components are log N(Fe)a = 7.55, log N(Fe)b = 7.60, log N(C)a = 8.52, log N(C)b = 8.58, log N(N)a = 8.05, log N(N)b = 7.99, log N(O)a = 8.73, log N(O)b = 8.76.  相似文献   

14.
High pressure in situ synchrotron X-ray diffraction experiment of strontium orthophosphate Sr3(PO4)2 has been carried out to 20.0 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a volume of V 0 = 498.0 ± 0.1 Å3, an isothermal bulk modulus of K T  = 89.5 ± 1.7 GPa, and first pressure derivative of K T ′ = 6.57 ± 0.34. If K T ′ is fixed at 4, K T is obtained as 104.4 ± 1.2 GPa. Analysis of axial compressible modulus shows that the a-axis (K a  = 79.6 ± 3.2 GPa) is more compressible than the c-axis (K c  = 116.4 ± 4.3 GPa). Based on the high pressure Raman spectroscopic results, the mode Grüneisen parameters are determined and the average mode Grüneisen parameter of PO4 vibrations of Sr3(PO4)2 is calculated to be 0.30(2).  相似文献   

15.
As part of our study of the components of the hierarchic quadruple system ADS 11061, we acquired spectroscopic observations of the binary 40 Dra. Echelle spectra showing the separation of the components’ lines were obtained in the spectral range 3700–9200 Å. Effective temperatures and surface gravities were derived for the components from BV photometry and the hydrogen-line profiles. The components of the 40 Dra system have parameters close to T eff a = 6420 K, log g a = 4.17, T eff b = 6300 K, and log g b = 4.20. We find the microturbulence velocity in the component atmospheres to be V t = 2.6 km/s. The abundances of iron, carbon, nitrogen, and oxygen in the atmospheres of both components are estimated to be log N(Fe)a = 7.50, log N(Fe)b = 7.46, log N(C)a = 8.39, log N(C)b = 8.45, log N(N)a = 8.12, log(N)b = 8.15, log N(O)a = 8.77, log N(O)b = 8.74.  相似文献   

16.
The thermoelastic parameters of the CAS phase (CaAl4Si2O11) were examined by in situ high-pressure (up to 23.7 GPa) and high-temperature (up to 2,100 K) synchrotron X-ray diffraction, using a Kawai-type multi-anvil press. P–V data at room temperature fitted to a third-order Birch–Murnaghan equation of state (BM EOS) yielded: V 0,300 = 324.2 ± 0.2 Å3 and K 0,300 = 164 ± 6 GPa for K′ 0,300 = 6.2 ± 0.8. With K′ 0,300 fixed to 4.0, we obtained: V 0,300 = 324.0 ± 0.1 Å3 and K 0,300 = 180 ± 1 GPa. Fitting our P–V–T data with a modified high-temperature BM EOS, we obtained: V 0,300 = 324.2 ± 0.1 Å3, K 0,300 = 171 ± 5 GPa, K′ 0,300 = 5.1 ± 0.6 (?K 0,T /?T) P  = ?0.023 ± 0.006 GPa K?1, and α0,T  = 3.09 ± 0.25 × 10?5 K?1. Using the equation of state parameters of the CAS phase determined in the present study, we calculated a density profile of a hypothetical continental crust that would contain ~10 vol% of CaAl4Si2O11. Because of the higher density compared with the coexisting minerals, the CAS phase is expected to be a plunging agent for continental crust subducted in the transition zone. On the other hand, because of the lower density compared with lower mantle minerals, the CAS phase is expected to remain buoyant in the lowermost part of the transition zone.  相似文献   

17.
High-pressure in situ X-ray diffraction experiment of Fe- and Al-bearing phase D (Mg0.89Fe0.14Al0.25Si1.56H2.93O6) has been carried out to 30.5 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields values of V 0 = 86.10 ± 0.05 Å3; K 0 = 136.5 ± 3.3 GPa and K′ = 6.32 ± 0.30. If K′ is fixed at 4.0 K 0 = 157.0 ± 0.7 GPa, which is 6% smaller than Fe–Al free phase D reported previously. Analysis of axial compressibilities reveals that the c-axis is almost twice as compressible (K c  = 93.6 ± 1.1 GPa) as the a-axis (K a  = 173.8 ± 2.2 GPa). Above 25 GPa the c/a ratio becomes pressure independent. No compressibility anomalies related to the structural transitions of H-atoms were observed in the pressure range to 30 GPa. The density reduction of hydrated subducting slab would be significant if the modal amount of phase D exceeds 10%.  相似文献   

18.
We have modeled absorption lines of the 12CO and 13CO (Δυ = 2) molecular bands at λλ 2.29–2.45 µm in the spectrum of Arcturus (K2III). A grid of model atmospheres and synthetic spectra were computed for the red giant using T eff = 4300, log g = 1.5, and the elemental abundances of Peterson et al. (1993), with the exception of the abundances of carbon, log N(C), and oxygen, log N(O) and the carbon isotopic ratio, 12C/13C, which were varied in our computations. The computed spectra were compared to the observed spectrum of Arcturus from the atlas of Hinkle et al. (1976). The best fit between the synthetic and observed spectra is achieved for log N(C) = ?3.78, 12C/13C = 8 ± 0.5. We discuss the dependence of 12C/13C on log N(C) and log N(O) in the atmosphere of the red giant.  相似文献   

19.
A new synchrotron X-ray diffraction study of chromium oxide Cr2O3 (eskolaite) with the corundum-type structure has been carried out in a Kawai-type multi-anvil apparatus to pressure of 15 GPa and temperatures of 1873 K. Fitting the Birch–Murnaghan equation of state (EoS) with the present data up to 15 GPa yielded: bulk modulus (K 0,T0), 206 ± 4 GPa; its pressure derivative K′0,T , 4.4 ± 0.8; (?K 0,T /?T) = ?0.037 ± 0.006 GPa K?1; a = 2.98 ± 0.14 × 10?5 K?1 and b = 0.47 ± 0.28 × 10?8 K?2, where α 0,T  = a + bT is the volumetric thermal expansion coefficient. The thermal expansion of Cr2O3 was additionally measured at the high-temperature powder diffraction experiment at ambient pressure and α 0,T0 was determined to be 2.95 × 10?5 K?1. The results indicate that coefficient of the thermal expansion calculated from the EoS appeared to be high-precision because it is consistent with the data obtained at 1 atm. However, our results contradict α 0 value suggested by Rigby et al. (Brit Ceram Trans J 45:137–148, 1946) widely used in many physical and geological databases. Fitting the Mie–Grüneisen–Debye EoS with the present ambient and high-pressure data yielded the following parameters: K 0,T0 = 205 ± 3 GPa, K′0,T  = 4.0, Grüneisen parameter (γ 0) = 1.42 ± 0.80, q = 1.82 ± 0.56. The thermoelastic parameters indicate that Cr2O3 undergoes near isotropic compression at room and high temperatures up to 15 GPa. Cr2O3 is shown to be stable in this pressure range and adopts the corundum-type structure. Using obtained thermoelastic parameters, we calculated the reaction boundary of knorringite formation from enstatite and eskolaite. The Clapeyron slope (with \({\text{d}}P/{\text{d}}T = - 0.014\) GPa/K) was found to be consistent with experimental data.  相似文献   

20.
Between 1994 and 2006, we obtained uniform spectroscopic observations of SS 433 in the region of Hα. We determined Doppler shifts of the moving emission lines, Hα + and Hα ?, and studied various irregularities in the profiles for the moving emission lines. The total number of Doppler shifts measured in these 13 years is 488 for Hα ? and 389 for Hα +. We have also used published data to study possible long-term variations of the SS 433 system, based on 755 Doppler shifts for Hα ? and 630 for Hα + obtained over 28 years. We have derived improved kinematic model parameters for the precessing relativistic jets of S S 433 using five-and eight-parameter models. On average, the precession period was stable during the 28 years of observations (60 precession cycles), at 162.250d ± 0.003d. Phase jumps of the precession period and random variations of its length with amplitudes of ≈6% and ≈1%, respectively, were observed, but no secular changes in the precession period were detected. The nutation period, P nut = 6.2876d ± 0.00035d, and its phase were stable during 28 years (more than 1600 nutation cycles). We find no secular variations of the nutation cycle. The ejection speed of the relativistic jets, v, was, on average, constant during the 28 years, β = v/c = 0.2561 ± 0.0157. No secular variation of β is detected. In general, S S 433 demonstrates remarkably stable long-term characteristics of its precession and nutation, as well as of the central “engine” near the relativistic object that collimates the plasma in the jets and accelerates it to v = 0.2561c. Our results support a model with a “slaved” accretion disk in S S 433, which follows the precession of the optical star’s rotation axis.  相似文献   

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