COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3630

                                                  Konkoly Observatory
                                                  Budapest
                                                  24 June 1991

                                                  HU ISSN 0374 - 0676


             1982-1990 UBV OBSERVATIONS OF AM LEONIS


The W UMa system AM Leo is the brighter component of ADS 8024 = Sigma 1503. The
magnitude difference between the faint and bright components of the visual
double was measured at maximum light to be 1.55 mag in the yellow and 1.69 mag
in blue light by Eggen (1967). The system was observed photoelectrically
without a filter by Worley and Eggen (1956) and Abrami (1959); in B and V
filters by Binnendijk (1969); and in 5125 A, 5170 A and B filters
by Hoffmann and Hopp (1982). Observations by Hoffmann and Hopp form complete
light curves in 1977, but incomplete (only 60%) light curves in 1980 and 1981.
The spectral type F8 was assigned to the system by Hill et al. (1975), but
unfortunately no radial velocity curve was published for this system. Thus the
absolute dimension of AM Leo is not known. The light curves of AM Leo are so
variable in time that the type of the system sometimes changes from A-type to
W-type or vice versa. The system was W-type in 1959 and 1969 observation, but
A-type in 1977 observations. It shifted back to W-type in 1980 and 1981
observation.

In order to follow light curve variations we included AM Leo in our observing
program in 1982, and have observed it in every observing season since then.
The photoelectric observations in U, B and V filters were made with the 30 cm
Maksutov telescope at Ankara University Observatory, including the light of
the faint visual double star component. Differential observations (4 nights
in 1982, and 3 nights each in 1988, 1989 and 1990) were secured by using EMI
6256S photomultiplier in 1982, and EMI 9789QB in the following years. The same
comparison star BD+10d 2235 as used by Binnendijk (1969) was observed
frequently. Differential brightness measurements of the comparison with
respect to the check star (BD+10d 2233) were found sensibly constant during the
observations. The individual magnitude determinations were corrected for
differential atmospheric extinction. Thus altogether 51 differential
measurements in each filter in 1982, 107 differential measurements in 1988
and 97 differential measurements in 1989 were secured. The phase of the


                             [FIGURE 1]

          Figure 1. 1982 - 1990 B-light curves of AM Leo

                             [FIGURE 2]

          Figure 2. 1982 - 1990 V-light curves of AM Leo


observations was calculated by using Binnendijk's (1969) light elements

          MinI = H.J.D. 2439936.8337 + 0.36579720d * E

and the light curves in V and B passbands are plotted in Figures 1 and 2 for
the years 1982, 1988, 1989 and 1990 separately. Although the observing
intervals are not long in every observing season, the spread in the 
observations, particularly in U filter, was found somewhat larger than expected.
The 1982 observations cover only 25% of the light curve in the rising branch of
the primary maximum. The 20 % of the 1988 light curve is missing in the
primary maximum but whole light curves were obtained in the 1989 and 1990
observing seasons. The primary minimum is deeper in 1989 and 1990 while the
secondary minimum was deeper (~0.03 mag in B) in 1988 light curves. The
primary minimum was found to be total occultation by Binnendijk. Thus the
system was W-type in 1969 observations, A-type in 1977 observation, W-type
again in 1980 and 1981 observations (cf. Hoffmann and Hopp, 1982). We found
that the system was A-type again in 1988. It is still in W-type but we expect 
it will shift again to A-type probably in 1991 or 1992.


                              ETHEM DERMAN
                              OSMAN DEMIRCAN
                              HUSEYIN DUNDAR
                              Ankara University Observatory
                              Science Faculty, Tandogan
                              06100 Ankara, Turkey

References:

Abrami, H.: 1959, Mem. Soc. Ast. Italia, 30, 303.  [BIBCODE 1959MmSAI..30..303A ]
Binnendijk, L.: 1969, AJ., 74, 1031. [BIBCODE 1969AJ.....74.1031B ]
Eggen, O.J.: 1967, Mem. Roy. Ast. Soc., 70, 111. [BIBCODE 1967MmRAS..70..111E ]
Hill, G., Hilditch, D.M., Younger, F., Fisher, W.A.: 1975, Mem. Roy. Astr.
      Soc., 79, 131. [BIBCODE 1975MmRAS..79..131H ]
Hoffmann, M., Hopp, U.: 1982, Ap SS, 83, 391. [BIBCODE 1982Ap&SS..83..391H ]
Worley, C.E., Eggen, O.J.: 1956, PASP, 68, 452. [BIBCODE 1956PASP...68..452W ]