2 Observations and results

The data consist of 8 photoelectric series in the U and B photometric bands with a duration from 1.6 to 3.3 hours. Apart from these series, there are 35 additional measurements in the standard UBV system obtained from July 1992 to October 1993. The integration time for all observations was 10 s and star "C" (see Walker 1954) served as a comparison star. The photoelectric data are summarized in Tables 1 and 2. All observations were carried out with the one-channel photometers attached to the 60-cm Carl Zeiss telescopes of the Rozhen and Belogradchik Observatories of the BAS. The observational data were processed with the reduction software described by Kirov et al. (1991).

  

Table 2: UBV observations of MV Lyr

  

Figure 1: U(B) and V(B) diagrams for the UBV observations in 1992 (open circles) and 1993 (points)

The UBV data are shown in Table 2 and Fig. 1. They cover the ascending branch top end of the long-term light curve after the star had left its 1979-1989 low state (Wenzel & Fuhrmann 1989; Kraicheva & Genkov 1992; Rosino et al. 1993). During all the nights of observations the star was in active state and reached its maximal brightness gradually: for a year the mean brightness increased by about 0.15 mag in the V and B bands and 0.20 mag in the U band. The behaviour of another member of the VY Scl novalikes, TT Ari, was the same after returning to high state (Kraicheva et al. 1987). The MV Lyr colors varied between -0.05 and -0.23 for B-V and between -0.90 and -1.09 for U-B. According to Robinson et al. (1981) and Rosino et al. (1993) at low and intermediate state the colors of MV Lyr are usually somewhat bluer with $B-V \simeq -0.35$ and $U-B \simeq -1.25$. Our observations showed a linear correlation between U, B and V magnitudes (Fig. 1). The slopes of the dependencies U(B) and V(B) are $1.16 \pm 0.10$and $0.89 \pm 0.07$, respectively, and indicate that the largest change is in U and the least is in V band. The data obtained in 1992 as well as those obtained in 1993 follow the same tracks.