COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2510

                                      Konkoly Observatory
                                      Budapest
                                      27 April 1984

                                      HU ISSN 0374-0676

                 INFRARED PHOTOMETRY OF R CrB

  R CrB is the prototype of a class of irregular variables that are characterized
by an overabundance of carbon and undergo sudden decreases in visual
brightness at irregular intervals. During the minima the decrease in brightness
in the near infrared is less than that in the visible. In the L band
(3.4 microm) R CrB shows variations unrelated to the sudden visual drops.
Strecker (1975) found L magnitude variations for R CrB on a time scale of
about 1100 days. However, whether these variations are periodic is not known.
  We have observed R CrB in the J, H, K, L bands (at 1.2, 1.6, 2.2, 3.4 microm,
respectively) on three occasions including one (March 6, 1984) during the
current minimum. Observations were made with the 104 cm telescope of the
Uttar Pradesh State Observatory at Nainital using a liquid nitrogen cooled
InSb photometer. The measured J, H, K, L magnitudes are listed in Table I,
wherein the measurements by Glass (1978) and Shenavrin et al. (1979) are also
given.

                                  Table I
                      R CrB: Infrared photometry
Date                J      H      K      L      visual   References
                                                phase
Feb. 1 to 12,1975   5.04   4.82   4.26   2.62   bright   Glass (1978)
June 1,1977         -      7.22   5.27   2.91   faint    Shenavrin
                                                         et al,(1979)
Feb. 18,1980        5.10   4.80   4.10   2.20   bright   present work
March 25,1980       5.10   4.80   4.10   2.30   bright   present work
March 6,1984        8.15   6.61   4.93   -      faint    present work

  The four new measurements in the L band made subsequent to the observations 
of Strecker (1975) do not fit a periodic extrapolation of the L light
curve for R CrB given by Strecker (1975). It is not clear whether the low
L brightness during the 1977 visual minimum is related to the drop in the
visible light or is a part of an independent long term variation in the
L band.


         N.M. ASHOK, T. CHANDRASEKHAR and H.C. BHATT
              Physical Research Laboratory
                Ahmedabad-380009, India

References:

Glass, I.S.: 1978, Mon.Not.R.Astr.Soc, 185, 23 [BIBCODE 1978MNRAS.185...23G ]
Shenavrin, V.I., Taranova, O.G., Moroz, V.I. and Grigorev, A.A.: 1979,
  Sov.Astron. 23, 567 [BIBCODE 1979SvA....23..567S ]
Strecker, D.W.: 1975, Astron.J., 80, 451 [BIBCODE 1975AJ.....80..451S ]