COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1773

                                     Konkoly Observatory
                                     Budapest
                                     1980 April 16


           NEW PHOTOMETRIC ACTIVITY IN U CEPHEI


Crawford and Olson (1979) have summarized photometric disturbances in primary
eclipses of U Cep from 1974 to 1977. The frequency of photometrically
disturbed eclipses gradually declined during this time. Eclipses of UT 1978
September 2 and 27 (observed with the 1 m Prairie Observatory reflector) were
nearly free of contaminating light, and the eclipse of 1979 September 6
(observed with the No. 4 0.4 m Kitt Peak National Observatory reflector) just
satisfied the Crawford-Olson criterion (d>0.075 day) for an "undisturbed"
eclipse. The eclipse of 1980 February 25 (KPNO) was the cleanest yet observed
by the authors, from the ultraviolet to the infrared. We have been unable to
observe any other primary minima this year.

Olson (1978) has discussed large light losses often present outside primary
eclipse during active periods, particularly near orbital phase 0.6. We now
report the sudden recurrence of such activity, as shown in Figures 1
(Stromgren-Crawford ultraviolet) and 2 (near-infrared transformed to the Kron
I). The ultraviolet light on 1980 February 24 (triangles) was at its
undisturbed level, while on 1979 September 7 (diamonds) some depression is
evident (both KPNO nights were of marginal quality, accounting for the large
scatter). Following the clean eclipse of 25 February, observations under
photometric conditions at Prairie Observatory on 1980 March 15 and 22 (octagons
and squares) showed a large dip in the light curve. This depression matches
the most prominent dip seen earlier (see Figure 3b of Olson 1978). Features
similar to the small "peak" at phase 0.55 have been observed many times before
under depressed light conditions and were unquestionably real. The size of the
light loss increased monotonically from infrared to ultraviolet where up to
half of the light was lost, and the phenomenon was very similar to the earlier
episodes. Past experience suggests that the dip can disappear on a time scale
of about 5 days, and that new episodes of activity can reappear on a scale of
months. Eclipse light curves can also be expected to vary significantly.

                         [FIGURE 1]

   Figure 1 - Stromgren-Crawford U-observation of U Cep near phase
   0.5. Diamonds, UT 1979 September 7; triangles, 1980 February 24;
   octagons, 1980 March 15; squares, 1980 March 22.

                         [FIGURE 2]

   Figure 2 - Near-infrared observations of U Cep, transformed to
   the Kron system. Symbols are the same as in Figure 1.

We urge observers to obtain multicolor photometry of this active Algol-like
binary at all possible phases.


R.C. CRAWFORD
E.C. OLSON
University of Illinois
Department of Astronomy
Urbana, Illinois 61801

References:

Crawford, R.C., and Olson, E.C. 1979, Publ. A.S.P., 91, 413 [BIBCODE 1979PASP...91..413C ]
Olson, E.C. 1978, Ap.J., 220, 251 [BIBCODE 1978ApJ...220..251O ]