COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3281

                                                         Konkoly Observatory
                                                         Budapest
                                                         9 January 1989

                                                         HU ISSN 0374 - 0676


          ON THE VARIABILITY OF THE Am STAR 68 Tau (HD 27962)

The star HD 27962 (HR 1389=68 Tau=V776 Tau) is one of the few Am stars
in which magnetic field has been measured (Babcock 1958), so it was included
into our programme of photoelectric observations of magnetic stars with the
aim of ascertaining the existence of light variations and determining the
period, if any. The observations, in the UBV natural system, were carried
out in 1973 and 1974 at the Stellar Station of the Catania Astrophysical
Observatory using the 90 cm telescope and the equipment described elsewhere
(Blanco et al. 1978).
   The comparison stars used were: HD 27295 (HR 1339 = 53 Tau, B9 Mn) and
HD 27934 (HR 1387 = 65 Tau, A7IV). After the reduction of the observations,
HD 27295 was found to be variable, so it was eliminated from the programme:
its periodicity has been investigated separately (Catalano et al. 1988). The
second comparison (HD 27934) in turn was found in the literature to be a
suspected delta Sct star. However, during our observing session, it did not
show evidence of variability.
   UBV observations of HD 27962 by Winzer (1974) and Kuvshinov et al. (1976)
are available in the literature with different results: Winzer (1974), using
HD 27819 (HR 1380 = 64 Tau, A7V) as a comparison, found HD 27962 to be constant
to better than 0.01 mag on a time-base of 20 days, while Kuvshinov et al.
(1976), using the same comparison and on a time-base of about 700 days,
found it to be variable with a period of 57.25 days, which they find to be
also the period of the orbital motion and of the magnetic field variation.
It has to be noted that practically in the same time Conti et al. (1974) did
not find any significant radial velocity variation from coude spectra 
(resolution 10 A/mm) thus questioning that HD 27962 is a spectroscopic binary.
This negative result was later confirmed by Haupl (1980).
   In this very unclear situation we decided to search for periodicity,
using all sets of UBV data and transforming Kuvshinov et al.'s observations
and ours into the Winzer's system. By means of the procedure described by


                            [FIGURE 1]

 Figure 1  U light curve of HD 27962. The phase is computed according to 
 formula (1) in the text. Code is the following:
 Open circles: observations by Winzer (1974)
 triangles: Kuvshinov et al. (1976)
 crosses: Catalano and Leone (this paper)


Deeming (1975) we found that the data could be best represented by the
elements:

        JD (Max. U light) = 2440604.34 + 21.2637d E           (1)

   The resulting U light curve is reported in Figure 1, where a small amplitude
variation is evident. Using all three sets of data no acceptable phase diagram
was obtained with the 57.25 days period given by Kuvshinov et al. (1976).


              F.A. CATALANO 1,3  and F. LEONE  2,3


1. Istituto di Astronomia - Universita di Catania
   Citta Universitaria - Viale A. Doria 6
   I 95125 Catania Italia

2. Osservatorio Astrofisico di Catania

3. C.N.R. - G.N.A. - Unita di Ricerca di Catania



References:

Babcock, H.W., 1958, Astrophys. J. Suppl. 3, 141. [BIBCODE 1958ApJS....3..141B ]
Blanco, C., Catalano, F.A., Strazzulla, G., 1978, Astron. Astrophys. Suppl.
   31, 205. [BIBCODE 1978A&AS...31..205B ]
Catalano, F.A., Leone, F., Vaccari, S., 1988, Inf. Bull. Var. Stars. No. 3220.
Conti, P.S., Hensberge, H., van den Heuvel, E.P.J., Stickland, D.J., 1974,
   Astron. Astrophys. 34, 393, [BIBCODE 1974A&A....34..393C ]
Deeming, T.J., 1975, Astrophys Space Sci. 36, 137. [BIBCODE 1975Ap&SS..36..137D ]
Haupl, W., 1980, Astr. Nachr. 301, 207. [BIBCODE 1980AN....301..207H ]
Kuvshinov, V.M., Hildebrandt, G., Schoneich, W., 1976, Astr. Nachr. 297, 181. [BIBCODE 1976AN....297..181K ]
Winzer, J.E., 1974, Thesis University of Toronto. [BIBCODE 1974PhDT........61W ]



                               ERRATUM

In the ephemerides of the U light curve of HD 27295 (IBVS No. 3220) the
initial epoch refers to the minimum light instead of the maximum light
given by a clerical mistake.


                 F.A. CATALANO and F. LEONE