COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    NUMBER 646

                                        Konkoly Observatory
                                        Budapest
                                        1972 March 24


            HD 21242: A NEW BRIGHT VARIABLE STAR


Photoelectric observations of the bright spectroscopic binary HD 21242 = BD
+28deg532 have shown it to be a variable star. We plan to continue observing
this binary until it sets, and then to publish all of our observations together
elsewhere.

We obtained 26 three-color observations on eight nights with the Dyer
Observatory 60-cm reflector using a refrigerated 1P21 photomultiplier. The
observations were made differentially with respect to the comparison star 
62 Ari, corrected for atmospheric extinction and transformed to the UBV system 
in the usual way. The constancy of the comparison star was verified to within
+-0.01m by means of 6 differential observations on 4 nights with respect to
the check star HR 999.

The observations were made during the 33 day interval between 2,441,356.53
and 2,441,389.54, and there is every indication that the brightness of 
HD 21242 is varying approximately in phase with the 6.43791d orbital period
determined spectroscopically by Carlos and Popper (1971). The amplitude of the
variation, in the sense maximum minus minimum, is given approximately by
Delta V=-0.12m, Delta(B-V)=+0.015m, and Delta(U-B)=+0.025m. If we
accept the UBV magnitudes of the comparison star given by Nekrasova, et al.
(1965), we find that the variable ranges between V=6.37m and 6.49m and
that the mean color indices are about B-V=0.91m and U-B=0.48m.

The light curve is roughly sinusoidal, although somewhat skewed. Minimum light
occurs at 0.1p and maximum at 0.4p, zero phase being the time of conjuction
(hotter component behind) computed with the ephemeris of Carlos and Popper.
Eclipses are certainly not producing the light variation.

According to Carlos and Popper, HD 21242 is a member of a class of binaries
which have a giant or subgiant secondary and in which one or both components
shows strong H and K emission. The other members of this class happen to be
eclipsing binaries and many exhibit variations outside eclipse which are quite
similar to these we see now in HD 21242; RS CVn is perhaps the best example.
And the strange photometric behavior of the spectroscopic binary CC Eri,
recently discussed by Evans (1971), also seems to be analogous to that we have
found in HD 21242.


March, 17, 1972

ROBERT E. MONTLE
DOUGLAS S. HALL
Dyer Observatory
Vanderbilt University
Nashville, Tennessee 37235
U.S.A.

References:

Carlos, R.C. and Popper, D.M. 1971, P.A.S.P. 83, 504. [BIBCODE 1971PASP...83..504C ]
Evans, D.S. 1971, M.N. 154, 327. [BIBCODE 1971MNRAS.154..329E ]
Nekrasova, S.V., Nikonov, V.B., and Rybka, E. 1965 Izv.
   Krymsk. Ap. Obs. 34, 69. [BIBCODE 1965IzKry..34...69N ]




         A PERIOD OF 60d IN THE LIGHT FLUCTUATIONS OF FG Sge


Photoelectric observations of FG Sge in V and B colours from 36 nights in 1971
have shown that its light changes with a period of about 60d and with
amplitudes of 0.2 and 0.45 mag in V and B, respectively. Two maxima were
observed in 1971, J.D. 2441162 and J.D. 2441224. On the basis of our
observations it is possible to verify the existence of fluctuations with
cycles of 10 to 20 days (W. Wenzel, W. Furtig, Die Sterne 43, 24. 1967; V.P.
Archipova, AZ 553, 3. 1970).


Astronomical Institute
University J.E. Purkyne
Brno, Czechoslovakia

J. PAPOUSEK