Investigation of magnetic fields on the sun

Magnetic fields of sun and effects on events near eart

Near-Limb Zeeman and Hanle Diagnostics

"Weak" magnetic-field diagnostics in faint objects near the bright solar disk are discussed in terms of the level of non-object signatures, in particular, of the stray light in telescopes. Calculated dependencies of the stray light caused by diffraction at the 0.5-, 1.6-, and 4-meter entrance aperture are presented. The requirements for micro-roughness of refractive and reflective primary optics are compared. Several methods for reducing the stray light (the Lyot coronagraphic technique, multiple stages of apodizing in the focal and exit pupil planes, apodizing in the entrance aperture plane with a special mask), and reducing the random and systematic errors are noted. An acceptable level of stray light in telescopes is estimated for the V-profile recording with a signal-to-noise ratio greater than three. Prospects for the limb chromosphere magnetic measurements are indicated.Comment: 11 pages, 3 figure

An active region filament studied simultaneously in the chromosphere and photosphere. II. Doppler velocities

Paper I presents the magnetic structure of a filament that developed in active region (AR) NOAA 10781. In this paper we complement those results with the velocities retrieved from Doppler shifts measured at the chromosphere and the photosphere in the AR filament area. Various inversion methods with different numbers of atmospheric components and different weighting schemes of the Stokes profiles were used. The velocities were calibrated on an absolute scale. A ubiquitous chromospheric downflow is found in the faculae surrounding the filament, with an average velocity of 1.6 km/s. The filament region, however, displays upflows in the photosphere on both days, when the linear polarization (which samples the transverse component of the fields) is given more weight in the inversions. The upflow speeds of the transverse fields in the filament region average -0.15 km/s. In the chromosphere, the situation is different for the two days of observation. On July 3, the chromospheric portion of the filament is moving upwards as a whole with a mean speed of -0.24 km/s. However, on July 5 only the section above an orphan penumbra shows localized upflow patches, while the rest of the filament is dominated by the same downflows observed elsewhere in the facular region. Photospheric supersonic downflows that last for tens of minutes are detected below the filament, close to the PIL. The observed velocity pattern in this AR filament strongly suggests a scenario where the transverse fields are mostly dominated by upflows. The filament flux rope is seen to be emerging at all places and both heights, with a few exceptions in the chromosphere. This happens within a surrounding facular region that displays a generalized downflow in the chromosphere and localized downflows of supersonic character at the photosphere. No large scale downflow of transverse field lines is observed at the photosphere.Comment: Accepted for publication in Astronomy & Astrophysics, 15 pages, 8 figures, 4 tables; LaTeX links added, typos added, references update

SHORT-PERIODIC OSCILLATIONS OF THE MAGNETIC FIELD OF THE SUN AS A STAR

Abstract. Correlation analysis applied to recordings of the magnetic field and velocity of the Sun as a star reveals oscillations close to 300 s. The power spectrum of these oscillations is discussed. Numerous recent investigations have shown the presence of short-periodic oscillations of the brightness, velocity and magnetic field in separate parts of the solar surface (see, for instance, Tanenbaum et al., 1971). These oscillations with period ~300 s have dimensions of about 10"-20"; the coherence between the oscillations rapidly vanishes with distance. On the other hand, radio-astronomical observations have shown the presence of short-periodic oscillations in regions of about some arcminutes (Yudin, 1968). It seems interesting to investigate the behaviour of the Sun as a star, to clear up the question about the global short periodic oscillations of the whole Sun. To investigate this problem a parallel beam from the coelostat has been directed on the entrance slit of the spectrograph of the IZMIRAN tower telescope. The optical set-up is shown in The brightness, the longitudinal component of the magnetic field and the radial velocity in Fe I 5250 • were measured with the magnetograph of IZMIRAN. The Solar Physics 29 (1973) [385][386][387][388][389][390][391][392