COMMISSION 27 OF THE I. A. U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3525

                                                       Konkoly Observatory
                                                       Budapest
                                                       10 October 1990

                                                       HU ISSN 0374 - 0676


       VARIABILITY OF TWO SUPERGIANTS: HD 3940 AND HD 10494

   Most of the supergiants show light and/or radial velocity variations (see
e.g. Abt 1957, Rufener et al. 1978). The cause of the variation is probably
pulsation (e.g. Maeder 1980, Lovy et al. 1984) though there are other
suggestions (e.g. rotation, see Harmanec (1987)).
   Two supergiants have been observed with the 1-m (during 1984-86) and 50-cm
(during 1987-89) telescopes of Konkoly Observatory in Piszkesteto. The stars
are HD 3940 (A1 Ia) and HD 10494 (F5 Ia). They are members of the associations
Cas OB7 and Cas OB8, respectively (Humphreys 1978). Small amplitude radial
velocity variations in HD 10494 were discovered by Smolinski et al. (1980).
   HD 3940 was observed relative to BD+63d 82, the check star was BD+63d 87.
The check-comparison difference in V is 0.756m +- 0.013m. Only the V light
curve is displayed in Figure 1 (together with the check star magnitudes), which
shows that the mean V value of HD 3940 decreased by 0.15m in three years.
The U-B curve follows the same pattern while the B-V curve is its mirror image.
A period of 9.7d is expected from the PLC relation of Lovy et al. (1984), but
neither this nor any other reasonable value could be derived from the data.
The cause of the variation is unlikely to be pulsation, but there is
insufficient information now even to guess its origin.


                            [FIGURE 1]
                            [FIGURE 2]


   HD 10494 was observed relative to BD+60d 312, the check star was BD+60d 308. 
Their difference in V is 0.353m +- 0.006m. Figure 2 is a plot of the V
magnitudes of HD 10494 phased with a possible period of 12.7d. The amplitude
is 0.05m which is the expected value for an F5 supergiant (Maeder 1980). The
amplitudes of the colour curves are negligible.
   The period of the radial fundamental mode of an F5 supergiant is 39.8d
(using the T_eff, M_v and B.C. values given by Humphreys (1978)), while the
suggested period for HD 10494 is 12.7d. If this period is real, then it means
that either the star pulsates in overtone or the cause of the variability is
not pulsation.
   No further observations are planned, the data are available upon request.


                                              E. ZSOLDOS
                                              Konkoly Observatory
                                              Budapest XII. P.O. Box 67
                                              1525 Hungary



References:

Abt, H. A. 1957, Astrophys. J. 126, 138 [BIBCODE 1957ApJ...126..138A ]
Harmanec, P. 1987, Bull. Astron. Inst. Czechosl. 38, 52 [BIBCODE 1987BAICz..38...52H ]
Humphreys, R. M. 1978, Astrophys. J. Suppl. 38, 309 [BIBCODE 1978ApJS...38..309H ]
Lovy, D.; Maeder, A.; Noels, A.; Gabriel, M. 1984, Astron. Astrophys. 133, 307 [BIBCODE 1984A&A...133..307L ]
Maeder, A. 1980, Astron. Astrophys. 90, 311 [BIBCODE 1980A&A....90..311M ]
Rufener, F.; Maeder, A.; Burki, G. 1978, Astron. Astrophys. Suppl. 31, 179 [BIBCODE 1978A&AS...31..179R ]
Smolinski, J.; Climenhaga, J. L.; Harris, B. L. 1980, Acta Astron. 30, 427 [BIBCODE 1980AcA....30..427S ]