COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 877

                             Konkoly Observatory
                             Budapest
                             1974 March 18


     A PROBABLE PERIODICITY IN THE LIGHT VARIATION
          OF THE LMC SUPERGIANT HD 33579


Summary. Photometry of the brightest supergiant of the LMC
HD 33579 in 1971, 1972, 1973 and 1974 shows evidence for a
periodicity of around 90 days. The nature is probably pulsation.

1. Introduction
   In connection with the earlier and very recent investigations
on the theory of stellar evolution of very massive stars
(Ledoux, 1941; Schwarzschild and Harm, 1959; Simon and Stothers,
1970; Ziebarth, 1970; Appenzeller, 1970 a,b; Talbot, 1971 a,b;
Larson and Starfield, 1971, Barbaro, Bartelli, Chiosi and Nasi,
1973) it is of extreme interest to know whether such stars show
any long or short term light variation and whether these variations
are periodic. Rosendahl and Snowden (1971) carried out a
photometric program on five LMC supergiants amongst others
HD 33579 (V_J = 9.1, A3 Ia-0 (Feast, Thackeray and Wesselink, 1960))
and detected for all of them light variations of less than 0.1 mag,
probably caused by pulsation. The first observers to discover
that HD 33579 was slightly variable were Walraven and Walraven
(1966, 1971). Przybylski (1968) and Aller, Ross and Wares (1968)
analyzed the spectrum and Walraven and Walraven (1977) obtained
some atmospheric parameters with the same five-colour photometer
with which the observations presented here have been made. Wolf
(1972) made an extensive fine analysis of the atmosphere. Until
the present work there has been no evidence of periodicity in
the light variation.

2. The Observations
   The observations have been made with the Walraven five-colour
simultaneous photometer, attached to the 90-cm light-collector
of the Leiden Southern Station (at the SAAO- Annexe, formerly
the Republic Observatory Annexe) Hartebeestpoortdam, South Africa.
A description of the photometer and the photometric system is
given by Walraven and Walraven (1960) and Rijf, Tinbergen and
Walraven (1969). The comparison star was HD 33486 (8.1, B9). To
check its constancy a second comparison star was often used, viz.
HD 33117 (8.7, G5). Generally the variable was observed ten times
on the average, alternated by the comparison star. The average of
the brightness differences revealed one normal point. The integration
time for one observation was 0.5 or 1 min. The figure shows
these normal points (in log intensity) in the Walraven V (5590 A)
and (U 3620 A) bands, plotted against the calendar date.The error
bars indicate roughly the maximum mean error in one normal point.
Points connected with a line indicate normal points obtained in
the same night. In the near future the final reductions in all
five pass-bands will be published.

3. Discussion of light-curves and period
   The figure shows at least four cycles. Unobserved parts have
been dashed. The amplitudes are roughly 0.09 mag in V and 0.15 in
U. The B (4260 A) and L (3900) curves, which are not shown, have a
range of roughly 0.11 and 0.12 mag. There is certainly no strict
periodicity, but there seems to be some kind of regularity, with
an average period somewhere near 90 days. Some observations made
in October and November 1971 fit rather well when we extrapolate
the average light-curve with a period of 95 days.
   It is likely that the light variation is mainly caused by
pulsation. This can be concluded by the general shape of the
light-and colour curves and the fact that the star is blue at 
maximum, a conclusion already reached by Rosendahl and Snowden. 
However the light-curves are highly variable from cycle to cycle and
sudden drops or rises are present. These sudden changes are often
much more pronounced in U or sometimes seem to be only present in
the U band. Probably emission lines mainly active in this band,
caused by special atmospheric phenomena are here of account. In the
first cycle the rise in V and B started much earlier than in U
and also but less pronounced in L. However the U rise is generally
much more violent and reaches the maxima sometimes many days earlier
than that in V.

Acknowledgements.
I am indebted to Dr. Th. Walraven and Dr. M.W. Feast for reading and
commenting on the manuscript.

                       [FIGURE 1]

 The brightnesses HD 33579 minus comparison star (in log intensity)
plotted against the calendar date for the Walraven V (5590 A) and U
(3620 A) bands.


References:
Aller, L.H., Ross, J.E., Wares, G.W. 1968, Astrophys. Space Sci. 2, 344. [BIBCODE 1968Ap&SS...2..344W ]
Appenzeller, I. 1970 a, Astron. Astrophys. 5, 355. [BIBCODE 1970A&A.....5..355A ]
Appenzeller, I. 1970 b, Astron. Astrophys. 9, 216. [BIBCODE 1970A&A.....9..216A ]
Barbaro, G., Bertelli, G., Chiosi, C., Nasi, E. 1973 Astron. Astrophys.
      29, 185. [BIBCODE 1973A&A....29..185B ]
Feast, M.W., Thackeray, A.D., Wesselink, A.J. 1960 Mon. Not. R. Astron.
      Soc. 121, 337. [BIBCODE 1960MNRAS.121..337F ]
Larson, R.B., Starfield, S. 1971, Astron. Astrophys. 13, 190. [BIBCODE 1971A&A....13..190L ]
Ledoux, P. 1941, Astrophys. J. 94, 537. [BIBCODE 1941ApJ....94..537L ]
Przybylski, A. 1968, Mon.  Not. R. Astron.  Soc. 139, 313. [BIBCODE 1968MNRAS.139..313P ]
Rosendahl, J.D., Snowden, M.S. 1971, Astrophys. J. 169, 281. [BIBCODE 1971ApJ...169..281R ]
Rijf, R., Tinbergen, J., Walraven, Th. 1969, Bull. Astron. Inst. Netherl.
     20, 279. [BIBCODE 1969BAN....20..279R ]
Schwarzschild, M., Harm, R. 1959, Astrophys. J. 129, 637. [BIBCODE 1959ApJ...129..637S ]
Simon, N.R., Stothers, R. 1970, Astron. Astrophys. 6, 183. [BIBCODE 1970A&A.....6..183S ]
Talbot, R.J. 1971 a, Astrophys. J. 163, 17. [BIBCODE 1971ApJ...163...17T ]
Talbot, R.J. 1971 b, Astrophys. J. 165, 121. [BIBCODE 1971ApJ...165..121T ]
Walraven, Th., Walraven, J.H. 1966, private communication.
Walraven, Th., Walraven, J.H. 1960, Bull. Astron. Inst. Netherl. 15, 67. [BIBCODE 1960BAN....15...67W ]
Walraven, Th., Walraven, J.H. 1971, The Magellanic Clouds 117 (Ed.
     A.B. Muller, Reidel Publ. Co. Dordrecht, Holland). [BIBCODE 1971ASSL...23..117W ]
Wolf, B. 1972, Astron. Astrophys. 20, 275. [BIBCODE 1972A&A....20..275W ]
Ziebarth, K. 1970, Astrophys. J. 162, 947. [BIBCODE 1970ApJ...162..947Z ]





                          A.M. van GENDEREN
                          Leiden Southern Station
                          P.O. Box 13, Broederstroom 0240
                          Transvaal, South-Africa.