COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2287 Konkoly Observatory Budapest 1983 March 1 HU ISSN 0374-0676 PHOTOMETRIC OBSERVATIONS OF CATACLYSMIC VARIABLES * Photometric observations of 24 cataclysmic variables in the UBV colour system were carried out during 11 nights in 1978 and 1979 at the 1-m-telescope of the European Southern Observatory at La Silla. All measurements were taken with the ESO one-channel photometer. For details concerning the measurements and the data reduction, see Bruch (1982a). The results of the observations are given in Table I. In general, each star was observed once or twice in each colour. The errors of the brightness and colour indices were estimated from informations about photon statistics furnished by the photometer software (including statistical fluctuations of the night sky brightness, which is important for the faintest stars observed) and from the deviations of the individual measurements from the mean. Since the integration times per colour ranged between 60s and 100s and were thus not short compared to the flickering time scale, rapid brightness variations of the stars tend to enhance the errors. Light curves of some of the brighter stars were observed with a time resolution between 300s and 8s for a period between 38m and 297m. In these cases, Table I gives the mean values of brightness and colours for each observing run. Here, the errors were computed solely from the deviations of the individual measurements from the mean. For all light curves, the brightness difference DeltaV between the brightest and the faintest data point is also given in Table I in order to allow an estimate of the flickering amplitude. It is interesting to note that the flickering of the SU UMa - star WX Hyi (which belongs to those cataclysmic variables with particularly large flickering amplitudes; see Bruch, 1982a) is strongest on the decline from an outburst just before reaching the minimum stage. A comparatively low flickering amplitude is observed from the old nova HR Del; a fact which is interpreted elsewhere (Bruch, 1982b). Most of the cataclysmic variables observed exhibit colours which are within the range normally found for these objects. There are, however, three exceptions. * Based on observations collected at the European Southern Observatory Table I: UBV colours of cataclysmic variables Name Date Type1 Phase2 V B-V U-B N3 V J.D.2440000+ VY Aqr 4130 RN m 17.08+/- 0.22 -0.18+/- 0.25 -0.80+/- 0.17 2 VZ Aqr 4129 U m 16.51+/- 0.16 0.78+/- 0.20 -0.32+/- 0.26 1 AE Aqr 4129 NL 11.39+/- 0.03 0.85+/- 0.04 -0.09+/- 0.16 2 UU Aql 4129 U m 16.66+/- 0.18 0.71+/- 0.20 -1.28+/- 0.15 1 FO Aql 4128 U m 16.57+/- 0.14 0.66+/- 0.17 -0.58+/- 0.16 1 V 725 Aql 4130 U m 15.79+/- 0.11 1.52+/- 0,14 0.60+/- 0.47 2 AT Ara 4131 U m 14.25+/- 0.12 0.82+/- 0.09 -0.69+/- 0.12 2 WW Cet 4126 Z St? 14.04+/- 0.24 0.11+/- 0.24 -0.98+/- 0.15 13 0.88 4131 Z St? 14.16+/- 0.04 0.04+/- 0.05 -1.04+/- 0.02 2 BP CrA 4129 Z M 14.23+/- 0.07 0.10+/- 0.02 -0.79+/- 0.02 2 HR Del 3724 N m 12.16+/- 0.09 -0.05+/- 0.02 -0.84+/- 0.02 45 0.17 3727 N m 12.19+/- 0.05 -0.10+/- 0.01 -0.84+/- 0.02 23 0.16 3728 N m 12.14+/- 0.03 -0.09+/- 0.01 -0.82+/- 0.02 90 0.14 3729 N m 12.15+/- 0.04 -0.09+/- 0.01 -0.80+/- 0.02 99 0.12 3730 N m 12.10+/- 0.03* 500 0.14* IS Del 4129 Z St? 15.90+/- 0.07 0.09+/- 0.08 -0.65+/- 0.06 2 WX Hyi 3724 SU m 14.68+/- 0.37 0.08+/- 0.17 -1.14+/- 0.09 11 0.93 3727 SU m 14.85+/- 0.12 0.07+/- 0.11 -1.07+/- 0.11 35 0.53 3728 SU m 14.84+/- 0.11 0.01+/- 0.06 -1.10+/- 0.09 68 0.53 3729 SU m 14.75+/- 0.12 325 0.77 3729 SU m 14.72+/- 0.14* 350 0.68* 3730 SU m 14.76+/- 0.19 0.02+/- 0.07 -1.18+/- 0.09 125 0.94 4127 SU Dec 13.07+/- 0.09 0.20+/- 0.04 -0.02+/- 0.10 166 0.85 4129 SU Dec 14.21+/- 0.27 0.21+/- 0.11 -0.97+/- 0.15 170 1.43 4130 SU m 14.70+/- 0.16 0.08+/- 0.08 -1.16+/- 0.11 195 0.77 4131 SU m 14.66+/- 0.15 0.07+/- 0.07 -1.18+/- 0.10 141 0.65 Table I (continued) Name Date Type1 Phase2 V B-V U-B N3 V J.D* 2440000+ TU Ind 4129 U m 15.32+/- 0.04 0.22+/- 0.06 -0.89+/- 0.03 2 V 841 Oph 3724 N m 13.39+/- 0.03 0.40+/- 0.02 -0.55+/- 0.04 9 0.09 3727 N m 13.22+/- 0.04 0.43+/- 0.03 -0.60+/- 0.04 16 0.18 3728 N m 13.28+/- 0.04 0.40+/- 0.03 -0.58+/- 0.04 15 0.14 3729 N m 13.10+/- 0.10 0.40+/- 0.03 -0.58+/- 0.04 101 0.26 3730 N m 13.03+/- 0.05 0.40+/- 0.02 -0.61+/- 0.04 851 0.32* 3730 N m 13.44+/- 0.06* V2051 Oph 4128 U m 15.32+/- 0.06 0.00+/- 0.07 -0.90+/- 0.05 1 BI Ori 4131 U Dec? 14.56+/- 0.03 0.04+/- 0.04 -0.78+/- 0.03 2 CN Ori 4131 Z St? 12.81+/- 0.01 0.02+/- 0.01 -0.74+/- 0.01 2 RU Peg 4129 U m 12.64+/- 0.01 0.63+/- 0.02 -0.78+/- 0.05 2 RZ Sge 4129 U m 16.86+/- 0.23 0.56+/- 0.27 -0.78+/- 0.25 1 MM Sco 4131 U m 17.00+/- 0.16 1.53+/- 0.27 -0.70+/- 0.38 2 FQ Sco 4130 U m 16.83+/- 0.16 1.62+/- 0.28 -0.70+/- 0.44 2 V 478 Sco 4131 U m 16.27+/- 0.12 0.42+/- 0.14 -0.67+/- 0.11 2 UZ Ser 4128 U m 15.69+/- 0.08 0.14+/- 0.06 -0.71+/- 0.04 2 FY Vul 4128 Z m 14.80+/- 0.04 0.53+/- 0.04 -0.65+/- 0.04 2 1: Type N = nova 2: Phase m = minimum 3: N = number of individual U = U Gem star M = maximum measurements Z = Z Cam star St = standstill SU = SU UMa star Dec = decline * = B-magnitudes RN = recurrent nova NL = novalike variable MM Sco has an extremely red B-V - colour index, but is blue in U-B. This might indicate an extreme intensity distribution between the hot primary and the cool secondary. Vogt (1981) measured red colours both in B-V (0.8m...1.3m) and U-B (0.2m...0.8m). It is doubtful that this discrepancy can be explained by normal colour variation due to flickering. FQ Sco shows colours similar to MM Sco. However, it has a faint optical companion which might have been in the diaphragm and influenced the observations. The colours of V 725 Aql resemble those of the recurrent nova T CrB (Bruch, 1980; Walker, 1957). Since all three systems have been observed quite inadequately so far, the results for these stars await confirmation by independent observations. A. BRUCH Astronomisches Institut Domagkstrasse 75 D-4400 Munster Fed. Rep. Germany References: Bruch, A.; 1980: Inf. Bull. Var. Stars 1805 Bruch, A.; 1982a: "Kataklysmische Veranderliche in Beobachtung:, Statistik und Analyse", Ph.D. thesis, Munster* [BIBCODE 1982PhDT.......145B ] Bruch, A.; 1982b: Publ. A.S.P. 94, 916 [BIBCODE 1982PASP...94..916B ] Vogt, N.; 1981: "SU UMa - Sterne und andere Zwergnovae", Habilitation thesis, Bochum Walker, M.F.; 1957: IAU Sym. 3, 46 [BIBCODE 1957IAUS....3...46W ] * copies are available from the author on request