COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2343

                                   Konkoly Observatory
                                   Budapest
                                   31 May 1983

                                   HU ISSN 0374-0676

    THE LIGHT ELEMENTS OF EX Del, V502 Her, AND RT LMi


    EX Del, V502 Her, and RT LMi are eclipsing binaries of
W UMa type. They were included in a recent series of photoelectric 
observations of contact binaries with the 1.06m
telescope of Hoher List Observatory. During the observations
it turned out that their light elements deserve an urgent 
rediscussion.
1. EX Delphini
    This object was discovered by Hoffmeister (1949). A
first discussion was given by Huth (Gotz et al., 1957), but
the W UMa type of variability was found by Karamysh and
Mandel (1965), who gave a period of 0.3968d.
    In 1982 larger parts of the light curve were observed
in two nights. Because these observations could not be 
described by the hitherto known light elements, the Sonneberg
plate collection was examined. A total of 33 minima between
JD 2427338.343 and 2445209.392 could be used to determine the
new light elements:
Min. = JD 24338.343 + 0.3309882d*E
53 993 epochs are covered by the well distributed minima.
There is no indication for a period change.

2. V502 Herculis
    Again it was Hoffmeister (1949) who discovered the
variability of this eclipsing binary. Gessner (1966) determined 
its period to 0.3117d.
    Photoelectric photometry during six nights in 1982 and
new minimum times from the Sonneberg plates helped to determine 
the corrected light elements:

Min. = JD 2430938.493 + 0.3692768d*E

73 minima between JD 2430938.493 and 2445140.50 covering
38 459 epochs were available. No period change was found
during this time interval.

3. RT Leonis Minoris
    This variable was found by Hoffmeister (1949) too.
Meinunger (1961) gave a preliminary period of 0.374d, but,
although it is a moderately bright object (11m), no further
discussion on the light elements could be found in the 
literature.
    Photoelectric photometry in three nights in 1982 and a
thorough examination of the Sonneberg plate archive revealed
72 minima which span 24 362 epochs between JD 2435868.483
and 2445002.4147. The refined light elements are now:
Min. = JD 2435868.477 + 0.3749180d*E
The period remained constant during this interval within the
limits of accuracy.

M. HOFFMANN                L. MEINUNGER
Observatorium Hoher List   Sonneberg Observatory of
5568 Daun / Eifel, BRD     Central Institute for Astrophysics
                           of Academy of Sciences of the GDR





References:
Gessner, H., 1966, Veroff. Sternw. Sonneberg 7, H.2, 94
Gotz, W., Huth, H., Hoffmeister, C., 1957, Veroff. Sternw.
          Sonneberg 4, H. 2, 173
Hoffmeister, C., 1949, Erg. Astron. Nachr. 12, 1
Karamysh, V. F., Mandel, O. E., 1965, Variable Stars 15, 586 [BIBCODE 1965PZ.....15..586K ]
Meinunger, L., 1961, Mitt. Veranderliche Sterne Sonneberg No.
          564