COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2436

                                           Konkoly Observatory
                                           Budapest
                                           28 November 1983

                                           HU ISSN 0374-0676


                      ON THE PERIOD OF BD Cir


  The variability of BD Circini (BV510, B_ph = 9.8) was discovered by Miss
Leavitt (1907) on plates taken of the region centered at 15h-60d. She suggested
BD Cir to be an Algol type system with an amplitude of 0.8 mag. The
first photographic light curve was obtained by Schoffel (1965) who determined
a period of P = 0.86956d. The photographic light curve showed an amplitude
of 0.4 mag which was not in agreement with Miss Leavitt's result.
  We have included BD Circini in our UBV photoelectric observing program
since 1981. The observations were carried out with the 154 cm reflecting
telescope at Bosque Alegre Station of Cordoba Observatory during 32 nights
and 5 nights with the 60 cm reflector at Las Campanas Observatory of the
University of Toronto. A DC photometer consisting of a RCA 1P21 dry-iced 
photomultiplier and a set of standard UBV filters were used at Bosque Alegre,
while a pulse counting system with an S20 photomultiplier and UBVRI filters
were used at Las Campanas.
  A total of 672 complete UBV differential observations were obtained for
BD Cir in relation to the comparison star CPD-55d06213. No complete minima
were detected in the observations.
  Our photoelectric observations were not fitted either by the period given
by Schoffel or by their multiples. Therefore, we selected the close pair of
minima published by Schoffel and tried several multiples. Then by trial an
error we approached a period, giving a reasonable light curve for the UBV
observations. This procedure allowed the determination of a preliminary
ephemeris from the data obtained in 1981-1982. The resulting period was about
of 6.7907d days, i.e. more than twelve times the period suggested by Schoffel.
This fact explains why Mallama (1981) had troubles in detecting variability
while monitoring BD Circini. Our preliminary ephemeris successfully predicted
a minimum which was detected at partial phases in 1983. A light curve was
constructed for all photoelectric observations and a time of minimum light
was estimated, we found the last value listed in Table I, together with the
photographic minima given by Schoffel.

                     Table I
                  Minima of BD Cir
Min   Colour    J.D. Hel.      E     (O-C)   Remarks
----------------------------------------------------
I     Pg       2438205.284   -455    0.051     1
I     Pg       2438524.438   -408    0.021     1
I     Pg       2438592.250   -398   -0.079     1
I     Pg       2438877.452   -356   -0.105     1
I     Pg       2438884.457   -355    0.109     1
I     UBV      2444690.786    500    0.003     2
----------------------------------------------------

Remarks: 1) Schoffel (1965), 2) Present observations.
Finally, a least squares solution for a linear ephemeris gave:

      Primary Min = JD Hel 2441295.207 + 6.79115d x E
                               +-0.030 +-0.00007 m.e.

The resulting DeltaV light and Delta(B-V) colour curves are shown in Figure 1.


                          [FIGURE 1]


As it can be seen, BD Cir is an Algol type eclipsing binary whose primary
minima is 0.85 mag in depth while the secondary one is 0.2 mag.


           SILVANO F. MARTON AND ALBA GRIECO*

              Observatorio Astronomico
              Laprida 854 - 5000 Cordoba
              Argentina

              * Fellow of CONICOR

References:
Leavitt, H.M., 1907: Harvard Circ. 130 [BIBCODE 1907HarCi.130....1L ]
Mallama, A.D., 1981: Publ.Astr.Soc.Pacific 93, 774 [BIBCODE 1981PASP...93..774M ]
Schoffel, E., 1965: Inf.Bull.Var.Stars 118