COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1724

                                   Konkoly Observatory
                                   Budapest
                                   1980 January 7


       LIGHT ELEMENTS OF THE ECLIPSING BINARY LY AURIGAE


Light elements of the bright O-type eclipsing variable LY Aur published by now
have been based on observations which cover only a rather short time span.
Therefore, elements given by Wood (1971)

Pri.Min. = J.D. 2440942.649+4.002521d*E

as well as by Mayer and Horak (1971)

Pri.Min. = J.D. 2439061.463+4.002496d*E

may not be reliable.

Observation of a primary minimum made at Hvar Observatory on November 6, 1978,
allows a new determination of light elements. Measurements were made in B and
V colours and HD36212 served as a comparison star. Since the star HD 35619 was
used as a comparison one during former studies of LY Aur, both stars were
measured on several nights in order to get differences of their brightness.
From 5 nights (more than one hundred of individual measurements) the
differences Delta V=0.781m and Delta B=0.796m were found, HD 36212 being the
brighter one. The measurements of LY Aur are presented in Fig. 1 as differences
HD 35619 minus variable (points). In the figure the measurements obtained
during a minimum on J.D. 2440850 (Mayer and Horak, 1971) are also given
(circles).

The time of minimum light computed from the new measurements is J.D.hel.
2443820.4324+-0.0010. To get more epochs of minima, a mean primary minimum has
been computed from observations by Landolt and Blondeau (1972) and Hall and
Heiser (1972). All available epochs are listed in Table I; the first epoch is
an estimation only. The column (O-C)_old is computed from elements by Mayer
and Horak (1971). Since the minimum by Wood (1971) gives a large O-C, it was
not considered when applying LSM to correct the elements. The resulting
elements

Pri.Min. = J.D. 2439061.4640+4.0024943d*E
                        +-10      +-20

differ only insignificantly from the elements by Mayer and Horak. The
corresponding O-C are given in the column (O-C)_new.

                          [FIGURE 1]

Table I

Observed time   Mean
J.D.2400000+    error     Epoch  (O-C)_old   (O-C)_new  References
39061.463       0.002d       0    0.0d      -0.0010d
40858.5835      0.0015     449   -0.0002    -0.0004     Mayer and
                                                        Horak, 1971
40942.649                  470   +0.0129    +0.0127     Wood, 1971
91102.7381      0.0016     510   +0.0022    +0.0021     a mean minimum
                                                        (see text)
43820.4290      0.0010    1189   -0.0017    -0.0007     this note

The data presented in Fig. 1 as well as data by Landolt and Blondeau (1972) and
Hall and Heiser (1972) are consistent with the estimation (Mayer and Horak,
1971) that the totality lasts about 100 minutes. The bottom level of the
totality may change by 0.02m to 0.03m from one minimum to another one.


P. MAYER
Department of Astronomy and Astrophysics,
Charles University
Praha, Czechoslovakia

References:

Hall, D.S., and Heiser, A.M., 1972, Publ. Astr. Soc. Pacific 84, 33 [BIBCODE 1972PASP...84...33H ]
Landolt, A.O., and Blondeau, K.L., 1972, Publ. Astr. Soc. Pacific 84, 349 [BIBCODE 1972PASP...84..394L ]
Mayer, P., and Horak, T.B., 1971, Bull. Astr. Inst. Czechoslovakia 22, 327 [BIBCODE 1971BAICz..22..327M ]
Wood, F.B., 1971, I.B.V.S. No. 519