COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1582

                                  Konkoly Observatory
                                  Budapest
                                  1979 April 9



   SHORT TIME SCALE BRIGHTNESS FLUCTUATIONS IN BP TAURI


    An investigation of snort period brightness fluctuations in
T Tauri stars has been under way at the Cloudcroft Observatory
since November, 1978. The 1.2 meter f/6.5 Newtonian telescope is
equipped with a thermoelectrically cooled FW-130 photomultiplier
(S-20 surface) housed in a computer controlled single-channel
pulse-counting photometer. Differential Johnson U band magnitudes
are being obtained for the brighter T Tauri stars on a nightly
basis. In addition, several stars are being observed in a high
speed mode, consisting of sequential 5 second U band integrations
for durations up to 2 hours. Comparison stars are monitored both
before and after a high speed time sequence. The observations of
Hopp and Surawski (1979) and Kuan (1976) indicate that T Tauri
stars show significant variability on time scales less than half

                          [FIGURE 1]

an hour, and our high speed observations are designed to examine
the nature of this rapid variability. We report here on short
time scale variability in BP Tauri.
    Figure 1 shows our results for BP Tauri, an advanced
T Tauri star with a strong ultraviolet excess. Relative U band
intensity on an arbitrary scale is plotted versus time for nearly
two hours of 5 sec integrations. The start time of this observation 
was UT 06h26m05s on 05 December 1978. Comparison stars were
constant to +-0.01 mag during similar observations before and
after the BP Tauri observation. Figure 1 shows both systematic
brightness changes (15% intensity decrease during second half of
observation) and shorter period "flare-ups" with amplitudes of
5% and characteristic time scales of 10 minutes. These low-
amplitude brightenings are consistent with Kuan's (1976) postulated
Balmer continuum producing flares.





                     THIMOTHY J. SCHNEEBERGER
                     Air Force Geophysics Laboratory
                     The Cloudcroft Observatory and
                     Sacramento Peak Observatory
                     Sunspot, N.M. 88349 U.S.A.

                     S. P. WORDEN
                     Air Force Geophysics Laboratory
                     Sacramento Peak Observatory
                     Sunspot, N.M. 88349 U.S.A.

                     J. L. AFRICANO
                     The Cloudcroft Observatory and
                     Sacramento Peak Observatory
                     Sunspot, N.M. 88349 U.S.A.



References:

Hopp, U. and Surawski, U. 1979, I.B.V.S. No. 1550
Kuan, P. 1976, Astrophys. J. 210, 129 [BIBCODE 1976ApJ...210..129K ]