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1.
We have modeled stellar coronal loops in static conditions for a wide range of loop length, plasma pressure at the base of the loop and stellar surface gravity, so as to describe physical conditions that can occur in coronae of stars ranging from low mass dwarfs to giants as well as on a significant fraction of the Main-Sequence stars.Three alternative formulations of heat conduction have been used in the energy balance equation, depending on the ratio 0/L Tbetween electron mean free path and temperature scale height: Spitzer's formulation for 0/L Tless than 2 × 10–3, the Luciani, Mora, and Virmont non-local formulation for 0/L Tbetween 2 × 10–3 and 6.67 × 10–3 and the limited free-streaming formulation for 0/L Tlarger than 6.67 × 10–3.We report the characteristics of all loop models studied, and present examples to illustrate how the temperature and density stratification can be drastically altered by the different conductivity regimes. Significant differences are evident in the differential emission measure distribution vs temperature, an important observable quantity. We also show how physical conditions of coronal plasma, and in particular thermal conduction, change with stellar surface gravity.We have found that, for fixed loop length and stellar gravity, a minimum of loop-top plasma temperature occurs, corresponding to the highest value of base plasma pressure for which the limited free-streaming conduction occurs. This value of temperature satisfies the appropriate scalingT 10–9 L g, in cgs units.  相似文献   

2.
The brightness distribution of the Sun near the north pole at = 3 and 21 cm is obtained using the results of the partial eclipse of February 25, 1971. The solution obtained by expanding B (r) in orthogonal polynomials does not show any brightening at either frequency, but a sensible darkening. If this result is explained by the presence of spicules, the coronal emission must be negligible with respect to the emission coming from the transition region. This is possible, at = 21 cm, only if we assume the presence of a coronal hole near the pole.  相似文献   

3.
Computations of polarization and intensity of radiation from a unit stellar surface area are presented, as well as a study of the numerical characteristics of atmospheres — single-scattering albedo and the initial source function(), which define the polarization behaviour of atmospheres. The radiatively stable models of stellar atmospheres presented by Kuruczet al. (1974) and Kurucz (1979) have been used for calculations. Since the versus optical depth dependence is rather weak, it has been assumed that (=cost. With a fixed effective temperatureT eff maximum values of are characteristic of stars featuring the lowest surface gravity accelerationg. Among stars with radiatively stable atmospheres, maximum values of (=5000 Å) 0.4–0.6 are exhibited by supergiants withT eff=8000–20 000 K. The plot of () is characterized by discontinuities at the boundaries of spectral series for hydrogen and, sometimes, for helium. Maximum are attained in the Lyman region of =912–1200 Å, where can reach the value 0.7–0.9 for supergiants, this value being 0.3 for Main-Sequence stars. For stars withT eff 35 000 K, high values of also are attained for <912 Å. Within the infrared region, is always small because of bremsstrahlung absorption.A rapid growth of the source functionB with < typical for ultraviolet range (within the Wien part of spectrum), together with high values of results in the strong polarization of emission from a unit stellar surface element, sometimes exceeding the values for the case of a pure electron scattering. For longer wavelengths, where the limb-darkening coefficient is smaller, the plane of polarization abruptly turns 90° in the central parts of the visible stellar disk.  相似文献   

4.
Characteristics of the emission observed above the solar limb in four EUV lines, Sixii 499, Mgx 625, Neviii 770, and Ovi 1032 are discussed. The mean temperature of the corona derived from the ratios of the intensities of Sixii 499 and Mgx 625 is 1.8 million K. There do not appear to be significant temperature differences in regions with low EUV intensities and those with high EUV intensities, suggesting that the EUV emission from the lithium-like ions depends primarily on the integral of n e 2 along the line of sight.The EUV data are compared with K-coronameter measurements in order to yield new estimates of the abundances of Si, Mg, Ne and O relative to hydrogen. Within the uncertainties of the analysis, these coronal abundances are in agreement with the corresponding photospheric values.  相似文献   

5.
Six neutral atomic oxygen Fraunhofer multiplets were observed at nine disk positions at Sacramento Peak Observatory. I filtered the data, corrected them for the instrumental profile and obtained equivalent widths.The equation of transfer for a plane-parallel atmosphere is solved to yield an expression for the equivalent width of a line or multiplet as a function of disk position; line source function, S L, and relative population of the lower energy level of the transition. Comparison with the observations gives the abundance, average levels of formation of the lines and S L.The numerical results show that the weak lines are formed either in L.T.E. or pure scattering (i.e., S L B v (T e) J c), but for 7770 Å S L/B (T e) 0.6 ± 0.1 at c = 0.1. An analysis of the central intensities of 7770 Å yields essentially the same results. The results for 8446 Å are not reliable due to a possible blend with an iron line. The abundance of oxygen in the photosphere may be slightly less than that found by previous investigators.The results are consistent with the assumption that all levels of photospheric oxygen are populated as in L.T.E. with the exception of 35S, which is overpopulated by approximately 50% at c = 0.1. The overpopulation may be due to the metastability of this level.Based on National Center for Atmospheric Research Cooperative Thesis No. 9.  相似文献   

6.
In this paper we study the far-UV as well as the UV spectrum of the spectroscopic binary system SZ Psc in the wavelength ranges 1235–1950 Å and 2710–3090 Å, respectively, from spectra obtained with the International Ultraviolet Explorer (IUE). The UV spectrum of SZ Psc is mainly an emission spectrum. The short wavelength region includes emission lines formed from the low chromosphere to the transition region (e.g., Siiv,Civ, andNv) and also a deep and broad absorption line of Feii.The Mgii[1] resonance doublet at about 2800 Å presents a P Cygni profile and a multiple structure with two emission and two absorption satellite components. We also present the emission measure diagram in the temperature region 4.4T e <53.  相似文献   

7.
Spectral scans of the coma of comet P/Crommelin 1818. I have been obtained in the wavelength range 3200–6500 Å. Strong emission features of CN(3883 Å) and C2 Swan bands (4695, 5165, and 5538 Å) have been identified. Some weak emission features of CH(3890 Å), C3(4050 Å), CN(4200 »), and C2 + CH(4358 ») were also detected. Sodium was found to be absent in this comet. An estimate of CN and C2 abundances has been made and their production rate have been derived.  相似文献   

8.
A one-zone model for the late time SN II energized by the radioactive decay56Ni–56Co–56Fe is presented. The model succeeds in reproducing for the late time evolution of H and [Oi] 6300 emission lines in SN1970g for the reasonable set of parameters: mass of ejecta 4M , boundary velocityv 0=4000 km s–1 and amount of56NiM Ni=0.02M . However, a one-zone model does not account for the late time continuum. In the case of SN1980k the radioactive model fits H and [Oi] 6300 emissions att250 day satisfactory but fails at very late time, e.g.,t=670 day when the predicted value of the ratioL(H)/L(6300) is two orders of magnitude smaller than the observed one. We suggest that the strong H emission in SN1980k on the 670th day is due to the interaction of the supernova envelope with the pre-SN wind. The radioactive model for the late time SN II predicts strong Mgii 2800 line and detectable Hei 10830 line in emission and absorption.  相似文献   

9.
The excitation of the 2s22p2 ground configuration of Caxv is calculated for coronal densities and temperatures. The calculations include electron and proton excitation of the forbidden transitions and electron excitation via the first excited (2s2p3) configuration. It is shown that measurements of the line intensity ratio I( 5694)/I( 5446) are in good agreement with the predictions. The line to continuum observations for limb flares and coronal condensations are discussed. It is suggested that the calcium abundance in condensations is enhanced owing to diffusion processes.Present address: Department of Astronomy, University of Texas, Austin, Texas, U.S.A.  相似文献   

10.
The Sun-Earth-Moon system is modeled by the restricted problem of three bodies, and the curves of zero velocity are used to define the limits of stability of the Moon's orbit about the Earth. By holding the relative distances fixed, and maintaining the circular velocities of the Earth and Moon while their masses are varied by a common factor (=m E/m E=m M/m M), it is found that the possibility of the Moon leaving Earth orbit and orbiting the Sun exists for the range of values 0.005<<0.4.  相似文献   

11.
A high resolution spectrogram of the Mg b2 line from the quiet Sun disc centre is subjected to a coherence analysis. We find that the coherence between intensity fluctuations in the continuum and the wings of the line breaks down at a distance = 0.35 Å from line centre. From this and the r.m.s. intensity contrast as a function of we are led to the following simple model of temperature fluctuation T in the solar photosphere: A lower part (below 50 km, or 5000 > 0.25) with strongly inward increasing T and an upper part (above 50 km) with constant T = 75 K. The two parts are supposed to fluctuate incoherently.Mitteilungen aus dem Kiepenheuer Institut Nr. 166.  相似文献   

12.
Heinz Neckel 《Solar physics》1996,167(1-2):9-23
The limb-darkening data published by Neckel and Labs (1994) (5th-order polynomials P 5(), = cos ) are used to represent the limb darkening by the functions L n(), proposed first by Kourganoff (1949a). When plotted against wavelength, the coefficients of these functions show a rather low scatter and appear to be linear functions of either –1 or #x2212;5.  相似文献   

13.
Slitless flash spectrograms in heights below 8000 km above the solar limb were obtained by the University of Kyoto Expedition at Atar, Mauritania. The integrated intensities of Fexiv 5303, Fex 6374, Fexi 7892, and the continuum are measured as a function of height above the solar limb at eleven points (P.A. = 284–300°) around the third contact point. It is found that a significant amount of the emission in Fex 6374 originates in chromospheric levels well below 8000 km. This implies that the interspicular region of the chromosphere is occupied by coronal material. The average values of the electron temperature and the electron density in the interspicular region are derived from the Fex 6374 and the Fexi 7892 intensities on the assumption of spherical symmetry: T e = 0.9–1.1 × 106 K and N e = 9–10 × 108 cm–3. The intensity variations of the coronal lines and the continuum with position angle are also studied. Strong correlations between Fexiv 5303 and the continuum and between Fex 6374 and Fexi 7892 are found. From the Fex 6374 intensities it is inferred that there is a density fluctuation in the innermost corona by at least a factor of two.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 271.  相似文献   

14.
We present new images of the well-known molecular outflow and Herbig-Haro complex L 1551-IRS 5. Deep, high-resolution images of the central region of the flow in [SII] 6716,6731 and H (6565 Å) are complemented by a mosaic of much of the CO outflow in H2 v=1-0 S(1). While the optical data trace the intermediate-to-high excitation shocks in the flow (v shock > 30 – 50 km s–1), the near-IR data reveal the lower-excitation, molecular shocks (v shock 10–50 km s–1). In particular, the H2 data highlight the regions where the flow impacts and shocks ambient molecular gas.  相似文献   

15.
On the slit spectrogram obtained at the 1970 eclipse in Mexico, the intensities of four coronal lines (Nixiii 5116, Fexiv 5303, Fex 6374, and Nixv 6702) and the continuum were measured as a function of distance along the slit. It is found that there exist a lot of fine fluctuations both in the lines and in the continuum intensities superposed on a large scale formation. The correspondence of such fluctuations between the continuum and the lines is good, with the exception of the line 6374 which shows a peculiar fluctuation. It is shown that the intensities of the three lines 5116, 5303, and 6702 seem to be proportional to the square of the continuum intensity while the 6374 line intensity may be proportional to the fourth power or more.  相似文献   

16.
In this paper, a technique of recursive analysis is developed for the integral transform A of the exponential integral functionsE n which is denoted as n (). The main result of this analysis enables us to establish a two-term recurrence formula for n (0) and a three-term recurrence formula for n (); 0. A computational algorithm based on these formulae is also constructed and its numerical results forn=2(1)25 are presented to 15-digit accuracy.  相似文献   

17.
Term values for the 1s 2s states of H– are calculated with the use of simple eigenfunction approximations constructed on the basis of available Hartree-type functions for the 1s 2 and 2s 2 states of the ion. The results seem to support a tentative identification of the interstellar diffuse absorption bands at 4890 and 6180 as due to negative hydrogen.  相似文献   

18.
Center-to-limb measurements of the Ca i 6573 intercombination line and the Ca ii 7324 forbidden line are compared with synthetic profiles based on a simple representation of the non-LTE Ca-Ca+ ionization equilibrium. The effects of photoionizations from low lying excited states of neutral calcium are found to reduce the sensitivity of the 6573 center-to-limb behavior as a thermal structure diagnostic. The synthetic center-to-limb behavior is also sensitive to uncertainties in the nonthermal broadening. Nevertheless, the measured center-to-limb behavior of 6573 favors a cool photospheric model similar to the Vernazza, Avrett, and Loeser model M over hotter models based on the Ca ii K wings. The non-LTE calcium abundance obtained from the disk center equivalent widths of 6573 and 7324 using the best fit model is A Ca2.1±0.2 × 10-6 (by number relative to hydrogen). Applications of these lines as diagnostics of the Ca-Ca+ ionization equilibrium in other stars are briefly discussed.Visiting Astronomer, Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.  相似文献   

19.
S. N. Osipov 《Solar physics》1985,102(1-2):29-32
The blanketing effect for the solar disc center and its value near the limb (cos = 0.23) are obtained for the rocket ultraviolet region using the Harvard center and limb spectra. The value of for the disc center appears to be 0.67 (on average) relative to the quasicontinuum. The essential decrease of towards the limb is also revealed.  相似文献   

20.
We report on a new ESB source, as defined by Allenet al. (1991), with Wolf-Rayet (WR) bands in its optical spectrum. The WR bump at 4605-4686 is detected. The bump consists of broad HeII 4686, NV4605-4619, NIII4634-41, and possibly, CIII4647-52 emission. The narrow nebular lines are clearly discernable on our spectrum. The number of WR stars derived from the luminosity of HeII4686 is about 8100. The oxygen abundance is about 9.06×10–4, greater than the solar value.  相似文献   

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