COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 342

                                  Konkoly Observatory
                                  Budapest
                                  1969 April 4


          A STANDARD COMPARISON SEQUENCE
         TO THE FLARE STAR YZ CANIS MINORIS

      Standard two-colour photoelectric observations of
comparison stars in the field of the flare star, YZ CMi,
have been made by J. Eksteen at the Boyden Observatory.
Several different magnitude sequences are currently being
utilized to reduce flare observations of this star and this
new photometry should improve the standardisation of
material. With present increasing attention towards the
secondary, possibly secular, variations of flare stars these
results may be particularly valuable. The colour and
magnitude sequence is also suitable for the description of
flares observed visually and photographically with amplitudes
of one and two magnitudes, respectively.
      The 16-inch Nishimura reflector equipped with an
E.M.I. 6256 photomultiplier and standard B and V filters
was employed on two nights, 13 and 14 March 1969. 
Transformation to the Johnson standard photometric system was
effected by the observation on each night of five bright
stars (See Table 1) from the Arizona-Tonantzintla Catalogue
(Ref. 1), observed before and after the sequence.

       Table 1
 BS        V     B-V
2646      3.43m  1.72m
2827      2.44  -0.09
2970      3.93   1.02
3045      3.35   1.25
3165      2.25  -0.27

                        Since the H.T. voltage was
                        lowered for these bright
                        stars, the zero point 
                        constants for each night in
                        the V transformation were
                        determined for the sequence
                        by means of a fainter star
                        in the field which had
    [FIGURE 1]
                        been observed earlier in
                        the Johnson system (star c
                        in Ref. 2). The magnitude
                        and colour transformation
                        equations: in standard 
                        notation, were found to be:
                        V = v_0 - 0.04(B-V) + const. +/- 0.034
                        B-V = 1.13(b-v)_0 + {0.683} +/- 0.025
            				    {0.653}	 

The large mean error in V for these bright stars reflects
the scatter in the original measures (Ref.1) due no doubt
to the rather large zenith distances employed at Catalina
and Tonantzintla. This uncertainty is reduced, however, in
our sequence by taking the local zero point star. Atmospheric
extinction coefficients, typical of Boyden, k_v = 0.23
and k_b-v = 0.10, were applied at the small air masses 
encountered which were never greater than 1.3.
     Photometric results from the two nights are given
in Table 2, together with two additional fainter stars from
Ref. 2. In Fig. 1 star a is HD 62525. A comparison of common
stars in the photovisual and photographic sequences 
presently in use shows that of Mosidze and Chuadze (Ref. 3) to
be in fair agreement, but that of Bateson et al. (Ref. 4) to
be systematically 0.6m brighter. An unpublished photoelectric
sequence by Solomon (private communication) shows agreement
for our star b but large differences in colour and magnitude
for star e which has consequently been removed from our
sequence.

                    Table 2

Star        Nightly Values            Adopted Sequence
           V              B-V           V         B-V
a    8.08m   8.12m  0.89m     0.88m    8.10m      0.89m
b   10.52   10.53   0.43      0.51    10.52       0.47
c     -       -     0.47      0.51    10.72       0.50
d   10.71   10.74   1.49      1.48    10.72       1.49
e   10.95   10.99   0.94      0.85      -          -
f   10.98   19.01   0.26      0.28    11.00       0.27
g   11.70   11.70   0.17      0.16    11.70       0.17
h     -       -      -         -      12.46       0.95
k     -       -      -         -      12.47       1.13

     YZ CMi was observed on both nights and the results
are given in Table 3. No sensible variation is evident as
compared with my previous measures (Ref. 2).



          Table 3
J.D.         V     B-V
-2440000
294d804    11.24m  1.60m
295.794    11.24   1.56



REFERENCES
1) H.L. Johnson et al, Com. of Lunar and Plan. Lab. No. 63
  (1966). [BIBCODE 1966CoLPL...4...99J ]
2) A.D. Andrews, I.B.V.S., No. 285, (1968).
3) L.N. Mosidze and A.D. Chuadze, Abastumani Obs. Bull. 32 p. 21.
  (1965).
4) F.M. Bateson et al, Charts for Southern Variable Stars
   Series 5 (issued from Mt. John University Obs. New Zealand).


Armagh Observatory
28 March, 1969                             A.D. ANDREWS