COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1977

                                  Konkoly Observatory
                                  Budapest
                                  1981 June 19

                                  HU ISSN 0374-0676


       OBSERVATIONS OF SOUTHERN dMe STARS IN 1975 +


     In November 1975 (JD 2442721 to JD 2442736) 13 southern
red dwarfs have been measured several times each night with
the 50cm ESO telescope (La Silla/Chile) and its standard UBV
photometer. The aim was to detect small scale BY Dra type
variability. Besides the well known dMe star AU Mic two
other dMe stars showed a significant variability. For 
"detectability limit"the following definition has been adopted:
For a given night the comparison stars yield an empirical 
relation photometric error (standard deviation) / magnitude.
Variability is then assumed, if the measurements of a 
programme star vary by more than twice the photometric errors
for each single night of comparison stars with comparable
brightness.
     The dMe stars satisfying this condition are:
1 ) AU Mic
    With the light elements
            JD 2442720.75 + 4.865d E
the B and V light curves in Figs. 1 and 2 have been plotted.
The period is by Torres and Ferraz Mello (1973). Since their
observations of 1971 the V amplitude has dropped from 0.30m
to 0.12m. The (B-V) amplitude is now 0.02m. The shape of the
light curve has also changed considerably. The complete rise
to the maximum takes only 0.20p. Since the magnitude at maximum 
has slightly decreased and the brightness of the minimun
has increased, it can be concluded that the variability 
causing spots on AU Mic are now spread more uniformly over all
longitudes.

+ Based on observations made at the European Southern Observatory 
 (La Silla/Chile)

                         [FIGURE 1]

           Figure 1   B light curve of AU Mic

                         [FIGURE 2]

           Figure 2   V light curve of AU Mic

2) Gliese 54.1
Although no significant BY Dra syndrome could be detected, 
this star showed the strongest variability among the
programme stars: during one night it exhibited a flare with
a B amplitude of at least 0.73m. Measurements of that night:

JD hel.2442733.6222   V 11.911m
              .6653     11.725
              .6687     11.761
              .7131     11.824
              .7494     11.895
JD hel.2442733.6204   B 13.873m
              .6636     13.147
              .6653     13.239 
              .7099     13.641
              .7131     13.673
              .7470     13.747
3) CD-23d693
Unlike the other programme stars this one shows a 
sinusoidal brightness modulation of 0.015m amplitude. Although
this amplitude is small, it satisfies formally the above
mentioned condition, which would set a significance limit
at 0.010m. The V light curve is shown in Fig. 3.

                         [FIGURE 3]

           Figure 3   V observations of CD-23d 693

  A doubtful case is CD-37d15492. The 65 observations of
this dMe star (the brightest of the programme stars and 
excellently placed in the sky for observations) form an 
irregularly variable sequence on a time scale of a few days with
an amplitude of 0.015m. Perhaps a longer observing run on
this object can reveal a periodicity for this modulation.
     The author likes to acknowledge helpful comments by
Dr. R. Rufener gratefully.





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

Reference:
Torres, C. A. O., Ferraz Mello, S., 1973, Astron. Astrophys.
           27, 231 [BIBCODE 1973A&A....27..231T ]