COMMISSION 27 OF THE I. A. U.
                  INFORMATION BULLETIN ON VARIABLE STARS
                               Number 2473


                                                      Konkoly Observatory
                                                      Budapest
                                                      8 February 1984

                                                      HU ISSN 0374-0676

                         EPOCHS OF  MINIMUM LIGHT,

               DISPLACED SECONDARY ECLIPSE OF  SW LACERTAE


  SW Lac (BD+37d4717) is a W Ursae Majoris - type system which has long been
noted for its period changes and variations in the shape of its light curve.
Recent period studies have been conducted by Frasinska and Kreiner (1977)
and Faulkner and Bookmyer (1980).
  Two Indiana University telescopes were used to observe SW Lac during the
autumn of 1983. Three of the present authors (E.E.E., D.H.G., E.J.M.) used
the 30-cm refractor of the Kirkwood Observatory, while one author (DRF) used
the 41-cm reflector of the Morgan-Monroe Station of the Goethe Link Observatory.
The Morgan-Monroe observations were made with standard B and V filters and a
1P21 photomultiplier tube cooled with dry ice. The Kirkwood observations were
made with an unfiltered and uncooled Optec SSP-3 photometer, which employs a 
silicon photodiode. At both observatories differential measurements were made, using
BD+37d4715 as the comparison star and BD+37d4711 as the check star.
  The Hertzsprung method was used to determine times of minimum light from
the observations and are presented in the table below.

Hel. J.D.
2445000+  Min.    O-C    Inst.

542.8279    I    0.0002   M-M
554.8542   II   -0.0005   M-M
575.8630    I    0.0012   M-M
579.8695   II   -0.0013   M-M
586.7678    I    0.0015   M-M
610.6588   II   -0.0011   Kirk
634.7124   II   -0.0014   M-M
646.7412    I    0.0004   Kirk
660.5327    I    0.0009   M-M



   The final column in the table identifies the instrument used to observe each
eclipse, where "M-M" stands for Morgan-Monroe and "Kirk" stands for Kirkwood.
The epochs of minimum light from the Morgan-Monroe observations represent the
average of individual determinations made in each filter.
   The following light elements were obtained from a linear least squares
fit to the times of minimum light in the table:

          JD Hel.Min.I = 2445586.7663 + .3207195
                                  +-8       +-22

Residuals were formed using these elements, and are also presented in the
table. From these it can be seen that all of the secondary eclipses have
negative residuals, indicating that secondary minimum was displaced toward the
preceding primary minimum. The magnitude and sense of the displacement is
similar to the displacement which Bookmyer (1965) found to occasionally be
present. Bookmyer further argued that the displacement was not due to orbital
eccentricity, but rather to variations in the shape of the light curve that
would affect the determination of times of minimum light. Small variations
in the shape of the light curve similar to those noted by Bookmyer were indeed
seen in the present observations.





                DANNY R. FAULKNER
                ERNEST E. EVANS III
                DANIEL. H. GROSSOEHME
                EDWARD J. MOYER Jr.

                Astronomy Department
                Swain Hall West 319
                Indiana University
                Bloomington, IN 47405 U.S.A.





References:
Bookmyer, B. B. 1965, A.J., 70, 415 [BIBCODE 1965AJ.....70..415B ]
Faulkner, D. R. and Bookmyer, B. B. 1980, Pub. Astr. Soc. Pac., 92, 92. [BIBCODE 1980PASP...92...92F ]
Frasinska, Z. and Kreiner, J. M. 1977, Inf. Bull. Var. Stars No. 1285.