COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 1043

                                  Konkoly Observatory
                                  Budapest
                                  1975 September 9



         ECLIPSE TIMINGS OF CATACLYSMIC VARIABLES



The following heliocentric times of mid-eclipse of the cataclysmic 
variables EM Cyg, U Gem, DQ Her, and EX Hya are based on
observations made at Kitt Peak National Observatory.

I) EM Cyg          O-C
   ---------------------
   JD hel
   2442000+
   515.8789      -0.0041

The residual is with respect to the elements given by Mumford
(1969). Pringle (1975) has indicated that the period of  this
system is decreasing. This single observation is consistent with
that conclusion.

II) U Gem             O-C
    ----------------------
    JD hel
    2442000+
    511.7073        +0.0070
    513.6535        +0.0072
    514.7151        +0.0074
    516.6610        +0.0073

O-C values are with respect to the elements given by Krzeminski
(1965). These results in combination with previously published
times of minima, when analyzed in the manner suggested by Pringle
(1975), indicate a statistically significant deviation from  a
linear relation and lead to the conclusion that the period of the
system is increasing. However, Pringle (private communication)
reports that this result is not so clear-cut when additional,
currently unpublished times of minima are included in the analysis. 
For now, Pringle's (1975)  linear solution provides the best
ephemeris for this system.

III) DQ Her             O-C
     ------------------------
     JD hel
     2442000+
     513.9039         +0.0004
     514.8722         +0.0006
     515.8405         +0.0008

The O-C values are with respect to new linear elements  given
by Pringle (1975). At this time there is little or no evidence
for a period chance.

IV)  EX Hya         O-C
     --------------------
     JD hel
     2442000+
     511.7921     -0.0001
     513.7707     -0.0003
     513.8390     -0.0002
     515.7488     -0.0010
     515.8174     -0.0006
     516.7720     -0.0013
     516.8415      0.0000

The O-C values are with respect to the elements given by Mumford
  (1967). Considerable flaring took place near the times of minima
with the three large residuals.




                            G. S. MUMFORD
                           Tufts University
                           Medford, Mass. U.S.A.


References:

Krzeminski, W., 1965, Astrophys. J., 165, 369 [BIBCODE 1965ApJ...142.1051K ]
Mumford, G.S., 1967, Astrophys. J. Suppl., 15, 1 [BIBCODE 1967ApJS...15....1M ]
Mumford, G.S., 1969,    Mass Loss from Stars, M. Hack ed.,
      D. Reidel Pub. Co., 204
Pringle, J.E., 1975, Mon. Not. R. Astr. Soc., 170, 633 [BIBCODE 1975MNRAS.170..633P ]