Damping constant and turbulence in the solar atmosphere

In the region of the formation of weak and medium-strong lines, the microturbulence increases with height (V _ver=0.7–0.9 km s^-1, V _hor= 1.1–1.5 km s^-1), the macroturbulence decreases (V _ver=1.6–1.4 km s^-1, V _hor= 2.4–1.5 km s^-1), and the total velocity field (vertical component) is depth-independent (1.7 km s^-1). The empirical damping constants for Fe, Ti, Cr, Ni lines are equal 1.3₆, 1.7₆, 1.6₆, 1.6₆, respectively. The correlation length (the Kubo-Anderson process has been used) in the solar photosphere is 520–550 km.     

The NLTE Formation of Iron Lines Used in Solar Polarimetry

We study in some detail one-dimensional NLTE effects in solar Fei lines. The lines selected are frequently used in solar polarimetry, and also in studies of line asymmetries and for abundance determinations. Our model atom for Fei–Feii–Feiii is realistic: it takes account of multiplet structure and it includes over 200 bound–bound and bound–free transitions in detail. We use very efficient iterative methods for the self-consistent solution of the kinetic and radiative transfer equations (Auer, Fabiani Bendicho, and Trujillo Bueno, 1994). We have applied these fast methods of solution because they are suitable for the investigation of 2D and 3D NLTE transfer effects with multilevel atoms, which constitutes the next step of our ongoing research project on the iron line formation problem.     

On the asymmetry of selected Fraunhofer lines

An analysis is made of the asymmetry of Fraunhofer lines observed with the double-pass monochromator of the horizontal solar telescope ASU-5 of the Main Astronomical Observatory of the Ukrainian Academy of Sciences. The conclusion is that the character of macromotion in the radial direction varies with height; in a tangential direction the motions at different depths are homogeneous. The asymmetry of weak lines is due to convection rather than to wave motions.     

On the possible mechanism of formation of emission rim in hydrogen filaments

Hα filtergrams of the chromosphere show an emission rim in many hydrogen filaments. We suppose that formation of this rim is due to photospheric radiation reflected by the filament in the direction of the chromosphere. The calculations show that: (1) the maximum contrast of the rim relative to the undisturbed chromosphere amounts to 1.4; (2) the larger the optical thickness of the filament and the closer to the solar limb it is situated, the brighter and wider is the rim; (3) the rim was not observed in filaments whose heights exceeds 10000km above the chromosphere. These results are in close agreement with observations.     

Influence of magnetic field on propagation of five-minute oscillations in the sun’s atmosphere: Phase shifts

From results of spectral (in Ba II λ 455.4-nm line) and spectropolarimetric (in Fe I λλ 1564.3–1565.8-nm lines) observations of the active region (an isolated faculae at the solar disk center) with the German vacuum tower telescope (VTT) at the Institute of Astrophysics on the Canary Islands, the peculiarities of propagation of five-minute oscillations from the photosphere base (h = 0 km) to the lower chromosphere (h = 650 km) were investigated. At the height of the continuum formation (h = 0 km), the nature of wave propagation in the active region does not differ much from that in the quiet region: 80–90% of the investigated areas are occupied by waves moving up and down. In the lower chromosphere (h = 650 km), differences in the behavior of the waves are fundamental. In a quiet area, the waves become standing for 90% of the cases. In contrast to this, in the presence of moderate and strong magnetic fields (B = 30–180 mT), in 47% of the cases, the waves are running upward, which gives the principal possibility to heat the active region. The investigations revealed the presence of the waves in the active region, for which the phase shift Φ _T,V of the temperature and velocity oscillations is between ?90° and 0°. These waves cannot propagate in a quiet atmosphere.     

On the asymmetry of selected fraunhofer lines,II

The asymmetry of 11 absorption lines of neutral iron was determined from observations made with the double-pass system on the horizontal solar telescope Asu-5. An attempt was made to interpret this asymmetry in terms of progressive sound waves. The value of asymmetry computed theoretically was shown to be on average only 20 % of the observed value.     

The interpretation of absorption-line shifts in the solar spectrum

The shifts of Fraunhofer lines of different chemical elements in a homogeneous medium with a plane monochromatic progressive adiabatic sound waves are derived. The calculations indicate that lines of neutral elements (6 ₀ 14) with lower excitation potentials ₀ i= 0–2 eV are red shifted, those with excitation potential ₀ i= 4–12 eV are blue shifted, and with ₀ i= 3 eV are both blue and red shifted. The lines of ions are shifted toward the blue. The shifts of Fraunhofer lines are found to decrease from the centre of the solar disk to the limb. These results agree qualitatively and quantitatively with observations.