COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1933

                                  Konkoly Observatory
                                  Budapest
                                  1981 March 11

                                  HU ISSN 0374-0676



      B AND MG BAND OBSERVATIONS OF AH Vir IN 1977


     AH Vir (BD+12d2437) is a frequently observed eclipsing
binary of W Ursae Majoris type (e.g. Binnendijk, 1960; Bakos,
1977). It is known as an active system with well established
period jumps and light curve changes. Its primary minimum is
an occultation; so it belongs to Binnendijk's (1970) subclass
"W", whose members are famous for their instabilities.
     AH Vir has been observed on March 24 and 25, 1977 with
the 61cm Bochum telescope at the European Southern Observatory 
(La Silla/Chile). The telescope was equipped with its
standard photometer, but the observations have been made in
B and two narrow band regions (512.5nm/4.5nm Hw., 517.0nm/
4.0nm Hw.). The narrow band filters cover the Mg "b" triplet
and a neighbouring line-poor region. Main comparison star
has been BD+12d2436.
    Minima times have been determined as follows (epochs
and O-C's according to JD 2442155.6164+0.40753162d E, the most
recent period given by Bakos):
	JD hel. 2443227.6270   Ep. 2630.5   O-C +0.0005d
        	2443227.8310   	   2631.0       +0.0007d
        	2443228.6445       2633.0       -0.0008d
        	2443228.8510       2633.5       +0.0019d
                         
Apparently the last period was still valid in 1977.

                        [FIGURE 1]

            Fig. 1   Measurements of AH Vir in B

                        [FIGURE 2]

         Fig. 2   Measurements of AH Vir at lambda512.5nm

    Figs. 1, 2, and 3 show the measurements in the 
individual colours. The light curves exhibit only minor 
distortions. The minima have slightly declining slopes and there
are marginal "shoulders" at phases 0.15 and 0.35 (external
tangencies) - invisible in the "continuum" band, indicated
in B, and better visible in the Mg "b" band. At these two
latter phases the only deviations (0^m.02) from a straight
line in a plot of the Mg "b" minus continuum index, which
is not shown here, could be found. From geometrical 
considerations the conclusion can be drawn that close to the inner
Lagrangian point L_1 a region with lower temperature is facing
the observer around 0.25p. On the other hand the second maximum 
is in general fainter than the first one. This has only
a very small influence on the colour indices. From the 
present data alone an interpretation seems to be difficult. 
    The light outside the eclipses (phases 0.16...0.34,
0.66...0.84) can be described by
    l_B = 0.9086 - 0.0141 cos Theta - 0.0750 cos 2Theta
                + 0.0078 sin Theta - 0.0065 sin 2Theta

                        [FIGURE 3]

       Fig. 3   Measurements of AH Vir at lambda517.0nm

No correction for the light of the secondary has been made.
The negative sin 2delta coefficient shows that the above mentioned 
asymmetry of the minima can be traced up to the maxima.
    Grants of observing and reduction facilities by the
Deutsche Forschungsgemeinschaft (Schm 160/9, 160/13, 167/12)
shall be gratefully acknowledged.





                      M. HOFFMANN
                  Observatorium Hoher List
                  5568 Daun / Eifel, BRD


References:
Bakos, G. A., 1977, Bull. Astron. Inst. Czech. 28, 157 [BIBCODE 1977BAICz..28..157B ]
Binnendijk, L., 1960, Astron. J. 65, 358 [BIBCODE 1960AJ.....65..358B ]
Binnendijk, L., 1970, Vistas in Astronomy 12, 217 [BIBCODE 1970VA.....12..217B ]