COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2322

                                    Konkoly Observatory
                                    Budapest
                                    25 April 1983

                                    HU ISSN 0374 - 0676




      COORDINATED ULTRAVIOLET, OPTICAL AND RADIO OBSERVATIONS
                   OF RS CVn AND FLARE STARS IN
                    OCTOBER 1983 AND MARCH 1984



  Time has been allocated on the International Ultraviolet Explorer (IUE)
satellite to four groups based at Armagh Observatory (N. Ireland), Catania
University (Italy), JILA/NBS University of Colorado (Boulder, USA) and 
Lockheed Research Lab. (Palo Alto, USA) by ESA and NASA to observe RS CVn and
flare stars during the periods October 3-7, 1983 and March 26-30, 1984. the
total time allocated is 17 eight-hour shifts, split into 10 shifts in October
and 7 in March. We hope to monitor changes in the stars' UV spectra during
their spat cycles and, in addition, to derive spatial resolution of 
atmospheric structures using eclipses. In the case of the flare stars, 
time-resolved spectroscopy during flares will be attempted as in previous years.
  Similar programs were successfully carried out in October 1981 and February 
1983. Preliminary results from the October 1981 program will be found in
ADVANCES IN ULTRAVIOLET ASTRONOMY (NASA CP-2238), THIRD EUROPEAN IUE CONFERENCE 
(ESA SP-176) and ACTIVITY IN RED DWARF STARS (IAU Colloquium No: 71, Reidel, 
in press).
   In the coming year we are planning to observe the three RS CVn stars
AR Lac, HD 5303 (October 1983) and RS CVn (March 1984). Flare stars will be
chosen from among the following list: UV Cet, Gliese 867A, EQ Peg, EV Lac 
(October 1983) and Proxima Cen, YZ CMi, Gliese 182 and AD Leo (March 1984). 
Concurrent photoelectric, spectroscopic and radio observations of these stars
would add considerably to the scientific results of the IUE data.
   Simultaneous ground-based observations are highly desirable for the RS CVn
program, in particular during the eclipses. One of the principal aims of these
observations is the detection of surface inhomogeneities in the outer 
atmospheres of these stars using the occulting disk of the companion to scan the
surface of the active star. Obviously it is crucial that we know of any 
temporal variations in either the optical or radio output of the star at these
times. Moreover, it is important to obtain complete UBV (or at least V) light
curves for the purpose of establishing the shape and phase-shift of the 
migrating "photometric waves". Therefore, the photometric observations of RS CVn
stars need to be carried on over a one-two month interval including the period
of IUE observing.
   In the case of flare stars, simultaneous ground-based observations are 
essential for a proper interpretation of the UV and radio data. Such 
observations should aim at covering the period of the IUE program as completely 
as possible. Specifically, we are seeking continuous monitoring of the flare
stars photometrically, spectroscopically and with radio receivers. Photometric
monitoring should be in the Johnson U or B-band, where signal levels permit,
and with as short an integration time as possible. In addition we would ask
that the program stars should be measured in the Johnson UBVR bands at least
twice per night, i.e. before and after the times of continuous monitoring, in
order to establish possible or known BY Draconis wave-like variability. Again,
observations outside of period of IUE observing could be necessary to obtain
as complete as possible light curves.

   Transformation to the standard UBV system is important so that observations 
from different observers can be intercompared.
   Spectroscopic observations should aim. at obtaining time-resolved spectra
in the region near H_alpha, H_beta, H_gamma, H_delta and/or Ca II H and K emission
lines to monitor continuum and line profile variability, especially 
during the course of
flare events. The best attainable time and spectral resolution should be
sought.
   Radio monitoring of program stars should be preferably carried out at
several wavelengths simultaneously, including a cm-wavelength, if possible
   As soon as possible, the final scheduling details, as well as suggested
comparison stars and, if required, finding charts will be communicated 
directly to those who indicate their interest by writing or telexing the 
undersigned.




                           MARCELLO RODONO
                     for the Armagh, Catania, JILA and
                           Lockheed Groups

                         Institute of Astronomy
                          University of Catania
                           Viale A. Doria 6.
                          95125 Catania, Italy
                         Telex No. 970359 ASTRCT I