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\IBVShead{4412}{19 December 1996}

\centerline{\ft NEW VARIABLES IN THE FIELD OF  RE J0725-002} 
\vskip 8mm

\begintext

The sky was surveyed in the extreme ultraviolet (EUV) region of the
spectrum by the EUVE satellite (Malina et al., 1994) and the ROSAT
satellite (Pounds et al.  1993) and catalogs of the sources included RE
J0725-002 = EUVE J0725-00.4 = BD $-$00\degr 1712 = GSC\,4817\_468.  The star was
one of the subjects of an investigation by Jeffries (1995), who
concluded from spectral observations that it was a pair of nearly identical 
K5 dwarf stars orbiting with a 1\fd40 period. 

The automated 0.5-m.  telescope, Cousins R filter and CCD camera of the
Climenhaga Observatory of the University of Victoria (Robb and Honkanen,
1992) were used to make photometric observations of RE J0725-002.  Using 
IRAF \footnote{IRAF is distributed by National Optical
Astronomy Observatories, which is operated by the Association of
Universities for Research in Astronomy, Inc., under contract to the
National Science Foundation} routines the frames were de-biased and 
flat fielded, and the magnitudes were found from 5 arc
second aperture photometry after using the Gaussian centering option of
the PHOT package. 

The field of stars we observed is shown in Figure 1 and 
their designations, coordinates (J2000) and magnitudes from
the Hubble Space Telescope Guide Star Catalog (GSC) (Jenkner et al., 1990) 
and the $\Delta$R magnitudes are tabulated in Table 1.  
The $\Delta$R differences in magnitude are found from our data in the
sense of the star minus GSC\,4817\_386.  The standard deviation of
the differences during a night ranged from 0\fm 006 for a bright star on
a good night to 0\fm030 for the faint stars on poor nights.  The
$\Delta$R magnitude given in the table is the mean 
of the thirteen nightly mean differential magnitudes and 
the standard deviations measure night to night variations.
The stars 4817\_468 and 4817\_788 have large standard deviations and 
are variable from night to night.   
Due to the small field of view extinction effects were
negligible and no corrections have been made for them.  No corrections
have been made to transform the R magnitude to a standard system. 

Photometric observations were made from 25 February to 25 March 1996 UT. 
Brightness variations in RE J0725-002
were evident both during a night
and from night to night.  A least squares fit of a single sine wave to
the data shows a deep minimum in $\chi^{2}$ at a period of 1\fd404.
A period finding routine based on that of Jurkevich (1971) found the
best period to be 1\fd412.
Two other possible periods are rendered less likely by
the spectral observations (Jeffries 1995);
namely 0\fd5836, which is a one cycle per day alias,
and 2\fd824, which is twice the adopted period.

So in agreement with Jeffries (1995) the best ephemeris from our data is:
\vskip 1mm
\centerline{HJD of Minima = 2450137\fd46 + 1\fd412 $\times$ E}
\hspace*{8.0cm}$\pm$\fd10\ \ \,$\pm$0\fd024
\vskip 1mm

A plot of the 1051 differential R magnitudes phased at this period is
shown in Figure 2 with different symbols for each of the different nights.  
While the light curve does show a possible ``primary eclipse'' the lack of a
corresponding secondary eclipse leads us to believe that this is not
an eclipsing system; a possibility suggested by Jeffries (1995). 
We suspect\vfill \eject
\centerline{2}
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\centerline{Table 1. Stars observed in the field of RE J0725-002}
\begin{center}
\begin{tabular}{ccccc} \hline \hline
 GSC No. & RA  & Dec. & GSC & $\Delta$R \\
         &  J2000.   &      J2000.    &  Mag.       &  Mag.  \\ 
\hline \\
4817\_468 & 07\fh25\fmm14\fs  & $-$00\degr25\farcmm 39\farcss&  10.2 &$-$1.698 $\pm$ .034 \\
4817\_788 & 07\fh25\fmm05\fs  & $-$00\degr24\farcmm24\farcss &  12.4 & $-$0.767 $\pm$ .130\\
4817\_386 & 07\fh25\fmm15\fs  & $-$00\degr27\farcmm42\farcss &  10.5 & --   \\
4817\_508 & 07\fh24\fmm59\fs  & $-$00\degr24\farcmm44\farcss &  13.9 & +2.298 $\pm$ .013\\
4817\_1294& 07\fh25\fmm02\fs  & $-$00\degr24\farcmm55\farcss &  12.7 & +1.780 $\pm$ .010 \\
4817\_904 & 07\fh25\fmm22\fs  & $-$00\degr24\farcmm29\farcss &  13.1 & +1.923 $\pm$ .009 \\
4817\_1422& 07\fh25\fmm07\fs  & $-$00\degr24\farcmm21\farcss &  13.9 & +2.862 $\pm$ .018 \\ \hline
\end{tabular}
\end{center}


\vskip -5mm
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\begin{center}
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Figure 1.  Finder chart of the field labeled with the GSC 
numbers (Jenkner et al., 1990)
\end{center}

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\centerline{\epsffile{4412-f2.ps}}
\begin{center}
Figure 2.  Light curve of the differential R data of RE J0725-002 for 1996
\end{center}

\vfill \eject

\centerline{3}
\vskip 1mm
\centerline{Table 2. Differential observations of GSC\,4817\_788}
\normalsize
\begin{center}
\begin{tabular}{ccccccccccc} \hline \hline
 HJD & $\Delta$R && HJD & $\Delta$R && HJD & $\Delta$R && HJD & $\Delta$R\\
\hline \\
2450138.7 &$-$0.627 && 2450145.7 &$-$0.646 && 2450156.7 &$-$0.803 &&2450165.7 &$-$0.917 \\
2450142.8 &$-$0.619 && 2450148.6 &$-$0.677 && 2450160.8 &$-$0.870 &&2450166.7 &$-$0.928 \\
2450143.8 &$-$0.638 && 2450154.7 &$-$0.788 && 2450162.7 &$-$0.887 &&2450167.7 &$-$0.938 \\ 
2450144.7 &$-$0.636 \\
\hline
\end{tabular}
\end{center}
\large
\vskip 2mm
\noindent that one or both stars have large active regions on them causing 
the brightness variations and the large EUV emission.  
The light curve does show shifts of a few hundredths of a magnitude 
in mean level from night to night, likely due to differential rotation or
active region evolution and could be studied by further photometric 
observations. 


As a possible comparison star
GSC\,4817\_788 was monitored but was found to vary
from night to night.  The differential R magnitudes are given in Table
2.  The star was at maximum brightness on approximately HJD 2450142 and
decreased in brightness at roughly 0\fm01 per day during our observations.



The star GSC 4817\_508 was also found to vary in
brightness during a night.  Using a period finding
routine based on that of Jurkevich (1971) our best estimate is 3.465
cycles per day. Using the method of Kwee and Van Woerden (1956),
Heliocentric Julian dates of primary minimum were found to be 
2450144.6908 and 2450154.7935 and times of secondary minimum were
2450142.8352, 2450145.7157 and 2450156.6867. The precision of the minima
determinations were nominally $\pm0\fd0010$, but this does not include 
an allowance for the asymmetry of the minima.
In Figure 3 the data are plotted as a function of phase 
according to the ephemeris:

\centerline{HJD of Minima = 2450138\fd64 + 0\fd2886 $\times$ E}
\hspace*{8.0cm}$\pm$\fd10\,$\pm$\ 0\fd0005


\epsfysize=9cm
\centerline{\epsffile{4412-f3.ps}}
\begin{center}
Figure 3. Light curve of the differential R data of GSC\,4817\_508 for 1996
\end{center}
\vfill\eject

\centerline{4}
\vskip 1mm

To help classify the two serendipitously discovered variable stars 
color information was sought.  Unfortunately only a V frame and an I frame
were obtained under non-photometric conditions.  
While not definitive they are indicative of the type of stars.  
Assuming RE J0725-002 has the V$-$I of a normal K5V 
(Jeffries 1995), then GSC\,4817\_788 is an extremely late M star and 
GSC\,4817\_508 has the color of approximately an early K star.
Therefore GSC\,4817\_788 is likely a long period or irregular variable
and GSC\,4817\_508 is most likely an ellipsoidal or eclipsing binary 
and not a Delta Scuti
type star.  The shape of the light curve, small amplitude and difference 
in maxima are consistent with a W UMa star seen with a small inclination.

Further photometric and spectroscopic observations 
will be valuable to confirm our conclusions as to the reason for the 
variability of these stars.


\vskip 1cm

\beginauthors
\authorsrightcol
R.M. ROBB
M.D. GLADDERS
Climenhaga Observatory 
Dept. of Physics and Astronomy
University of Victoria
Victoria, BC, CANADA,  V8W 3P6
Internet: robb@uvastro.phys.uvic.ca
Internet: gladders@astro.utoronto.ca
\endauthors

\references

Jeffries, R. D., 1995, {\it MNRAS}, {\bf 276}, 397

Jenkner, H., Lasker, B., Sturch, C. McLean, B., Shara, M., Russell, J., 1990, 
{\it AJ}, {\bf 99}, 2082

Jurkevich, I., 1971, {\it Ap.\&Sp. Sci.}, {\bf 13}, 154
  
Kwee, K.K. and Van Woerden, H., 1956, Bull. Astr. Inst. Neth., {\bf 12}, 327

Malina, R. F., et al., 1994, {\it AJ}, {\bf 107}, 751

Pounds, K.  A., et al., 1993, {\it MNRAS}, {\bf 260}, 77
 
Robb, R. M.  and Honkanen, N.  N., 1992, {\it A.S.P. Conf. Ser.}, {\bf 28}, 105,
Automated Telescopes for Photometry and Imaging, ed.  Adelman, Dukes and
Adelman
%Original: {\it A.S.P. Conf. Ser.}, {\bf 38},
%Corrected: Tue Sep 27 09:13:06 MEST 2005
 
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