COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 274

                                   Konkoly Observatory
                                   Budapest
                                   1968 May 21


     PHOTOELECTRIC OBSERVATIONS OF YZ CANIS MINORIS


During the second part of the YZ CMi international patrol, planned for 1968 by
the working group on flare stars, we carried out observations of this star with
a 91 cm Cassegrain-telescope at our stellar station in Serra La Nave (Catania).
Our photometer was equipped with an EMI 6256 A unrefrigerated photomultiplier
and BG 12(1mm)+ GG13(2mm) filters (lambda equ=4300 A).

From February 21 to March 7 we collected about 17 hours of observations in
three nights. The photoelectric coverage is summarized in Tab. I and the
characteristics of the four observed flares in Tab. II. The flare light
curves are drawn in the figures. The coverage times include the sky light
measurements, which lasted about 30 seconds and were made every 15-20 minutes.

TAB. I

Photoelectric coverage.

Day                 U T                Total
February 26/27  20^h01^m - 21^h47^m
                21  52   - 22  31
                22  35   - 01  21     4^h11^m
March 1/2       18  28   - 00  56     6  28
"     3/4       18  25   - 00  51     6  26

We notice that during the first night of our observations we made two
measurements of a comparison star because we were interested also in long
period variations at minimum. During the second of these measurements, made
from 22^h31^m to 22^h35^m (TU), a second flare happened and we could observe
only part of the decay branch. The time of maximum given for this flare has
been deduced by a rough extrapolation.

TAB. II

Observed flares.

     Date of the maximum                         Rise time     Total dur.
                                                 (minutes)     (minutes)
                                      Delta m    d      d'     D        D'
No      UT                   JD_hel   (max.)
 1   Feb. 26  21^h26.^m1   913.3972   0.^m24   0.^m9   0.^m3   7.^m2  0.^m8
 2    "       22  33.4     913.4440   -        -       -       -      -
 3   Mar. 1   19  59.9     917.3371   0.^m62   1.4     0.6     ?      1.7
 4   Mar. 3   20  01.3     919.3380   0.^m23   1.4     0.9    23.3   11.4


                          [FIGURE 1]
                          [FIGURE 2]
                          [FIGURE 3]
                          [FIGURE 4]


As far as it concerns the total duration (D) of the flare No. 3, the
uncertainty is due to its very slow decay after a first relatively rapid
decrease. In order to avoid this difficulty we have introduced (1) the
parameters d'(time rise) and D'(total duration) both referred to that part of
the flare, for which we have

Delta m>=20%(Delta m)_max

Some more details will be published in the "Memorie della Societa Astronomics
Italiana".


Catania Astrophysical Observatory
May 10, 1968.
                                        S. CRISTALDI M. RODONO

Reference:

(1) S. Cristaldi, M. Narbone, M. Rodono, Mem. Soc. Astr. Ital., 1968 (in
   press).