COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3524

                                                 Konkoly Observatory
                                                 Budapest
                                                 9 October 1990

                                                 HU ISSN 0374 - 0676

         PHOTOELECTRIC PHOTOMETRY OF TZ BOOTIS


The W UMa system, TZ Bootis, has exhibited several period
changes since its discovery in 1926. The most recent change
occurred during 1977-78, at which time the period suddenly
shortened by 0.6 s (Grobel, 1). Observations of period changes
may help solve light curve irregularities in TZ Bootis reported 
by Hoffmann (2, 3), and may increase our understanding of
interactions between close binary systems.
   BV differential photometry was conducted on TZ Bootis during
two nights in April, 1989, with Lowell Observatory's 107 cm
reflector on Anderson Mesa. Comparison stars were the same as
used by Hoffmann (2). Primary (transit) minimum was observed on
JD Hel 2947640.6925 +- 0.0005. Using Grobel's (1) ephemeris of

       JD Hel Min_tr = 2443655.5278 + 0.29715665 E

for observations after JD 2443300 an O-C of -0.0031d was 
obtained. Thus, there is no evidence for a significant change in
the period of TZ Bootis since 1978.
   Hoffmann (3) found that the primary and secondary minima
alternate in depth with a period of approximately 3.5 years. As
can been seen in Fig. 1, the minima were nearly equal in depth
with the primary minimum only slightly deeper than the secondary
minimum. This is consistent with Hoffmann's prediction that the
system should have been changing from a stage with a deep primary
minimum (1988.8) to a stage with equal minima (1989.6).


                        [FIGURE 1]

 Fig. 1   B and V light curves of TZ Bootis, April 1989. The Delta(B-V)
 curve is based on normal points with bin widths of 0.04p.


   The author is grateful to the Lowell Observatory for the use
of its facilities, and is indebted to Tobias Kreidl and Andrew
Odell for their encouragement and assistance.


                                      DAVID SCHAUB
                                      CBIS Federal Inc.
                                      2255 N. Gemini Dr.
                                      Flagstaff, Arizona 86001
                                      USA

                                      Visiting astronomer
                                      Lowell Observatory
                                      Flagstaff, Arizona
                                      USA



References:

(1) Grobel, R.   : 1989, IBVS No. 3299
(2) Hoffmann, M. : 1978, Astron. Astrophys. Suppl. 33, 63 [BIBCODE 1978A&AS...33...63H ]
(3) Hoffmann, M. : 1980, Astron. Astrophys. Suppl. Ser. 40, 263 [BIBCODE 1980A&AS...40..263H ]