COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3301

                                        Konkoly Observatory
                                        Budapest
                                        9 March 1989

                                        HU ISSN 0374 - 0676


              1989 V-BAND LIGHT CURVE OF RT AND


We report on the continuation of our long-term project at Capilla Peak
Observatory of photometry of the chromospherically-active RS CVn stars. We
have previously made single-channel observations of RT And (= BD+52d3383A) at
UBVR in 1981 (Zeilik et al., 1982) and CCD observations in 1988 at BVRI (Zeilik
et al., 1988). These latter data have been completely analyzed by Zeilik et
al. (1989), who find a single spot group at longitude=260deg, latitude=46deg,
radius=9.7deg, and a temperature difference relative to the photosphere of -1200
K.  Our project aims at revealing how these starspot parameters change with
time and hence the nature of any magnetic activity cycles.

We made V and I band observations on the 15, 17, 18, and 21 January 1989 UT of
RT And (#163 in the catalog of Strassmeier et al. 1988). We used a CCD camera
with an RCA SID501EX chip on our 61-cm telescope (Laubscher et al., 1988) in
the mode of a multichannel photometer. The variable, sky, and comparison star
(BD +52d3384) were observed simultaneously and reduced with a software mask
with an effective aperture of 34". We now have a new Schott glass filter set
(Beckert and Newberry, 1989) in which the V-band filter has an effective
wavelength of 551.1 nm and a bandpass of 74.2 nm; the I-band filter and
effective wavelength of 815.1 nm with a 137.3 nm bandpass. Unfortunately,
conditions of high and rapidly changing humidity rendered the I-band


                           [FIGURE 1]

         Figure 1. RT Andromedae, V-band, Capilla 1989

                           [FIGURE 2]

         Figure 2. RT Andromedae, V-band, Capilla 1989


observations useless. The V-band data are acceptable, although the overall
error is about 0.02 mag, about twice as large as we usually aim to achieve.
Figure 1 shows the results in the instrumental system with the delta magnitude
in the sense of (variable-comparison). Figure 2 shows an optimized model fit
to the observations using the technique of Budding and Zeilik (1987). A fit of
a single, black, circular spot to the distortion wave resulted in the following
star spot parameters: longitude=252deg, latitude=48deg, radius=16.5deg. (The
latitude optimization was barely acceptable by our curvature Hessian test.) We
could not calculate a temperature because of the lack of the I-band data. We
note that, compared to our 1987 data, the active region has not shifted
significantly in position, but it has grown almost 3 times larger in effective
area. Continuing observations will show if this trend continues.


M. ZEILIK, D. BECKERT, D. COX, J. DOLBY,
M. LEDLOW, M. NEWBERRY, M. RHODES
Capilla Peak Observatory
Institute for Astrophysics
The University of New Mexico
Albuquerque, NM 87131 U.S.A.

References:

Beckert, D., and Newberry, M., 1989, preprint. [BIBCODE 1989PASP..101..849B ]
Budding, E., and Zeilik, M., 1987, Ap.J., 319, 827-835. [BIBCODE 1987ApJ...319..827B ]
Laubscher, B., Gregory, S., Bauer, T., Zeilik, M., Burns, J., 1988, Pub.
   Astron. Soc. Pacific, 100, 131-136. [BIBCODE 1988PASP..100..131L ]
Strassmeier, K., Hall, D., Zeilik, M., Nelson, E., Eker, Z., and Fekel, F.,
   1988, Astron. Astrophys. Suppl. Series, 72, 291-345. [BIBCODE 1988A&AS...72..291S ]
Zeilik, M., Elston, R., Henson, G., Scholke, B., Smith, P., 1982, 
   IBVS No. 2090.
Zeilik, M., Beckert, D., de Blasi, C., Ledlow, M., Rhodes, M., and Williams,
   T., 1988, IBVS No. 3173.
Zeilik, M., Cox, D.A., De Blasi, C., Rhodes, M., and Budding, E., 1989,
   submitted to Ap.J. [BIBCODE 1989ApJ...345..991Z ]