COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                       Number 1098

                                  Konkoly Observatory
                                  Budapest
                                  1976 February 9


     ON THE SHORT PERIOD LIGHT VARIATION OF NOVA CYGNI 1975
                      (V 1500 Cyg)


    The photoelectric observations of the short period light
variation detected in Nova Cygni 1975 (Tempesti, 1975a; Koch and
Ambruster, 1975a), pursued at the Teramo Observatory till the 
beginning of October, showed a steady decrease of the amplitude from
0.15m to 0.03m in V light. However on October 27 Marcocci et al. 
observed an amplitude as great as 0.26m (Marcocci et al., 1975);
therefore the range of the fluctuation appears to be highly variable. 
Also the shape of the light curve results strongly variable
from one cycle to the other, with differences even greater than
those appearing among the light curves already shown in this 
Bulletin (Tempesti, 1975b; Semeniuk, 1975).
   The period on the contrary shows only small variations around
a mean value of about 0.139d. The Teramo observations allowed to 
secure light minima at J.D._hel 42665.438, 665.572, 667.409, 667.552,
670.368, 670.503 and 688.440; maxima at J.D._hel 665.483, 667.463,
670.437, 670.564, 681.377 and 688.383. These determinations, 
together with other published times (Koch and Ambruster, 1975a and b;
Semeniuk, 1975; Lindgren and Lindegren, 1975), give indication of a
continuous variation of the period length which ranges from 0.137d
to 0.141d with an O-C period, if any, of the order of 20 days, 
although the possibility that abrupt changes have occurred cannot be
ruled out.
   From the available material no conclusive evidence could be
drawn about the existence of two kinds of maxima or minima which
should alternate yielding a value 0.28d for the period.



                          P. TEMPESTI
                 Osservatorio Astronomico di Teramo, Italy



References:

Koch, R.H., Ambruster, C.W. 1975a, IAU Circ. 2837. [BIBCODE 1975IAUC.2837....2D ]
Koch, R.H., Ambruster, C.W. 1975b, IAU Circ. 2839. [BIBCODE 1975IAUC.2839....1H ]
Lindgren, H., Lindegren, L. 1975, IBVS 1074.
Marcocci, M., Messi, R., Natali, G., Rossi, L. 1975, Private comm.
Semeniuk, I. 1975, IBVS 1058.
Tempesti, P. 1975a IAU Circ. 2834. [BIBCODE 1975IAUC.2834....1K ]
Tempesti, P. 1975b IBVS 1052.