COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         NUMBER 841


	                                Konkoly Observatory
        	                        Budapest
                	                1973 October 25


     ON THE BRIGHTNESS VARIATIONS OF A STAR IN THE VICINITY
         OF Cyg X-I WITH THE TIME-SCALE OF TEN MS


At the Crimean Astrophysical Observatory a special TV method is used
to detect short-periodic light variations (pulsations) of stellar 
objects with periods down to  0.001 sec (1). Its principle is as follows.
Periodic stepwise variations of electro-magnetic field applied  to the
image tube, used as a light preamplifier, cause discrete shifts of the
image on the TV screen. If the field  variation period equals the light
variation period of the object the multiple picture of  the object on
the screen covers all phases of its light variation. In other words, we
get a resolution of the light into phase intervals. To detect an object
with unknown pulsation period the period of resolution has to be varied
constantly.
Using such a method  a blue star of
17th magnitude situated  3.3' westward
from the X-ray source Cyg X-I labeled 
by v in Fig. 1 was observed in 1971
and 1972 with a 50 cm telescope (F=
6.5 m). The observable field was 1.5                
                                                   [FIGURE 1]
which enabled to photograph some
neighbouring stars together with the
mentioned star. The search for 
pulsations of the star has been carried
out with the resolution into eight
phase intervals, the resolution 
periods varying in the limits between 0.0731 an  0.0754 sec. A comparison
star labelled by a in Fig. 1 chosen inside the field  was also observed.
Three pairs of histograms for both stars showing frequencies of deviation 
from the mean brightness were plotted using three random samples
each amounting to about hundred  brightness measurements of both stars.
As can be seen in Figure 2, the brightness scattering of the star under
consideration is about twice larger than that of the control star. 
Besides, the histograms of the star under consideration are asymmetric
and have different shapes on the right and left wings. This might be
due to short-time brightness variations having a non-periodic 
or quasi-periodic character. 
From the observational 
material obtained on July 30, 1971
(30 sec exposures) it was 
possible to reveal the periodicity
of the pulsations of the star                 
                                                [FIGURE 2]
with p=0.0745 sec, and according
to the observations of August 18,
1972 (60 sec exposure) the period
was 0.07395 sec. In both cases
the characteristic radiation
nurses had a duration of about
10 msec.
The brightness and B-V colour of the star obtained from television
pictures taken on October 31,1972 was m_v=17.21m +/- 0.10, 
B-V = 0.57m+/-0.10. In the colour-luminosity diagram (Fig. 3)
the object is situated in the white dwarf 
region, if being at a distance of  about
100 ps, or near the region of the  X-ray
source Sco X-I and the pulsar NP 0532, if
being, at a distance of 1.2-1.5 kps.                
                                               [FIGURE 3]
The detected peculiarities of  the
star are similar to those predicted for
the black holes accreting  interstellar
gas (2). 
                           
   References:   
  (1)Abramenko A.N., Gollandskij O.F., 
     Prokofjeva V.V., Izvestija of  the
     Crimean astroph. obs., 1972,  49, 89. 
  (2) Schwartzman V.F., Astr.Journ. of the 
     USSR, 1971. 48, 479. [BIBCODE 1971AZh....48..479S ]
                           
Crimean Astrophysical Observatory of the		A.N. ABRAMENKO
Academy of the Sciences of the USSR.			O.P. GOLLANDSKIJ
October 8, 1973						V.V. PROKOFJEVA