• F. Farnik

• M. Varady

• J. Kreckova, E-mail: kreckova@asu.cas.cz

 X-ray emission of hot solar  plasma (mostly observed in solar
 flares)  is an  important source  of information  on physical
 processes which  we would like to  understand in more detail.
 Non-thermal X-ray emission may  help to discover acceleration
 mechanisms causing  beams of particles  to be accelerated  to
 very  high  energies  in  solar  flares.  Unfortunately,  the
 short-wavelength  band  of  the  electromagnetic  spectrum is
 absorbed by  the Earth's atmosphere and  can be observed from
 spacecraft only.  The group activities  are therefore focused
 on scientific analysis of top-quality satellite data obtained
 in broad international cooperation  as well as on development
 of its own instruments for space projects.
 F.Farnik  closely collaborates  with the  'Yohkoh group', the
 scientific   investigators  operating   the  Japanese  Yohkoh
 satellite, (he has spent nearly half  a year so far in Japan)
 and   studies   the   physical   relation  between  pre-flare
 brightenings and  following flares as  well as large  coronal
 structures observed  in X-rays (together  with Zdenek Svestka
 from the Netherlands). He  is also the principal investigator
 of two instruments (hard X-ray spectrometers) which are under
 development for the European CESAR project (the project which
 is led by  the Italian Space Agency, to  be launched in 2000)
 and  for a  DoD (USA)  satellite (to  be launched  in 1999 as
 a flare forecaster, in cooperation with the Space Environment
 Laboratory in Boulder).
 M.Varady tries  to model physical processes  in flaring loops
 mathematically and  to compare his  results with observations
 from the Yohkoh satellite.
 J.Kreckova  supports the  group by  necessary programming and
 computers managing.  She is also helpful  to other groups and
 departments solving network and system problems.

 Recent results:

 So far we have failed to launch our own instrument into orbit
 (both projects we are participating in have been delayed) and
 therefore we depend on data  from other projects. Analysis of
 Yohkoh data in broad  international collaboration has enabled
 us to publish classification and description of large coronal
 structures observed  in soft X-rays. Two  papers were already
 published  and  another  two  are  under  final  preparation.
 Studies  of  pre-flare  brightenings   led  to  an  important
 conclusion    that    these    brightenings    originate   at
 approximatelly  the same  altitude as  the following  flares;
 also this topic is still under more thorough study.