COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1768

                                Konkoly Observatory
                                Budapest
                                1980 April 8


   REQUEST FOR COOPERATION FROM OPTICAL AND RADIO OBSERVERS


Time has been allocated on the International Ultraviolet Explorer satellite
jointly by NASA, the British SRC, and ESA to three groups based at JILA,
Colorado, USA, Armagh Observatory, Northern Ireland and Catania Observatory,
Sicily to observe a Flare Star/BY Draconis variable. The total time allocated
is many times the mean inter-arrival time between flares and comparable to the
period of the BY Dra variations. As a result it is hoped to be able to monitor
changes taking place in the star's UV spectrum during a flare and during a
complete cycle of the BY Dra variations, with particular reference to those
lines indicative of conditions in the chromosphere, transition region and lower
corona.

AU Mic (=HD 197481; V=8.9, B-V =+1.4 and U-B =+1.1; alpha(1980)=20h44m54s,
delta(1980)=-31d24.7') has been chosen as the most suitable target. It is
known to be both a Flare Star (Harding, 1970 and Kunkel, 1973) and a BY Dra
variable of relatively large amplitude and a period of 4.865 days (Torres et
al. 1972). The amplitude of the BY Dra variations as reported by Torres et
al. is delta V~0.3m making it one of the largest amplitude BY Dra variables
known. Harding (1970), observing with a 1-meter telescope, recorded one flare
per 2.4 hours in the Johnson U-band under adverse, bright-sky conditions, while
Kunkel (1973) registered 31 U-band flares with a 1.5-meter telescope in 6.7
hours of observation, many of which were of much smaller amplitude than those
of Harding.

A total of nine eight-hour shifts on IUE has been assigned to the project
totalling 72 hours in all. Thus as many as 30 moderately large flares may be
recorded during this period. A single UV flare spectrum has already been
recorded with IUE on the star Gliese 867A and the UV out-of-flaring spectrum of
this star is similar to that of AU Mic (Andrews, Butler and Byrne 1980). In
addition it is hoped to spread the time over about four days to maximize the
phase coverage with respect to the BY Dra variations. In order that the best
possible use be made of these UV data at least optical photometry of the
programme star of a type suitable for detecting flares and the phase of the BY
Dra variations will be needed. To this end we are appealing to all optical
observers in the southern hemisphere or at the lower northern latitudes, spread
over as wide a range of longitude as possible to cooperate in providing the
necessary coverage. In addition we would like to appeal to any who may be able
to secure spectra of AU Mic during the appropriate times to do so particularly
if these can be time-resolved. In order that the information be as complete as
possible an invitation is also being extended to radio observers and to a
number of groups involved in X-ray astronomy.

Observations should consist of continuous photometric monitoring in the near
ultraviolet (e.g. Johnson U or similar wavebands) with integration times of
between 1s-10s. It is important for investigating the BY Dra phenomenon that
we be able to establish the amplitude and phase at the time of the IUE
observations. Measurements should therefore be made of AU Mic and at least two
nearby comparison stars of similar colour in U, B and V at least once but
preferably two or three times per night. Spectroscopic observations should
cover as much of the visible spectrum as possible with preference being given
to the blue end longward of, but including, H_beta.

Final observing dates have not yet been set but one of two intervals is being
sought. The first is during the second week of July and the second would be in
the first week of August. As soon as they are available final details will be
published in this bulletin but individual observers interested are invited to
contact the undersigned.


P.B. BYRNE
Armagh Observatory
Armagh BT61 9DG
Northern Ireland

References:

Andrews, A.D., Butler, C.J. and Byrne, P.B., 1980, Private communication from a
   paper in preparation.
Harding, G.A. 1970, M.N.A.S.S.A., Vol. XXIX, 130 [BIBCODE 1970MNSSA..29..130H ]
Kunkel, W.E., 1973, Astrophys. J. Suppl. Ser., 25, 1 [BIBCODE 1973ApJS...25....1K ]
Torres, C.A.O., Ferraz Mello, S. and Quast, G.R., 1972, Astrophys. Lett., 11,
   13 [BIBCODE 1972ApL....11...13T ]