1979年9月19日3B级耀斑光谱分析:金属线的不对称性和线心位移

本文研究了1979年9月19日3B级耀斑金属谱线的不对称性和线心位移.结果表明:强金属线红不对称占主要地位,少数弱金属线也有蓝不对称存在;不对称程度极大发生于线心强度极大之前;不对称性有时可由蓝变红;不管不对称程度如何,线心的位移却很小,总体上仅表现为极微弱的蓝移.文中认为,耀斑爆发时色球压缩区的向下扩展及由此引起的温度极小区上下的物质运动这个动力学过程可基本解释这些观测现象.金属线的研究是对H_α和CaIIK线光谱研究的补充.     

On a possible explanation of chromospheric line asymmetries of solar flares

We discuss the relationship between the chromospheric downward motions and the line asymmetries in solar flares by using a simple model. It is found that both the blue asymmetry and red asymmetry of the H line can be caused by downward motions, as long as the moving material is confined to different heights in the chromosphere. The Ca ii K line, however, mainly shows a red asymmetry. The results can qualitatively explain some observations.     

Caii K line asymmetries in two well-observed solar flares of October 18, 1990

Two-dimensional evolutions of two flares of October 18, 1990 have been well observed in the Caii K line with a CCD camera at Norikura station of National Astronomical Observatory in Japan. There are two common characteristics for the flares: 3 - 5 min before the impulsive phase, the heating already begins at the footpoints of the flares, but no asymmetry in line emission has been detected. After the onset of the impulsive phase, Caii K line emission at the footpoints shows strong red asymmetry, with the maximum asymmetry occurring at the same time as the peak of the radio bursts. The maximum downward velocity is about 30 50 km s^–1. For flare 1, blue and red asymmetries were observed in two sides of the footpoint area. They developed and attained a maximum nearly at the same time and the inferred Doppler velocities are comparable (30 40 km s^–1). This implies that two mass jets started from a small region and ejected along a loop but in opposite directions with roughly equivalent momentum. A possible mechanism has been discussed.     

On the occurrence of blue asymmetry in chromospheric flare spectra

We present observations of optical spectra of a flare in which blue line asymmetry was seen for more than 4 min close to the flare onset. The maximum blue asymmetry coincided with the maximum of a hard X-ray and microwave burst. We discuss possible interpretations of the blue asymmetry and conclude that the most plausible one is electron-beam heating with return current. Although this process predicts downflows in the lower transition region and upper chromosphere, its ultimate effect on the line profiles can be blue asymmetry: the upper layers moving away from us absorb the radiation of the red peak thus lowering its intensity in comparison to the blue one.     

A study on the Hα line asymmetry of chromospheric flares

The asymmetry of H_α line profiles is an important characteristic in the spectral observations of chromospheric flares, as well as one of the important observational facts of the dynamical process in solar flares. Based on the observed data of the solar spectrograph of Purple Mountain Observatory, some typical asymmetric H_α line profiles are presented. Taking the effects of the nonthermal excitation and ionization of hydrogen atoms into consideration, the asymmetry characteristics of H_α line profiles under different atmospheric models are calculated, and a semi-empirical study on the observed line profiles is thereby made. The results indicate that the downward motion of the chromospheric condensation region can cause the red and blue asymmetries of H_α spectra. We have tried to reproduce the observed asymmetry characteristics in specific flares. It is found that, besides the energy flux of nonthermal particles, the magnitude of spectral index and the height of the velocity field affect the line profile, the flare's atmospheric background model also has some influence on the line profile.     

Short period line profile and light variations in the Be star ω Orionis

We present the results of a multisite spectroscopic and photometric campaign on the Be star ω Orionis. From the photometry and radial velocity variation of several spectral lines, we confirm that the star is a variable with period     . Only one period can be extracted from both the photometric and radial velocity observations. We find that the projected rotational velocity from the helium lines     is considerably smaller than from the metal lines     . The line profiles show an excess absorption feature moving from blue to red for half the period and from red to blue for the other half of the period. Another excess absorption feature moves exactly out of phase. The excess absorption features are present in photospheric lines as well as in lines which are significantly affected by circumstellar material, such as H β . From this we conclude that the periodic variations are most probably associated with corotating circumstellar material.     

Flare asymmetry as seen in offband Hα filtergrams

Narrow-band Hα filtergrams at ±1 Å and ±2 Å from the line center were used to study the asymmetry of flares. Of the 60 flares studied, 92% show red asymmetry while 5% show blue asymmetry. Typically, the filtergrams show a striking dominance of the red wing over the blue wing from onset until late in the decay phase. The difference in intensity of the flare emissions is further augmented by the extensiveness of the emission area in the brighter wing. New kernel-like emissions were often found many minutes after the flare maximum. Spatially they are displaced from the previous kernels. The late emissions show the same asymmetry as that of the earlier part of the flare.     

A study on the asymmetries in flare lines

We calculate the H and CaII K profiles under different velocity models with chromospheric condensations and investigate the effect of the velocity in different layers on the profiles from a semi-empirical standpoint. The results show that the short-time, H blue asymmetry in the early stage of the flare can be caused by condensations in the transition zone, that the subsequent red asymmetry is the result of the downward motion of matter in the upper chromosphere, while the later CaII K asymmetries can be explained by downward velocities of 10–20 km/s in the middle and lower chromosphere.     

High-resolution spectral observation during the impulsive phase of a flare

High-resolution observations of the flare on October 21, 1989 were made with the Domeless Solar Telescope of the Hida Observatory. The following new results have been obtained: (a) during the impulsive phase of the flare, the spectral line asymmetry has spatial fine structures of 1–2; (b) for several points in the flare region the line profile alternatively changes between blue asymmetry and red asymmetry within a few seconds. A possible explanation has been suggested.     

FLARE MULTI-LINE 2D-SPECTROSCOPY

A small flare was observed at the Teide Observatory on October 5, 1994. Simultaneous data were obtained at the German Vacuum Tower Telescope (VTT) with the MSDP spectrograph providing high-resolution imaging spectroscopy in two chromospheric lines, and the Gregory Coudé Telescope (GCT) providing information about the magnetic field. Basic flare characteristics are:The area of the flare kernel ( 2 x 2 arc sec) is similar in H and Caii 8542 Å.The early phase of the flare is characterized by a blue asymmetry in H and a red one in Caii 8542 Å line.The evolutions of line profiles are different; the red asymmetry observed in the Caii line is detected a few seconds later in H.The maximum asymmetry of the Caii line does not coincide with the maximum brightness.The flare occurs in a region of a strong horizontal gradient of the line-of-sight component of the magnetic field.Brightness and asymmetry in H and Caii are discussed in the context of standard flare models and velocity fields. Our observations suggest that a magnetic reconnection could occur at low levels of the solar atmosphere.     

Spectroscopic studies of the classical Cepheid ζ Gem: Analysis of the velocity field in the atmosphere and manifestation of the presence of a circumstellar envelope

Based on five high-resolution spectra in the range 5625–7525 ?A taken in 1995 and covering the ascending branch of the light curve from minimum to maximum, we have performed spectroscopic studies of the classical Cepheid ζ Gem. The atmospheric parameters and chemical composition of the Cepheid have been refined. The abundances of the key elements of the evolution of yellow supergiants are typical for an object that has passed the first dredge-up: a C underabundance, N, Na, and Al overabundances, and nearly solar O and Mg abundances. We have estimated [Fe/H] = +0.01 dex; the abundances of the remaining elements are also nearly solar. The metal absorption lines in all spectra show a clear asymmetry and the formation of secondary blue (B1 and B2) and red (R1 and R2) components, just as for the Cepheid X Sgr. The Hα absorption line is also split into blue (B) and red (R) components with different depths changing with pulsation phase. To analyze the velocity field in the atmosphere of ζ Gem, we have estimated the radial velocities from specially selected (with clear signatures of the B1, B2, R1, and R2 components) absorption lines (neutral atoms and ions) of metals (38 lines) and the B and R components of the Hα line. Analysis of these estimates has shown that their scatter is from ?22 to 36 km s^?1 for all pulsation phases but does not exceed 35–40 km s^?1 for each individual phase, while it does not exceed 22 km s^?1 for the Hα line components. The radial velocity estimates for the metal lines and their B1 and B2 components have been found to depend on the depths, suggesting the presence of a velocity gradient in the atmosphere. No significant difference in velocities between the atoms and ions of the metal lines is observed, i.e., there is no significant inhomogeneity in the upper atmospheric layers of the Cepheid. Since the averaged radial velocity estimates for the cores of the metal lines and their B1 and B2 components change with pulsation phase and coincide with those for the B component of the Hα line, they are all formed in the Cepheid’s atmosphere. The formation and passage of a shock wave due to the κ-mechanism at work can be responsible for the stronger scatter of the B1 and B2 components in their velocities at phases after the Cepheid’s minimum radius. The averaged velocities of the R1 components also change with pulsation phase and differ only slightly from the remaining ones. On the other hand, the mean velocity estimate for the R component of the Hα line at all phases is +32.72 ± 2.50 km s^?1 and differs significantly from the bulk of the velocities, suggesting the formation of this component in the envelope around the Cepheid. The unusual behavior of the mean velocities for the R2 components of the metal absorption lines can also point to their formation in the envelope and can be yet another indicator of its presence around ζ Gem.     

Broad reprocessed Balmer emission from warped accretion discs

Double-peaked broad emission lines in active galactic nuclei are generally considered to be formed in an accretion disc. In this paper, we compute the profiles of reprocessing emission lines from a relativistic, warped accretion disc around a black hole in order to explore the possibility that certain asymmetries in the double-peaked emission-line profile which cannot be explained by a circular Keplerian disc may be induced by disc warping. The disc warping also provides a solution for the energy budget in the emission-line region because it increases the solid angle of the outer disc portion subtended to the inner portion of the disc. We adopted a parametrized disc geometry and a central point-like source of ionizing radiation to capture the main characteristics of the emission-line profile from such discs. We find that the ratio between the blue and red peaks of the line profiles becoming less than unity can be naturally predicted by a twisted warped disc, and a third peak can be produced in some cases. We show that disc warping can reproduce the main features of multipeaked line profiles of four active galactic nuclei from the Sloan Digital Sky Survey.     

Variations of UV chromospheric emissions during a pulsation period ofϱ Puppis (HD 67523)

The peculiar δ Del-variable ? Puppis (F6IIp) has been analysed on nine UV high-resolution spectra in the region of Mgii h- and k-lines. This analysis has shown: (1) The Mgii emission is present during the whole pulsation period and increases with increasing luminosity. Maximum emission fluxes seem to occur at phases 0.96–0.12. (2) The phase shift between intensity maxima of Caii and Mgii chromospheric emissions is probably about 0.26. Moreover, it seems that the phase shift between ? Pup and the Cepheid β Dor is longer for the Mgii emission (～0.44) than for the Caii one (～0.27). (3) Violet-red asymmetries are present in emission components. Moreover, the violet component K1V has always an intensity higher than the red one K1R. (4) The averaged radial velocity (RV) curve obtained from three metallic lines is in agreement with that obtained in the optical region. The RV curves of red emission and absorption components are rather similar to that of the metallic lines. Near the minimum of this RV curve, the chromospheric emissions show an intensity enhancement with a negative phase shift similar to that of light curve (～?30 deg). (5) A model with an emitting extended atmosphere around the star is proposed to explain an emission like feature in the self-reversed absorption component K3 and in K1.     

A possible E-W asymmetry of the coronal emission line intensities and K-corona brightness

The analysis of the daily measurements of the coronal green and red line intensities as well as the K-corona brightness, which have been collected by the Pic-du-Midi Observatory, for the time period 1944–1974, has revealed some very interesting features. North-South (N-S) asymmetries for all these coronal intensities are confirmed again for this time period. The main point of this analysis is a strong evidence of longitudinal distribution of the coronal intensities as derived from the data record. In our effort to confirm this asymmetry, we have examined the yearly and monthly distribution of the asymmetry coefficient in each solar quadrant showing that the northeast (NE) quadrant appears the most active of all. We have also examined the intensity ratios measured at the East and West solar limbs which is continuously greater than the unit.A seasonal variation of this ratio has also been reported with a maximum during the winter period and a minimum during the summer period.     

UV and optical emission lines from the z∼ 2.6 radio galaxy 0828+193: spatially resolved measurements

We present an investigation into the spatial variation of the rest-frame ultraviolet (UV) and optical line and continuum emission along the radio axis of the z ∼ 2.6 radio galaxy 0828+193, using long-slit spectra from the Keck II and Subaru telescopes. Line brightnesses, line ratios and electron temperatures are examined, and their relationship with the arm-length asymmetry of the radio source is also investigated. We find that on the side of the nucleus with the shortest radio lobe, the gas covering factor is higher, and the ionization parameter is lower. The contrasts in environmental density required to explain the asymmetries in the line brightness and the radio arm-length asymmetries are in fair agreement with each other. These results add further weight to the conclusion of McCarthy, van Breugel & Kapahi – lobe distance asymmetries in powerful radio sources are the result of an asymmetry in the environmental density.
We also note that the brightness of both the UV and optical continuum emission shows a similar spatial asymmetry to that shown by the line emission. While the UV continuum asymmetry can be wholly explained by the expected asymmetry in the nebular continuum, the optical continuum asymmetry cannot. We argue that, at least at optical wavelengths, the starlight and/or the scattered light must also be strongly spatially asymmetric.     

耀斑色球压缩区的传播与谱线的不对称性

色球压缩区是耀斑大气动力学过程的一个基本特征，是产生色球谱线红不对称性的基础。本文基于压缩区从大气高层向低层传播的理论公式，在二种不同情况下，计算得到了压缩区内物质运动速度随高度和时间的变化．结果表明，色球蒸发区压力增量Δｐ为常数时压缩区之寿命比压缩区波阵面后的压力ｐ２为常数时要长得多，这就大大缓解了以往谱线不对称性的延续时间的理论值比观测值小的矛盾。形成高度不同的谱线具有不同程度的不对称性这一观测现象也同色球压缩区的传播特性相一致。     

North-South asymmetry in sudden disappearances of solar prominences

This paper presents the results of a study of the N-S asymmetry in sudden disappearances (SD) of solar prominences during solar cycles 18–21, obtained as a part of a more extensive research on SD and reappearances during years 1931–1985 (Ballester, 1984). As can be seen, the N-S SD asymmetry curve is not in phase with the solar cycle and peaks about the time of solar minimum, the asymmetry reverses in sign during the solar maximum, being, this change of sign, coincident with the reversal of the Sun's magnetic dipole. The SD asymmetry curve can be fitted by a sinusoidal function with a period of eleven years. On the other hand, the SD asymmetry curve shows a strong coincidence with the N-S asymmetries presented by other solar activity manifestations as studied by different authors.     

3D simulations of rotationally-induced line variability from a classical T Tauri star with a misaligned magnetic dipole

We present 3D simulations of rotationally induced line variability arising from complex circumstellar environment of classical T Tauri stars (CTTS) using the results of the 3D magnetohydrodynamics (MHD) simulations of Romanova et al., who considered accretion on to a CTTS with a misaligned dipole magnetic axis with respect to the rotational axis. The density, velocity and temperature structures of the MHD simulations are mapped on to the radiative transfer grid, and corresponding line source function and the observed profiles of neutral hydrogen lines (Hβ, Paβ and Brγ) are computed using the Sobolev escape probability method. We study the dependency of line variability on inclination angles ( i ) and magnetic axis misalignment angles (Θ). We find the line profiles are relatively insensitive to the details of the temperature structure of accretion funnels, but are influenced more by the mean temperature of the flow and its geometry. By comparing our models with the Paβ profiles of 42 CTTS observed by Folha & Emerson, we find that models with a smaller misaligngment angle  (Θ < ∼15°)  are more consistent with the observations which show that majority of Paβ are rather symmetric around the line centre. For a high inclination system with a small dipole misalignment angle  (Θ≈ 15°)  , only one accretion funnel (on the upper hemisphere) is visible to an observer at any given rotational phase. This can cause an anticorrelation of the line equivalent to the width in the blue wing  ( v < 0)  and that in the red wing  ( v > 0)  over half of a rotational period, and a positive correlation over the other half. We find a good overall agreement of the line variability behaviour predicted by our model and those from observations.     

Dynamical processes in the June 26, 1999 flare

The evolutionary and spatial characteristics of the motions in the flaring chromosphere of a 2B/M2.3 flare are investigated by analyzing the asymmetry in the H_α profiles. The possibility of reconciling the results of observations with the theory of chromospheric evaporation is considered. The spectroscopic H_α observations of the flare performed with the KG-2 CrAO coronagraph with a temporal resolution of 5–10 s and a spatial resolution as high as 1 arcsec cover all stages of flare development. The following results have been obtained: (1) The H_α profile asymmetry is a general characteristic of the flare emission irrespective of its intensity and its belonging to different structural features and phases of flare development. (2) Most of the H_α emission profiles in flare regions exhibit a red asymmetry. However, a blue asymmetry was observed in small local regions at all stages of flare development. (3) A red asymmetry that appeared before the onset of the impulsive phase and persisted after its end was observed at the sites of main energy release, i.e., the energy source responsible for the dynamical processes in the flare came into operation earlier and existed longer than the HXR emission. (4) The asymmetry pattern changed with flare phase: the red wing intensity dominated in the pre-impulsive phase and at the onset of the impulsive and gradual phases (while the line core was unshifted or slightly shifted). At the maximum of the impulsive phase, the nearly symmetric profiles with extended wings were redshifted as a whole, i.e., the entire emitting volume moved down with a velocity of several tens of km/s. This type of asymmetry cannot be explained by the dynamical model of chromospheric condensation (Canfield and Gayley 1987). (5) The H_α profiles show no evidence of chromospheric heating by a beam of nonthermal electrons during the impulsive phase (Canfield et al. 1984). (6) The lifetime of the downflows and the change in their velocities with time are inconsistent with the dynamical model of chromospheric condensation (Fisher 1989). (7) The morphological features of the velocity field are also inconsistent with the theory of chromospheric evaporation, because the highest differently directed velocities were detected at the flare loop tops, not at the sites of main energy release. We conclude that the investigated flare shows spectral features that are inconsistent with the standard chromospheric evaporation model.     

Proper Motions and Velocity Asymmetries in the RW Aur Jet

We present adaptive optics spectro-imaging observations of the RW Aur jet in optical forbidden lines, at an angular resolution of 0.4″. Comparison with HST data taken 2 yr later shows that proper motions in the blueshifted and redshifted lobes are in the same ratio as their radial velocities, a direct proof that the velocity asymmetry in this jet is real and not an emissivity effect. The inferred jet inclination to the line of sight is i = 46±3°. The inner knot spacing appears best explained by time variability with at least two modes: one irregular and asymmetric (possibly random) on timescales of ≤3–10 yr, and another more regular with ?20 yr period. We also report indirect evidence for correlated velocity and excitation gradients in the redshifted lobe, possibly related to the blue/red velocity and brightness asymmetry in this system.