COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                   Number 3101


                                   Konkoly Observatory
                                   Budapest
                                   19 October 1987

                                   HU ISSN 0374 - 0676





    PRE-OUTBURST LIGHT CURVE OF NOVA CYGNI 1975 (V1500 Cyg)


Renewed interest in the very faint magnetic nova Cygni 1975 (Chlebowski &
Kaluzny 1987; Schmidt, Smith & Elston 1987) prompts me to report findings
from my recent inspection of two plates taken with the Palomar 1.2m Schmidt
telescope in 1969 and 1970. These are the only Palomar Schmidt plates taken
of the region of Nova Cygni between 1953 and August 1975.


Plate PS14992 by J. Kristian is a two-color 103aO plate, exposed 1969 August
17 for 5 min behind a GG13 filter and 50 min behind UG1, as part of a (B,UV)
survey. The nova image is not seen. I have estimated B > 18.0 using the
comparison sequence of Kaluzny and Semeniuk (1987). A scratch directly
across the position of the nova B image precludes obtaining a reliable
fainter limit, although comparison star C3 (B ~/= 19.9) is clearly seen.
Probably the nova was fainter than 19.


Plate PS15900 by M. V. Penston is a IIIaJ plate exposed 1970 July 31 for 60
min behind a Wratten 4 filter (the "g" passband). There is a slight clumping
of plate grain at the nova position; other similar clumpings visible under
high magnification correspond to faint images on the finding chart of Kaluzny
and Semeniuk. These images are at least 1 mag fainter than star C3. The
nova was therefore at least as faint as 20.5 mag.


Kukarkin and Kholopov (1975) have reported some pre-discovery images of Nova
V1500 Cyg during the weeks just before the eruption in 1975 August. They
also report upper limits of 19 mag in 1972 and 17.9 in 1974 December. The
limits reported here are slightly more remote in time from the outburst than
those of Kukarkin and Kholopov, but the limit for PS15900 is substantially
fainter. These limits are closer in time to the outburst than the 1967 October 
limit of 19.5 from Asiago plates (Rosino & Tempesti 1977). Thus they
provide additional constraints fro evaluation whether Nova Cygni 1975
followed the "hibernation" scenario that has been put forward by Shara et al.
(1986). More generally, they bear on the question whether novae have the same 
brightness before and after eruption (cf. Robinson 1975). The present
brightness of V1500 Cygni varies about V = 17. (Kaluzny & Semeniuk 1987).

Thanks due to Dr. R. J. Weynmann, Director of the Mt. Wilson & Las Campanas
Observatories, for permission to use the plate material. Drs. A. Sandage and
A. Saba, and Mr. B. Katem were instrumental in helping me locate and inspect
the plates.


				RICHARD A. WADE
				Steward Observatory
				University of Arizona
				Tucson, AZ 85721
				U.S.A.

References:

Chlebowski, T. & Kaluzny, J. 1987, I.A.U. Circ. 4413. [BIBCODE 1987IAUC.4413....3C ]
Kaluzny, J. & Semeniuk, I. 1987, Acta Astronomica in press. [BIBCODE 1987AcA....37..349K ]
Kukarkin, B.V. & Kholopov, P.N. 1975. Astr. Tsirk. No. 889. [BIBCODE 1975ATsir.889....1K ]
Robinson, E.L. 1975. Astron. J. 80, 515. [BIBCODE 1975AJ.....80..515R ]
Rosino, L. & Tempesti, P. 1977. Sov. Astron. 21, 517.
Schmidt, G.D., Smith, P. & Elston, R. 1987. I.A.U. Circ 4415. [BIBCODE 1987IAUC.4415....2S ]
Shara, M.M., Livio, M., Moffat, A.F.J. & Orio, M. 1986. Astrophys. J. 311, 163. [BIBCODE 1986ApJ...311..163S ]