COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 3402

                                     Konkoly Observatory
                                     Budapest
                                     11 December 1989

                                     HU ISSN 0374 - 0676


      CCD PHOTOMETRY OF V1500 CYGNI IN 1987 AND 1989

   Seventy-one "V" CCD images of V1500 Cygni (Nova Cygni 1975) were
obtained by D. Pascu, R. E. Schmidt, and P. K. Seidelmann in 1987
and 1989 using the U. S. Naval Observatory 1.55-meter astrometric
reflector at Flagstaff, Arizona. The Caltech Mark IV 800 x 800
charge-coupled device (CCD) camera, with a Space Telescope F569W wide
"V" filter was used. Comparison stars were C1, C2, and C3, as defined
by Kaluzny and Semeniuk (1987). The following expressions were used
in the reductions:

      Max (HJD) = 2443369.7169 + 0.1396131 * E.    (1)
      Min (HJD) = 2443369.6546 + 0.1396131 * E.    (2)

   Differential magnitude light curves were constructed with phase
given by equation (1). Instrumental magnitudes of the nova were
converted to "V" magnitudes using the Kaluzny and Semeniuk (1987)
values for C1 and C3. Figure 1 shows the light curve for 5 August,
1989. Vertical bars are standard errors of DAOPHOT aperture
photometry (Stetson, 1987). Horizontal bars indicate length of
exposures (200 seconds). The nova's mean "V" magnitude was 17.75 on 5
August, 1989, continuing its slow decline at the present rate of 0.23
magnitude per year. The maximum "V" magnitude was 17.17 +/- 0.03 and
the minimum was 18.55 +/- 0.05. Flickering of amplitude 0.2 "V"
magnitude at maxima and minima was observed.
   Times of maxima and minima obtained by Pogson's method are
compared to the above ephemerides (Table I). Figures 2 and 3 show our
times of maximum and minimum (solid dots) with all known observations
in the literature (crosses). The following references contributed
times of observed maxima or minima: Semeniuk et al. (1977), Patterson
(1979), Lanning and Semeniuk (1981), Pavlenko and Prokof'eva (1981),
Pavlenko (1982,1983), Kruszewski (1983), Kaluzny and Semeniuk (1987).
A least-squares fit of all positive cycles indicates corrections of
-0.0053 day to the epoch of maximum in equation (1) and of -0.0056
day to the epoch of minimum in equation (2), yielding the following
linear ephemerides:

       Max (HJD) = 2443369.7116 + 0.1396131 * E.     (3)
       Min (HJD) = 2443369.6490 + 0.1396131 * E.     (4)

No significant change to the period was detected.


                            [FIGURE 1]
                            [FIGURE 2]
                            [FIGURE 3]




Table 1. Observed epochs of maximum and minimum




HJD Maximum        HJD Minimum    Cycle     (O-C)


                   2447055.715    26401     -0.005
                   2447743.871    31330     -0.002
2447743.931                       31330     -0.004
2447744.912                       31337     -0.000




                RICHARD E. SCHMIDT
                JAMES A. DeYOUNG
                BRITT C. WAGNER

                U.S. Naval Observatory
                Nautical Almanac Office
                34th E Mass. Ave. NW
                Washington, DC 20392 USA






References:

Kaluzny J., and Semeniuk, I., 1987, Acta Astron., 37, 349. [BIBCODE 1987AcA....37..349K ]
Kruszewski, A., Semeniuk, I., and Duerbeck, H.W., 1983, Acta
  Astron., 33,339. [BIBCODE 1983AcA....33..339K ]
Lanning, H.H., and Semeniuk, I. 1981, Acta Astron., 31,175 [BIBCODE 1981AcA....31..175L ]
Patterson, J., 1979 Ap. J. 231,789. [BIBCODE 1979ApJ...231..789P ]
Pavlenko, E. P., and Prokof'eva, V. V., 1981, Izv. Krym. Astrofiz
  Obs. 64,67. [BIBCODE 1981IzKry..64...67P ]
Pavlenko, E. P., 1982, Astron. Tsirk. No. 1239, 3. [BIBCODE 1982ATsir1239....3P ]
Pavlenko, E. P., 1985, Izv. Krym. Astrofiz Obs. 67, 40. [BIBCODE 1983IzKry..67...50P ]
Semeniuk, I., et al., 1977, Acta Astron. 27, 4, 301. [BIBCODE 1977AcA....27..301S ]
Stetson, P. B., 1987, P. A. S. P., 99, 191. [BIBCODE 1987PASP...99..191S ]