COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 691

                                       Konkoly Observatory
                                       Budapest
                                       1972 June 30


               ANSWER TO IBVS NO 656


In the IBVS No. 656, an argument was presented criticizing our simultaneous
three-color observations of flare stars at the Tokyo Astronomical Observatory.
The present note is to answer this question.

1. The relation between delta U/delta B and delta B at maximum flare activity
is shown in the Fig. 1 which compares our results with those of Cristaldi and
Rodono (IBVS No. 525, 600) and of Mumford (Publ. Astr. Soc. Pacific 81, 890,
1969). There seems to be no appreciable systematic difference between our
results and other observers' results.

                           [FIGURE 1]

2. Another evidence supporting the correctness of our observations is the
Fig. 2 in which color indices of the maximum flare activity are shown. Our
values again show no systematic difference compared with Kunkel's values
(Ap.J., 161, 503, 1970).

                           [FIGURE 2]

3. Our three-color photometer together with its amplifier and recorder has
been carefully inspected, and no departure from linearity of response was
found. The linearity of the equipment is further supported by actual
observations of many photometric standard stars.

4. Our phototube, EMI 6256B has a somewhat different spectral response
compared with RCA 1P21. If some sort of stellar flares having an unusually
strong emission in the far ultraviolet is observed, there may appear a
systematic difference in delta U in the sense that 6256B emits less
photoelectrons than 1P21 does. The low altitude (370 m above sea-level) of
our observing station can exaggerate this effect by blocking radiations in the
far ultraviolet. The observational material used in the IBVS No. 656
might include such cases. This point may be investigated in future
observations.


K. OSAWA and K. ICHIMURA
Tokyo Astronomical Observatory