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\IBVShead{4172}{16 March 1995}


\centerline{\ft NEW MINIMA TIMES AND PERIOD BEHAVIOUR FOR THE ECLIPSING}
\centerline{\ft VARIABLES RT ANDROMEDAE, 44i BOOTIS AND GO CYGNI}
\vskip 8mm

\begintext

In the present report new photoelectric minima times of RT
And, 44i Boo and GO Cyg are given as they were derived from our
observations made either in Greece or in Romania.

The photoelectric observations of RT And  and 44i Boo were
made during 1989 and 1994, respectively with the two-beam,
multi-mode, nebular-stellar photometer of the National Observatory
of Athens, attached to the 48-inch Cassegrain reflector
at the Kryonerion Astronomical Station.  While those of GO Cyg
were made during 1994 with an EMI 9502 B type photocell,
attached to the 50 cm Cassegrain telescope of the Bucharest
Observatory.  The filters used in both cases are in close
accordance with the standard UBV and the reduction of the
observations has been made in the usual way (Hardie, 1962).


{\bf RT Andromedae}

The short period variable RT And (BD +52\degr 3383A, HD\,218915)
is a very interesting eclipsing binary with many peculiarities
in its light curve.  It is classified as an RS CVn-type system
with both components to be main-sequence stars in contrast to
the main group, which contains active sub-giant stars (Budding
and Zeilik, 1987).

From our observations made during 1989, 5 new minima times
were derived and given in Table I. The O$-$C diagram of the
system based on all minima times found in the literature (614
points) is presented in Figure 1; a quadratic least squares
fitting applied to all of them, improves Williamon's (1974)
ephemeris formula to:
\vskip 1mm
\begin{center}
 Min I = 2441141.6401 + 0\fd 62893928 $\times$ E $-$ 1\fd 16 $\times$ 10$^{-10} \times$ E$^2$
\end{center}
\vskip 1mm
 \noindent showing that its orbital period is decreasing.

 A detailed analysis of the period variations of RT And has
been recently made (Rovithis-Livaniou et al., 1994).  Moreover
our new 5 minima times together with the last photoelectric ones
yield the following linear ephemeris:
\vskip 1mm
\hspace*{3cm} Min I = 2447756.3385 + 0\fd 628929355 $\times$ E \hfill (1)
\hspace*{6.2cm}           $\pm$.0003\ $\pm$\ \ \ .000000010
\vskip 1mm
\noindent which is proposed for the future observations of RT Andromedae.
\vskip 2mm
\centerline{Table I. Photoelectric Minima Times of RT And}
\vskip 1mm
\begin{center}
\begin{tabular}{cccr}
\hline        
           Hel. JD  &       (O$-$C)$_I$&    (O$-$C)$_{II}$&   (O$-$C)$_{III}$\\
         2440000+   &      days  &     days    & days\\
\hline
\\       
         7756.3385&        $-$.0056&      $-$.0022&      .0000\\
         7758.5390&        $-$.0062&      $-$.0029&     +.0008\\
         7759.4832&        $-$.0054&      $-$.0021&     +.0001\\
         7760.4256&        $-$.0064&      $-$.0031&     $-$.0009\\
         7763.5711&        $-$.0052&      $-$.0023&     $-$.0001\\ 
\hline
\end{tabular}
\end{center}
\vfill \eject

\centerline{2}
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\epsfysize=7.3cm
\centerline{\epsffile{4172-f1.ps}}
\begin{center}
Figure 1. The O$-$C diagram of RT And based on 44 photographic (squares) and
84 photoelectric (diamonds) minima times. The C values have been calculated
using Williamon's (1974) linear ephemeris.
\end{center}
\vskip 1mm
    
\noindent In Table I the residuals (O$-$C)$_I$, (O$-$C)$_{II}$ and (O$-$C)$_{III}$
have been calculated according to Williamon's (1974) ephemeris formula:
\vskip 1mm
\centerline{Min I = 2441141.8888 + 0\fd 62892984 $\times$ E}
\vskip 1mm         
\noindent Kholopov's (1985):
\vskip 1mm
\centerline{Min I = 2241141.88902 + 0\fd 628929513$\times$ E}
\vskip 1mm

\noindent and our new one, given by equation (1), respectively.
They are the mean values of our B and V observations and have
been computed using Kwee \& Van Woerden's (1956) method.


{\bf 44i Bootis}

 The eclipsing binary 44i Boo is the fainter companion (B+C)
of the close visual binary ADS 9494.  It is one of the mostly
observed systems, since its light curves exhibit ``active" and
``quiet" periods and its period is variable (e.g. Bergeat et al.,
1972; Rovithis et al., 1990; Oprescu et al., 1989 \& 1991;
Gherega et al., 1994).

From our recent photoelectric observations of 44i Boo, two
new minima times have been found and given in Table II.
\vskip 1mm
\centerline{Table II. Photoelectric Minima Times of 44i Boo}
\vskip 1mm
\begin{center}
\begin{tabular}{cccccc}
\hline 
 Hel. JD    &   Min & Fil.&(O$-$C)$_I$ & (O$-$C)$_{II}$ & (O$-$C)$_{III}$\\
 2440000+  &       &     & days  &   days  &   days\\
 \hline  
 9489.3479  &    I   &  V  &  0.0393   &  0.0028 &   $-$0.0173\\
 9489.3490  &    I   &  B   & 0.0414   & 0.0039  &  $-$0.0162\\
 9489.4832  &    II  &  V   & 0.0407   &  0.0042  &  $-$0.0159\\
 9489.4825  &    II  &  B   & 0.0400   &  0.0035  &  $-$0.0166\\
\hline
\end{tabular}
\end{center}
\vskip 1mm        

In Table II the residuals (O$-$C)$_I$, (O$-$C)$_{II}$ and (O$-$C)$_{III}$ have been
calculated using Kwee \& Van Woerden's method (1956) and according
to the following ephemeris formulae:
\vskip 1mm
\centerline{Min I = 2439852.4903 + 0\fd 2678159 $\times$ E}
\centerline{(Duerbeck, 1975)}

\vfill \eject

\centerline{3}
\vskip 1mm 
\centerline{Min I = 2439852.4644 + 0\fd 2678176 $\times$E}
\centerline{(Rovithis et al., 1990)}
         and
\centerline{Min I = 2443604.5880 + 0\fd 26781856 $\times$ E}
\centerline{(Oprescu et al., 1991)}
\vskip 2mm

\noindent They fit pretty well the last (O$-$C) diagram for 44i Bootis
(Gherega et al., 1994) -- based on Oprescu's et al. (1991) ephemeris
formula -- showing that the period of the system continues
to increase.

      
{\bf GO Cygni}

The eclipsing binary GO Cyg (BD +34\degr 4095) has been observed
photoelectrically many times after its discovery and many minima
times can been found in the literature from which 
its period was found to be variable (e.g. Purgathofer and Prochazka,
1967; Sezer et al. 1985, Hall and Louth, 1990).

From our recent observations of GO Cyg three new minima
times were derived and are presented in Table III.
\vskip 1mm
\centerline{Table III. Photoelectric Minima Times of GO Cyg}
\vskip 1mm
\begin{center}
\begin{tabular}{cccccc}
\hline
 Hel. JD  &Min  & Fil.&(O$-$C)$_I$& (O$-$C)$_{II}$&(O$-$C)$_{III}$\\
2440000+ &     &     &  days    &          days  &   days\\
\hline
\\
        9605.34526   & II &    B &   0.0546 &    0.0143 &    0.0377\\
        9605.34585   & II &    V &   0.0552 &    0.0149 &   0.0383\\
        9623.29007   & II &    V &   0.0555 &    0.0149 &    0.0386\\
 \hline
\end{tabular}
\end{center}
\vskip 2mm

\noindent In Table III the residuals (O$-$C)$_I$, (O$-$C)$_{II}$ and (O$-$C)$_{III}$ have been
calculated using Kwee \& Van Woerden's method (1956) and
 according to formulae:
\vskip 1mm
\centerline{Min I = 2433930.40561+ 0\fd 71776382 $\times$ E}                     \centerline{(Kholopov, 1985)}
\vskip 1mm
\centerline{Min I = 2445865.4056 + 0\fd 71776707$\times$ E}
\centerline{(Sezer et al., 1985)}
and

\centerline{Min I = 2446351.328 + 0\fd 7177632 $\times$ E}
\centerline{(SAC, 1989)}

The newly observed minima times are in accordance with the O$-$C
diagram of GO Cyg (Sezer et al., 1985) showing that the period
of the system continues increasing.  A detailed analysis of the
period variations of GO Cyg -- based on the new method developed
by Kalimeris et al., (1994) -- will be done later.


Acknowledgement: This work was partly supported by NATO, grant
No.\,921208/1993.
\vskip 1cm

\beginauthors
H. ROVITHIS-LIVANIOU            
P. ROVITHIS                   
Section of Astrophysics        
Astronomy \& Mechanics            
Dept. of Physics                
Athens University                
157 84 Zografos                  
Greece
\authorsrightcol
 G. OPRESCU
A. DUMITRESCU
Astronomical Institute
Academia Romana
Street Cutitul d'Argint 5
75212 Bucharest 28
Romania
\vskip 6mm
\endauthors                                 
\vfill \eject

\centerline{4}
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\references

 Bergeat J., Lunel M., Sibile F. \& Van't Veer F.: 1972, {\it A\&A}, {\bf 17}, 215

 Budding E. \& Zeilik M.: 1987, {\it ApJ}, {\bf 319}, 827

 Duerbeck H. W.: 1975, {\it IBVS}, No.\,1023

 Gherega O., Farkas L. and Horvath A.: 1994, {\it IBVS}, No.\,4045

 Hall D. and Louth H.: 1990, {\it J. A\&A}, {\bf 11}, 271

 Hardie R. H.: 1962, in W.A. Hiltner (Ed.) Stars and Stellar
 Systems Vol. II, Astronomical Techniques, The University
 of Chicago Press, Chicago

 Kalimeris A., Rovithis-Livaniou H. \& Rovithis P.: 1994, {\it A\&A}, {\bf 82},
  775

 Kholopov P.N.: 1985, General Cataloque of Variable Stars, Moscow

 Kwee K.K. \& Van Woerden H.: 1956, {\it Bull. A. I. Neth.}, {\bf 12}, 327

 Oprescu G., Suran M.D. \& Popescu N.: 1989, {\it IBVS}, No.\,3368

 Oprescu G., Suran M.D. \& Popescu N.: 1991, {\it IBVS}, No.\,3560

 Purgathofer A. \& Prochazka F.: 1967, {\it Mitt. Un. Stern Wien}, {\bf 13}, 151

 Rovithis P. \& Rovithis-Livaniou, H.: 1990, {\it A\&ASS}, {\bf 86}, 523

 Rovithis-Livaniou H., Rovithis P., Kalimeris A., Oprescu G., 
 Dumitrescu A. \& Suran M.D.: 1994, {\it Rom. Astron. J.} (in press)

 SAC 1989: Rocznik Astronomiczny Observatorium Krakowskiego, No.\,60

 Sezer C., G\"ulmen O. \& G\"ud\"ur N.: 1985, {\it IBVS}, No.\,2743

 Williamon R.M.: 1974, {\it PASP}, {\bf 86}, 924
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