COMMISSIONS 27 AND 42 OF THE IAU
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 3871

                                                     Konkoly Observatory
                                                     Budapest
                                                     20 April 1993

                                                     HU ISSN 0374 - 0676


               TIMES OF MINIMUM NEEDED FOR AR AURIGAE!


The well-known bright (6.15m-6.82m) eclipsing binary AR Aurigae (HD 34364, HR
1728, B9 V_p + B9.5 V, P = 4.13d) is one of the very few early-type stars with
a radius small enough that it must be essentially unevolved. In fact, a recent
analysis (Johansen & Nordstrom 1993) shows that the secondary may still be
contracting towards the ZAMS. At the same time, at least one of the components
is a Bp star of the Hg-Mn variety. Thus, determining the masses, radii, and
other physical properties of the components of AR Aur to the highest modern
standards becomes a matter of priority in order to optimise the value of this
system as a test object for evolution models of young stars around 2M_Sun.
(cf. Andersen 1991)

Among its several unusual features, AR Aur is also a triple system with a
near-circular orbit of period ~24 yr as revealed by the light time effect on
the observed times of minimum (Chochol et al. 1988). The light-time orbit has
also been studied in our reanalysis of the system, taking into account the
recent photoelectric minima observed by Busch (1989, 1991).

             MinI = HJD 2438402.1847 + 4.1346662d * E


                             [FIGURE 1]


The two curves show two light-time orbit fits to the data, assuming either the
Chochol et al. orbital period of the eclipsing system, or the slightly longer
value of 4.13466645d.

It is clear that, with the present distribution of the observations, the fit is
poorly constrained, and the two orbital motions cannot be separated with
certainty. In order to remove this ambiguity, it is important to cover the
impending maximum of the O-C curve with several well-observed (i.e.
photoelectric) times of minimum over the period 1993-1998. As AR Aur is bright
and of conveniently short period, this is a task which can be accomplished by
amateurs and professionals alike with modest-size telescopes.

In previous photometry of AR Aur, it has been a problem that several promising
comparison stars have later proved to be variable (Johansen & Nordstrom 
1993). We therefore propose to use (always) two of the following:

HR 1734 (6.49m, A7V), HR 1738 (5.52m, A3V), or HR 1749 (5.23m, B3V) HR 1734 has
a faint (11.8m) companion at a distance of 3.8" which always should be
included.

It is the purpose of this note to call the attention of interested observers to
this favourable opportunity to contribute significantly to our knowledge of
this important binary system.



              B. NORDSTROM
              K.T. JOHANSEN
              The Niels Bohr Institute of Astronomy, Physics, and Geophysics
              Astronomical Observatory
              Brorfeldevej 23
              DK-4340 Tollose
              Denmark

REFERENCES

Andersen J., 1991, A&AR 3, 91. [BIBCODE 1991A&ARv...3...91A ]
Busch H., 1989, Mitt. Verand. Sterne, Sonneberg 12, 16
Busch H., 1991, Mitt. Verand. Sterne, Sonneberg 12, 103 [BIBCODE 1991MitVS..12..103B ]
Chochol D., Juza K., Mayer P., Zverko J., Ziznovsky J., 1988, B.A.C. 39, 69 [BIBCODE 1988BAICz..39...69C ]
Johansen K.T., Nordstrom B., 1993, A&A, preprint. [BIBCODE 1994A&A...282..787N ]