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\IBVShead{4144}{12 January 1995}                      % Use it with dummy or empty arguments

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\title{AW VIRGINIS: PHOTOELECTRIC TIMES}
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\title{OF MINIMUM AND IMPROVED PERIOD}

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The variable star AW Virginis ($\alpha$=13\fh 25\fm 0, 
$\delta$=+03\degr 10\farcm 0; 1950.0) was discovered by Hoffmeister (1935).
Jensch (1935) classified this star as a W UMa type system based on the first
photographic light curve. He also obtained fourteen times of minimum light
and derived the following ephemeris:
\vskip 1mm
\hspace*{35mm}Min I=J.D.hel.\,2427871.495+0\fd 353998$\times$E \hfill(1)
\vskip 1mm
Whitney (1955) and Koch (1961) published photographic times of minimum light and
the first author calculated an orbital period of P=0.3539968 days. More recently,
Hoffmann (1983) determined two additional photoelectric times of minimum.

Figure 1 shows the BV light curves obtained in April 1988 at Las Campanas
(Chile) with the 60 cm telescope of the David Dunlap Observatory and in
March 1989 at the Complejo Astronomico El Leoncito --CASLEO-- (San Juan, Argentina).
An RCA 1P21 photomultiplier refrigerated by dry ice, and a photon-counting
system were used in the first case and the Vatican Observatory photo-polarimeter
VATPOL (Magalh\~{a}es et al., 1984) with two dry-ice cooled RCA\,31034 Ga-As
photomultipliers were employed in the second.

The measurements were made differentially with respect to a comparison star.
No variation in the light of this star was detected. All the observations
were corrected for first and second order differential extinction. As the
comparison is located very near to the variable the corrections were small.
Absolute photometry of the comparison star allowed to determine a V$_{max}$=10.93
for the variable star.

A total of 608 observations in each BV passband were obtained. These observations
well cover the orbital period and show minima of approximately the same depth
of $\sim$ 0.7 mag (see Figure 1). From these measurements we determined 17 times 
of minimum light (9 times of primary minimum and 8 times of secondary minimum)
using the bisection-of-chords method. A linear least squares fit to our
photometric data yields an updated ephemeris:
\vskip 1mm
\hspace*{35mm}Min I=J.D.hel.\,2447269.82175 + 0\fd 35399736$\times$E \hfill(2)
\hspace*{7.6cm}$\pm$0.00012\,\ \ $\pm$0.00000029
\vskip 1mm
We compiled all the previously determined times of minimum as well as those 
reported is this note. Using a linear least squares solution we derived an
improved ephemeris:
\vskip 1mm
\hspace*{35mm}Min I=J.D.hel.\,2447269.82135 + 0\fd 353997025$\times$E \hfill(3)
\hspace*{7.6cm}$\pm$0.00016\,\ \ $\pm$0.000000046
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\centerline{2}
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\centerline{Figure 1}
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\centerline{Figure 2}
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Table 1. Photoelectric times of minimum light of AW Virginis
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\begin{tabular}{ccrrrc}
\hline
Min.&JDhel.&E\ \ \ \ &(O$-$C)$_{(3)}$&(O$-$C)$_{(2)}$&reference\\
    &2400000.+& & & & \\
\hline
\\
II&25680.429&$-$60987.5&0.001& &(1)\\
I&25735.468&$-$60832.0&$-$0.006& &(1)\\
II&26363.652&$-$59057.5&0.010& &(1)\\
II&26771.459&$-$57905.5&0.012& &(1)\\
II&27155.522&$-$56820.5&$-$0.011& &(1)\\
I&27180.472&$-$56750.0&$-$0.018& &(1)\\
I&27191.465&$-$56719.0&0.001& &(1)\\
I&27539.466&$-$55736.0&0.023& &(1)\\
II&27543.498&$-$55724.5&$-$0.016& &(1)\\
I&27573.427&$-$55640.0&0.000& &(1)\\
I&27866.541&$-$54812.0&0.005& &(1)\\
I&27871.493&$-$54798.0&0.001& &(1)\\
I&27873.619&$-$54792.0&0.003& &(1)\\
I&27874.674&$-$54789.0&$-$0.004& &(1)\\
I&34425.385&$-$36284.0&$-$0.008& &(2)\\
I&34750.716&$-$35365.0&$-$0.001& &(2)\\
I&34886.711&$-$34981.0&0.060& &(3)\\
II&45002.645&$-$6404.5&$-$0.002& &(4)\\
I&45022.645&$-$6348.0&$-$0.003& &(4)\\
I&47257.7843&$-$34.0&$-$0.0011&$-$0.0016&(5)\\
I&47257.7855&$-$34.0&0.0001&$-$0.0003&(5)\\
II&47259.7330&$-$28.5&0.0006&0.0001&(5)\\
II&47259.7331&$-$28.5&0.0007&0.0003&(5)\\
II&47259.7332&$-$28.5&0.0008&0.0004&(5)\\
I&47268.7593&$-$3.0&$-$0.0000&$-$0.0004&(5)\\
I&47268.7597&$-$3.0&0.0004&$-$0.0000&(5)\\
II&47269.6447&$-$0.5&0.0004&$-$0.0000&(5)\\
II&47269.6451&$-$0.5&0.0008&0.0003&(5)\\
I&47269.8224&0.0&0.0011&0.0006&(5)\\
I&47269.8224&0.0&0.0011&0.0006&(5)\\
II&47270.7068&2.5&0.0005&0.0001&(5)\\
II&47270.7070&2.5&0.0007&0.0003&(5)\\
II&47270.7064&2.5&0.0001&$-$0.0003&(5)\\
I&47615.6770&977.0&0.0006&$-$0.0002&(5)\\
I&47615.6773&977.0&0.0009&0.0001&(5)\\
I&47615.6772&977.0&0.0008&0.0000&(5)\\
\hline
\end{tabular}
\end{center}
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\noindent Note: (1) Jensch (1935); (2) Whitney (1955); (3) Koch (1961); (4)
Hoffmann; (5) this note.
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Table 1 lists all the times of minimum light used to derive equation (3).
The columns give: the Julian date corresponding to each minimum, the epoch
number, and the (O$-$C) residuals calculated from equation (3). For the
new times of minimum light we included the residuals derived from equation (2).
Figure 2 shows the (O$-$C) vs E diagram corresponding to equation (3).
The residuals are, in general, randomly distributed and except for one
minimum (Koch, 1961) the amplitude of the dispersion is of $\sim$0.002 days.
According to the precision of the ephemerides the orbital period of the
system seems to have remained practically constant over the last $\sim$50
years. However, additional times of minimum distributed on a longer time base 
are needed to confirm this preliminary result.
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% Call for macros \authors - \authorsrightcol - \endauthors
\beginauthors
\authorsrightcol
E. LAPASSET and
M. G\'OMEZ
Observatorio Astron\'omico
Universidad Nacional de C\'ordoba
Laprida 854, 5000 C\'ordoba
Argentina
\endauthors

% Call for macro \references
\references

Hoffmann, M., 1983, {\it Inf. Bull. Var. Stars}, No.\,2344

Hoffmeister, C., 1935, {\it Astronomische Nachrichten}, {\bf 255}, 401

Jensch, A., 1935, {\it Astronomische Nachrichten}, {\bf 256}, 279

Koch, R. H., 1961, {\it AJ}, {\bf 66}, 35

Magalh\~{a}es, A. M., Benedetti E., and Roland, E. H., 1984, {\it PASP},
{\bf 96}, 383

Whitney, B. S., 1955, {\it AJ}, {\bf 60}, 453

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