COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2127

                                 Konkoly Observatory
                                 Budapest
                                 1982 April 21

                                 HU ISSN 0374-0676




           PHOTOELECTRIC MINIMUM TIMINGS OF ALGOL




   The Algol system was observed from July, 1981 through December, 1981
with the 20 cm Newtonian reflector and photoelectric photometer described
by Bower (1982), The Optec photometer uses a silicon photodiode and has
a diaphragm which covers an area of sky 2.9' in diameter. The comparison
star was Pi Persei which is approximately 3d away from Algol. The sequence
of observation was: comparison - comparison background - variable - variable
background - comparison - comparison background. All observations were
corrected for differential extinction, with an assumed extinction coefficient
of 0.25m, and were transformed to V of the UBV system, Since the comparison
and variable stars are close together and were observed when both were at
least 30d above the horizon, the error in the assumption that the extinction
coefficient was 0.25m is reduced.
   Figure 1 presents the observations, plotted as a function of phase
according to the ephemeris that will be calculated from the times of minimum
presented here. A list of the observations is available as IAU Commission
27 File No. 98. Assuming that the light curve described. a parabolic function
a least-squares fit of the light curve yielded the following times of minimum:
HJD 2444904.60 +- 0.05 and HJD 2444947.62 +- 0.05, A minimum between the two

                          [FIGURE 1]

determined minima, HJD 2444924.68 +- 0.05, was selected as the epoch for
equation (1). (O-C) residuals were calculated for the ephemerides from
Guinan et al. (1976) and Kukarkin et al. (1969) and are listed in Table I.
   A new period was determined from each of these two ephemerides by the
following method. Each (O-C) residual was divided by the respective number
of cycles that had elapsed since the given epoch. This value was added to
the published value of the period, and the new periods are listed in Table I.



                           Table 1



         Paper                    (O-C)         (O-C)/E          Period
---------------------------------------------------------------------------

   Guinan et al. (1976)           0.0635      0.000044813        2.8672208d
   Kukarkin et al. (1969)        -0.0489     -0.000025750        2.8673643d

---------------------------------------------------------------------------


    The average of the new periods is 2.86729d + 0.00010. The ephemeris
calculated from the analysis of this light curve is:

         Pr. Min. = HJD 2444924.68 + 2.86729d E (1)
                            +-0.05 +-0.00010d

    The analysis of this light curve does not take into account the three
types of variation in the interval between times of minimum in the Algol
system: one with a period of 1.8y due to the orbital motion of Algol AB
around Algol C; one with a period of 33y, due to apsidal motion; and a 
longterm variation described by Batten (1973).
    I am grateful to R. M. Genet and N. D. Morrison for their assistance in
the preparation of this paper.


               GARY A. BOWER
               Fulton Observatory
               1203 Labrador Blvd.
               Garden City, KS 67846
                    USA

References:
Batten, A. H., 1973, Binary and Multiple Systems of Stars (Oxford: Pergamon
  Press), pp. 86-92. [BIBCODE 1973bmss.book.....B ]
Bower, G. A.: 1982, IAPPP Communications, in press.
Guinan, E. F., McCook, G. P., Bachmann, P. J., and Bistline, W. G.: 1976,
  Astron. J., 81, 58. [BIBCODE 1976AJ.....81...57G ]
Kukarkin, B. V. et al., 1969, Gen. Cat. of Var. Stars, Moscow. [BIBCODE 1969gcvs.book.....K ]


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