COMMISSION 27 AND 42 OF THE IAU
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3805

                                                      Konkoly Observatory
                                                      Budapest
                                                      13 November 1992

                                                      HU ISSN 0374 - 0676


  MINIMUM TIMES FOR SEVERAL SOUTHERN EARLY-TYPE ECLIPSING BINARIES  *1)

During two observing periods with the 50 cm ESO telescope at La
Silla in February/March and May 1992, several early-type
eclipsing binaries were measured in the UBV system. Here the
minimum times - and, in some cases, new ephemeris - are reported
for FZ CMa, QZ Car, V606 Cen and MY Ser.
   FZ CMa (HD 52942, B2.5 IV-Vn) : for this variable, a light
time effect due to a third body was reported by Moffat et al.
(1983). The secondary minimum time measured by us is JDhel.
2448688.6343 +- 0.0004d. The depths of this minimum were 0.39m,
0.37m and 0.36m in U,B and V, respectively. From the light curve
published by Moffat et al. (1983) a secondary minimum depth of
about 0.36m is apparent (in Stromgren v colour); this may
indicate that the minima have meanwhile deepened. Such change can
be due to a change of the orbital inclination, as has been
demonstrated in the case of the eclipsing triple system IU Aur by
Mayer and Drechsel (1987). Time-dependent variations of the
orbital inclination and corresponding changes of the depth of
eclipse minima are to be expected in a three-body system, where
the orbital planes of the eclipsing binary and that of the third
body orbiting around the mass center of the triple system are
non-coplanar.
   QZ Car (HD 93206, O9 III): a spectroscopic and photometric
multiple system. The eclipse minimum for this star was not
completely covered, however from the measured parts of the light
curve, a minimum time can be estimated. The ephemeris of this
star was given by Morrison and Conti (1980) as


Pri.Min. = JDhel. 2443192.4 + 5.9981d*E.
                        +-2      +-9

Using an additional minimum given by Walker and Marino (1972), we
obtained the improved ephemeris

Pri.Min. = JDhel. 2448687.16 + 5.99857d*E.
                         +-2      +-10

The period is very close to six days, which means, that in subsequent years,
the minima are observable from limited geographic longitudes only:

1993: Australia
1994: New Zealand
1997, 1998: South America
2001: South Africa

   The comparison and check stars were HD 93131, 93695 and 92740,
which match the colours of QZ Car well, and no variability was
found. The V light curve resulting from a preliminary reduction
of our data is plotted in Fig. 1. Both maxima seem to be of
different height. When the light curve is compared with the one


                         [FIGURE 1]

 Fig. 1. V light curve of QZ Car. Differences Var-HD 93131 are
 plotted. Points - data from JD 2448682 to 2448687, open circles -
 data from JD 2448688 to 2448692, crosses - data from JD 2448749
 to 2448753.


of Walker and Marino, the amplitude appears to be smaller than
given in the GCVS: the depths of the primary and secondary minima
can be estimated to be 0.25m and 0.20m, respectively.
    V606 Cen (HD 115937, B1-2 Ib-II): the spectral type as given
in the GCVS is, however, doubtful due to the short period, which
probably excludes a supergiant nature of the star. The only data
published so far for this variable is an ephemeris given by
Hertzsprung (1950):

Pri.Min. = JDhel. 2427952.354 + 1.495093d*E.

We observed three secondary minima:


       JDhel      Error     O - C

2448684.8118    +-.0004d    +.0002d
    687.8020    +-.0003     +.0002
    690.7916    +-.0002     -.0004


The resulting new ephemeris is

Pri.Min.= JDhel. 2448687.8018 + 1.4950931d*E.
                          +-2         +-2

   The O-C values in the preceding table were calculated using our
new ephemeris. The comparison star was HD 116003, check HD
115223. The depths of the secondary minimum are: U: 0.85, B:
0.80, V: 0.80. Due to the particularly difficult period of the
star, we were unable to observe the light curve around the
primary minimum.
   MY Ser (HD 167971, sp. type O8 Ib(f)p according to Walborn,
1972): spectroscopic and photometric evidence exists that this is
a multiple system. Lorenz et al. (1991) gave the ephemeris

    Pri.Min. = JDhel. 2446232.612 + 3.32160d*E

(unfortunately there was an error in JD in the above cited
paper). Now a new primary minimum was observed at JDhel.
2448753.7130 +- 0.0010d. The comparison and check stars were HD
168112 and BD -12d4282, respectively. Again, some asymmetry in
the shape of the minimum is apparent, hence the real error of the
minimum time might be somewhat larger than the formal one. The
new ephemeris

Pri.Min. = JDhel. 2446232.6125 + 3.321609d*E
                          +-10        +-2

has been calculated using times of primary minima only.


Pavel Mayer                       Horst Drechsel, Reinald Lorenz

Astronomical Institute            Dr. Remeis Observatory
Charles University                University Nuerenberg-Erlangen
Svedska 8, 150 00 Praha 5         Sternwartstrasse 7
Czechoslovakia                    D-8600 Bamberg, Germany


References:

Hertzsprung E. 1950 Ann. Leiden 20, 119. [BIBCODE 1950AnLei..20..119H ]
Lorenz R., Drechsel H., Mayer P. 1991 IBVS No. 3629.
Mayer P., Drechsel H. 1987 A&A 183, 61. [BIBCODE 1987A&A...183...61M ]
Moffat A.F.J., Vogt N., Vaz L.P.R., Gronbech B. 1983 A&A 120, 278. [BIBCODE 1983A&A...120..278M ]
Morrison N., Conti P. 1980 ApJ 239, 212. [BIBCODE 1980ApJ...239..212M ]
Walborn N.R. 1972 AJ 77, 312. [BIBCODE 1972AJ.....77..312W ]
Walker W.S.G., Marino B.F. 1972 IBVS No. 681.


*1) Based on observations collected at the European Southern
Observatory, La Silla, Chile