COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         NUMBER 674

                                               Konkoly Observatory
                                               Budapest
                                               1972 May 11


              VARIABLE STARS AND X-RAY SOURCES


The positions of the X-ray sources given by Giacconi, et al. (1971 "The Uhuru
Catalogue of X-ray Sources" ASE-2855 preprint Ap.J.,in press) in the Uhuru
Catalogue have been compared to known variable stars (Kukarkin, et al. GCVS
1969) since the few stellar identifications for X-ray sources have all been
with stars which are variable in light.

In Table I we present all of the known variable stars (with the exception of
those already known as X-ray stars) found within the 90% certainly boxes given
in the Uhuru Catalogue or a box 10% larger (as noted); the sizes of the boxes
in square degrees are given in column 2. We list all of the variables found,
but some are unlikely sources for the X-rays.

In view of the binary nature of Cyg X-1 and probably Cen X-3, we consider V506
Sco and V845 Oph potentially interesting possibilities. Further, the
interesting irregular nebular variable RX Ori could be the X-ray source. X
Per^+ is nearly centrally placed in the error box, and its variable
spectrum, emission characteristics, and irregular light variations are well
known. The RR Lyrae star and the semi-regular variables seem to us unlikely
identifications but have been included for completeness. The character of the
variation of 100215 and 7831 is unknown. Unfortunately little is known about
the spectral characteristics of all of these stars.

The probability of finding some variable stars within the error boxes is large,
so that further investigation is necessary to show if any of these might be the
source of the X-rays.


                          D.J. MacCONNELL and A.P. COWLEY
                            The University of Michigan

^+ The possibility that X Per might be the Xray source has recently been
pointed out by Braes and Miley (1972 Nature 235, 273) and Van den Bergh (1972
Nature 235, 273).

Table I

Variable Stars within or very near the Error Boxes in the Uhuru Catalogue
                                                                                                        Likelihood of
X-ray Source   Sq. Deg.   Variable Star    Magnitude   Type of Variable    Remarks                      Identification
2ASE 0240+44    0.45       CSVS 100215     13.9            ?                                               ?
     0352+30     .023       X Per           6.0- 6.6     Irreg.            B0nne; spec. var.; V/R em.     good
                                                                           var.; nearly central in box
     0440+7     0.59        BZ Tau         13.7-15.8     Semi-reg.         late type                      unlikely
     0525-6     2.30        RX Ori         13.7-(17.2    Irreg.            in diffuse nebula              fair
     1440-39    0.90        V544 Cen       14.9-15.9     Eclipsing         p=3.10d; 0.1deg out of box     fair
     1718-39     .14        V506 Sco       13.3-16.0     Eclipsing         p=2.14d                       good
     1735-28     .045       V845 Oph       13.8-14.5     Eclipsing         p=3.83d                       good
     1757-33     .14        V1720 Sgr      14.3-15.1     Semi-reg.?                                       unlikely
     1822+0      .073       CSVS 7831      15.0-16.8       ?                                                ?
     1822-37     .26        V593 CrA       12.6-14.3     RR Lyrae          p=0.39d; nearly central       unlikely
                                                                           in box
     2130+47    0.07:       V628 Cyg       12.6-13.0     W UMa             p=0.65d; just outside           ?
                                                                           box