COMMISSION 27 OF THE I. A. U.
               INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3686

                                               Konkoly Observatory
                                               Budapest
                                               5 December 1991

                                               HU ISSN 0374 - 0676


                     UBV OBSERVATIONS OF SN1991T


We report on UBV observations of SN1991T in the galaxy NGC 4527 (alpha_1950.0 =
12h31m14s, delta_1950.0 = +2d56'28") carried out at Serra La Nave stellar
Station of Catania Astrophysical Observatory in 1991 from May 7 to May 22, with
the 91cm Cassegrain telescope equipped with a photon counting cooled photometer
using an EMI 9789QA tube.

As comparison stars we used HD 108202 and HD 107498, the same employed by
Cutispoto (1991) in his observations of the supernova at La Silla in May, 16
(IAU Circ.  No.  5239).  For these stars we have derived the following 
magnitudes and color indices by observing standard stars in the Coma cluster:

 star         V              B-V           U-B
HD 108202  10.265+-.006  1.176+-.012   1225+-.022
HD 107498  8.415+-.014   0.824+-.007   0.549+-.015

Mean nightly JD_hel., V magnitudes, colors and the number of measurements
during each run of observations of SN1991T are shown in Table 1.

Table I. SN1991T: UBV measurements from Serra La Nave

J.D.hel.        V                  B-V               U-B            No.
2448384.4996    11.6558+-0.0030   0.3722+-0.0061   -0.1903+-0.0050  24
2448388.4751    11.8314+-0.0092   0.5166+-0.0066   -0.0400+-0.0119   4
2448389.3921    11.9307+-0.0030   0.5343+-0.0033   -0.0152+-0.0066  24
2448392.4247    12.0754+-0.0050   0.7065+-0.0047    0.1349+-0.0082  16
2448394.4904    12.1776+-0.0063   0.8429+-0.0083    0.1589+-0.0157  12
2448398.3889    12.3984+-0.0021   1.0474+-0.0231    0.2125+-0.0215   4
2448398.4636    12.4177+-0.0137   1.0487+-0.0152    0.1762+-0.0209   4
2448399.4152*   12.5938+-0.0300   1.1214+-0.0289    0.3334+-0.0718   8
*bright moon

Our B and V magnitudes are plotted in Figure 1 together with values deduced
from photoelectric measurements by other observers, from April 16 to July 18,
as communicated in IAU circulars.  The time in the abscissa is given in days
starting from April 16, i.e.  the date of the first UBV photoelectric
measurement of the supernova by Cutispoto (IAU Circ. No. 5239).  In the V
magnitude plot, estimates of visual magnitudes are also shown for the period of
exponential decline of the light curve.


                              [FIGURE 1]

 Figure 1: B and V light curves of SN 1991T from April 16 to July 15. Filled
 circles represent our observations.


The decrease of B magnitude (~0.1 mag./day) during the declining phase after
the peak brightness, is consistent with a typical SNIa light curve, as
confirmed by the presence of SiII absorption in the spectra taken near the peak
(Sivaraman 1991).  On the other hand, from the inspection of B - V values,
dereddened for a color excess E(B - V) = .15 typical of NGC 4527 galaxy (de
Vaucouleurs et al. 1976), we deduce a trend similar to that of the mean B - V
curve for SNIa phenomena (Wheeler 1991).

We are grateful to Dr. R. Ventura who contributed in the observations and to
Prof. N. Panagia for his helpful comments on these data.



 Carlo Blanco                         Ettore Marilli
 Institute of Astronomy               Catania Astrophysical Observatory
 Catania University                   Observatory
 Citta Universitaria I-95125 Catania  Citta Universitaria I-95125 Catania

References

Cutispoto G., 1991, private communication
de Vaucouleurs G., de Vaucouleurs A., Corwin H.G.Jr, 1976, Second Reference
  Catalogue of Bright Galaxies, Univ. of Texas Press
Sivaraman K. R., 1991, in IAU Circ. No. 5255 [BIBCODE 1991IAUC.5255....1S ]
Wheeler J.C., 1991, in Supernovae, J.C. Wheeler, T. Piran and S. Weinberg
  eds., World Scient. Publish., p. 1