共查询到20条相似文献，搜索用时 218 毫秒
1.
The calculation of a gas stream offers two modes of the stream. In any case the stream cannot be detected optically. The calculated line profiles caused by the disc are demonstrated.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986 相似文献
2.
Emission line spectra observed at the limb of the solar disc are presented for transitions of singly ionized silicon at 1816.93, 1817.45 and 1808.01. The profiles show self-reversals in the line cores. A non-LTE analysis for a simplified model of the silicon ion is presented and calculated line profiles are compared with the observations. The study indicates that some modification of the Vernazza et al. (1973) model of the solar chromosphere in the transition region is needed to reconcile the calculated and observed profiles. 相似文献
3.
James M. Ryan 《Solar physics》1986,105(2):365-382
Much of the evidence for second stage particle acceleration in solar flares lies in the temporal variation of solar X- and -ray emissions. However, the solar flare X- and -ray burst time-intensity profiles are governed not only by the production or acceleration of electrons and protons but by the propagation of these particles in the solar atmosphere. The effects of particle propagation on X-ray and -ray time profiles are illustrated and compared through the use of three models with the result that a variety of particle propagation schemes reproduce effects commonly associated with second stage acceleration. The first model is that of a closed uniform density trap. The other two models employ particle diffusion from a trap to denser regions of the solar atmosphere to produce the high energy radiation. These calculations show that delayed peaking of the photon flux with respect to particle production and reduction in the impulsiveness of the high energy emission is to be expected, effects commonly associated with second stage acceleration. Thus, well understood physical processes are capable of producing so-called time delays in the high energy emission independent of any delays produced by additional particle acceleration processes. Diagnostic differences between these models are also discussed. 相似文献
4.
Additional observations of He ii (304 Å) and Si xi (303 Å) were obtained from a high resolution rocket spectrograph flown on 30 August, 1973 and 20 January, 1975. The profile of the He ii (304 Å) line is everywhere clearly non-gaussian across the solar disk, except in bright active areas. Near the limb, the profile is distinctly reversed. The profile of the Si xi (303 Å) line is essentially gaussian for all regions across the solar disk. Measurements of the He ii/Si xi intensity ratio indicate that the average value of this ratio across the disk depends markedly on solar activity, being about 101 for a moderate level of activity and 301 for a quiet Sun. 相似文献
5.
Atmospheric models of He-peculiar stars: synthetic He I line profiles and absolute visual magnitudes
Rodolfo Vallverdú Lydia Cidale René Rohrmann Adela Ringuelet 《Astrophysics and Space Science》2014,352(1):95-102
We analyze the influence of magnetic pressure effects on the atmospheric structure of B peculiar type stars, as well as, on the emergent He?I line profiles and absolute visual magnitudes. We consider a photosphere in local thermodynamic and hydrostatic equilibrium. The hydrostatic equilibrium equation is modified to include the Lorentz force. Atomic occupational numbers are computed in LTE considering non-ideal effects in the gas equation of state. We depict the influence of a magnetic field on local He?I line profiles and discuss the effects of the helium abundance in magnetic B-type stars. The Lorentz force might explain local variations up to 7 % in the equivalent width of helium lines, while local enhancements of He chemical abundances would produce larger changes. To analyze the line variations in real stars we computed the net contribution of a bipolar magnetic field over the stellar disk. The resulting disk-averaged magnetic field predicts variations with the rotation phase up to 2–3 % in the line EWs for a dipolar magnetic field of 1000 G. 相似文献
6.
《天文和天体物理学研究(英文版)》2016,(9)
We present a catalog including 11 204 spectra of 10 436 early-type emission-line stars from LAMOST DR2, among which 9752 early-type emission-line spectra are newly discovered. For these earlytype emission-line stars, we discuss the morphological and physical properties of their low-resolution spectra. In this spectral sample, the Hα emission profiles display a wide variety of shapes. Based on the Hα line profiles, these spectra are categorized into five distinct classes: single-peak emission, single-peak emission in absorption, double-peak emission, double-peak emission in absorption, and P-Cygni profiles. To better understand what causes the Hα line profiles, we divide these objects into four types from the perspective of physical classification, which include classical Be stars, Herbig Ae/Be stars, close binaries and spectra contaminated by H II regions. The majority of Herbig Ae/Be stars and classical Be stars are identified and separated using a(H-K, K-W1) color-color diagram. We also discuss 31 binary systems that are listed in the SIMBAD on-line catalog and identify 3600 spectra contaminated by H II regions after cross-matching with positions in the Dubout-Crillon catalog. A statistical analysis of line profiles versus classifications is then conducted in order to understand the distribution of Hα profiles for each type in our sample. Finally, we also provide a table of 172 spectra with Fe II emission lines and roughly calculate stellar wind velocities for seven spectra with P-Cygni profiles. 相似文献
7.
P. Maltby 《Solar physics》1976,46(1):149-157
The wavelength dependence of filament features is studied, using high-resolution filtergrams taken at seven wavelengths in H. The observed contrast profiles are compared with profiles calculated on the basis of Beckers' (1964) cloud model. The deviation between observed and calculated profiles is used to suggest a progression among the observed profiles that depends on the height of the filament feature.Both upward and downward velocities are detected. The fine scale features in the filament and the corresponding velocity field vary with a time constant of a few minutes. 相似文献
8.
We briefly review the status of models of optical flare heating by electron bombardment. We recompute Brown's (1973a) flare model atmospheres using considerably revised radiative loss rates, based on Canfield's (1974b) method applied to , L, and H–. Profiles of are computed and compared with observation. The computed profiles agree satisfactorily with those observed during the large 1972 August 7 flare, if spatial and velocity inhomogeneities are assumed. The electron injection rate inferred from is one order of magnitude less than that inferred from hard X-rays, for this event. This may be due to either (1) the neglect of a mechanism that reduces the thick-target electron injection rate or (2) failure to incorporate important radiative loss terms. 相似文献
9.
Based on high resolution spectroscopic observations hydrogen-line profiles of six Bootis stars: HD 31295, HD 101108, HD 105058, HD 106223, HD 142703 and HD 183324 are presented. Peculiar line profiles with weak cores and broad but shallow wings are found for four of the stars. Influence of metallicity parameter [Z/H] and effective temperature on the appearance of the observed hydrogen lines is discussed. 相似文献
10.
Jay L. Inge 《Icarus》1973,20(1):1-6
Approximately 1300 measurements of the positions of 101 features in Jupiter's atmosphere have been made using blue-light photographs of the planet obtained by the International Planetary Patrol from 1970 to 1972. The longitudinal positions of features were read directly with orthographic grids superimposed on optically projected images of Jupiter. For each feature, least-squares linear fits were made on plots of the longitude measurements as a function of time, in order to derive drifts rates relative to System I or II. Drift rates were used to compute rotation periods; and, by combining the data from various latitudes, short-term rotation profiles were constructed. These short-term profiles are compared with a “mean” multiple-year profile, and differences in detail are evident. Slightly shorter rotation periods were found near the edges of the equatorial jet than at its center in 1970 and 1971. In 1972, one feature at +37° north was found to exhibit an abrupt change in period amounting to an increase of 95.1 seconds. 相似文献
11.
The oscillations of the half-width of the Ba II 4554 ? and Ca II 8542 ? spectral lines have been analyzed using observations at the base of solar coronal holes (CHs). The observed variations (~50 m ? for Ca II and ~4 m ? for Ba II) exceed considerably the thermal broadenings of these lines calculated from the measured intensity oscillations, suggesting their nonthermal nature. We point out a number of observational facts that hamper an unambiguous interpretation of the periodic Ba II and Ca II profile variations solely by the manifestation of torsional Alfve´ n waves in the lower solar atmosphere. 相似文献
12.
J. Jakimiec V. V. Korneev V. V. Krutov I. A. Zhitnik S. Pŀocieniak B. Sylwester J. Sylwester 《Solar physics》1975,44(2):391-401
High resolution profiles of the Mg xii 8.42 Å line in the solar X-ray spectrum were recorded from the Intercosmos 7 satellite. The Mg xii line intensity provides a sensitive indicator of the hot plasma content (T ? 3 × 106 K) in coronal condensations and X-ray flare volumes. The ratio of the line intensity to the intensity of the adjacent continuum has been used to compute approximate thermal models of the emitting regions. For all the investigated coronal condensations the temperature distribution of plasma has been found to be a function monotonically decreasing with temperature. But for some X-ray bursts there occurred a distinct excess of the hot plasma of temperature between 6–10 × 106K. FWHM values of the Mg xii line profiles have been used to estimate ion temperature in the emitting regions. 相似文献
13.
The influence of the chromospheric condensation on H line profiles for the thermal model of a solar flare has been empirically studied in this paper. The so-called thermal model here means that there is no temperature increase relative to the quiet-Sun chromosphere but with a chromospheric condensation in the lower part of its transition region, which case is assumed to represent the early stage of the impulsive phase. The main results include: when the temperature within the condensation region is assumed to be equal to that in front of it, the influence is to create an additional absorption profile overlapping on the original one; by increasing the condensation strength, the H line profile changes from a little line-center increase to broadened red asymmetry, then to the reversed red asymmetry, and finally to two independent absorption profiles; the thickness of the condensation determines the absorption of the additional profile; descending the transition region has no obvious effect on the basic characteristic of the H line profile except a little increase in the line center. Assuming that the temperature within the condensation is higher than that ahead of the condensation, the calculated H line profiles may be strong enough to be comparable with the observations. This means that if the condensation in the purely thermal model can reach a higher temperature, we may also use only thermal origin to explain a chromospheric flare.Alexander von Humboldt Research Fellow, on leave from Purple Mountain Observatory, Nanjing, China. 相似文献
14.
During the total solar eclipse of 11 June, 1983, an imaging dual-channel Fabry-Pérot interferometer was used to obtain line profiles simultaneously in the green 5303 Å [Fe xiv] and the red 6374 Å [Fe x] coronal lines at various positions in the corona. Extensive microdensitometry followed by multi-Gaussian curve-fitting analysis has resulted in the determination of coronal temperatures and velocity separations between different pockets of coronal gas in the line of sight over a large extent of the corona. Fewer high temperature zones are to be found in the corona of 1983 compared with our similar green-line measurements of the solar maximum corona of 1980. The data are consistent with a temperature maximum occurring at 1.2 R
, as found at the 1980 eclipse, but our new data are insufficient to observe farther out than this radius and so determine the position of a maximum. The velocity field in the corona at the 1983 eclipse is less structured compared with that at the 1980 eclipse and is mainly confined to the zone 20–30km s–1. 相似文献
15.
M. I. Stodilka 《Kinematics and Physics of Celestial Bodies》2011,27(4):161-174
An integrated effect of small-scale magnetic fields on online absorption coefficient is analytically estimated. The formation
of magnetically sensitive Fe I lines under the conditions of undisturbed solar photosphere in the presence of small-scale
magnetic fields is studied. It is shown that these fields can broaden the wings of magnetically sensitive lines. 相似文献
16.
F. Xiang E. Rudometkin E. Churazov W. Forman H. Böhringer 《Monthly notices of the Royal Astronomical Society》2009,398(2):575-582
We evaluate the impact of gas shock heating by a central active galactic nuclei (AGN) in M87 on the radial distribution of heavy elements. The propagation of a shock creates an inverted entropy profile, and the subsequent rearrangement of the gaseous atmosphere transports metal-rich gas from the central region to larger radii. We show that for the parameters of the relatively weak shock, recently found in M87, the abundance profile is not strongly affected by the redistribution of the shock heated gas (except for the very central region). At the same time, the energetics of the source is fully sufficient to broaden the metal distribution to match the observations, strongly suggesting that mechanisms other than direct shock heating must operate in cluster cores. The absence of a very strong abundance peak at the very centre of M87 suggests that the central AGN produces frequent (every few 10 Myr) and relatively weak outbursts, rather than rarer (every few 100 Myr) and an order of magnitude more powerful events. 相似文献
17.
The H line profile in a flare atmospheric model superposed by a spatially correlated velocity field is studied in detail in this paper. The computations are carried out with the assumption that the velocity field is represented by a Kubo-Anderson process. It is found that the shape and the intensity of the H line profile depend greatly on the parameters of the velocity field. The variation of the profile and its relative deviation with respect to different correlation lengths is more complex than in the case of absorption lines. It is also shown that such a profile cannot be matched by those produced in the usually-used micro- and macro-turbulent approaches, especially for the velocity field with an intermediate correlation length. The results imply that the flare atmosphere should be highly turbulent in order to explain the observed H line profile with only weak central reversal in the flare spectra. Particularly, the effects of meso-turbulent fields should be taken into account in order to improve the spectral diagnostics and modelling of the flare atmosphere. 相似文献
18.
A new determination of the granular and intergranular velocities is described, based on a new approach. The method involves measurement of the granule/intergranule contrast as a function of wavelength on a sequence of filtergrams taken with the CSIRO computer-controlled 1/8 Å filter in the photospheric line Fe i 6569.2. A procedure based on a simple but realistic morphological model of the granulation pattern is used to correct for spatial smearing. The effects of spectral smearing and of scattered light are also taken into account.The present observations reveal a one hundred per cent correlation between brightness and the sense of the vertical velocity component and thus demonstrate beyond doubt the convective origin of the granulation. The new measurements yield a value of 1.8 km s–1 for the difference between the upward and downward velocities associated with an average granule. With certain plausible assumptions this leads to granular and intergranular velocities of 0.7 km s–1 (upward) and 1.1 km s–1 (downward) respectively.Estimates are also obtained for the (true) central intensities and line broadening parameters of the line profile, separately for the average granule and intergranular lane. 相似文献
19.
A. J. Lim 《Astrophysics and Space Science》1995,233(1-2):273-280
In shocked media of high preshock ionisation, the lack of thermal contact between atoms in the neutral component of the gas can prevent the formation of a thermal equilibrium independent of the ionic component. The behaviour of the neutral gas in such a shock is dominated by the atomic processes driven by the postshock ionic component.A transport equation for the velocity distribution of the neutral gas is explicitly solved under the physical conditions of a 1D ionic shock transition. The resulting distributions are used to calculate predicted H
line emission from such a system. 相似文献
20.
Photographic observations of the time development of the profile of the L line of hydrogen during flares were obtained with the NRL spectrograph on ATM. The profiles for the 15 June, 1973 and 21 January, 1974 flares reported here cover both core and wings of the line. The time sequences begin before flare maximum, and continue well into the decay phase. Careful attention has been given to photometry and absolute calibration. In the case of the 15 June, 1973 flare, data are presented both first-order corrected and uncorrected for incomplete filling of the spectrograph slit by flaring material. Correction of the 21 January, 1974 flare was not possible. We discuss core symmetry and shift, and show that our observations imply integrated flare L/H intensity ratios within a factor of two of unity for these two flares. 相似文献