共查询到20条相似文献，搜索用时 15 毫秒
1.
V. A. Sheminova 《Kinematics and Physics of Celestial Bodies》2013,29(4):176-194
A brief overview of the results of the study of the red giant Arcturus is given. One-dimensional LTE modeling of the atmospheres of Arcturus and the Sun as a star is carried out on the basis of calculation of the extended wings of the H and K Ca II lines. It is found that the local continuum in this spectral region is underestimated by an average of 12% in the atlases of Arcturus. The average deficit in UV absorption amounts to 43% (Arcturus) and 9% (the Sun). The correction factor to the opacity in continuum for the wavelengths of 390.0, 392.5, 395.0, 398.0, and 400.0 nm equals 2.20, 1.90, 1.70, 1.55, and 1.45 (Arcturus) and 1.20, 1.20, 1.20, 1.17, and 1.15 (the Sun), respectively. Model calculations agree completely with the estimates of the parameters of the Arcturus atmosphere (T eff = 4286 K and logg = 1.66) and the elemental abundances that were presented by Ramirez and Allende Prieto [56]. The obtained model of the atmosphere of Arcturus is presented in tabular form. 相似文献
2.
A. S. Gadun 《Astronomische Nachrichten》1994,315(6):413-418
The iron abundance and microturbulent velocities in Arcturus, Canopus, and α CenA have been determined from Fel and Fell lines relative to the Sun. α CenA is found to have an enhanced iron abundance, while Canopus and Arcturus are found to have a deficiency of iron. The behaviour of the determined microturbulent velocities is discussed. 相似文献
3.
B. N. Dwivedi 《Astrophysics and Space Science》1990,172(1):47-50
Emission line intensities from MgVI, SiVIII, andSX ions of nitrogen sequence have been computed by use of the model atmosphere of Kopp and Orrall (1976) for the quiet Sun and coronal holes and compared with observational data available from rocket and satellite. 相似文献
4.
F. P. Keenan 《Solar physics》1984,91(1):27-31
Non-Maxwellian collision rates of the Be-sequence ions Ciii and Ov in the solar transition region are derived for quiet Sun and flare conditions using the electron velocity distribution functions of Shoub. The rates are found to be enhanced relative to the Maxwellian values but only at low temperatures where the fractional abundances of these species is very small. This implies that the electron density and temperature diagnostics used by previous authors for the transition region will be unchanged by non-Maxwellian effects. It is noted that such effects will only be important for species that are formed at low temperatures and have large transition energies such as Hei. 相似文献
5.
The spectroscopic variability of Arcturus hints at cyclic activity cycle and differential rotation. This could provide a test of current theoretical models of solar and stellar dynamos. To examine the applicability of current models of the flux transport dynamo to Arcturus, we compute a mean‐field model for its internal rotation, meridional flow, and convective heat transport in the convective envelope. We then compare the conditions for dynamo action with those on the Sun. We find solar‐type surface rotation with about 1/10th of the shear found on the solar surface. The rotation rate increases monotonically with depth at all latitudes throughout the whole convection zone. In the lower part of the convection zone the horizontal shear vanishes and there is a strong radial gradient. The surface meridional flow has maximum speed of 170 m/s and is directed towards the equator at high and towards the poles at low latitudes. Turbulent magnetic diffusivity is of the order 1015–1016 cm2/s. The conditions on Arcturus are not favorable for a circulation‐dominated dynamo (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
E. Biémont 《Solar physics》1978,56(1):79-86
Oscillator strengths calculated by the STF method for selected transitions of V i and Co i have permitted to deduce, from an LTE study of weak lines, photospheric abundances in agreement with those obtained from carbonaceous chondrites. A summary of results is also presented for all the iron-group elements. 相似文献
7.
B. N. Dwivedi 《Solar physics》1991,131(1):49-52
The off-limb spectra, recorded by the NRL Skylab spectrograph, have been used to infer electron densities from theoretical curves of Si viii and S x density-sensitive line ratios. The derived densities are found to be in agreement with those reported by Feldman et al. (1978). Computed line intensities using the Kopp and Orrall (1976) model have also been used to estimate densities in the quite Sun and coronal holes from these curves. 相似文献
8.
Diagnostics of solar ions Nevi, Mgvi, Siviii, and Mgviii in an active region observed by SERTS have been presented. Density, temperature, and electron pressure in the emitting source have been derived from theoretical line-ratio curves and its EUV spectrum obtained by SERTS. The variation of neon-to-magnesium and silicon-to-magnesium abundances has been discussed in the interpretation of the active region spectrum obtained by SERTS. 相似文献
9.
G. O. Boeshaar P. C. Boeshaar S. J. Czyzak L. H. Aller B. M. Lasker 《Astrophysics and Space Science》1980,68(2):335-346
Spectrophotometry of many regions within 30 Doradus in the Large Magellanic Cloud provides chemical abundances and densities for this nebular complex. The helium to hydrogen abundance ratio is about one-tenth by number and the heavier elements are underabundant compared to Orion, with nitrogen showing the greatest deficit. The forbidden lines of singly-ionized sulphur show wide density variations across this object. The distribution of the intensities in these sulphur lines suggests that supernova shocks may have played an important role in producing the composite appearance of this giant HII region. 相似文献
10.
We have performed non-LTE calculations for O I with a multilevel model atom using currently available atomic data for a set of parameters corresponding to stars of spectral types from A to K. Departures from LTE lead to a strengthening of O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The non-LTE correction does not exceed 0.05 dex in absolute value for visible O I lines for main-sequence stars in the entire temperature range. For the infrared O I 7771 Å line, the non-LTE correction can reach ?1.9 dex. The departures from LTE are enhanced with increasing temperature and decreasing surface gravity. We have derived the oxygen abundance for three A-type mainsequence stars with reliably determined parameters (Vega, Sirius, HD 32115). For each of the stars, allowance for the departures from LTE leads to a decrease in the difference between the abundances from infrared and visible lines, for example, for Vega from 1.17 dex in LTE to 0.14 dex when abandoning LTE. In the case of Procyon and the Sun, inelastic collisions with HI affect the statistical equilibrium of OI, and agreement between the abundances from different lines is achieved when using Drawin’s classical formalism. Based on the O I 6300, 6158, 7771-5, and 8446 Å lines of the solar spectrum, we have derived the mean oxygen abundance log ? = 8.74 ± 0.05 using a classical plane-parallel model solar atmosphere and log ? +3D = 8.78 ± 0.03 by applying the 3D corrections taken from the literature. 相似文献
11.
Oxygen and nitrogen abundances for a selection of 113607 cold objects from the Sloan Digital Sky Survey (SDSS) spectra are
derived. Values of oxygen abundances 12 + log(O/H) are obtained using three parametric N calibrations, one of which is constructed
in this work. Values of nitrogen abundances 12 + log(N/H) are found with two N calibrations. The values of oxygen abundances
that are derived using three parametric N calibrations are consistent within 0.05 dex for the vast majority of the objects.
It is not improbable that there are systematic differences between the values of oxygen abundances which do not exceed 0.05
dex. The differences between the values of nitrogen abundances which are obtained using ON and NS calibrations reach 0.1 dex. We show that the vast majority of cold SDSS objects are in the same area of the diagram O/H—N/O
as cold H2 regions of nearby galaxies, for which the oxygen and nitrogen abundances are derived through the T
e
-method. This is indirect evidence that the values of oxygen and nitrogen abundances that are found with parametric N calibrations
are reliable. 相似文献
12.
C. Esteban J. M. Vilchez A. Manchado M. G. Edmunds 《Astrophysics and Space Science》1989,157(1-2):3-7
We report on extensive spectroscopic observations of the WR-ring nebulae NGC 2359 and RCW 78, respectively, excited by the WN5 stars HD 56925 and WN8 HD 117688. For the first object we have determined abundances for O/H, Ne/H, N/H, and He/H in many different positions, including the ionized gas in the bubble, inside the optical shell structure, and the outermost zones associated with the S 298 Hii region. We do not find any significant difference in the N/H and O/H abundances over the entire nebula. The O/H and N/H abundances expected are close to those for a normal Hii region located at similar distance. In the case of He/H we find indication of local enhancements which sum to the abundance of metal rich galactic Hii regions like M17. RCW 78 appears to show slight overabundances of He/H and N/H in the two observed positions.The ionising temperature for the WN central star (HD 56925) of NGC 2359 is determined from the observed Hii region spectrum giving a value of 50000 K, appropriate to its spectral type. 相似文献
13.
The algorithm of the determination of abundances in atmospheres of stars of spectral classes F, G, and K using fits to the observed spectral lines or selected parts of the blended lines is discussed. The technique allows to determine the parameters of the atmosphere, i.e., gravity, microturbulent velocity, rotational velocity of the star, and abundance of elements, for a given effective temperature of the star. At each stage of the iterative process the model atmosphere is recalculated for a new set of input data. The results of applying the procedure for the analysis of the spectra of the Sun (G2 V) and HD 101348 (G3 V) are discussed. 相似文献
14.
In order to investigate the high chromosphere and the low transition region in a coronal hole, we have analysed Ca ii, Mg ii and hydrogen resonance lines, recorded by the OSO-8 spectrometer in 1975. We present the comparison between average profiles observed in and out of the equatorial coronal hole which was at the center of the solar disk between 27 and 29 November, 1975. We separate internetwork and quiet-Sun (network+internetwork) profiles: for the internetwork, we observe that the hydrogen and Mg ii profiles recorded in the hole are stronger than the profiles recorded out of the hole; a similar result, but with a much lower contrast, is found for the quiet Sun. We discuss this surprising result. 相似文献
15.
L. H. Aller 《Astrophysics and Space Science》1982,83(1-2):225-238
Theoretical models are calculated for 15 planetary nebulae of medium-to-high excitation, following procedures previously described. Initial stellar energy distributions are adopted from Cassinelli (1971), but are subsequently modified to obtain the best representation of optical spectra for the selected objects. Other adjustable parameters include the stellar radius,R
(*), the nebular density,N
H, the truncation radius,r
c, for the nebular shell, and the chemical composition. Excitationsensitive ratios are usually well-represented as are the actual observed intensities of spectral lines. Forbidden lines arising from 3p
3 configurations, e.g., those of [SII], [ArIV], and [ClIII] offer difficulties. For this sample of nebulae, the mean abundances seem to agree well with those found in an earlier study where the models were used as interpolation devices (Aller, 1978). Our objective is not to use the models to derive abundances explicitly, but rather to use them to find ionization correction factors. Some cautions and limitations of this procedure are described. 相似文献
16.
O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 106 K, and a non-thermal velocity (NTV) of 49 km s–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines. 相似文献
17.
Predicted allowed and forbidden EUV line intensities of Fe xv and Ni xvii are presented in explicit graphical form, clarifying and extending the earlier treatment of Bely and Blaha (1968). In the case of the former ion a detailed comparison with available observations leads to questioning or rejection of some presently accepted line identifications (323.57 Å, 317.61 Å), and on the other hand suggests that a quiet Sun line at 304.853 Å is due to Fe xv. For the little known ion Ni xvii estimates of level structure and line wavelengths are given and a preliminary comparison is made with recent flare observations. 相似文献
18.
Data obtained by the OSO-7 spectroheliograph on strong XUV lines of five, different Fe ions from the outer equatorial corona are presented. Interpretation of the data with a spherically symmetric model atmosphere gives average ion abundances for lines of sight at 0.3R
from the limb. Fe xvi is usually more abundant than Fe xv, xiv, xii and ix, but there are times when Fe xii is more abundant than the other ions. The deviation of measured relative abundances of Fe xii, xiv, and xvi from predictions of ionization equilibrium at one temperature seems to indicate that there are appreciable temperature variations along lines of sight. Element abundances are very uncertain since they appear to depend so heavily on likely but unknown density irregularities along lines of sight. 相似文献
19.
Ionization equilibrium is a useful assumption which allows temperatures and other plasma properties to be deduced from spectral observations. Inherent to this assumption is the premise that the ion stage densities are determined solely by atomic processes which are local functions of the plasma temperature and electron density. However, if the time scale of plasma flow through a temperature gradient is less than the characteristic time scale for an important atomic process, deviations from the ionization stage densities expected for equilibrium will occur which could introduce serious errors into subsequent analyses. In the past few years, significant flow velocities in the upper solar atmosphere have been inferred from observations of emission lines originaing in the transition region (about 104–106 K) and corona. In this paper, three models of the solar atmosphere (quiet Sun, coronal hole, and a network model) are examined to determine if the emission expected from these model atmospheres could be produced from equilibrium ion populations when steady flows of several kilometers per second are assumed. If the flows are quasi-periodic instead of steady, spatial and temporal averaging inherent in the observations may allow for the construction of satisfactory models based on the assumption of ionization equilibrium. Representative emission lines are analysed for the following ions: C iii, iv, O iv, v, vi, Ne vii, viii, Mg ix, x, Si xii, and Fe ix–xiv. Two principle conclusions are drawn. First, only the iron ions are generally in equilibrium for steady flows of 20 km s–1. For carbon and oxygen, ionization equilibrium is not a valid assumption for steady flows as small as 1 km s–1. Second, the three models representing different solar conditions behave in a qualitatively similar manner, implying that these results are not particularly model dependent over the range of temperature gradients and electron densities thus far inferred for the Sun. In view of the flow velocities which have been reported for the Sun, our results strongly suggest caution in using the assumption of ionization equilibrium for interpreting spectral lines produced in the transition region.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
We identify the Balmer 9 and 11 lines of He ii at 959 Å and 942 Å in solar spectra. These lines are produced mainly by recombination following photoionization of He ii by coronal XUV radiation. From analysis of the line intensities, we confirm the theoretical model of Avrett et al. (1976), who found that an appreciable amount of He++ is present at temperatures of 1–2 × 104 K and that the anomalously strong He ii 304 line is produced primarily by collisional excitation. We also confirm the suggestion of Kohl (1977) that the photoionization-recombination process is more important in active regions than in the quiet Sun, and we find that the 304 line is produced largely by recombination in solar flares. 相似文献