COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1985

                                   Konkoly Observatory
                                   Budapest
                                   1981 July 2

                                   HU ISSN 0374-0676



  A PHOTOELECTRIC TIME OF MINIMUM OF TV Cas IN FOUR COLOURS


   During the winter of 1980-1981 TV Cas was observed at the 
wavelengths 4720,6720,7820 and 8710A of the Utrecht Photometric
System (Provoost, 1980) using the 40 cm f/12.5 reflector of the     
Astronomical Institute at Utrecht. This telescope is located at
the Dutch Observatory in Ausserbinn, Switzerland (lambda = -8d8'44",
phi=46d23'05", alt.= 1350 m) and is equipped with a single-channel
photometer containing a refrigerated RCA 31034 A tube. The data
were reduced with the comparison star BD+58d0024. The primary
minimum of J.D.2444602(28/29 Dec.1980) is recorded approximately 
from phase 0.92 to 0.06. In each colour 34 observations are
available.
Several methods (e.g. Gauss-curve fit, parabolic fit) were
used to find the time of minimum light in each wavelength.
Although these methods all yield practically the same value, the
error is hard to determine. This is due to model-dependence and
the small number of points. The best way to arrive at a good
estimation of the error in a time of primary minimum is to compare
independent measurements of that minimum, for instance by taking
those obtained in several colours. The results presented in Table
I were determined by a "folding-method", which is in principle a
midpoint-method. This table also shows the standard deviation
and the number of observations involved. Of course this can only
be done on the assumption of wavelength-independence of the time
of minimum.
The ephemeris of Margrave (1980) 2441595.3582+ 1.8125944*E
was used to calculate the O-C values for the most recent 
photoelectric timings of primary minimum in Table II. These results
seem to indicate a slight increase in period of TV Cas.

                   Table I


An Observed Heliocentric Time of Minimum of TV Cas

filter
lambda_0  Hel. JD.- 2,444,000.0   Number of observations used

4720       602.4530(+-.0008)        29
6720       602.4538(+-.0009)        29
7820       602.4539(+-.0012)        29
8710       602.4528(+-.0013)        31
mean       602.4534 +-.0004        118
           
                    Table II


O-C Values of the Most Recent Timings of Primary Minimum of TV Cas


Hel. JD.- 2,440,000.0    E      O-C       Source

3786.7841               1209   -.0007    IBVS 1869
3795.9491               1214   +.0003    "
4094.9264               1379   +.0005    "
4114.8657               1390   +.0013    "
4453.8209               1577   +.0013    IBVS 1930
4602.4534               1659   +.0011    this paper


A more thorough investigation of this problem will be published
separately (De Landtsheer, 1981). In the meantime it is clear
continuous observation of TV Cas is needed.



                      A.C. DE LANDTSHEER

                      The Astronomical Institute at
                      Utrecht
                      Zonnenburg 2
                      3512 NL Utrecht
                      The Netherlands     



References:

De Landtsheer, A.C., 1981, to be submitted to Astron. Astrophys.
Margrave, T.E., 1980 IBVS 1869
Margrave, T.E., 1981 IBVS 1930
Provoost, P., 1980, Astron. Astrophys. Ser. 40, 129 [BIBCODE 1980A&AS...40..129P ]