F. Kneer

OSO-8 observations of CaII H and K, MgII h and k, L? and L? above a sunspot

Observations with the French (L.P.S.P.) experiment on board OSO-8 of a sunspot and nearby plage region are described. The behaviour of the emission cores of the Ca II H and K and Mg II h and k resonance lines is very similar and the correspondence in intensity between the four lines persists in all observed features. In contrast, the Lyman lines show little correlation with the other lines. Their emission regions appear broader in the spectroheliograms than the underlying sunspot structure and must not necessarily possess a counterpart in lower layers. From the central intensity of Lα above the umbra an electron density of 4.3 × 1010 cm-3 ≲ne* ≲2.3 × 1011 cm-3 at 20 000 K is estimated.

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 Hα and Caii 8542 Å.The early phase of the flare is characterized by a blue asymmetry in Hα 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 Hα.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 Hα 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.

Diagnostics and Dynamics of the Solar Chromosphere

Research of the chromosphere of the Sun is exciting, as it has been over more than a century. The present contribution can only give glimpses into the wealth of chromospheric structures and dynamics. Likewise, in view of the limited space, it is not possible to present in due balance the published work on the solar chromosphere. The reader is referred to the monographs by Bray and Loughhead (1974, with a historical account and many references to early work) and by Athay (1976) for the state of knowledge two decades ago. Among the conferences dealing meanwhile with the chromosphere we mention the proceedings edited by Bonnet and Delache (1976) and by Ulmschneider et al. (1991). Withbroe and Noyes (1977) treated the mass and energy flow in the chromosphere and corona; a throughout account of the Ca II K2v cell grains is given by Rutten and Uitenbroek (1991); the review by Narain and Ulmschneider (1996) deals with chromospheric and coronal heating mechanisms. Last but not least, the book “Le Soleil” by Secchi (1877) is historically precious and full of still viable ideas.

Observations of chromospheric lines from OSO-8

The line profiles of Lα, Ca ii K and Mg iik were measured with the spectrometer of the ‘Laboratoire de Physique Stellaire et Planétaire’ on board of OSO-8. The results of these measurements are presented.