COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3093 Konkoly Observatory Budapest 6 October 1987 HU ISSN 0374-0676 ADDITIONAL PHOTOMETRIC DATA FOR THE X-RAY SOURCE TT ARIETIS DURING 1985-1986 As a part of the programme for the study of anti-dwarf novae (or VY Scl stars) carried out at the Department of Astronomy of the Bulgarian Academy of Sciences, after the organization of regular photometric observations of KR Aur, in 1985 observations of TT Ari, another member of this group, were initiated, During the past two seasons, besides estimates of the brightness of the star in a standard UBV system (Table I), the behaviour of the object in the night of August 22/23, 1985 was followed for 3 hours ( Fig. 1 ) and a patrol was carried out in the "u" region in the night of November 1/2, 1986 (Fig. 2), Photoelectric observations were carried out with the 60 cm telescope of the National Astronomical Observatory Rozhen. Star "c" (see Wenzel et al. 1986) served as comparison star. For transformation of the instrumental u,b,v stellar magnitudes to the standard U,B,V magnitudes the relations Delta V= Delta v+0.105 Delta (B-V) Delta (B-V) = 1.118 Delta (b-v)+0,034 Delta (b-v) x Delta (U-B) = 0.800 Delta (u-b)+0,056 Delta (u-b) x were used. The integration time was 10s. Our observations show the following results: 1. During all the nights of the observations the star was in its "active" state. The mean of the resulting points yields the following magnitudes for TT Ari in 1985: U=9.94, B=10.85, V=10.78. For 1986 the mean magnitudes are U=9.76, B=10.67, V=10.78, In 1986 an increase of the average brightness by 0.16 mag in V and 0.18 mag in B and U was found, 2. Our 3 hours of observations were carried out one night after simultaneous X-ray (EXOSAT) and optical observations in the night of August 21/22,1985. Unfortunately the time interval was not sufficiently long. But three-colour measurements show a well-expressed maximum, The start and the end of the observations are in the neighbourhood of brightness minima, The wave-shaped variations are ~ 0.25 mag in V and ~ 0.32 mag in B and U. This is in agreement with the results of coordinated observations (see Hudec et al. 1987). The position of the maximum "C" calculated from the photometric elements given by Wenzel et al, (1986) is plotted in Fig 1. [FIGURE 1] [FIGURE 2] 3. Patrol observations during the night of November 2/3, 1986 show quasiperiodic fluctuations with an amplitude up to 0.25 mag and duration up to 3 minutes, The cycle length does not seem to be constant, but varying between 3 and 6 minutes. Observations of Rossiger (1987)carried out a month earlier show quasiperiodic fluctuations of brightness with cycle length between 14 and 21 minutes, Wenzel et al. (1986) found a cycle length of about 10+/-5 minutes. It seems that the length of the cycle is varying not only during the night but, more essentially, from night to night. During the patrol observations there occurred an unusually deep dip in the brightness (Delta u ~ 2.3 mag ) with the duration of about 10 minutes. For the first 4-5 minutes the star decreased in brightness by 0.7 mag and in the following 2 minutes it decreased further by 1.6 mag, For the next 3 minutes the star reached the brightness typical of the night. Seven minutes later a new dip of the brightness with an amplitude up to 0.8 mag and duration of about Table I Magnitude estimates of TT Arietis JD 244... V B-V U-B 6264.5431 10.95 +/-0.01 -0.06 +/-0.02 -0.91 +/-0.02 5496 10.83 +/-0.01 -0.09 +/-0.01 -0.95 +/-0.02 6267.5321 10.94 +/-0.02 -0.11 +/-0.02 -0.99 +/-0.02 .5392 10.98 +/-0.01 -0.16 +/-0.02 -0.98 +/-0.02 .5442 11.01 +/-0.03 -0.05 +/-0.04 -0.89 +/-0.02 6289.5531 10.93 +/-0.01 -0.09 +/-0.01 -0.94 +/-0.03 .5590 10.92 +/-0.01 -0.06 +/-0.01 -0.89 +/-0.03 6671.4993 10.78 +/-0.01 -0.10 +/-0.02 -0.89 +/-0.02 .5110 10.72 +/-0.01 -0.10 +/-0.02 -0.90 +/-0.02 6672.5189 10.78 +/-0.01 -0.11 +/-0.01 -0.90 +/-0.01 .5304 10.85 +/-0.01 -0.14 +/-0.02 -0.92 +/-0.01 .5400 10.87 +/-0.02 -0.08 +/-0.03 -0.90 +/-0.02 .5498 10.87 +/-0.02 -0.05 +/-0.03 -0.89 +/-0.02 6697.4112 10.76 +/-0.03 -0.18 +/-0.07 -0.95 +/-0.07 .4147 10.74 +/-0.03 -0.06 +/-0.07 -0.98 +/-0.07 .4181 10.73 +/-0.03 -0.09 +/-0.07 -0.95 +/-0.07 .4187 10.73 +/-0.03 -0.13 +/-0.07 -0.95 +/-0.07 6736.4882 10.71 +/-0.01 -0.12 +/-0.02 -0.89 +/-0.02 .4961 10.75 +/-0.01 -0.10 +/-0.02 -0.84 +/-0.02 10+-3 minutes occurred. It has to be noted that at 21h07m(UT), 35 minutes before the deep dip, our observations showed a decrease of the brightness too (Delta u max ~0.8mag, Delta t-about 13 minutes). This part of the observations is not plotted in Fig. 2 because, unfortunately, the recording was performed during a period of stabilisation of the parameters of the instrument. A month before our patrol Rossiger (1987) observed also a deep dip in brightness up to 0.9 mag in the "b" region. In our opinion, further patrol observations would be very useful for elucidating the nature of TT Arietis. Z. KRAICHEVA, A. ANTOV, V. GENKOV Department of Astronomy Bulgarian Academy of Sciences 72 Lenin Blvd Sofia 1784 Bulgaria References: Hudec, R. et al, 1987, Astrophys,Sp.Sci, 130, 255 [BIBCODE 1987Ap&SS.130..255H ] Rossiger, S., 1987, Inf.Bull.Var.Stars No. 3007 Wenzel, W., et al., 1986, Preprint