COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    NUMBER 873

                              Konkoly Observatory
                              Budapest
                              1974 March 4

     COORDINATED CAMPAIGN FOR OBSERVATIONS OF X-RAY BINARIES
     I.A.U. COMMISSION 42 IN COORDINATION WITH COMMISSION 44

  The Committee for Coordinated Observing Programs (Chairman,
K. Gyldenkerne) of the IAU commission 42, in collaboration with its
Committee for Astronomical Observations from Outside the Earth's 
Atmosphere (Chairman, Y. Kondo), announces its sponsorship of a 
coordinated campaign to observe X-ray binaries. The campaign is also 
being coordinated with the IAU Commission 44 (President, A. D. Code).

  The objects selected for this campaign include in the first place
3U1653+35 (=Her X-1 = HZ Her), 3U1956+35 (=Cyg X-1 = HDE226868),
3U0900-40 (= HD77581) and 3U1700-37 (=HD153919). In addition to these
the following objects, for which possible optical identifications have
been made or proposed, will be treated in the campaign communications and
will perhaps be included in this campaign: 3U1118-60 (=Cen X-3 = the star
suggested by Krzeminski in IAU Circular No. 2162), 3U0115-73 (=SMC X-1 =
Sanduleak 160), 3U0352+30 (= X Per), Cep X-4 (= HD 206267, a 7th magnitude
O6 spectroscopic binary, P = 3.7 days), 3U0032+24 (= zeta And, P=17.8d days,
an elliptical variable?), 3U0918-55 (= kappa Vel, variable radial velocity),
3U0527-05 (= Theta2 Ori A, a 5th magnitude 09.5 V spectroscopic binary,
P = 21.0 days, massive invisible companion, within the error box of the
X-ray source), and 3U1820-30 (= Variable Star No. 14 of the globular
cluster NGC 6624, within the error box of the X-ray source). This
additional list of objects are based primarily on the suggestions kindly
offered by Dr. W. Liller. Other objects may be added subject to future
optical identification. For additional information on these binaries
selected for the campaign the reader is referred to the recent issues of
the IAU Circulars (published by Smithsonian Astrophysical Observatory),
I. B. V. S. and the Astrophysical Journal (especially Part II), among
other publications. 3U numbers refer to those given in the third Uhuru
Catalogue of X-ray sources, which is soon to be published.
  Sometime after the end of March 1974, the University College London X-ray
experiment on the Copernicus satellite is scheduled to observe Her X-1
in the energy range 3-1 kev. The exact schedule is expected to be
available about 10 days prior to the onset of the observing period. Active
participants in the campaign will be informed of these dates as soon as
they are determined. Most X-ray experimenters on the UK5, ANS and OSO-I
satellites have already expressed their interests in participating in
the Campaign. The UK5 satellite is currently scheduled for launch in
June 1974, while the ANS is slated to be launched in August, 1974.
OSO-I is planned for launch in March, 1975. Dr. S. S. Holt, the NASA
project scientist for the UK5, states that preliminary observing
schedules for it will be established a few months in advance although
the actual observing plans may not be finalized until a few weeks prior
to the execution. According to Dr. H. Gursky, the principal investigator
for the ANS hard X-ray experiment, the ANS observing plans are expected to
be established a few months in advance.
   If you are involved in X-ray binary research and interested in
participating in this campaign, you are invited to write to the coordinator
briefly describing your current and near future plans. Although we shall
be primarily concerned with space and ground observations, those
interested in theoretical interpretation are also encouraged to 
participate in this campaign through suggestions to observers. The status of
the reported ongoing research activities will be contained in the 
forthcoming issues of the campaign circulars. X-ray satellite observing plans
will also be announced and kept current in the Circular Letters and/or
Special Bulletins.


   Communications to the coordinator should be addressed to:

        Y. Kondo
        Astrophysics Section (TN23)
        Johnson Space Center
        Houston, Texas 77058 U. S. A.





KJELD GYLDENKERNE           YOJI KONDO
Chairman                    Coordinator
Committee for Coordinated   Coordinated Campaign for Observations
Observing Programs          of X-Ray Binaries
IAU Commission 42           IAU Commissions 42 and 44