COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2277 Konkoly Observatory Budapest 1983 February 14 HU ISSN 0374-0676 OBSERVATIONS OF V711 TAURI IN OCTOBER 1981/JANUARY 1982* The observations of V711 Tau were obtained in ESO, La Silla; Chile during two photometric programmes: 1. the uvby photometry with the 50 cm Danish telescope in October 1981, 2. the UBVRI (Cousins) photometry with the 50 cm ESO telescope in January 1982, The same comparison star 10 Tau was used on both occasions. The uvby photometric data for the comparison star based on 9 nights are: V = 4.287, (b-y) = 0.366, m1 = 0.173, c1 = 0.374 (m.e. +/- 0.002 in all cases); they agree very well with the previous results of Olsen (1977). The UBVRI mean data based on 6 nights are: V = 4.36 +/- 0.01, (B-V) = 0.550 +/- 0.003, (U-B) = 0.031 +/- 0.005, (V-R)c = 0.349 +/- 0.005, (V-I)c = 0.689 +/- 0.009. When compared with the previous UBV data they reveal a reasonably good agreement of the (B-V) and (U-B) colours and an unexplained drop in V which is probably caused by some transformation problem. The differential observations of V711 Tau are listed in Tables I and II and are plotted in Fig. 1. The ephemeris used to compute phases was based on the spectroscopic one by Bopp and Fekel (1976; cf. also Dorren et al. 1981): MJD 42765.569 + 2.83782 E; it predicts moments of conjuction with the more active component in front. We would like to point out the following: 1.The light curve has a long lasting depression and a short maximum at phases around 0.7 to 0.8. 2.The location of this maximum is strengthened by addition of a few uvby observations by Olson (1982) made exactly on the same nights in October 1981 as the present uvby observations but plotted by Olson with a considerable and perhaps misleading phase shift. * Based on observations obtained at the European Southern Observatory, La Silla, Chile. 3.The UBVRI observations made in January 1982 agree well with those obtained by Mohin et al. (1982), They indicate an increase in the minimum light level by about 0.06 mag. in 2 months. Table I Differential uvby observations of V711 Tau October 1981 MJD (hel) Phase DeltaV Delta(b-y) Deltam1 Deltac1 (=JD-2400000.5) 44898.246 0.519 1.561 0.221 0.150 -0.111 44899.273 .881 1.495 0.221 0.166 -0.105 44900.239 .222 1.573 0.225 0.149 -0.112 44901.209 .564 1.540 0.220 0.150 -0.122 44905.196 .969 1.533 0.224 0.145 -0.124 44906.225 .331 1.563 0.226 0.141 -0.118 44907.248 .692 1.483 0.219 0.148 -0.112 44908.248 .044 1.558 0.224 0.146 -0.111 44909.247 0.396 1.564 0.227 0.137 -0.109 Table II Differential UBVRI observations of V711 Tau January 1982 MJD (hel) Phase DeltaV Delta(B-V) Delta(U-B) Delta(V-R) Delta(V-I) (JD-2400000.5) 44987.035 0.807 1.424 0.377 0.486 0.207 0.380 44988.092 .180 1.505 0.372 0.448 0.205 0.392 44989.041 .514 1.503 0.376 0.443 0.203 0.391 44990.037 .865 1.438 0.384 0.461 0.210 0.378 44992.037 .570 1.504 0.362 0.439 0.215 0.419 44993.041 0.924 1.504 0.369 0.449 0.221 0.412 [FIGURE 1] The light curve of V711 Tau obtained in October 1981 (filled circles) and January 1982 (crosses). Observations obtained simultaneously by Olson (1982) in October 1981 are also plotted (open circles). It is the pleasant duty to acknowledge that the present observations have been obtained during author`s association with the Max-Planck-Institut fur Astrophysik in Garching, West Germany. S. M. RUCINSKI Institute of Astronomy Madingley Road, Cambridge CB3 OHA (on leave from the Warsaw University Observatory) References: Bopp, B. W., Fekel, F.: 1976, Astron.J., 81, 771. [BIBCODE 1976AJ.....81..771B ] Dorren, J.D., Siah, M.J., Guinan, E.F., McCook, G.P.: 1981, Astron.J., 86, 572. [BIBCODE 1981AJ.....86..572D ] Mohin, S., Raveendran, A.V., Mekkaden, M.V., Jayakumar, K., Rosario, M.J.: 1982, IBVS No. 2190. Olsen, E.H.: 1977, Astron.Astrophys.Suppl., 29, 313. [BIBCODE 1977A&AS...29..313O ] Olson, E.C.: 1982, IBVS No. 2206.