COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1839

                                   Konkoly Observatory
                                   Budapest
                                   1980 September 8

                                   HU ISSN 0374-0676



         ERUPTIVE MASS-TRANSFER EVENTS IN RW TAURI



     Many years of intermittent mass-transfer events in U Cephei
have been observed and interpreted (for references, see Olson
1980a, 1980b). Most prominent among the photometric disturbances
in U Cep was the ultraviolet light excess seen during primary
eclipse, which sometimes changed the normal total eclipse to one
of "partial" shape. This light has most recently been explained
as an asymmetrical bulge that grows around the equator of the
mass-accreting B star in response to the impact of the stream
(Olson 1980b). Factors that determine the growth of the bulge
include the mass transfer rate and the contemporary (differential)
rotational speed of the hot star. Such bulges were never observed 
in a steady-state, within the observational time resolution
of a few days. We now report the occurrence of qualitatively
similar photometric perturbations in the totally-eclipsing system
RW Tau. Observations were obtained with the 1.0 M reflector of
Prairie Observatory, using a single channel pulse-counting photometer 
with RCA 31034A-02 photomultiplier tube. Four-color
u v b y and near infrared I_k data were obtained, and transformed 
to the Stromgren-Crawford and Kron standard systems; y-observations 
were transformed to Johnson V. Comparison star was
BD +27d623 (checked and used by Bookmyer 1977), and observations
of (variable minus comparison) were corrected for differential
extinction.
     Infrared and ultraviolet results are shown in Figure 1.
Observations were obtained on five nights, and only on the first
of these (UT Nov. 8 1978; squares in Fig.1) were the light curves
free of contaminating light. Three times of primary minima were
obtained (HJD-2440000.): 3820.7835+-0.0001, 4180.7319+-0.0001;

                      [FIGURE 1]

 Fig. 1 - Infrared and ultraviolet light curves of primary eclipses
 of RW Tau. Symbols and UT dates are: square, Nov. 8, 1978; octagon,
 Dec. 28, 1978; triangle, Nov. 3, 1979; plus, Nov. 14, 1978; X,
 Nov. 17, 1979. Some of the ultraviolet scatter at minimum is
 due to moonlight.

4797.8074+-0.0001. Infrared and ultraviolet times were omitted
from the last minimum, as they were late by ~ 0.001 day. Light
curves of Figure 1 were stacked with period 2.7688344 day.
     During disturbed eclipses, excess light was present at
all observed phases of primary eclipse, and can be detected
even in the infrared. As with U Cep, the excess light at second
contact exceeded the third contact excess; if an equatorial
bulge is responsible in RW Tau, it too is asymmetrical. The
maximum ultraviolet excess on the magnitude scale was ~1.2 mag
on Dec. 28, 1978 (octagons in Fig.1), but the actual light excess 
peaked near phase 9.97 - again, similar to U Cep. These
RW Tau observations differ from those of U Cep in showing no
light loss during eclipse egress.
     A quantitative discussion of these observations awaits
the accurate measurement of comparison star colors. RW Tau may
be entering an active phase, and may repay observations in the

coming season. We particularly urge interested observers to
use intermediate band, rather than broad-band filters, if possible.
     The author thanks the National Science Foundation for
support of this work, and the University of Illinois Research
Board for partial support of computations.







                         EDWARD C. OLSON
                         Department of Astronomy
                         University of Illinois
                         Urbana, IL 61801





References:
Bookmyer, B.B. 1977, Publ.A.S.P., 89, 533 [BIBCODE 1977PASP...89..533B ]
Olson, E.C. 1980a, Astroph. J., 237, 496 [BIBCODE 1980ApJ...237..496O ]
Olson, E.C. 1980b, ibid, in press [BIBCODE 1980ApJ...241..257O ]