COMMISSION 27 OF THE I. A. U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           NUMBER 812

		                                 Konkoly Observatory
		                                 Budapest
                		                 1973 July 20



 ON THE CHARACTER OF LIGHT VARIATIONS OF THE INFRARED CARBON STAR CIT 6



The object CIT 6 = IRC + 30219= RW LMi (1) represents the carbon
star with the largest colour index I-K in the catalogue of Neugebauer 
and Leighton (2). In order to find out the character of the light
variation of CIT 6 photographic observations in red passbands R' (plate
ORWO ZP3, filter RG1) or R (plate ORWO ZP1, filter RG1) similar to
that of W. Becker's system, as well as in V-, and less frequently in
B- and U- band have been carried out with the Schmidt camera of the
Radioastrophysical Observatory since the spring 1970.
According to 42 observations in R- band the star CIT 6 seems to
belong to the long period variable stars with a period of about 570 days
and an amplitude of about 1.5 mag.(see Fig.)
Besides general long period changes the observations in V- band,
only 14 in number, show a rapid decrease of brightness by approximately 
1 mag. within a time interval not more than seven days between J.D.
2441053 and 2441060, followed by a slower return to the "normal" value. 
Judging by the scanty R' - magnitudes a brightness drop has taken
place in the red light, as well.
In the following cycle of the light variation of CIT 6 we have
very few observations at the same phase (0.8 P). Nevertheless, a 
decrease of brightness in noticeable.
Fortunately, polarimetric and photometric observations of the star
made by Kruszewski happened to coincide with what seemed to be a 
similar phenomenon in the second cycle, and a sudden decrease of brightness 
in V-, B- and U- bands with amplitude of around 1 mag. as well as
a large and fast change of the degree of polarization during only three
days was established (3).
One more short minimum was observed in the light variation around
J.D.2441765 near the maximum brightness of the long period variations.
Possibly, in the case of CIT 6 we deal with an extremely sharply
expressed phenomenon inherent in many Mira-type stars, so called bump
or wave or secondary minimum, connected with a more or less definite
phase of long period variations for a particular star (4). If so, the
next interval of time favorable for observations of such a phenomenon
in CIT 6 might be expected in Feb.-March 1976. Some other explanations
of the phenomenon and a different time of its next appearance
cannot be excluded, the more so because CIT 6 has some other 
photometric peculiarities.
    Compared to other infrared or late type carbon stars (e.g. CIT 5,
CIT 13, IRC + 10216) the colour indices B-V=1.2 and U-B=1.0 are 
unusually small. If the anomaly of CIT 6 is due to the presence of a
bluer unresolved companion (5) the radiation in B- and even more so
in U-band refers mainly to the latter. The long period variations 
observed in R-band, on the other hand, are due to the very red carbon
star. If the observed fast decreases of brightness, indeed, depend
on long period variations, then their cause is connected with the 
carbon star component. Evidently, both components are influenced by the
same process, e.g., sudden ejection of dust shell. Detailed continuous
observations of the fast changes in CIT 6 might give some more 
definite conclusions.
    The two first of our observations in B do not agree with long
period variations in R magnitudes. The mean colour index B-R=4.1 for
these two measurements is considerably larger than for the latest 
observations (B-R=2.7). Possibly, this may reflect brightness changes
of the bluer companion.
    The alternate explanation of CIT 6 as a single star leads to 
unusual distribution of energy in its spectrum: in the ultraviolet and
visible part it corresponds to an early C-star. In the near infrared
strong bands of CN discovered by Wisniewski et al. testify to the fact
that CIT 6 belongs to the late C-stars.




Radioastrophysical Observatory,
Latvian Academy of Sciences,
Riga, U.S.S.R.



                                 A. ALKSNIS
                                 I. EGLITIS



                         [FIGURE 1]


References:
(1) B.V. Kukarkin, P.N. Kholopov, N.B. Perova, 1970, IBVS 480.
(2) G. Neugebauer, R.B. Leighton, 1969, Two Micron Sky Survey,
             Washington. [BIBCODE 1969tmss.book.....N ]
(3) A. Kruszewski, 1973, IBVS 781.
(4) L. Campbell, 1955, Studies of Long Period Variables, Cambridge,
            Mass., AAVSO. [BIBCODE 1955slpv.book.....C ]
(5) W.Z. Wisniewski et al., 1967, ApJ Letters, 148, L 29. [BIBCODE 1967ApJ...148L..29W ]