COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 1052

                                  Konkoly Observatory
                                  Budapest
                                  1975 October 16


     A SHORT PERIOD LIGHT VARIATION IN NOVA CYGNI 1975




  As already announced (Tempesti 1975) photoelectric monitoring
of Nova Cygni 1975 performed on September 9 with the 40 cm refractor 
of the Teramo Observatory showed the existence of periodic
brightness fluctuations having an amplitude of 0.15m in V light and
a period estimated at first glance at 3.2 hours. The observations
carried out during subsequent nights have shown the persistence of
the fluctuations and confirmed their periodic character; the accurate 
elaboration of all the observational material will take several
months: here only a short report is given, based on a preliminary
coarse reduction.
  Fig. 1a and 1c show the light-curves obtained during the nights
September 9/10 and 14/15, respectively. BD +47d3348, with the assumed 
V magnitude 6.46 (Ljunggren and Oja 1964), has been used as comparison 
star; the star BD +47d3340 has been measured each night 
alternatively with the comparison star along all the night runs: in
Fig. 1b and 1d the magnitude differences between these two stars
(check minus comparison) are plotted.
  On September 9/10 the amplitude resulted at least 0.15m (not all
the observations are reported in Fig. 1a); on September 14/15 the 
amplitude seems to be decreased to 0.12m and also the shape of the 
light-curve appears notably different from that one of September 9. On the
other hand the period is fairly well kept: the four minima of Fig. 1
allow to derive the value P = 0.137d and a preliminary computation
with the times of these minima gives residuals not exceeding 0.007p.
The minimum of September 15.00 appears 0.03m deeper than the preceding 
one; whereas the second observed minimum of September 9/10 appears 
only 0.01m deeper than the preceding one; considering the 3-
hours wave as a distinct phenomenon overlapping the steady decline
of the nova, the two minima of September 9/10 are of equal depth,
because the magnitude difference roughly equals the light decay of
the nova, at that epoch, in 0.14 days.
   I have ascribed the slight decrease of DeltaV which is noticeable
in Fig. 1b to a brightening of the check star; if, however, the
trend of the DeltaV is due to a fading of the comparison star, then
in reality the depth of the two minima differs in magnitude by
0.03m like the two minima of September 14/15. I hope that a closer
examination of the observational material will allow to settle the
question.
   The observational program is still going on: a detailed account
will be submitted for publication to the European Journal Astronomy 
and Astrophysics.




                        P. TEMPESTI
                      Collurania Observatory
                      64100 Teramo, Italy.




References:
Ljunggren, B., Oja, T. 1964, Arkiv for Astronomi 3, 439 [BIBCODE 1965ArA.....3..439L ]
Tempesti, P. 1975, I.A.U. Circ. 2834 [BIBCODE 1975IAUC.2834....1K ]


                       [FIGURE 1]

 Fig. 1. A) and c): light-curves of the nova. B) and d): magnitude
 differences between check and comparison stars (check minus 
 comparison), All the plotted data are corrected for extinction.



                [From IBVS 1057]

                ERRATA-CORRIGE




Correction to IBVS No. 1052
P. Tempesti: A SHORT PERIOD LIGHT VARIATION IN NOVA CYGNI 1975
At page 1, lines 18-20 instead of
    "On September 9/10 the amplitudes resulted at least 0.15m
(not all the observations are reported in Fig. 1 on September
14/15 the amplitude seems to be decreased to"
Must be read:
    "On September 9/10 the amplitude resulted at least 0.16m;.
on September 14/15 the amplitude seems to be lowered to...




                        P. TEMPESTI