COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 519

                                Konkoly Observatory
                                Budapest
                                1971 February 18


 Rosemary Hill Observatory, Department of Physics and Astronomy, 
         University of Florida, Gainesville, Florida,
                Contribution No. 20

            A NOTE ON LY AURIGAE = 35921

      In 1968, Pavel Mayer (1) announced that HD 35921
was an eclipsing variable with two deep eclipses and that
both spectra were visible. He pointed out that it had the
largest amplitude of light variation among brighter eclipsing 
stars of spectral-type O and thus would be important for
determining absolute dimensions.
      This system has now been observed photoelectrically
in three colors using the 30-inch reflector of the Rosemary
Hill Observatory of the University of Florida. The light
curve near the bottom of primary is shown as determined
from observations on two nights. The observations shown were
taken with a yellow filter on the natural scale of the 
telescope-photometer combination; they are very close to the
usual V system but have not yet been put on that system.
The comparison star was HD 35619 which was also used by
Mayer.

                       [FIGURE 1]

       The most interesting feature is the existence of a
total (or annular) phase of approximately three hours
duration. Observations on other nights agree With those
shown but suggest variation of a few hundredths of a magnitude 
on a time scale of a few hours. Comparison-check
readings suggest that the variations are in the variable
rather than the comparison star which has been rather 
carefully checked by Mayer.
       The primary minima occur about one hour earlier than
those predicted from Mayer's published elements,
JD 243 9061.48 + 4.0026d, and are much more in accord with
unpublished ones supplied by him, JD 243 9061.464+4.00251d.
For predictions in the near future, I suggest:
       Pr. Min. - JD 244 0942.649 + 4.002521d.
       S. Rucinski has called my attention to the fact that
the colors published by Mayer indicate the star is appreciably 
reddened. LY Aur lies only about 1/3 degree from the
open cluster NGC 1907. If fitted to the color-magnitude
diagram of the cluster as given by Gretchen L. Hagen's "Atlas
of Open Cluster Colour Magnitude Diagrams" (2) using Mayer's
values of V and B-V, the star falls close to, but slightly
to the right of, an extension of the upper main sequence;
if we correct the V to allow for the fact that we are dealing
with a double star, the agreement as anticipated is much
closer. The color excess, E_B-V as computed from the measures
listed by Mayer is approximately 0.49; that listed in the
Hagen catalogue is 0.42. The question of its membership in
this cluster should be investigated further.


1971, February 9           FRANK BRADSHAW WOOD

                         Rosemary Hill Observatory
                          University of Florida




References:
(1) 1968, Publ. Astr. Soc. Pacific 80, 81. [BIBCODE 1968PASP...80...81M ]
(2) 1970, Publ. of the David Dunlap Observatory, Vol. 4. [BIBCODE 1970PDDO....4....1H ]