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\IBVShead{4272}{28 November 1995}

\centerline{\ft IMPROVED EPHEMERIS AND PHOTOMETRIC ELEMENTS}
\centerline{\ft FOR HY VIRGINIS}
\vskip 8mm

\begintext

HY Vir (SAO \,139174, HD\,114125, BD $-$1\degr 2777) was originally announced 
as a variable star by Rodriguez et al. (1988). Additional observations carried 
out at Observatorio del Teide (Instituto de Astrofisica de Canarias) by 
Casas and Gomez-Forrellad (1989) confirmed the variable nature of HY Vir. 
They also showed that the star is a detached eclipsing binary system and 
gave the following preliminary ephemeris:

\vskip 1mm
\centerline{HJD Min.\,I = 2447240.97128 + 2\fd 73236 $\times$ E}
\hspace*{7cm}$\pm$0.00006 $\pm$0.00002
\vskip 1mm

This ephemeris and the original physical elements were obtained during a 
short time interval and from a reduced number of minimum timings. As a 
consequence, they could be affected by inaccuracies. To test the above 
mentioned ephemeris and elements, we observed HY Vir during several nights 
in April 1995 using the 0.4-m telescope at Observatorio de Mollet equipped 
with a LYNXX-2 CCD camera at and the 0.4-m telescope in conjunction with a 
ST-4 CCD camera at Observatorio de Monegrillo (Spain). Both CCD cameras 
were operated in the V band. HY Vir is also a visual binary (South 647). 
The optical companion (PPM\,178970, AGK3 $-$02\degr 0782) was used as the 
comparison star.

From the original set of data obtained in 1989 and the new data gathered 
now, we computed a list of O$-$C residuals for one Min.I and three Min.II. 
Times of minima were derived using the Sliding Integration Method 
(Ghedini, 1982). Table 1 summarizes the resulting O$-$C values.
\vskip 1mm
\centerline{Table 1}
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\begin{center}
\begin{tabular}{lcrr}
\hline
       HJD\,2440000+ &  Minimum &      Epoch& O$-$C\\
\hline
       7239.6051  &      II &         $-$0.5&      0.0000\ \ \\
       7627.60069 &      II &        141.5  &   +0.00047\\
       9813.47041 &      II &        941.5  &   $-$0.01781\\
       9817.56624 &       I &        943.0  &   $-$0.02052\\
\hline
\end{tabular}
\end{center}
\vskip 2mm
After performing a least-squares linear fit on the O$-$C residuals we found 
the following improved ephemeris for HY Vir:
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\centerline{HJD Min.\,I = 2447240.96964 + 2\fd 732338 $\times$ E}
\hspace*{7cm}$\pm$0.00009 $\pm$0.000002
\vskip 1mm
Although the observed minima during 1995 clearly indicate a shorter period 
for HY Vir, it is still too early to discern whether it is due to a lack 
of accuracy in the initial period estimate or true period changes. Therefore
more timings of minima are needed.

\vfill \eject

\centerline{2}
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\centerline{\epsffile{4272-f1.ps}}
\centerline{Figure 1. Synthetic light curve superimposed to observations.}

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\centerline{\epsffile{4272-f2.ps}}
\begin{center}
Figure 2. Computed residuals after subtracting the synthetic light curve 
from observations. Vertical scale is in magnitudes
\end{center}
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\centerline{Table 2}
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\begin{center}
\begin{tabular}{rcl}
\hline
 & & \\                             
mass ratio& = &  0.95 $\pm$0.05\\
         i& = & 80\fdg 6 $\pm$0\fdg 1\\
\end{tabular}
\end{center}
\begin{center}
\begin{tabular}{cc}
\hline           
           a$_g$ = 0.230 $\pm$0.005  &   a$_s$ = 0.140 $\pm$0.005\\
           b$_g$ = 0.227 $\pm$0.004  &   b$_s$ = 0.139 $\pm$0.005\\
           c$_g$ = 0.224 $\pm$0.004  &   c$_s$ = 0.139 $\pm$0.005\\
           d$_g$ = 0.231 $\pm$0.006  &   d$_s$ = 0.140 $\pm$0.005\\
               g$_1$ = 0.32          &     g$_2$ = 0.32\\
               x$_1$ = 0.60          &     x$_2$ = 0.60\\
               A$_1$ = 0.5           &     A$_2$ = 0.5\\
           T$_1$ = 7200K $\pm$40K    &   T$_2$ = 6900K $\pm$20K\\
           L$_1$ = 0.76 $\pm$0.01    &   L$_2$ = 0.24 $\pm$0.01\\
\hline
\end{tabular}
\end{center}

\vfill \eject

\centerline{3}
\vskip 1mm
Also, from the original photoelectric observations obtained in 1989, we 
derived new physical elements using Binary Maker 2.0 (Bradstreet, 1993), 
based on a preliminary set of elements computed by Alvaro Gimenez and Casas 
(1990) who used the computer program EBOP developed by Etzel (Popper, 1984). 
Taking into account that the combined spectrum of the system is F2V, the 
values of 0.32, 0.6 and 0.5 were assumed for the gravity darkening, limb 
darkening, and reflection coefficients respectively (Figure~1). Table 2 
summarizes these results.


In Figure 2 residuals are depicted after subtracting the synthetic light 
curve from the photometric observations. 
\vskip 1cm

\beginauthors
\authorsrightcol
Enrique GARCIA-MELENDO
Josep M. GOMEZ-FORRELLAD
Joaquin VIDAL-SAINZ
Grup d'Estudis Astronomics
Apartado 9481
08080 Barcelona
Spain
e-mail: jmgomez@astro.gea.cesca.es
\endauthors

\references

Bradstreet, D. H., 1993, Binary Maker 2.0 User Manual, Contact Software,
	Norristown, Pennsylvania

Casas, R., and Gomez-Forrellad, J. M., 1989, {\it IBVS}, No.\,3337

Casas, R., 1990, Private communication

Ghedini S., 1982, Software for Photometric Astronomy, Willmann-Bell Inc.,
	Richmond, Virginia

Popper, D. M., 1984, {\it Astron. J.}, {\bf 89}, 132

Rodriguez, E., Sedano, J.L., Lopez de Coca, P., and Rolland, A., 1988,
	{\it IBVS}, No.\,3174

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