COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1253

                                                    Konkoly Observatory
                                                    Budapest
                                                    1977 March 23


                  UBVR PHOTOMETRY OF SU TAURI

The variable star SU Tauri (alpha= 5h43m12s, delta = +19d02.0',
Delta alpha = +3.53s, Delta delta = +0.024'; 1900) belongs to the
R CrB class of variable star. According to the General Catalogue
of Variable Stars, it has a range in brightness 9.5 < V < 16.0.
The same source lists a spectral type of G0 ep. The R CrB stars
as a class spend much of their time at maximum brightness. Feast
(1975) gives a thorough discussion of the characteristics of
the R CrB class of variable star.
   SU Tauri was entering minimum brightness during late
1976 (see American Association of Variable Star Observers 
Circulars). Since few such stars are observed near minimum, a
short series of photoelectric observations was made at the Kitt
Peak National Observatory's 2.1-meter telescope on 26 November
1976 U.T. A dry ice cooled ITT FW 129 photomultiplier was used
together with standard UBVR filters. Standard stars were chosen
from Landolt (1973). Standards for the R filter were from faint
standards by Kunkel (1976), tied into the Johnson UBVRI photometric 
system.
   The results are presented in Table I. The heliocentric
Julian Days are known to within 10 seconds. The data consists
of 5 separate sets of measures. The average magnitude and color-
index values together with their corresponding r.m.s. errors
(of a single observation) are V = 16.86 +- 0.05, (B-V) = +1.08
+-0.11, (U-B) = +0.30 +- 0.15, and (V-R) = +0.5 +- 0.6. The (V-R)
value is especially poor since the sensitivity of the FW 129 is
very low near the R passband. SU Tauri appears to be at one of
its faintest minima.
   The spectra and colors of R CrB stars can change significantly 
as the star waxes and wanes. In particular, color indices
at minimum can be bluer than those at maximum brightness due to
the effects of emission lines (Feast 1975). Fernie, Sherwood
and DuPuy (1972) found (B-V) = ~+1.08 and (U-B) = ~+0.41 for
SU Tau near maximum. As one can see, the (B-V) color index is
unchanged, but the (U-B) color index at this minimum is slightly 
bluer.
   The author thanks the Director of the KPNO for the telescope 
time, and the staff for their aid at the telescope. This
work was supported in part by the NSF grant no. AST 75-01890.


                Table I

       UBVR Photometry of SU Tauri

   JDhel      V       B-V     U-B     V-R
2443000.0+

108.9893    16.82    +1.16   +0.13   +0.4
   .9914    16.89     0.95    0.49   -0.4
   .9943    16.82     1.20    0.37   +0.4
   .9965    16.83     1.09    0.18   +1.0
   .9987    16.92     1.00    0.33   +1.0


                                  ARLO U. LANDOLT

                                  LSU Observatory
                                  Baton Rouge, La. 70803
                                  U.S.A.



References:

Feast, M.W. 1975, in "Variable Stars and Stellar Evolution", IAU Symposium No.
  67, edited by V.E. Sherwood and L. Plaut (Boston: D. Reidel), p. 129 [BIBCODE 1975IAUS...67..129F ]
Fernie, J.D., Sherwood, V.E., and DuPuy, D.L., 1972, Astrophys. J. 172, 383 [BIBCODE 1972ApJ...172..383F ]
Kunkel, W.E. 1976, private communication
Landolt, A.U. 1973, Astron.J. 78, 959 [BIBCODE 1973AJ.....78..959L ]