COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3660  

                                              Konkoly Observatory
                                              Budapest
                                              18 September 1991

                                              HU ISSN 0374 - 0676


   NEW MAXIMA OF THE HYDROGEN-DEFICIENT PULSATING STAR V652 Her
         (BD+13d 3224) AND A REVISED CUBIC EPHEMERIS


The hydrogen-deficient hot star V652 Her (=BD+13d 3224) was discovered by
Landolt (1975) to be variable and shown by Hill et al (1981) to be radially
pulsating. Kilkenny & Lynas-Grey (1982, 1984) found that the period of the
star was decreasing and then that the decrease rate was itself decreasing; the
most recently published timings of maxima showed close agreement with the
previous findings, namely that a cubic ephemeris is necessary to fit the
observations (Kilkenny 1988). It seems likely that the decreasing period could
be due to contraction of the star as it evolves from the zero-age
horizontal-branch towards the helium main-sequence (Jeffery 1984) however, the
change in the decrease rate has not been satisfactorily explained, nor is there
a clear theoretical model for the pulsation (Saio 1986).

Because this remarkable, apparently unique star is likely to provide a
stringent test of theories of stellar evolution and pulsation, we have
continued to make timings of maxima. The results, listed in Table 1 were
obtained from series of 30 sec integrations using various filters in
conventional photoelectric photometers on the 0.5m and 1.0m telescopes of the
South African Astronomical Observatory.

Combining the Table 1 results with those from Landolt (1975), Kilkenny &
Lynas-Grey (1982, 1984) and Kilkenny (1988) and solving a cubic equation:

          HJDmax = T_0+nP_0+n^2k_1+n^3k_2

we obtain the coefficients:

T_0 = 244 2216.80406 +- 0.00035
P_0 = 0.107 992 733 +- 0.000 000 049
k_1 = (-44.553 +- 0.021) x 10^-10
k_2 = (+2.958 +- 0.024) x 10^-15


                              [FIGURE 1]

 Figure 1. (O-C) diagram for published maxima of V652 Her, including the
            Table I results and using the ephemeris derived in this paper.
            The abscissa is cycle number.


Table I. New timings of maxima of V652 Her

HJD              n     Tel.  filter
2447270.555    46885   1.0m   V       1988
   7354.2605   47663   1.0    V
   7354.368    47664   1.0    V
   7384.2775   47942   1.0    V
   7385.246    47951   1.0    V
   7675.4835   50649   1.0    y       1989
   8363.623    57048   0.5    B       1991
   8365.559    57066   0.5    B
   8368.569    57094   0.5    B
   8371.5795   57122   0.5    B
   8374.5885   57150   0.5    B
   8376.5245   57168   0.5    B
   8403.510    57419   0.5    B
   8406.4125   57446   0.5    B
   8409.4225   57474   0.5    B
   8410.4975   57484   0.5    B

from 98 observations of maxima. The errors are the formal errors from the
least squares cubic fit to the timings of maxima. The (O-C) residuals for the
above ephemeris are shown in Fig. 1.


                 DAVID KILKENNY & FRED MARANG
                 South African Astronomical Observatory
                 P O Box, 9 Observatory 7935
                 South Africa

References:

Hill, P.W., Kilkenny, D., Schonberner, D. & Walker, H.J., 1981.
    Mon. Not. R. astr. Soc., 197, 81. [BIBCODE 1981MNRAS.197...81H ]
Jeffery, C.S., 1984. Mon. Not. R. astr. Soc., 210, 731. [BIBCODE 1984MNRAS.210..731J ]
Kilkenny, D., 1988. Mon. Not. R. astr. Soc., 232, 377. [BIBCODE 1988MNRAS.232..377K ]
Kilkenny, D. & Lynas-Gray, A.E., 1982. Mon. Not. R. astr. Soc.,
    198, 873. [BIBCODE 1982MNRAS.198..873K ]
Kilkenny, D. & Lynas-Gray, A.E., 1984. Mon. Not. R. astr. Soc.,
    208, 673. [BIBCODE 1984MNRAS.208..673K ]
Landolt, A.U., 1975. Astrophys. J., 196, 789. [BIBCODE 1975ApJ...196..789L ]
Saio, H., 1986. IAU Colloq. No. 87, 425. [BIBCODE 1986ASSL..128..425S ]