COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2248

                                     Konkoly Observatory
                                     Budapest
                                     1982 December 14

                                     HU ISSN 0374-0676


         IDENTIFICATION OF HD 174429 AS AN RS CVn SYSTEM


  We present 1982 photoelectric observations of the RS CVn candidate
HD 174429.
   HD 174429 (= SAO 245781 = CP -50 10862) is included in a list of
southern RS CVn candidates by Weiler and Stencel (1979). Radial velocity
measurements and H & K line profiles are given by Stacy et al, (1980).
Optical variability was reported by Coates et al. (1980).
   HD 174429 was observed in the Johnson B & V passbands on sixteen nights
in the interval 1982 May to October at Monash Observatory, and at Siding
Spring Observatory. The standard stars used were HD 176557 (= SAO 245894 =
CD -50 12292) and HD 176664 (= SAO 245899 = CD -51 11893). The measurements
showed that the magnitude differences between the standards were constant at
1.260 +/- 0.005 in V, and 1.499 +/- 0.004 in B.


                            [FIGURE 1]



   The V light curve obtained is shown in Figure 1. The primary epoch is
HJD 2444443.0000, the period is estimated to be 0.943 days and DeltaV is relative
to HD 176557.
   Minimum light is now about 0.09 magnitude fainter than that reported by
Coates et al. (1980), while maximum light is about 0.01 magnitude brighter.
Also the shape of the light curve has altered radically from 1980 (see
Figure 2).

                             [FIGURE 2]


   Plotting the 1982 V data in the intervals 1982 May to July, and August
to October (Figures 3(a) and 3(b)) shows how the light curve has changed in
form within the 1982 observing season. The minimum at phase approximately
0.8 observed early in the season was no longer present when observations were
made at this phase in August. Such variation is typical of the RS CVn class
of stars.
  A plot of the colour index B-V versus V is shown in Figure 4. A least
squares straight line fitted to these data (solid line in Figure 4) was found
to be of negligible gradient, indicating that B-V for this system was
constant within the accuracy of our measurements at +0.77 +/- 0.01.
  Houk (1978) gives HD 174429 as spectral type K0 Vp. The B-V value
obtained from our observations is significantly bluer than would be expected
if the system was a single K0 V star. Using these colour data and assuming


                           [FIGURE 3]



                           [FIGURE 4]


that the system is a binary, with both components on the main sequence,
calculations indicate that the primary is near G5.
   Preliminary analysis suggests that if the variability of the system is
solely due to the presence of cooler active regions on the surface of the
secondary, then these regions need to be around 3000 K cooler than the K0 V
photosphere, and cover approximately 50% of the effective area of its
surface, in order to reproduce the observed V range without a detectable
colour change. This suggests an extremely high amount of activity on the
surface of the K0 star. However, we stress the tentative nature of our
conclusions about the sizes and temperatures of these regions.
   On the basis of these observations we identify HD 174429 as a member of
the RS CVn class. More observations are required to investigate this
system further.



       D.W. COATES, J.L. INNIS, T.T. MOON and K. THOMPSON
       Department of Physics, Monash University,
       Clayton, Victoria 3168, Australia.


References:

Coates, D.W., Halprin, L., Sartori, P. and Thompson, K.: 1980, 
  Inform. Bull. Var. Stars, No. 1849.
Houk, N.: 1978, Michigan Catalogue of Two Dimensional Spectral Types for the
  HD Stars (University of Michigan Astronomy Department, Ann Arbor), Vol. 2. [BIBCODE 1978mcts.book.....H ]
Stacy, J.G., Stencel, R.E. and Weiler, E.J.: 1980, Astron. J., 85, 858. [BIBCODE 1980AJ.....85..858S ]
Weiler, E.J. and Stencel, R.E.: 1979, Astron. J., 84, 1372. [BIBCODE 1979AJ.....84.1372W ]