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\IBVShead{4796}{9 November 1999}

\IBVStitle{Reduced Amplitude of V959 Ophiuchi}

\IBVSauth{Eric G. Hintz, Maureen L. Hintz, Michael D. Joner, and Lisa A. Joner}

\IBVSinsto{Brigham Young University, Dept.\ of Physics \& Astronomy, Provo, Utah, 84602, USA \\ \indent e-mail: doctor@shapley.byu.edu, romana@tardis.byu.edu, master@tardis.byu.edu}

\SIMBADobj{V959 Oph}

\begintext

V959 Ophiuchi ($\alpha_{2000} = 18\hr11\mm02\fsec9$, $\delta_{2000} =
+03\deg10\arcm36\farcs8$, GSC 00435-00926) was first reported as a variable star (S4211 Oph) by G\"{o}tz (1957). The star was observed on photographic plates over a span of 60 d.  From the data G\"{o}tz classified the star as an RRc variable with a period of 0\fday084857, an amplitude of 0\fmm7 and an average magnitude of $m_{p} = 12.7$.  G\"{o}tz (1957) found that V959 Oph had two distinct amplitudes for the maxima of 0.4 and 0.7 mag. From the description in G\"{o}tz (1957) the star may have shown oscillations similar to those found in stars like SX Phoenicis, or other multiperiodic variable stars. Since that time, the star has received effectively no attention.

Because of its high amplitude and possible similarity to SX Phe, we chose to observe V959 Oph in August 1997. These observations were made with the Burrell Schmidt Telescope (hereafter BST) at Kitt Peak National Observatory, with the S2KA CCD camera through a $V$ filter modeled after Bessell (1990). Four nights of supplemental data were obtained with the David Derrick 16\arcs\ Telescope of the Orson Pratt Observatory at Brigham Young University (hereafter DDT).  These data were secured with a Pictor
416 XT CCD mounted at the Newtonian focus of the DDT through the same $V$ filter mentioned above. The four nights ranged from 31 May until 19 July 1998. The CCD field for the DDT is shown in Fig.~1.

All frames were reduced using standard IRAF functions. Differential magnitudes were determined using the eight comparison stars and the methods detailed in Hintz et al.\ (1997). A mean apparent magnitude of $\langle m_{V}\rangle = 11.4$ was determined for V959 Oph from one night of data on which observations of SA 110 (Landolt 1992) were also secured. This is different from the published photographic magnitude of $m_{p} = 12.7$, even with a reasonable color correction.  We were confident in our identification of V959 Oph from the finder in G\"{o}tz (1957), but carefully checked all surrounding stars of similar brightness to determine if the star had been mis-identified. However, no other short period variables were found in the region. We concluded that we indeed monitored
the correct star.

Using the Period98 package the first term of a Fourier series was
fit to all five nights of data.  From this we determined a period
of $0\fday09880 \pm 0\fday0005$ and an amplitude of $0.0075 \pm 0.0010$.
This is clearly different than the period reported by G\"{o}tz
(1957). From the times of maximum light list in G\"{o}tz (1957) we
used a linear regression to re-calculate the period. A period of
$0\fday093042 \pm 0\fday00001$ was found.

\IBVSfig{10cm}{4796-f1.ps}{CCD field of V959 Oph with comparison stars
labeled. The field of view is $8\arcm\times12\arcm$.}

\IBVSfig{10cm}{4796-f2.eps}{Phased light curve of V959 Ophiuchi. The
solid line is the first term of a Fourier fit.}

This period is different than both the G\"{o}tz (1957) value and that given by our Fourier fit.  Using the period from the Fourier fit all five nights of new data were phased, as shown in Figure~2. Matching each night's data to the phased curve six times of maximum light were determined. These times are collected in Table~1. From these six times of maximum light a new ephemeris for V959 Oph was determined as given in Eq.~1.
\begin{equation}
{\rm HJD_{max}} = 2450665.7968 + 0.098772 (\pm 0.000001) \times E.
\end{equation}

This agrees with the value from the Fourier fit, but is clearly
different than the value from the G\"{o}tz data.  The exact nature
of the period change in V959 Oph is unclear due to the lack of
available data. However, there has been a change at some point
during the last 40 years.

\begin{table}
\caption{New Times of Maximum Light for V959 Ophiuchi}
\begin{center}
\begin{tabular}{cccc}
\hline
HJD & \lower6pt\hbox{Telescope} & \lower6pt\hbox{Detector} & \lower6pt\hbox{Cycle} \\[-3pt]
2400000.0+ & & & \\
\hline
    50665.797   & BST   & S2KA          & 0\\
    50964.779   & DDT   & Pictor 416    & 3027\\
    50964.880   & DDT   & Pictor 416    & 3028\\
    50965.767   & DDT   & Pictor 416    & 3037\\
    50985.718   & DDT   & Pictor 416    & 3239\\
    51013.773   & DDT   & Pictor 416    & 3523\\
\hline
\end{tabular}
\end{center}
\end{table}

In addition to the period change there was a substantial decrease in the amplitude of V959 Oph. A less dramatic example of a similar effect was seen in V1162 Orionis by Hintz et al.\ (1998). For comparison with V1162 Ori two pieces of information would be useful, Str\"{o}mgren indices and the rotational velocity. The Str\"{o}mgren indices would give V959 Oph's position with respect to the instability strip. The rotational velocity of V959 Oph should be compared to the values for other high amplitude $\delta$
Scuti stars. Solano \& Fernley (1997) found a rotation velocity for V1162 Ori of 46.4 km ${\rm s^{-1}}$.  This is the highest measured rotation rate for any high amplitude $\delta$ Scuti star. The difference in rotation velocities between high and low amplitude $\delta$ Scuti stars has been discussed by Breger (1980), Andreasen (1983), and McNamara (1985). Perhaps the disparity in the relative number of high and low amplitude $\delta$ Scuti stars can be traced to the rotational velocity. Perhaps more stars started as high amplitude stars but have become low amplitude stars.

\bigskip

We thank the Brigham Young University, Department of Physics and Astronomy for their support of research efforts using the BST. We also wish to thank Case Western Reserve University for the use of the BST\@.  We also acknowledge the assistance of Janet Mattei and Ennio Poretti.

\bigskip

\references

Andreasen, G. K. 1983, {\it A\&A}, {\bf 121}, 250

Bessell, M. S. 1990, {\it PASP}, {\bf 102}, 1181

Breger, M. 1980, {\it ApJ}, {\bf 235}, 153

G\"{o}tz, W. 1957, {\it Ver\"off.\ Sternw.\ Sonneberg}, {\bf 4}, 223

Hintz, E. G., Joner, M. D., McNamara, D. H., Nelson, K. A., Moody, J. W., \& Kim, C. 1997, {\it PASP}, {\bf 109}, 15

Hintz, E. G., Joner, M. D., \& Kim, C. 1998, {\it PASP}, {\bf 110}, 689

Landolt, A. U. 1992, {\it AJ}, {\bf 104}, 340

McNamara, D. H. 1985, {\it PASP}, {\bf 97}, 715

Solano, E. \& Fernley, J. 1997, {\it A\&AS, {\bf 122}, 131

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