COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1878 Konkoly Observatory Budapest 1980 December 5 HU ISSN 0374-0676 OBSERVATIONS OF THE SPOT STARS EQ Vir AND UZ Lib IN 1977 There is a rapidly increasing amount of observations substituting the existence of magnetic active stars on or in the vicinity of the lower main sequence. Ca II and even hydrogen emission lines are often combined with the so called BY Dra syndrome, a sinusoidal light change referred to star spots. EQ Vir is one of the better known stars of this type. Broad band photometry is known from the years 1977 (Ferraz Mello and Torres, 1977) and 1975 (Hartmann, 1976). The amplitude has changed during that time from 0.10m to 0.06m. [FIGURE 1] Figure 1: 1977 observations of EQ Vir. In a 24d interval in March and April, 1977 this star. has been observed photoelectrically in B with the 67 cm Bochum telescope at the European Southern Observatory (La Silla/Chile). The measurements are plotted in Fig. 1. The underlying ephemeris (period by Torres and Ferraz Mello, 1973) was 2443219.30 + 3.96d.E. Apparently the amplitude of the light variation has recovered to 0.08m. Also the shape of the light curve has changed, showing the complete rise in only a quarter of the period. It is not clear, if the observed minima of different years belong to the same spot groups. In such a case the change of the light curve shape could be a measure of differential rotation in late type dwarf stars. UZ Lib is a puzzle for now half a century. Parenago (1931) classified this star as RR Lyrae type with a period of 0.4413m. Wisniewski (1973) assumed that this object is a beta Lyrae type eclipsing binary, with a sinusoidal light curve and a period of 9.49976d. However Evans and Bopp (1974) suspected it to be a BY Dra type star with a period of 4.75d - as a consequence of its Ca II emission lines (Bidelman, 1954). This object has been observed during the same time interval as EQ Vir with the same instrument. The measurements are shown in Fig. 2. [FIGURE 2] Figure 2: 1977 observations of UZ Lib. They are plotted according to 2443222.15 + 4.75d E i.e. the period suggested by Evans and Bopp. There is no difference in shape of the light curve halves, if the data are drawn using Wisniewski's period twice that value. The shape of the light curve itself, however, has changed. The amplitude is only 0.26m compared with 0.32m five years earlier. There is a minimum 0.38p after maximum and secondary minimum around 0.70p. The light curve, sometimes of irregular shape is a further hint that this star belongs to the BY Dra class of stars. The observations are well in agreement with the assumption of two or more separated active regions on UZ Lib. Because of the variability of the light curve it is impossible to improve the period. Also it is again not clear, how long a certain spot group on this star can survive to be linked with later observations. The telescope, its equipment, and the reductions facilities have been supported by the Deutsche Forschungsgemeinschaft (grants Schm 160/9, 160/13, and 167/12). This should herewith be gratefully acknowledged. M. HOFFMANN Observatorium Hoher List 5568 Daun / Eifel, BRD References: Bidelman, W.P., 1954, Astrophys. J. Suppl. 1, No. 7 [BIBCODE 1954ApJS....1..175B ] Evans, D.S., and Hopp, B.W., 1974, Observatory 94, 80 [BIBCODE 1974Obs....94...80E ] Ferraz Mello, S., and Torres, C.A.O., 1971, I.B.V.S. No. 577 Hartmann, L., 1976, Phil.D.Thesis, University of Wisconsin [BIBCODE 1976PhDT........15H ] Parenago, P., 1931, Variable Stars (Russian), 3, 99 Torres, C.A.O., and Ferraz Mello, S., 1973, Astron.Astrophys. 27, 231 [BIBCODE 1973A&A....27..231T ] Wisniewski, W.Z., 1973, Monthly Notices Roy. Astron. Soc. 161, 331 [BIBCODE 1973MNRAS.161..331W ]