COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3473

                                            Konkoly Observatory
                                            Budapest
                                            7 June 1990

                                            HU ISSN 0374 - 0676


       A CALL FOR OPTICAL PHOTOMETRY AND SPECTROSCOPY OF
                 ACTIVE COOL STARS TO COMPLEMENT
                    ROSAT X-RAY OBSERVATIONS

  The ROSAT project is an international collaboration between the United
Kingdom, West Germany and the USA. The satellite is due to be launched on
a Delta-II rocket from Cape Canaveral on May 31st 1990 and consists of two
co-aligned imaging telescopes: The German X-ray telescope (XRT) operating in
the soft X-ray band (6-100 A), and the UK Wide Field Camera (WFC) operating
at extreme ultra-violet (XUV) wavelengths (60-600 A). ROSAT has two main
mission objectives to achieve during its 2-3 year lifespan. Firstly, a six month all-
sky survey of soft X-ray sources with a higher sensitivity than previously possible,
extending into the XUV region of the electromagnetic spectrum which has so far
remained largely unexplored. Secondly, there will be a programme of pointed
observations for detailed studies of hundreds of individual targets.

   The purpose of this communication is to solicit optical photometry and 
spectroscopy of some of the active cool stars which will be monitored by ROSAT 
during the all-sky survey. Simultaneous optical/XUV observations will be valuable
in mapping the magnetically defined structures which exist in these stars in their
photospheres, chromospheres and coronae. The ROSAT survey is in many ways
ideal for such an investigation. The scanning method employed means that objects
will be observed for about a minute once every ninety minute satellite orbit
over the duration of their visibility to ROSAT. This duration varies from 5 days
to several months, depending on the positions of the objects.

   Targets to be included in this campaign are members of the BY Dra class (BY
Dra, CC Eri e.t.c.), the RS CVn class (AR Lac, CF Tuc e.t.c.) and rapidly rotating
single dwarfs (AB Dor, PZ Tel). The target timeline is moderately well known
and some of the potential study objects will be visible to ROSAT for several weeks
enabling a detailed study of the correlation between XUV emission from active
coronal regions and starspot locations found by cotemporal optical diagnostics.

   Observers interested in participating in a coordinated campaign should in the
first instance contact the undersigned giving details of facilities and particular
objects of interest.



 R. D. JEFFRIES       			SPAN 19463::BHVAD::RDJ
 University of Birmingham,              BITNET RDJ%UK.AC.BHAM.SR.STAR
 School of Physics & Space Research, 	Tel: 021 414 3852
 PO Box 383,          			Fax: 021 414 6709
 Birmingham B15 2TT, U.K.               Telex: 338938 SPAPHY G