COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 1197

                              Konkoly Observatory
                              Budapest
                              1976 October 29




           BC DRACONIS - AN RR LYRAE VARIABLE


    BC Draconis (=Bamberg Variable No. 222) was discovered to
be variable (1) in the Bamberg sky survey and reported (2) to
be a cepheid of period 2.566033 days. Its spectral type was 
originally described (3) as late B and subsequently (4) as of
type F5. On the basis of period-luminosity relationships Irvine
(4) noted that BC Draconis was either a Population I cepheid
1730pc from the galactic plane or, more probably, a Population
II cepheid 950pc from the galactic plane. Szabados (5) obtained
a series of photoelectric observations of this star and in an
attempt to resolve the scatter about the light curve of period
2.566033 days he proposed that the light curve is modulated
with a beat period of 10.96 days. He suggested that the two 
periods present in the star were P_2= 2.566033 days and P_1= 3.351
days giving a period ratio P_2/P_1 = 0.766.
    Fourier analysis (in the range P>0.2 days) of Szabados'
observations has shown that the original period identification
is incorrect and is a 1 cycle/day alias of the true period P=
= 0.71957 days. The V and B light curves of the variable are
shown in Fig. 1. The scatter about the mean light curves has
a mean error of 0.036 mag in V and 0.035 mag. in B, consistent
with the observational error. Apart from the P/2 harmonic of
the main period no evidence was found for other periodicities
in the data. The light curve appears to be typical of a low 
amplitude, fundamental mode RR Lyrae variable. Adopting an RR Lyr
absolute magnitude of M_B =+1.1, photographic interstellar 
extinction of 1.1 mag (4) and mean apparent photographic 
magnitude of 11.7, the distance of BC Draconis from the galactic
plane is 380pc.


                 [FIGURE 1]

   Fig. 1. V,B observations of BC Dra plotted with phase
   phi = (JD - 2440000) * 1.38972



    It is interesting to note that in the Fourier analysis the
structure of the main peak at f = 1.38972 c/d is single as 
expected whereas the structure of the major alias peaks at f+-1 are
double. This unusual alias structure is a direct consequence of
the star being circumpolar at the latitude from which it was 
observed. Thus both the 1 c/d and 1 cycle/sidereal day (or 1.0027
c/d) aliases dominate the alias structure.
    From Szabados' observations we derive the following 
elements for maximum light

        JD (max. light) = 2442278.45 + 0.71957d E.
                               +-.01  +-.00001





           L. SZABADOS           R.S. STOBIE, D.A. PICKUP
           Konkoly Observatory   Royal Observatory Edinburgh
           Budapest              Blackford Hill
                                 Edinburgh EH9 3HJ
                                 Scotland


References:

1. Strohmeier, W. 1958. Kl.Veroff.Bamberg No. 23 
2. Strohmeier, W. and Knigge, R. 1961. Bamberg Ver., 5, No. 11 [BIBCODE 1961BamVe...5...11S ]
3. Gotz, W. and Wenzel, W. 1964. Mitt. Ver. Sterne Berlin-Babelsberg
        und Sonneberg, 2, H4, 85
4. Irvine, N.J. 1974. I.B.V.S. No. 858
5. Szabados, L. 1976. Multiple Periodic Variable Stars, IAU
        Colloquium No. 29, Budapest [BIBCODE 1976mpvs.conf..159S ]