COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3745 Konkoly Observatory Budapest 7 July 1992 HU ISSN 0374 - 0676 UBV - Observations of the Recent Outbursts of Three Cataclysmic Variables In this contribution I report about results of UBV measurements of three outbursting cataclysmic variables, namely Nova Pup 1991, HV Vir and OY Car, which were observed as targets of opportunity at the ESO 1-m-telescope on La Silla between 1992, April 16 and 25. All observations were obtained sequentially with the one-channel photometer. Measurements of E-region stars were used to tie the instrumental system into the standard UBV system. The formal accuracy of the transformation was found to be of the order of 0.01m in all passbands. However, the extraordinary colours which make cataclysmic variables bluer than the available standard stars may introduce an additional transformation error. The results of the photometry of the three target stars are given in Table 1. The errors quoted there were derived mostly from counting statistics (but see the case of OY Car below) and do not contain the contribution of the standard transformation. Nova Pup 1991 was detected by Camilleri (1992). UBV photometric measurements are reported by Gilmore (1992). A visual light curve was published by the AAVSO (AAVSO alert note 156 (1992)). According to these measurements, Nova Pup 1991 is a moderately fast nova. The present observations indicate a slight decline of the star over a time base of nine days. The present magnitudes and colours are significantly brighter and redder that those obtained at the same epoch by Gilmore (IAU Circ. No. 5527) who found V = 11.15, B - V = 0.13, U - B = -0.75 on April 19.40. The difference cannot be explained by accidental measurement errors but indicate a severe difference of the photometric systems. HV Vir was classified as a classical nova which had its outburst in 1929 (see Duerbeck 1987). The present outburst was detected by Schmeer (1992) on 1992, April 19.917. The characteristics reported in IAU Circ. Nos. 5503, 5505, 5509, 5516 and 5517 leave no doubt that the star must be reclassified as a dwarf nova of WZ Sge type. The present observations started on 1992, April 23.135 and could only be continued until April 25.265. During this time, HV Vir declined gradually. Outbursts of WZ Sge stars have all properties of superoutbursts of SU UMa stars. A comparison of the colours of HV Vir with those of SU UMa systems in superoutburst (Bruch 1984) indicates that it is slightly bluer in B - V than the SU UMa stars, but significantly bluer in U - B. Results of time series observations of HV Vir in white light on 1992 Apr. 23 and 24 will be reported in more detail at another place. OY Car was undergoing a superoutburst which started on 1992, April 7 (Horne 1992). Light curves in UBV were observed on April 16, 19 and 20. On April 23 and 24, white light observations were undertaken, complemented by a few UBV measurements. On April 124, a single UBV measurement was obtained. Here, I report only about the night-to-night variations of magnitude and colours, postponing an analysis of the light curves of the individual nights to a later publication. For April 16, 19 and 20, Table 1 contains mean out of eclipse magnitudes and colours. In this case the quoted errors are standard deviations, calculated from the individual UBV-measurements and are dominated by flickering activity and in particular by the effect of superhumps. They are therefore larger than the errors quoted otherwise in Table 1. In the course of time, OY Car shows a marked decline from superoutburst maximum, until on April 25 it had almost reached its quiescent magnitude which Vogt (1981) observed to be at V = 15.55. The colours during outburst as well as those close to quiescence differ somewhat from values observed at other epochs at similar phases (Vogt 1981). Moreover, U - B shows a marked variability during the course of the outburst. Table 1: UBV - data on Nova Pup 1991, HV Vir and OY Car Date J.D. (1992) UT 2448700+ V B-V U-B Nova Pup 1991 Apr. 16 0:58 28.540 10.94+/-0.02 0.27+/-0.01 -0.56+/-0.01 Apr. 19 1:52 31.578 10.93+/-0.01 0.26+/-0.01 -0.57+/-0.01 Apr. 20 0:11 32.508 10.96+/-0.01 0.29+/-0.01 -0.57+/-0.01 Apr. 22 23:43 35.488 10.98+/-0.01 0.27+/-0.01 -0.60+/-0.01 Apr. 23 23:55 36.497 11.00+/-0.01 0.27+/-0.01 -0.60+/-0.01 Apr. 24 23:48 37.492 10.98+/-0.01 0.23+/-0.01 -0.59+/-0.01 HV Vir Apr. 23 3:15 35.635 12.12+/-0.02 -0.14+/-0.02 -0.93+/-0.02 Apr. 24 2:49 36.617 12.44+/-0.02 -0.13+/-0.02 -0.91+/-0.02 Apr. 24 6:54 36.788 12.47+/-0.01 -0.09+/-0.02 -0.90+/-0.02 Apr. 25 6:21 37.765 12.63+/-0.01 -0.08+/-0.01 -0.87+/-0.01 OY Car Apr. 16 1:42-2:12 28.571-28.592 12.26+/-0.07 0.04+/-0.06 -0.86+/-0.08 Apr. 19 2:27-5:12 31.602-31.717 12.74+/-0.08 0.07+/-0.04 -0.63+/-0.07 Apr. 20 0:18-3:54 32.5013-32.663 12.65+/-0.11 0.08+/-0.04 -0.71+/-0.07 Apr. 23 0:00 35.500 12.97+/-0.03 0.05+/-0.01 -0.79+/-0.04 Apr. 24 0:12 36.508 13.54+/-0.07 0.04+/-0.04 -0.87+/-0.03 Apr. 24 2:21 36.598 13.73+/-0.03 0.00+/-0.05 -0.99+/-0.04 Apr. 25 0:14 37.510 15.20+/-0.08 0.19+/-0.12 -1.06+/-0.12 ALBERT BRUCH Astronomisches Institut Wilhelm-Klemm-Strasse 10 W-4400 Munster F.R.Germany References: Bruch, A.: 1984, Astron. Astrophys. Suppl. 56, 441 [BIBCODE 1984A&AS...56..441B ] Camilleri, P.: 1992, IAU Circ. No. 5422 [BIBCODE 1992IAUC.5422....1C ] Duerbeck, H.W.: 1987, Space Sc. Rev. 45,1 [BIBCODE 1987SSRv...45....1D ] Gilmore, A.C.: 1992, IAU Circ. Nos. 5422, 5430, 5455, 5483, 5493, 5527, 5538 [BIBCODE 1992IAUC.5422....1C ] [BIBCODE 1992IAUC.5430....3G ] [BIBCODE 1992IAUC.5455....2G ] [BIBCODE 1992IAUC.5483....3G ] [BIBCODE 1992IAUC.5493....2G ] [BIBCODE 1992IAUC.5527....4A ] [BIBCODE 1992IAUC.5538....2G ] Horne, K.: 1992, IAU Circ. No. 5494 [BIBCODE 1992IAUC.5494....2H ] Schmeer, P.: 1992, IAU Circ. No. 5502 [BIBCODE 1992IAUC.5502....1S ] Vogt, N.: 1981, SU UMa Sterne und andere Zwergnovae, habilitation thesis, Bochum