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1.
The λ 6708 Å and 6103 Å lithium lines in the high-resolution spectra of some sharp-lined roAp stars are analyzed using three spectral-synthesis codes STARSP, ZEEMAN2, and SYNTHM. The lines from the VALD database were supplemented with lines of rare-earth elements from the DREAM database and new lines calculated using the NIST energy levels. Our synthetic-spectrum calculations take into account magnetic splitting and other line-broadening effects. Lithium overabundances were found in the atmospheres of the stars based on our analysis of both lithium lines, along with high values of the 6Li-7Li isotope ratio (0.2–0.5). This can be explained if lithium is produced in spallation reactions and the surface 6Li and 7Li is preserved by strong magnetic fields in the upper layers of the stellar atmospheres, around the poles of the dipole field. The asymmetry of lithium lines to the red may be due to the action of shocks in the optically thin upper atmosphere, with the shocked material subsequently falling onto the star.  相似文献   

2.
The non-LTE formation of KI lines in the spectra of A-K stars is analyzed. The computations are based on a 36-level model of the neutral potassium atom for blanketed LTE Kurucz model atmospheres with T eff=4000–10000 K, logg=0.0–4.5, and [M/H]=(0.0)–(?2.0). The KI atoms in the atmospheres of these stars are in states of moderate and strong “over-recombination.” A number of atomic parameters are refined using the profiles and equivalent widths of five lines in the solar spectrum. The classical van der Waals damping constants must be increased by factors of 2–60 to fit the observed profiles. The non-LTE solar potassium abundance—logε (K)=5.14—corresponds to the meteoritic abundance. Non-LTE corrections to the potassium abundance are important and equal to ?0.4...?0.7 dex for the λ7699 Å line and ?0.15...?0.3 dex for the λλ12522, 12432, and 11769 Å lines.  相似文献   

3.
We have performed a detailed statistical-equilibrium analysis based on a 49-level model of the magnesium atom for the atmospheres of stars of various spectral types: T eff=4500–12000 K, logg=0.0–4.5, and [M/H]=0 to ?3. In the atmospheres of stars with T eff>5500 K, deviations from LTE for Mg I are due to photoionization by ultraviolet radiation from the 3p level; i.e., neutral magnesium is in a state of “superionization.” When T eff<5500 K, the populations of the Mg I levels differ from their LTE values due to radiative processes in bound-bound transitions. We analyzed Mg I lines in the solar spectrum in order to empirically refine certain atomic parameters (the van der Waals broadening constant C 6 and cross sections for photoionization and collisional interactions with hydrogen atoms) and the magnesium abundance in the solar atmosphere. We studied non-LTE effects for five Mg I lines for a wide range of stellar parameters. In the case of dwarfs and subdwarfs, the magnitude of non-LTE corrections to magnesium abundances does not exceed 0.1 dex for the λλ 4571, 4703, 5528, and 5711 Å lines but can be as large as ±0.2 dex for the λλ 3829–3838, 5172, and 5183 Å lines. The non-LTE corrections for giants and supergiants do not exceed 0.15 dex for the λλ 4571 and 5711 Å lines but can reach ±0.20 dex and even more for the λλ 4703, 5528, 3829–3838, 5172, and 5183 Å lines.  相似文献   

4.
The spectra of two roAp stars have been analyzed as part of a project to study lithium in magnetic Ap stars. Variability of the Li I 6708 Å resonance doublet and rare-earth lines was detected, which can be explained using an oblique rotator model with the lithium spots located at the magnetic poles. Synthetic spectra obtained at different rotational phases have yielded the first data on the atmospheric chemical compositions of these spotted stars. Using refined atomic data and the most complete line lists has enabled a detailed study of the spectra near the Li I 6708 Å line and computation of the Li I line profile taking into account the spotted distribution of the lithium over the stellar surfaces. The positions of two lithium spots and lithium abundances for each of the spots have been determined.  相似文献   

5.
We analyze the formation of lines of neutral sulfur in the spectra of F-K stars taking into account the effects of deviations from local thermodynamical equilibrium (LTE). Our calculations were carried out for Kurucz model atmospheres with T eff = 5000–6500 K, log g = 2?4 and [Fe/H] = ?4?0, using a 65-level model of the SI atom. Deviations from LTE affect lines of different multiplets of the sulfur atom differently. Non-LTE corrections, which are relatively small (to ?0.10 dex) for the 6543–6557 Å lines, increase to ?0.26 dex for the 8694 Å line, and reach ?1.1 dex for the 9212–9237 Å IR triplet. The model of the atom was verified by modeling the sulfur lines of the studied multiplets in the spectra of the Sun, two main sequence stars, and two supergiants. Good consistency with the observed line profiles was obtained. Failure to take into account strong non-LTE-effects may explain the large sulfur excesses detected in stars with very low metal abundances.  相似文献   

6.
We discuss the methodological problems and results of computations of the spectral energy distributions (SEDs) of L dwarfs. Over a wide wavelength interval (λλ4000–10 000 Å), the spectra of these stars are determined to a considerable extent by absorption in resonance lines of potassium (7666.961, 7701.031 Å) and sodium (5891.518, 5897.489 Å). We compute the extended wings of these lines using the theory of quasi-stationary broadening. We compute the cores and nearby wings (up to Δλ = 40 Å from the line center) of the KI and NaI lines in a collisional approximation (van der Waals theory). In our modeling of the SED of the ultracool dwarf 2MASS J15232263+3014562 (L8), we find that the observations agree best with the COND atmospheric models of Allard et al. with T eff = 2200 K and log g = 6.0.  相似文献   

7.
We have derived the atmospheric parameters of the R CrB carbon star DY Per. The spectrum of DY Per near its maximum brightness was obtained using the 2.6-m ZTSh telescope of the Crimean Astrophysical Observatory, and has a resolution of about 1.74 Å per pixel. We compare the absolute observed and theoretical spectral energy distributions (SEDs) of DY Per for λλ 430–730 nm for the first time. The model atmospheres were computed using a code written by Ya.V. Pavlenko in the classical approximation, taking into account the main opacity sources in carbon-star atmospheres. The theoretical SEDs were computed using the list of atomic lines from the VALD database and the molecular line lists from CD-ROM No. 18 of Kurucz’s database. The estimated by spectral synthesis effective temperature of DY Per is in the range of 2900–3100 K, if we assume log g = 0. We find a metal deficiency in the atmosphere of DY Per. Quantitative estimates of the overall metallicity, carbon and nitrogen abundances, and the H/He ratio are somewhat uncertain: ?2 ≤ [Fe/H] ≤ ?0.5, 0.65 ≤ [C/Fe] ≤ 1.35, 0.0 ≤ [N/Fe] ≤ 0.8, 1/9 ≤ H/He ≤ 9/1. These high H/He values do not quite agree with qualitative observational estimates made by other authors. Our results confirm that DY Per is a unique stellar object. This is the coolest and possibly the most metal-poor of all known R CrB stars. We conclude that the large deficiencies of metals and hydrogen lead to [C/Fe] values in the atmosphere of DY Per characteristic of R CrB stars.  相似文献   

8.
We have obtained spectral energy distributions for 41 7m–8m stars near the celestial equator (δ=±3°). The λλ3100–7600 Å spectral range is studied with a spectral resolution of 50 Å. The relative rms error in the visible is 1–2%, increasing to 3–5% towards the edges of the wavelength interval studied. All stars are referenced to a single standard, the circumpolar star HD 221525. The synthetic colors of common stars are compared with those observed in four photometric systems: U BV, W BV R, uvby, and that of the TYCHO catalog. The program stars are recommended as secondary spectrophotometric standards.  相似文献   

9.
Taking into account blending of the lithium 6108 Å line profile by adjacent rare-earth lines together with their spotted surface structure does not appreciably affect lithium abundance estimates for the atmospheres of HD 83368 and HD 60435 but provides a better fit of the observed and stimulated line profiles. Our computed non-LTE corrections reduce the lithium abundance estimates by 0.1–0.2 dex for both stars. Given the uncertainties in the lithium abundances, it is not possible to be certain whether the lithium abundances in roAp stars, or at least in their spots, exceed the cosmic (primordial) value.  相似文献   

10.
Fission tracks and point defects in natural zircon are directly observed by a 1 MV electron microscope at atomic resolution for three types of samples adjusted to the 100 orientation. Lattice planes intersecting the fission tracks at high angles are distorted in a rather irregular manner over a wide region up to more than 100 Å wide. Diameter of the tracks, ranging from 25 Å to 40Å, is much narrower than those so far reported for the U-doped synthetic zircon (100–200 Å), UO2 thin film (100 Å), mica (66 Å, 240 Å) or fluorophlogopite (150 Å). The fact that fairly long tracks thousands of angstroms in length are observed in thin 100-oriented sample hundreds of angstroms in thickness and that some of them are nearly parallel to a low index lattice plane suggest a possible occurrence of channelling in the process of track formation. Parallel tracks often observed in chemically etched specimens support the idea of channelling. Slightly bent tracks are sometimes observed. It is concluded from computer simulation that many contrast anomalies of bright and dark spots in the lattice image are due to point defects of vacancies and interstitial atoms, mainly produced by the direct atomic collision with α-particles or by passage of ionizing nuclear particles. Optimum conditions of the observation of point defects with highest contrast are studied. One interstitial Zr atom or one Zr ion vacancy will give very low contrast and will be not detectable unless the crystal is less than two unit cells thick. A pair of Zr ion vacancies, however, yields extended detectable limit of thickness. Some of the observed defects are in good accordance with those simulated.  相似文献   

11.
Fine-granular (<0.1 mm) flattened colorless transparent crystals of ivsite form white aggregates. The empirical formula (Na2.793Cu0.056)2.849HS2.016O8 is close to the ideal Na3H(SO4)2. The structure was refined up to R = 0.040. Ivsite has a monoclinic symmetry, P21/c, a = 8.655(1) Å, b = 9.652(1) Å, c = 9.147(1) Å, β = 108.76(1)°, V = 723.61(1) Å3, Z = 4. Na atoms occur at six- and seven-fold sites (NaO6 and NaO7); S atoms, in isolated SO4 tetrahedrons; these polyhedrons form a three-dimensional framework. The diagnostic lines of powder diffraction patterns (d[Å]–I–hkl) are 4.010–53–12-1, 3.949–87–012, 3.768–100–210, 3.610–21–20-2, 3.022–22–031, 2.891–42–22-2, 2.764–49–31-1, and 2.732–70–13-1.  相似文献   

12.
A study of the optical spectra of three Herbig Ae/Be stars is presented: MWC 361,MWC 614, AB Aur. Variations of the equivalent widths, radial velocities, and profiles of spectral lines formed in different regions of the circumstellar environments of these stars are analyzed. The most active spectral variations are observed in the Hα, Hβ, and He I 5876 lines. Other emission lines, such as Si II λλ6347, 6371 Åand [O I] λλ6300, 6363 Å, also display variations, but these are much smaller. Interstellar DIBs at λλ5780 and 5797 ?A were detected for the stars MWC 361 and MWC 614 for the first time. The active processes that are underway in the circumstellar environments of these systems can also reach more distant, outer parts of their circumstellar disks.  相似文献   

13.
The power spectra of radial-velocity and intensity oscillations are analyzed using ground-based (the Si I 10 827 Å and He I 10 830 Å lines) and Solar Dynamics Observatory (the Fe I 6173, 1700 Å, He II 304 Å, and Fe IX 171 Å lines) data, with the aim of searching for frequency modes that most efficiently penetrate into the solar corona from the lower layers of solar faculae. Analysis of the spatial distribution of the oscillation power at various heights indicates that fan structures in the corona (at the height of the 171 Å emission) are better reproduced at frequencies of 1–1.5 mHz. This means that oscillations with periods of 10–15 min dominate in coronal loops above faculae regions. The five-minute oscillations that universally dominate in radial-velocity measurements in low layers of faculae are appreciable in coronal loops only in individual compact fragments.  相似文献   

14.
We have determined the position of deuterium atoms in δ-AlOOD by neutron powder diffraction at ambient pressure. As previously reported by theoretical and experimental studies, the deuterium atoms are located in the tunnel formed by the chains of AlO6 octahedra. The data are best fit with the P21 nm structure, producing bond lengths of D–O1 of 1.552(2) Å, O2–D of 1.020(2) Å and O1–O2 of 2.571(2). This study confirms that the hydrogen bond is asymmetric at ambient conditions in agreement with recent single-crystal synchrotron study for δ-AlOOH.  相似文献   

15.
Rietveld refinement of X-ray synchrotron data was performed for two synthetic tetrahedrite samples, with 0.61 and 1.83 Fe atoms, and two synthetic tennantite samples with 0.10 and 1.23 Fe atoms p.f.u. M12(Sb,As)4S13. Measurements were performed at 25 and 250°C. For both the phases, increased Fe substitution is reflected in the increased tetrahedral ‘Cu1’–S distance (‘Cu1’ is a site of Fe substitution) and Cu2–S distances. Cu2 was refined as a split position; the Cu2–Cu2 split about the plane of the S12S2 triangle is about 0.56 and 0.65 Å for tetrahedrite and tennantite, respectively. Cu2–Cu2 distances in the structure cavity are 2.8–2.9 Å. Between 25 and 250°C, the lattice parameter a increased by 0.02–0.04 Å and the interatomic distances by 0.01 Å on an average. Thermal expansion coefficients of little-substituted samples are similar to those of unsubstituted samples, whereas thermal expansion appears to decrease with increasing substitution by Fe. The Cu2–Cu2 split increases at 250°C by about 0.1 Å for tetrahedrite and by more than 0.15 Å for tennantite but the cage expansion is minimal so that the Cu2–Cu2 distances in the cavity decrease with temperature. Difference Fourier maps indicate that there is little residual electron density left between the two Cu2 half-sites in tetrahedrite but this inter-site density is substantially higher in tennantite. It increases with temperature, especially in the little-substituted tennantite sample.  相似文献   

16.
The angular diameters, radii, and effective temperatures of 16 G0–G5 main-sequence stars with color excesses 0.60≤B-V≤0.68 and parallaxes derived from Hipparcos data have been determined using their infrared fluxes, obtained from JHKLM photometric observations. For all the stars except BS 483, these effective temperatures differ from the spectroscopic temperatures by no more than 1–2%. Such differences are within the uncertainties expected for the IR-flux method. The effective temperatures of BS 483 derived from its infrared fluxes are 3% higher than those indicated by spectroscopic observations; this may be due to the specific atmospheric structure of this star. Spectroscopic observations at 3400–7500 Å and JHKLM photometric observations are compared with analogous solar data and Kurucz models. The best agreement with the model with T eff=5750 K and logg=4.5 in the interval 4400–7500 Å was obtained for BS 7503 and BS 7504 (16 Cyg A and 16 Cyg B). The infrared color indices H-K, K-L, and K-M for these stars differ from the corresponding solar indices, and their angular diameters grow with wavelength, which is not the case for the Sun. H-K for BS 6060, currently considered to be the closest analog to the Sun, is near the solar value. The vast majority of the stars studied (13 of 16) have higher luminosities than the Sun. These include 16 Cyg A, 16 Cyg B, and 51 Peg, which thus cannot be considered full “twins” of the Sun.  相似文献   

17.
We have analyzed for the first time profiles of the SiIII 1892 Å and CIII 1909 Å intercombinational lines in HST spectra of the stars RY Tau and RU Lup. The widths of these optically thin lines exceeded 400 km/s, ruling out formation in the stellar chromosphere. Since the intensity of the Si line exceeds that of the C line, it is unlikely that a large fraction of the observed line flux is formed in a stellar wind. The observed profiles can be reproduced in the framework of an accretion shock model if the velocity field in the accretion zone is appreciably nonaxisymmetric. In this case, the line profiles should display periodic variations, which can be used to determine the accretion zone geometry and the topology of the magnetic field near the stellar surface; corresponding formulas are presented. In addition, periodic variations of the 0.3–0.7 keV X-ray flux should be observed.  相似文献   

18.
We analyze low-dispersion (1.8 Å per pixel) spectra of the recurrent nova RS Oph taken between the 10th and 241st days after its outburst on February 12, 2006. The spectra exhibit various stages in the development of the outburst, from its coronal phase to its nebular phase. We identified about 200 spectral lines at 3700–7500 Å, and fluxes were determined for the strongest lines. The spectral behavior of this outburst does not differ strongly from the previous one. One of the main differences is the presence of flux variations in the forbidden [NII] 5775 Å, [OI] 6300 Å, [OIII] 4959 Å, [OIII] 5007 Å, [KIV] 6101 Å, [FeVII] 6086 Å, and [FeX] 6375 Å lines, as well as in the HeI 5876 Å, HeI 6678 Å, HeII 4686 Å lines. We also obtained high-dispersion (0.06 Å per pixel) spectra in the region of the Hα and HeI 5876 Å lines between the 9th and 113th days after the outburst. The HeI 5876 Å profile has three components. This shape of the profile may result from the formation of an envelope after the aspherical explosion.  相似文献   

19.
《Applied Geochemistry》2000,15(6):879-889
Direct evidence of the structure of thioantimonide species in alkaline aqueous solutions is provided by X-ray absorption spectroscopy. Twenty solutions containing thioantimonide species were prepared by dissolving stibnite (Sb2S3) in deoxygenated aqueous NaHS solutions; the solution pH range was 8–14, the [Sbtot] 1–100 mM and the [HS−] 0.009–2.5 M. The structural environment of the dissolved Sb was determined by EXAFS analysis of the Sb K-edge over the temperature range 80–473 K.Many of the solutions contain a species with Sb bonded to four S atoms at 2.34 Å, consistent with the presence of a [Sb(V)S43−] species, demonstrating that oxidation of Sb(III) to Sb(V) has occurred on dissolution. There is evidence that the complementary reduced phase is H2. In three solutions, the Sb has three nearest neighbor S atoms and two of these solutions have an additional S shell of two atoms at 2.9Å, with one showing evidence of an Sb shell at 4.15 Å. This provides evidence of the presence of multimeric Sb(V) thioantimonide species. Analysis of several solutions reveals the presence of a species with three Sb–S interactions of 2.41–2.42 Å, supporting the presence of a Sb(III) species such as Sb2S2(SH)2. Six solutions have S coordination numbers from 2.7–4 Å and Sb–S distances of 2.37–2.39 Å, and are likely to contain mixtures of at least two species in concentrations such that each make a significant contribution to the EXAFS. There was no clear relationship between either [Sbtot] or [HS−] and the type of species present, but Sb(III) species were only present in the solutions with high pH. The effect of temperature was most significant in one solution, where at 423 K partial hydrolysis occurred and the presence of a species such as Sb2S2(OH)2, with an Sb–O distance of 1.91 Å, is indicated.The study provides new information on the coordination environment of thioantimonide species, complementary to previous studies and provides a basis for a better understanding of Sb speciation in aqueous solutions found in hydrothermal systems, anoxic basins and man-made, high pH environments. In particular it demonstrates the need for Sb(V) to be considered in theoretical and experimental studies of such systems. However, more definitive interpretation of some of the data is inhibited by the presence of mixtures of species and the lack of information on the outer coordination shells that would confirm the presence of multimeric species.  相似文献   

20.
Mechanisms for the formation of the optical (λλ500–950 nm) spectra of L dwarfs—stars and sub-stellar objects with T eff<2200 K—are discussed. Their spectral energy distributions are determined primarily by the K I and Na I resonance-doublet absorption lines. The equivalent widths of these absorption lines formally computed using the dusty model atmospheres of Tsuji can reach several thousand angstroms. In this case, the extended wings of these lines form a pseudo-continuum for weaker absorption lines and even molecular bands. Mechanisms for the broadening of alkali-element lines in the atmospheres of late-type stars due to interactions between neutral atoms and hydrogen molecules are analyzed. The computed optical spectral energy distributions of several L dwarfs are compared with their observed spectra.  相似文献   

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