On the Line Formation in Stellar Magnetized Atmospheres

1 INTRODUCTIONIn the previous paper (on et al. 1999, hereafter Paper I), we investigated the wavelength-dependence of four colltribution functions (CFs) derived from dmerent formal solutions andreferring to different emergellt quantities in the unpolarized case. Because one cannot generallyassign a single formation region to the whole line band in a real stellar atmosphere, e.g., the solaratmosphere, instead, the line formation region can be defined as the layers deviating farthestfrom t…     

Chromospheric Internetwork Oscillations at Various Locations of the Quiet Sun

We analyze oscillation behaviours in chromospheric internetwork regions using spectral observations of the CⅡ1334 A line obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) aboard Solar and Heliospheric Observatory (SOHO). Three areas, 26 ×120arcsec2 each, at the various latitudes from the disk center to the north polar coronal hole, were rastered with a cadence of about 40-60 s in the solar minimum year. We obtained the time evolution of two-dimensional (2D) line intensity, continuum and line core shift. The continuum and the line shift show -3 min chromospheric oscillations in the internetwork regions underlying the coronal hole as well as at the disk center. We find that the CⅡ1334A line shift oscillates with an average speed of -1.7 km s-1, independent of the latitude, while its coherent scale decreases with latitude. On the other hand, the oscillation amplitude of the continuum around the 1334 A and the phase delay between the Doppler shift and continuum sli     

The Hβ Chromospheric Magnetic Field in a Quiescent Filament

We observed the line-of-sight magnetic field in the chromosphereand photosphere of a large quiescent filament on the solar disk on September 6, 2001 using the Solar Magnetic Field Telescope in Huairou Solar Observing Station. The chromospheric and photospheric magnetograms together with Hβ filtergrams of the filament were examined. The filament was located on the neutral line of the large scale longitudinal magnetic field in the photosphere and the chromosphere. The lateral feet of the filament were found to be related to magnetic structures with opposite polarities. Two small lateral feet are linked to weak parasitic polarity. There is a negative magnetic structure in the photosphere under a break of the filament. At the location corresponding to the filament in the chromospheric magnetograms, the magnetic strength is found to be about 40-70 Gauss (measuring error about 39 Gauss). The magnetic signal indicates the amplitude and orientation of the internal magnetic field in the filament. We discuss several possible causes which may produce such a measured signal. A twisted magnetic configuration inside the filament is suggested .     

Multi-wavelength Diagnostics of Bombardment by Non-thermal Particles in Solar Flares

Chromospheric lines, including Ha, Lyα, Lyβand CaⅡK, CaⅡ8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyαline calculation and a smaller intensity enhancement in the Ha line-centers is found than in the previous results of Fang et al.     

Cloud modeling of a network region in Hα

In this paper, we analyze the physical properties of dark mottles in the chromospheric network using two‐dimensional spectroscopic observations in Hα obtained with the Göttingen Fabry‐Perot Spectrometer in the Vacuum Tower Telescope at the Observatory del Teide, Tenerife. Cloud modeling was applied to measure the mottles' optical thickness, source function, Doppler width, and line‐of‐sight velocity. Using these measurements, the number density of hydrogen atoms in levels 1 and 2, total particle density, electron density, temperature, gas pressure, and mass density parameters were determined with the method of Tsiropoula & Schmieder (1997). We also analyzed the temporal behaviour of a mottle using cloud parameters. Our result shows that it is dominated by 3 minute signals in source function, and 5 minutes or more in velocity (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solar Activity and Classical Physics

1 INTRODUCTION The Sun is close enough to observe in some detail, and it shows that a star is more than the traditional stable self-gravitating thermonuclear body established half a celltury ago. For the fact is that out of sight beneath the visible surface the outward flow of heat from the thermonuclear core drives hydrodynamics that generates magnetic fields. It is the complicated dynamics of those magnetic fields that produces the modern mysteries of the active Sun. The…     

Magneto-induced Line Broadening of Magneto-sensitive Lines in Solar Magnetized Atmospheres

We analyze the spectral line broadening of those magneto-sensitive lines in solar magnetized atmospheres. The broadening at the line wings is due to the increase of the effective width of energy levels involved in Zeeman splitting, and the broadening at the line core also originated in Zeeman splitting under the condition that the Zeeman components are mixed. Therefore, the magnetoinduced or Zeeman broadening take effects on the whole line. The observed Stokes parameter data in a sunspot and outside it acquired by Solar Stokes Spectrum Telescope (S3T) are analyzed for the demonstration of this mechanism, and the Zeeman broadening rates are calculated for FeI6302.5 under some assumptions. Our result shows that the broadening is increased as the magnetic field strength becomes stronger, but the rate of increase at the line core is decreased as the field strength increases, while the rate at the wing does not show such an obvious regularity. The broadening is more effective in the line core than in the wings.     

A Study of Surges: II. On the Relationship between Chromospheric Surges and Coronal Mass Ejections

Liu et al. (Astrophys. J. 628, 1056, 2005a) described one surge – coronal mass ejection (CME) event showing a close relationship between solar chromospheric surge ejection and CME that had not been noted before. In this work, large Hα surges (>72 Mm, or 100 arcsec) are studied. Eight of these were associated with CMEs. According to their distinct morphological features, Hα surges can be classified into three types: jetlike, diffuse, and closed loop. It was found that all of the jetlike surges were associated with jetlike CMEs (with angular widths ≤30 degrees); the diffuse surges were all associated with wide-angle CMEs (e.g., halo); the closed-loop surges were not associated with CMEs. The exclusive relation between Hα surges and CMEs indicates difference in magnetic field configurations. The jetlike surges and related narrow CMEs propagate along coronal fields that are originally open. The unusual transverse mass motions in the diffuse surges are suggested to be due to magnetic reconnections in the corona that produce wide-angle CMEs. For the closed-loop surges, their paths are just outlining stable closed loops close to the solar surface. Thus no CMEs are associated with them.     

Physical Parameters of a Flare Derived from Multi-line 2D Spectroscopy

1 INTRODUCTIONGround-based observations of flares reveal relevant signatures at chromospheric leve1s,whose interpretation plays a crucial role in the identification of the fundamental physical pro-cesses responsible for the fiare phenomenon. A better understanding of the flare phenomenonrequires multi-line observations and 2D spectroscoPy which can reveal the dynamic behaviorof flares at different lOcations and at differeni depths.The most obvious feature of line profiles fOr solar flare…     

Multilevel Line Transfer with the Implicit Integral Method

Once the need for an iterative procedure in order to solve the problem of the formation of spectral lines in the case of a model atom with many energy levels, the sequel is to seek for the most effective form of such an iterative scheme. It is an almost universal is assumed within all the iterative methods for the solution of those radiative transfer problems, in which the transfer equations are coupled to the state of the matter, to take as the input of each step of iterations the values of the opacity coefficients obtained as a result of the previous one. This is, for instance, the procedure used to correct the temperature in the computation of stellar atmosphere models, or that to build the -operator (either the exact or the approximated one) within the Accelerated Lambda Iteration methods. Yet, if we assume, in order to solve the multilevel line transfer problem, that at each step of iterations the line opacities are known, we can express via the statistical equilibrium equations the populations of the energy levels - and consequently the source functions of the relevant spectral lines - as a linear function of the full set of the corresponding mean intensities of the radiation field. Once such linear forms for the source functions, we are able to solve without the need of any further approximation the radiative transfer equations for are obtained lines, now linearly coupled through the above linear forms of the statistical equilibrium equations. This is achieved by means of the Implicit Integral Method that we already presented in a series of previous papers.     

MSX mid-infrared imaging of massive star birth environments – I. Ultracompact H ii regions

In solar extreme ultraviolet spectra the He  i and He  ii resonance lines show unusual behaviour and have anomalously high intensities compared with other transition region lines. The formation of the helium resonance lines is investigated through extensive non-local thermal equilibrium radiative transfer calculations. The model atmospheres of Vernazza, Avrett & Loeser are found to provide reasonable matches to the helium resonance line intensities but significantly overestimate the intensities of other transition region lines. New model atmospheres have been developed from emission measure distributions derived by Macpherson & Jordan, which are consistent with SOHO observations of transition region lines other than those of helium. These models fail to reproduce the observed helium resonance line intensities by significant factors. The possibility that non-Maxwellian electron distributions in the transition region might lead to increased collisional excitation rates in the helium lines is studied. Collisional excitation and ionization rates are recomputed for distribution functions with power-law suprathermal tails that may form by the transport of fast electrons from high-temperature regions. Enhancements of the helium resonance line intensities are found, but many of the predictions of the models regarding line ratios are inconsistent with observations. These results suggest that any such departures from Maxwellian electron distributions are not responsible for the helium resonance line intensities.     

Distribution of Helical Properties of Solar Magnetic Fields

We summarize studies of helical properties of solar magnetic fields such as current helicity and twist of magnetic fields in solar active regions (ARs), that are observational tracers of the alpha-effect in the solar convective zone (SCZ). Information on their spatial distribution is obtained by analysis of systematic mag-netographic observations of active regions taken at Huairou Solar Observing Station of National Astronomical Observatories of Chinese Academy of Sciences. The main property is that the tracers of the alpha-effect are antisymmetric about the solar equator. Identifying longitudinal migration of active regions with their individual rotation rates and taking into account the internal differential rotation law within the SCZ known from helioseismology, we deduce the distribution of the effect over depth. We have found evidence that the alpha-effect changes its value and sign near the bottom of the SCZ, and this is in accord with the theoretical studies and numerical simulations. We discuss     

Formation of Solar Delta Active Regions： Twist and Writhe of Magnetic Ropes

We analyze the process of formation of delta configuration in some well-known super active regions based on photospheric vector magnetogram observations. It is found that the magnetic field in the initial developing stage of some delta active regions shows a potential-like configuration in the solar atmosphere, the magnetic shear develops mainly near the magnetic neutral line with magnetic islands of opposite polarities, and the large-scale photospheric twisted field forming gradually later. Some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, supposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and not entirely consistent with the relationship with magnetic shear in some delta active regions. (3) T     

Wavelet Analysis of the Schwabe Cycle Properties in Solar Activity

Properties of the Schwabe cycles in solar activity are investigated by using wavelet transform. We study the main range of the Schwabe cycles of the solar activity recorded by relative sunspot numbers, and find that the main range of the Schwabe cycles is the periodic span from 8-year to 14-year. We make the comparison of 11-year‘s phase between relative sunspot numbers and sunspot group numbers. The results show that there is some difference between two phases for the interval from 1710 to 1810, while the two phases are almost the same for the interval from 1810 to 1990.     

An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz

The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with zero right-handed circular polarization (RCP). We examine this structure in terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic field models. The raised electron density is found to be 1.4 × 1011 cm-3 at the chromosphere base.     

On the Positronium Continuum and 0.511 MeV Line in Solar Flares

We have studied the influence of the density of the annihilation region on the positronium continuum. A relation between the ratio 3γ/2γ and the densityis explicitly given, with which one can derive directly from the observed 3γ/2γ the density where the annihilation occurs. A unique solution may be found from the observed width of the 0.511MeV line. We applied the method to three flares observed by GRS/SMM. It is shown that due to the measuring uncertainties in the 0.511 MeV line width, we cannot distinguish a chromospheric source from a coronal source, though both accurately localized. To improve the measuring accuracy of the 0.511MeV line and the ratio 3γ/2γ will be an important step for a better understanding of the annihilation process in solar flares.     

Unusually Broadened Spectral Profiles Observed in Solar Prominences

After surveying the spectra of 39 prominences observed by the Multichannel Infrared Solar Spectrograph at Purple Mountain Observatory and the 25 cm coronagraph at the Norikura Solar Observatory, we found that about 28% of them show small spatial scale (6"- 8") and short time scale (tens of seconds to a few minutes), unusual large broadening and large shift velocities in spectral lines including Hα, Hβ, Hε, Ca Ⅱ H, Ca Ⅱ K, Ca2Ⅱ 8542 A, He Ⅰ D3 and HeⅠ 10830 A. We present in detail two typical events observed respectively on 2002 May 27 and 1981 August 2. The full-width at half maximum of the widest profile of the 2001 prominence is 1.8 A for Ha and 2.9 A for He I 10830 A, while that of the 1981 prominence is 5.3 A for Hβ, 3.6 A for Ca Ⅱ K, 4.0 A for Ca Ⅱ H and 2.8 A for He Ⅰ D3. Such broadenings generally occur at a level of several-thousand kilometres above the chromosphere. Further, most of these prominences manifest a rotation of (0.4-1.35) ×10-2 rad s-1 pointing to the Sun and large line     

Chromospheric changes in K stars with activity

We study the differences in chromospheric structure induced in K stars by stellar activity, to expand our previous work for G stars, including the Sun as a star. We selected six stars of spectral type K with  0.82 < B − V < 0.90  , including the widely studied Epsilon Eridani and a variety of magnetic activity levels. We computed chromospheric models for the stars in the sample, in most cases in two different moments of activity. The models were constructed to obtain the best possible match with the Ca  ii K and the Hβ observed profiles. We also computed in detail the net radiative losses for each model to constrain the heating mechanism that can maintain the structure in the atmosphere. We find a strong correlation between these losses and   S _Ca II  , the index generally used as a proxy for activity, as we found for G stars.