COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2158

                                 Konkoly Observatory
                                 Budapest
                                 1982 June 10

                                 HU ISSN 0374-0676




      A NEW beta CEPHEI STAR IN HARVARD STANDARD REGION E4




   The star Q.81 in Harvard Standard Region E4 (HD78616), frequently
used as a "standard star", was found to be variable by T Lloyd Evans in
1980. This had been suspected (Cousins & Stoy 1962) but had not 
previously been confirmed. The spectral type is B2 II/III (Houk, 1978).
The following observations indicate that the star is beta Cephei type variable.

   The star was intensively observed in 1981 by Laing (at Sutherland)
and Cousins (at Cape Town) using E region standards as comparison stars.
The individual light curves pointed to a period of about 5 hours, but
as the amplitude is small (0.05 mag) and the light curve seemed to vary
in shape it was difficult to define the period precisely.

   A periodogram of the 1981 observations gave 4.636 d^-1 as the most
probable reciprocal period, with an uncertainty of +- 0.001 d^-1. By
including more recent observations (1981 Nov and 1982 Mar, Apr) this
could be refined to 4.6361 +- 0.0001 d^-1 (P = 0.21570 d). The aliases,
+- 1 cycle per day and +-  1 per year can be eliminated because they 
produce phase shifts as functions of U.T. or J.D. After whitening this
material, by removing the fundamental period and its harmonics, the
periodogram shows no evidence of a secondary period.

   A mean light curve has been derived from the 1981 and 1982 V 
observations by Fourier analysis and these are shown together in Figure 1.

                             [FIGURE 1]

Figure 1. V magnitudes and light curve of E4-81 plotted against phase =
4.63611 (JD -2440000). The light curve is a third order Fourier fit to
the observations.

   There is a large phase error when the above period is extended back
to 1980, but the 1980 and 1981 observations can be reconciled by adopting
p^-1 = 4.6351 +- 0.0002. This is compatible with the 1981 period but is
not acceptable for later observations, and the period is evidently variable.
A quadratic ephemeris (with the period increasing at a rate of about
0.0004 d per year) would describe the phase changes from 1978 to 1982 but
is not acceptable for earlier observations.

   There is no significant change in the colour of this star accompanying
the light changes, the mean values being B-V = -0.002m, U-B = -0.752m (1981
observations), V-R_c = 0.024, V-I_c = 0.023 (Cousins 1980). The star is
a close visual binary with nearly equal components so the true range of
variation will be about twice the observed value. The colours imply that
these stars are somewhat reddened.

   One of the comparison stars used in 1981, E4-40 (= HD79416, B8V(pSi))
was found to be a micro-variable with night-to-night changes of one or two
hundredths of a magnitude, necessitating a re-reduction of the observations
of E4-81. This star will be discussed in a separate note.

   The author wishes to thank L.A. Balona for the use of his computer
programs, and J.D. Laing and T Lloyd Evans for observations.





             A.W.J. COUSINS

             South African Astronomical Observatory
             P O Box 9
             OBSERVATORY 7935
             SOUTH AFRICA





 References:
 
 Cousins, A.W.J., 1980. S.A.A.O.   Circ., 1, 234. [BIBCODE 1980SAAOC...1..234C ]
 Cousins, A.W.J. & Stoy, R.H, 1962  R.Obs.Bull. No. 49.  [BIBCODE 1962RGOB...49....1C ]
 Houk, N., 1978. Michigan Catalogue of Two-dimensional Spectral
      Types of HD stars, vol. 2, Ann Arbor, Michigan, U.S.A. [BIBCODE 1978mcts.book.....H ]