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\begin{document}

\IBVShead{4643}{27 October 1998}

\IBVStitletl{V842 S\lowercase{co}: PHOTOELECTRIC TIMES OF MINIMA}{ AND A PERIOD STUDY}

\IBVSauth{Miguel Angel CERRUTI}

\IBVSinsto{IAFE, CC 67 - Suc 28, 1428 Buenos Aires, Argentina, e-mail: miguelan@iafe.uba.ar}

\IBVSabs{The period for V842 Sco has remained constant from the epoch}
\IBVSabs{of the discovery, during about 40000 cycles}
\SIMBADobj{V842 Sco}
\IBVStyp{ EW/KW }
\IBVSkey{photometry}

\begintext

We present here the first photoelectric determinations of minima of the
eclipsing binary V842 Sco = GSC\,7898:1918 = CoD\,$-$43\deg12132. The other
minima are photographic (Kooreman 1966).
The observations were made during two runs both from Cerro Tololo Inter-American
Observatory\footnote{Operated by AURA Inc.\ under cooperative agreement
with the NSF} in Chile and with the Lowell telescope and single-channel 
photon counting techniques and standard UBV filters. In 1982 a refrigerated phototube EMI 2070 was used while in 1995 a refrigerated phototube RCA 31034A
was utilised. GSC\,7898:1728 served as the comparison and GSC\,7898:1382
= HD 163046(A0V) as the check.
Although the light curve is not complete, eclipses are of almost equal
depth viz.\ A$_{V_{Min{ }I}}$=0.20--0.66 while A$_{V_{Min{ }II}}$=0.20--0.64 so the system displays
a W UMa light curve. This can be inferred from the partial light curves displayed
into Figure 1.

The resulting times of minima were determined by the polynomial 
line method (Guar\-nie\-ri et al.\ 1975, Ghedini 1982) and are the last entries
in Table 1. Also, included in this table are the 
photographically determined times of minima.
The dispersion for each minimum is 
in  brackets following the minimum itself; for the photographic minima,
the dispersion was estimated from a linear solution with equal weights,
we assign a dispersion
of 0.015 to all these minima. The Table also contains the associated 
cycle number, E, and in the last column the corresponding residual, O$-$C.
We made a least square weighted linear solution taking into account all 
available
minima to derive an improved ephemeris and a possible period variation.
\begin{equation}
\begin{array}{r@{}r@{}l}
{\rm Min~I = HJD}~2431233.5446 &{} + 0\fday498284426 &{} \times E        \\
{} \pm 0\fday0031 &{} \pm 0\fday000000098 & {~\rm m.e.}\\
\end{array}
\end{equation}

We  conclude that the period has not changed significantly  over the 
40000 revolutions (cycles) covered by the available observations, a fact
that is very scarce in systems displaying a W UMa light curve. 
The behaviour of the O$-$C residuals are depicted in Figure~2.

The author would like to thank the staff 
and Director of CTIO for their hospitality.

\vfill\eject

\begin{table}
\caption{Times of minima and residuals for V842 Sco}
\begin{center}
\begin{tabular}{|c|c|c|r|r|r|}
\hline
Ref. & Min. & Band &  HJD 2400000+ (sigma) &\multicolumn{1}{c|}{E} & \multicolumn{1}{c|}{O$-$C} \\
\hline
  1 & I  & pg.        &  29794.4960(0.0150) & $-$2888.0 & $-$0.0032  \\
  1 & I  & pg.        &  29794.5180(0.0150) & $-$2888.0 &  0.0188  \\
  1 & I  & pg.        &  29813.4180(0.0150) & $-$2850.0 & $-$0.0160  \\
  1 & I  & pg.        &  29816.4300(0.0150) & $-$2844.0 &  0.0063  \\
  1 & II & pg.        &  30149.5230(0.0150) & $-$2175.5 & $-$0.0039  \\
  1 & II & pg.        &  30149.5450(0.0150) & $-$2175.5 &  0.0181  \\
  1 & II & pg.        &  30218.2930(0.0150) & $-$2037.5 &  0.0029  \\
  1 & I  & pg.        &  30286.3070(0.0150) & $-$1901.0 &  0.0011  \\
  1 & I  & pg.        &  30557.3690(0.0150) & $-$1357.0 & $-$0.0037  \\
  1 & I  & pg.        &  30559.3830(0.0150) & $-$1353.0 &  0.0172  \\
  1 & I  & pg.        &  30574.3090(0.0150) & $-$1323.0 & $-$0.0053  \\
  1 & I  & pg.        &  30574.3300(0.0150) & $-$1323.0 &  0.0157  \\
  1 & I  & pg.        &  31233.5600(0.0150) &      0.0 &  0.0154  \\
  1 & I  & pg.        &  31287.3350(0.0150) &    108.0 & $-$0.0243  \\
  1 & I  & pg.        &  31287.3570(0.0150) &    108.0 & $-$0.0023  \\
  1 & I  & pg.        &  31288.3660(0.0150) &    110.0 &  0.0101  \\
  1 & I  & pg.        &  31292.3060(0.0150) &    118.0 & $-$0.0362  \\
  1 & I  & pg.        &  31292.3710(0.0150) &    118.0 &  0.0288  \\
  1 & I  & pg.        &  31312.2560(0.0150) &    158.0 & $-$0.0176  \\
  1 & I  & pg.        &  31312.2780(0.0150) &    158.0 &  0.0044  \\
  1 & I  & pg.        &  31318.2680(0.0150) &    170.0 &  0.0150  \\
  1 & I  & pg.        &  31321.2560(0.0150) &    176.0 &  0.0133  \\
  1 & II & pg.        &  31325.4540(0.0150) &    184.5 & $-$0.0241  \\
  1 & II & pg.        &  31371.2670(0.0150) &    276.5 & $-$0.0533  \\
  1 & II & pg.        &  31371.2880(0.0150) &    276.5 & $-$0.0323  \\
  1 & II & pg.        &  31668.3010(0.0150) &    872.5 &  0.0032  \\
  1 & II & pg.        &  31669.3370(0.0150) &    874.5 &  0.0426  \\
  1 & II & pg.        &  31670.2740(0.0150) &    876.5 & $-$0.0169  \\
  1 & II & pg.        &  31672.3030(0.0150) &    880.5 &  0.0189  \\
  1 & I  & pg.        &  33411.5240(0.0150) &   4371.0 & $-$0.0219  \\
  1 & I  & pg.        &  33411.5350(0.0150) &   4371.0 & $-$0.0109  \\
  1 & I  & pg.        &  33411.5490(0.0150) &   4371.0 &  0.0031  \\
  2 & II & U          &  45222.6313(0.0014) &  28074.5 &  0.0006  \\
  2 & II & B          &  45222.6331(0.0018) &  28074.5 &  0.0024  \\
  2 & II & V          &  45222.6330(0.0011) &  28074.5 &  0.0023  \\
  2 & II & U          &  45232.5968(0.0010) &  28094.5 &  0.0004  \\
  2 & II & B          &  45232.6004(0.0012) &  28094.5 &  0.0040  \\
  2 & II & V          &  45232.5981(0.0019) &  28094.5 &  0.0017  \\
  3 & I  & U          &  49947.6142(0.0005) &  37557.0 &  0.0014  \\
  3 & I  & B          &  49947.6124(0.0009) &  37557.0 & $-$0.0004  \\
  3 & I  & V          &  49947.6079(0.0014) &  37557.0 & $-$0.0049  \\
  3 & I  & U          &  49949.6026(0.0007) &  37561.0 & $-$0.0033  \\
  3 & I  & B          &  49949.6088(0.0018) &  37561.0 &  0.0029  \\
  3 & I  & V          &  49949.6040(0.0013) &  37561.0 & $-$0.0019  \\
\hline
\end{tabular}
\begin{tabular}{c}
References: 1) Kooreman; 2) Cerruti 1982 present paper;\\
3) Cerruti 1995 present paper.\\
\end{tabular}
\end{center}
\end{table}



\IBVSfig{9.0cm}{4643-f1.ps}{The partial light curves for V842 Sco. The vertical
scale is for the visual differential magnitude.}

\IBVSfig{7.0cm}{4643-f2.ps}{Behavior 
of the O$-$C residuals for V842 Sco from Eq.\ (1). Hollow
circles stand for primary minima, vertical bars are for errors}

\vfill\eject

\references

Ghedini S. 1982, {\it Software for Photometric Astronomy}, 
Willman-Bell Inc.\ Press, Richmond, p.\ 59.

Guarnieri A., Bonifazi A., Battistini P. 1975, {\it Astron.\ Astrophys.\ 
Suppl.}, {\bf 20}, 199.

Kooreman C.J. 1966, {\it Leiden Ann.}, {\bf XXII}, No 5, 159.

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