COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                        Number 2562

                                           Konkoly Observatory
                                           Budapest
                                           26 July 1984

                                           HU ISSN 0374-0676


    A PHOTOMETRIC ANOMALY AROUND THIRD CONTACT IN EPSILON AURIGAE


    Beginning on the night of JD 2445646, the Automatic Photoelectric
Telescope at Fairborn Observatory West in Phoenix, Arizona began observing
the long-period eclipsing binary epsilon Aurigae. Although these observations 
are continuing, this paper provides results through JD 2445785. During 
this time, 144 group observations were made on 79 different nights,
while observations were not made on 60 nights, primarily due to poor weather. 
Each group observation consisted of 33 different 10-second observations 
in three bandpasses of the variable, comparison star, check star, and
sky. The total telescope time devoted to this variable was about 19.7
hours, while the total time spent actually integrating starlight was about
13.2 hours. Thus we see that roughly one third of the telescope time is
needed to move the telescope, acquire the stars, and change the filters.
Often 3 or 4 group observations were made on the clear nights prior to
JD 2445700, but there were some six gaps in the observations due to 
extended cloudy weather. After JD 2445700 there were fewer group observations 
per night, because the telescope's observing program had been expanded 
from 29 to 71 different groups, but this was compensated for somewhat 
by the greater percentage of clear nights.
   Individual magnitudes, including differential check minus comparison
magnitudes, are available from the I.A.U. Commission 27 Archive for Unpublished 
Observations of Variable Stars (Breger 1982). File No. 131 contains 
the observations prior to JD 2445700, while file No. 136 contains
the remainder. The comparison star used for all observations was HD 32655,
while the check star was HD 31964. The difference between the comparison
star and the check star remained sufficiently constant during the period
of observation to inspire confidence in the photometry.
   The operation of the Automatic Photoelectric Telescope and the reduction 
of the data have been discussed by Boyd, Genet, and Hall (1984 ab).
The data have been corrected for differential extinction and transformed
to the standard UBV system.
    In the light curves in Figure 1 each point is an average of three
separate differential magnitudes taken one after another. There it can be


                             [FIGURE 1]

 Figure 1   Observations of epsilon Aurigae made by the Automatic 
 Photoelectric Telescope before, during, and after the third contact. The 
 ordinate is differential magnitude in the sense variable minus comparison 
 and the abscissa is the last three digits of the Julian date. An 
 anomalous brightening, most pronounced and persistent in the U, began 
 around JD 2445695.


seen that an anomalous brightening began about JD 2445695 and peaked about
15 days later. This peak was most pronounced in the U, as was the 40-day
decline of 0.18m. Recovery from the decline started first in the V and was
followed shortly by a recovery in B, but there was a pronounced delay of
almost 25 days before the recovery began in U. While the anomaly began
with a decided colour shift towards the blue, it ended with a definite shift
to the red. This colour reversal and its occurrence so near third contact
may help interpret the enigma that is epsilon Aurigae.
   The beginning of this anomaly has been independently observed and
previously reported by Oki, Sekiya, and Hirayama (1984). We wish to thank
Robert E. Stencel for first bringing this anomaly to our attention.


                LOUIS J. BOYD
                Fairborn Observatory West
                629 North 30th Street
                Phoenix, Arizona 85008

                RUSSELL M. GENET
                Fairborn Observatory East
                1247 Folk Road
                Fairborn, Ohio 45324

                DOUGLAS S. HALL
                Dyer Observatory
                Vanderbilt University
                Nashville, Tennessee 37235

References:
Boyd, L. J., Genet, R. M., and Hall, D. S. 1984a, I.A.P.P.P. Communication
  No. 15, 20.
Boyd, L. J., Genet, R. M., and Hall, D. S. 1984b, I.B.V.S. No. 2511.
Breger, M. 1982, I.B.V.S. No. 2246.
Oki, T., Sekiya, I., and Hirayama, K. 1984, I.B.V.S. No. 2496.


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