COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                         Number 986

                                       Konkoly Observatory
                                       Budapest
                                       1975 April 12


     BLUE-INFRARED BEHAVIOUR OF SOME VARIABLES OF MIRA TYPE

    During the study of the new infrared variables found by the writer 
in the field of M 16 - M 17 (Maffei, 1975), a new phenomenon has
been discovered: some stars are variable if observed in infrared 
radiation and constant in blue light.
    The following variables showed this behaviour: M 137, M 190,
V 1975 Sgr, M 246 and M 238. M 137, V 1975 Sgr and M 238 may be SR,
the remaining two of Mira type. The variables M 246 and M 238 are 
situated in a field centred on gamma Cygni, which at present is still being
studied by the writer in collaboration with Miss Brunella D'Onofrio.
    The Fig. 1, 2 and 3 reproduce the light curves in blue (m_{pg}) and
infrared (m_{ir}) radiation for the variables: M 190, V 1975 Sgr and M 246.
All the plates (103a-O and I-N (hypers.) + RG 5, respectively) have been
collected with the 65/90 cm Schmidt telescope of the Osservatorio 
Astrofisico of Asiago. The coincidence of the infrared image with the
blue one has been tested by means of the positive-negative method.
    In order to explain this behaviour one needs multicolour observations 
connected with spectroscopic researches. Now we believe that
the most obvious explanation is the coexistence of an infrared variable 
star of Mira or SR type with a blue companion. It is interesting
to remember that the existence of blue-infrared binary stars has been
recently suggested by Humphreys and Ney (1974).
   The percentage of the long period variables with this behaviour
appears to be not negligible. Only 9 of the Mira or SR infrared variables 
observed in the field of M 16 - M 17, were visible also in blue
light; three of these proved to be constant.

    For the near future the writer hopes to react, a statistically
significant result by means of researches in four other stellar fields
that he began in 1967 and that are still in progress.


                                          PAOLO MAFFEI
                                 Cattedra di Astrofisica della
                                        Universita di Roma

References:
R.M. Humphreys and E.P. Ney (1974) - Astrophys.J. vol. 190 p. 339 [BIBCODE 1974ApJ...190..339H ]
P. Maffei (1975) - I.B.V.S. No. 985


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