COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3977 Konkoly Observatory Budapest 19 January 1994 HU ISSN 0374 - 0676 PHOTOMETRY OF THE PROGENITOR OF NOVA CASSIOPEIAE 1993 ON ASIAGO SCHMIDT ARCHIVE PLATES Nova Cassiopeiae 1993 was discovered by K. Kanatsu on Dec. 7, 1993 (cf. IAU Circ. 5902). It has been well known since Kraft's (1964) paper that classical novae are short period binary systems (with an orbital period of a few days to a few hours). The current picture is that classical novae are semi-detached binaries in which a Roche lobe filling secondary (usually a main sequence K-M star) transfers mass to a WD companion. Pre- or post- outburst novae can then be classified among the cataclysmic variables, which are known to show a large variety of photometric activity, including outbursts with an amplitude of some magnitudes. So far, observations of pre-nova objects have been supplied only from general sky surveys or patrol programs. For the majority of the novae, the progenitor was fainter than plate limits. However, a modest body of data exists from which pre-nova light curves for a dozen or so objects can be reconstructed (e.g. Robinson 1975). Fast novae - like GK Per or V1500 Cyg - show that there was a significant rise in brightness for 1 to 5 years prior to the outburst (Warner 1989). Nova Cas 1993 lies in a region of the Milky Way for which many plates exist in the archive of the 67/92 cm Schmidt telescope of the Asiago Astrophysical Observatory. We have gone through the archive and found 21 plates in the B,V and I bands deep enough to have the nova progenitor recorded. The plates are listed in Table 1. In order to facilitate the correct identification, we took some V band plates with the same Schmidt telescope on UT Dec. 12.85, 1993 and compared them with the archival ones. On the new plates the nova shines at V=6.7+-0.1. Our identification of the progenitor is shown in Figure 1. The progenitor is a member of a very close double star (separation of the order of a very few arcsec and components of similar brightness) which on all plates but the one reproduced in Figure 1 appears as a merged pair. Skiff (1993, IAU Circ. 5904) measured the progenitor image on the POSS-I prints and concluded that the progenitor is a member of a very close double star appearing merged on the POSS-I prints (he estimated ~2 arcsec separation). He indicated the northern component as the true progenitor. With the Iris microphotometer of the Asiago Astrophysical Observatory we have measured the progenitor merged pair against a set of 16 nearby reference stars on the B and V plates listed in Table 1 (we choose such a large number of comparisons in order to reduce any influence by possible variability of any of them). We did not have a well calibrated and faint enough photometric comparison sequence around the progenitor. However, we had a known relation between image diameter and relative magnitudes derived from measurements made on some open cluster fields with the same equipment used for Nova Cas 1993. We applied this calibration to the 16 reference stars and set the zero point by adopting the values B=15.0 and V=14.0 for the star labelled A in Figure 1. When actual B,V magnitudes for this star are obtained, all the magnitudes in Table 1 can be scaled accordingly. [FIGURE 1] Figure 1. Comparison of the Nova Cas 1993 field as seen in V band on UT Dec. 11.85, 1993 (top panel) and on UT Oct. 11.93, 1985 with the 67/92 cm Schmidt telescope of the Asiago Astrophysical Observatory. The progenitor appears to be the northern component of a very close double star (arrowed). North is up and East is to the left. Each panel covers 6 arcmin on a side. Table 1 List of Asiago Schmidt plates on which the progenitor of Nova Cas 1993 is recorded and that have been measured in search for brightness variations of the latter during the quiescence period. For the zero point of the magnitude scale in both B and V bands see the text. a = progenitor visible but of a brightness too close to the plate limit for meaningful measurement. -------------------------------------------------------------------------------- date UT Exp.time Plate type Filter B V Notes (start) (min) -------------------------------------------------------------------------------- Nov.4 1978 21.29 20 103a-D GG14 17.5 Dec.3 1980 25.14 30 103a-D GG14 17.1 Dec.23 1984 20.23 30 103a-D GG14 17.1 Aug.18 1985 23.25 30 103a-D GG14 17.4 Oct.11 1985 22.10 30 103a-D GG14 17.0 Nov.6 1985 21.26 30 103a-D GG14 17.1 Oct.5 1970 22.50 30 103a-O GG13 18.5 Nov.26 1970 20.32 30 103a-O GG13 18.4 Nov.4 1978 21.02 20 103a-O GG13 18.0 Nov.1 1981 21.16 30 103a-O GG13 18.5 Nov.20 1981 22.15 30 103a-O GG13 18.3 Aug.21 1985 23.38 30 103a-O GG13 18.1 Oct.5 1970 23.32 40 I-N RG5 a Nov.2 1970 24.23 40 I-N RG5 a Nov.4 1978 22.01 30 I-N RG5 a Oct.1 1980 23.16 30 I-N RG5 a Nov.1 1981 21.56 30 I-N RG5 a Nov.20 1981 22.51 30 I-N RG5 a Jan.2 1982 21.45 30 I-N RG5 a Jan.7 1984 21.13 30 I-N RG5 a Dec.23 1984 19.43 30 I-N RG5 a -------------------------------------------------------------------------------- The observations reported in Table 1 started ~23 yrs and stopped ~8 yrs before the nova outburst. We can conclude from the data in Table 1 that during this time interval: *no erratic or outburst-like variability with an amplitude larger than 0.2-0.3 mag affected the nova progenitor in quiescence *no systematic and long-term trend in the mean brightness was observable in quiescence. This also holds true for the I-N + RG5 infrared observations. We did not measure these plates because the progenitor was too close to the plate limit. However, eye inspection of these plates at the microscope (made in a separate and independent way by all of us) confirmed that no variability larger than 0.3 mag affected the progenitor in the infrared during the quiescence period covered by the observations reported in Table 1. Acknowledgements. The help of I. Rigoni and S. Dalle Ave in the recovery of plates from the archives and work in the darkroom is acknowledged. T.V.T., L.H. and P.H. would like to thank the Asiago Astrophysical Observatory for the kind hospitality during the period in which this note has been prepared. Part of this research has been sponsored by the Bulgarian National Foundation for Scientific Research under contract F-35/1991. LADISLAV HRIC ULISSE MUNARI Astron. Inst. Slovak Acad. Science Asiago Astrophysical Observatory, 05960 Tatranska Lomnica I-36012 Asiago (VI), Italy, The Slovak Republic, E-Mail 39003::munari E-Mail astrhric@asu.savba.sk TOMA V. TOMOV PAVEL HAZUCHA NAO Rozhen, P.O.Box 136, Hlohovec Astronomical Observatory, 4700 Smolyan, Bulgaria, 92001 Hlohovec E-Mail ttomov @ bgearn.bitnet The Slovak Republic References: Kraft, R.P. 1964, Astrophys. J., 139, 457 [BIBCODE 1964ApJ...139..457K ] Robinson, E.L. 1975, Astron. J., 80, 515 [BIBCODE 1975AJ.....80..515R ] Warner, B. 1989, in Classical Novae, M.F. Bode & A. Evans eds., Wiley Publ., p. 1 [BIBCODE 1989clno.conf....1W ]