COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3403


                                         Konkoly Observatory
                                         Budapest
                                         12 December 1989

                                         HU ISSN 0374 - 0676


             1988 LIGHT CURVES OF RX HERCULIS

  RX Her (HD 170757, GC 25274) is a detached eclipsing binary with
algol type light curves. It was listed by Popper (1959) as one of
four early spectral type eclipsing binaries with well determined
properties. Wood (1948) obtained one unfiltered light curve and
determined a solution using the Russell-Merrill method. Other light
curves obtained were never solved because no significant
differences were noticed between new and old light curves (Popper,
1959). Olson(1975) and Hill and Hilditch (1975) observed the system
at five different phases in Stromgren filters. From these
observations the C index indicates a B9.5 spectral type, while the M
index for both primary and secondary stars shows nothing peculiar in
the metal abundance (Jeffreys, 1980). Jeffreys (1980) obtained a
V light curve and determined a solution using Wood's (1971) WINK
computer model. He found that RX Her is a binary system with
similar components (B9.5 primary and A0 secondary). He also found
some asymmetry during ingress of the secondary due to a small
eccentricity (e = 0.022).
  We obtained new differential photoelectric observations in each
U, B, V filters during May and August 1988. An EMI 9789QB
photomultiplier attached to the 30 cm Maksutov telescope of the
Ankara University Observatory has been used to secure the data.
Differential observations in three colors were made with respect to
the comparison star BD+12d3547. BD+11d3518 was used as the check
star. The differential brightness measurements of the comparison
with respect to the check star were found to be sensibly constant
during the observations. The individual differential brightness
determinations were corrected for differential atmospheric


                        [FIGURE 1]

    Figure 1. The UBV observations of RX Herculis.


extinction. The observations in the sense variable minus
comparison are plotted in Figure 1 together with color curves. The
light elements used in phase calculation were given in GCVS 1985
as

Hel. JD Min I = 2433170.398 + 1.7785724d*E.




      Table 1. The new times of minima of RX Her

  Hel.Min.          No Filter E    O-C   Remark
  2447300+          of
                    obs

  39.3930 +- 0.0020 11    U 7966 -0.0020 Min. II
  39.3947 +- 0.0009 16    B 7966 -0.0004 Min. II
  39.3946 +- 0.0010 16    V 7966 -0.0004 Min. II
  47.3989 +- 0.0006 15    U 7971 +0.0003 Min. I
  47.3991 +- 0.0008 15    B 7971 +0.0005 Min. I
  47.4003 +- 0.0013 13    V 7971 +0.0017 Min. I
  71.4032 +- 0.0031  9    U 7984 -0.0062 Min. II
  71.4072 +- 0.0002  9    B 7984 -0.0021 Min. II
  71.4078 +- 0.0030 11    V 7984 -0.0015 Min. II
  79.4139 +- 0.0004 32    U 7989 +0.0010 Min. I
  79.4141 +- 0.0003 30    B 7989 +0.0012 Min. I
  79.4139 +- 0.0005 32    V 7989 +0.0010 Min. I
  88.3067 +- 0.0009 20    U 7994 +0.0009 Min. I
  88.3059 +- 0.0005 20    B 7994 +0.0001 Min. I
  88.3068 +- 0.0013 20    V 7994 +0.0010 Min. I

  During the observations we secured three primary and two
secondary minima. The new minimum times (see Table 1 ) confirm
the apsidal motion and thus eccentric orbit of the system.
  We thank to B. Gürol for the generous help during the
observations and their reductions.


                       OSMAN DEMIRCAN
                       ETHEM DERMAN

                    Ankara University Observatory
                    Science Faculty, Tandogan
                    06100 Ankara / Turkey

References:
Hill G., Hilditch, R. W.: 1975, Mem. R. Astron. Soc., 79, 123. [BIBCODE 1975MmRAS..79..101H ]
Jeffreys, K. W. : 1980, Astron and Astrophys. Suppl., 42, 285. [BIBCODE 1980A&AS...42..285J ]
Olson, E. C.: 1975, Astrophys. J., Suppl., 29, 43. [BIBCODE 1975ApJS...29...43O ]
Popper, D. M.: 1959, Astrophys. J., 129, 659. [BIBCODE 1959ApJ...129..659P ]
Wood, D. B.: 1971, Astron. J., 76, 701. [BIBCODE 1971AJ.....76..701W ]
Wood. F. B.: 1948, Astrophys. J., 110, 463. [BIBCODE 1949ApJ...110..465B ]