COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3135 Konkoly Observatory Budapest 21 January 1988 HU ISSN 0374-0676 UBV OBSERVATION OF NOVA VULPECULAE 1987 Beckmann and Collins (1987) discovered a nova at R.A. = 19h02.1m Dec. = + 21 40' (equinox 1950.0) on Nov. 15.042 and Nov, 15.128 UT. UBV observations reported here were made from three days after the discovery to mid-December 1987 with a 20-cm reflector at Tamashima, Japan. The photometer used consists of a microcomputer controlled photon counter and an uncooled Hamamatsu R 647-04 photomultiplier (bi-alkali cathode) and UBV filters ( Schott GG495 (2-mm) for V, GG385 (2-mm) + BG12 (1-mm) for B, and UG1(2-mm) for U ). Actual observations were made differentially with respect to HR7267 (V= 6.23, B-V = +0.40, U-B = +0.01, F3V ) as a comparison star and the comparison star was also checked with HR7306 (V = 4.77, B-V = -0.05, U-B = -0.54, B4IV according to Hoffleit (1982) ). In the data reduction, the dead time corrections of the photon counter and the atmospheric extinction corrections were carried out. Not only the first order extinction for differential air mass but also the second order extinction for colors were taken into account because the observations were made at relatively large zenith distances. The transformation coefficients to the UBV system were determined from observation of standard stars. The obtained V magnitudes and colors are given in Table I and also plotted in Figure 1. Visual observations of early time of discovery are also shown for comparison in the figure. For the check of the quality of observations on the respective nights, the differential magnitudes and colors between the comparison and the check stars are given in Table II. It was found that the magnitude of the nova was decreasing slowly, and both B-V and U-B colors became bluer with time, It is presumed that the light maximum must have been about the day discovered Nov. 15 UT) according to V magnitudes and colors presented here. This is supported by the study of van den Bergh and Younger ( 1987 ) ; novae with smooth light curves exhibit a sharp reddening pulse in both B-V and U-B which is centered within one day of maximum light and the half-width of these reddening pulses run up to 7 days for slow novae. Table I UBV photometry of Nova Vulpeculae 1987 No. Hel.J.D. n V B-V U-B 2447000+ mean s.d. mean s.d. mean s.d. 1 117.9087 8 7.39 0.01 0.86 0.01 0.42 0.03 2 119.9002 7 7.17 0.01 0.73 0.01 0.03 0.02 3 123.8988 8 7.28 0.01 0.67 0.02 -0.02 0.01 4 128.8902 9 7.28 0.01 0.64 0.01 -0.25 0.02 5 130.8991 6 7.30 0.01 0.65 0.02 -0.34 0.02 6 131.8940 9 7.07 0.01 0.66 0.01 -0.22 0.03 7 132.8849 4 7.22 0.02 0.61 0.01 -0.49 0.04 8 133.8790 10 7.62 0.01 0.67 0.02 -0.19 0.02 9 136.8869 8 7.99 0.01 0.59 0.01 -0.49 0.01 10 142.8685 1 8.13 - 0.57 - -0.56 - 11 143.8815 7 7.87 0.01 0.67 0.02 -0.50 0.06 12 145.8806 4 8.06 0.01 0.54 0.00 -0.67 0.02 13 148.8853 5 7.93 0.01 0.58 0.02 -0.78 0.03 "n" in the third column denotes the number of single observations with 20-seconds integration time for each band. [FIGURE 1] Figure 1 Light and color curves of Nova Vulpeculae 1987. Filled circles refer to photoelectric observations; open circles to visual observations by Beckmann and Collins (1987). Table II Observed differential magnitudes and colors between the comparison and the check stars No. J.D. n DeltaV Delta(B-V) Delta(U-B) 244700+ 1 117.9 4 1.45 0.46 0.54 2 119.9 1 1.44 0.48 0.51 3 123.9 1 1.45 0.45 0.54 4 128.9 1 1.44 0.47 0.56 5 130.9 2 1.45 0.47 0.53 6 131.9 2 1.44 0.45 0.57 7 132.9 1 1.46 0.45 0.56 8 133.9 2 1.47 0.46 0.53 9 136.9 2 1.47 0.44 0.55 10 142.9 1 1.44 0.50 0.52 11 143.9 1 1.47 0.42 0.57 12 145.9 2 1.46 0.45 0.53 13 148.9 2 1.48 0.42 0.57 mean 1.46 0.46 0.54 B.S.Catalogue 1.46 0.45 0.55 I would like to express my hearty thanks to Prof. M. Kitamura of Tokyo Astronomical Observatory and Dr. A. Yamasaki of Tokyo University for their encouragements and advice. OSAMU OHSHIMA Member of Japan Amateur Photoelectric Observers Association ( JAPOA ) Tamashima 3-10-18, Kurashiki, Okayama 713, Japan References: Beckmann, K. and Collins, P. 1987, I.A.U. Circular No. 4488. [BIBCODE 1987IAUC.4488....1B ] Hoffleit, D. 1982., The Bright Star Catalogue, 4th edition, Yale University Observatory, van den Bergh, S. and Younger, P.F. 1987, Astron. and Astrophys. Suppl. Ser., 70, 125. [BIBCODE 1987A&AS...70..125V ]