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\IBVShead{5430}{17 June 2003}

\IBVStitletl{New Observations of the Pulsating DA White Dwarf}{ G117-B15A}

\IBVSauth{Steininger, Bruno$^1$; Papar\'o, Margit$^2$; Vir\'aghalmy, G\'eza$^2$; Zsuffa, D\'avid$^2$; \\Breger, Michel$^1$}

\IBVSinst{Institut f\"ur Astronomie, T\"urkenschanzstr. 17, A-1180 Wien, Austria}
\IBVSinst{Konkoly Observatory, P.O.Box 67, H-1525 Budapest XII, Hungary}

\SIMBADobjAlias{G117-B15A}{RY LMi}
\IBVSabs{G117-B15A is a pulsating DA White Dwarf (ZZ Ceti type star) with a}
\IBVSabs{dominant period at 215.2s. We present the data of two nights of}
\IBVSabs{CCD photometry obtained during a one week observing run at the }
\IBVSabs{Konkoly Observatory in February 2002.}


\begintext

G117-B15A is a well observed pulsating DA White Dwarf or ZZ Ceti type
star. It has 6 pulsation modes (Kepler et al., 1982) where the dominant
mode has a period of 215.2s. In this paper we present the data of two nights of observation obtained during a one week observing run at the Konkoly Observatory in February 2002.
\\
Our primary goal is to assist the derivation of the rate of change of
the main pulsation period of the star, in particular to assist the
work done by Kepler et al. over the past 20~years. Therefore we will
present new light curves and the Fourier spectra of the star and the
epochs of the light maxima.
\\\\
We observed G117-B15A for two nights on the 1m-reflector of the
Konkoly Observatory mountain station at Piszk\'estet\H o, Hungary. The
telescope has a focal length of 13.5m and is equipped with a 1024$\times$1024
Thomson TH7896M CCD chip, which has its maximum sensitivity in the
visual band. In order to collect as much light as possible, no filter
was used. Furthermore only a small area on the CCD frame was used to
minimize the integration time. We collected 16 hours of data for our
target.\\ 

\vspace*{-0.5cm}

\begin{table}[h]
\begin{center}
\begin{tabular}{ll}
\hline
\noalign{\smallskip}
RA (Eq. 2000):& 9\hr24\mm16\sec\\
Dec. (Eq. 2000):& 35\deg 16\farcm9\\
Spectral Type:& DAV (ZZ Ceti)\\
Magnitude (V):& 15.54\\
\noalign{\smallskip}
\hline
\end{tabular}
\end{center}
\caption{Coordinates, Spectral Type and Magnitude of G117-B15A}
\end{table}

We used the IRAF package for image-processing and photometry. Two
stars  on the same frame were used as comparison stars (GSC2.2 N23332237260 and N2333223509).\\
The significance level, shown in Figure 2, is based on an amplitude signal/noise ratio of
$\sim{4.0}$, which was proposed as a criterion to distinguish between
pulsation and noise by Breger et al. (1993).
\\


\IBVSfig{8cm}{5430-f1.eps}{Part of the light curve of G117-B15A. Since the periods are short in respect to the amount of data, we chose a narrow
  region of the light curve for this presentation. The fitted curve represents
  the composite of the three detected frequencies.}
%%\IBVSfigKey{5430-f1.eps}{G117-B15A}{light curve}

During the two nights of observation 3 of the 6 previously detected
frequencies (Kepler et al., 1982) could be derived. The values for the
frequencies, amplitudes and phases are listed in Table 2. We also
quote the values derived by Kepler et al. for comparison reasons.\\\\

\begin{table}[!ht]
\begin{center}
\begin{tabular}{lccccc}\hline
\noalign{\smallskip}
Mode & Frequency & Amplitude & Epoch of & \multicolumn{2}{c}{Frequencies
and Amplitudes derived}\\
& & & maximum light &\multicolumn{2}{c}{by Kepler et al. (1982)}\\
     & mHz & mmag & HJD & mHz & mmag\\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
&&$\pm$0.86 & 245 2307+ & $\pm0.005$ & \\
f1 & 4.65 & 17.45 & .498979 & 4.645 & 22.0\\
f2 & 3.29 &  6.17 & .499047 & 3.285 & 7.5\\
f3 & 3.71 &  5.61 & .497840 & 3.690 & 6.7\\
f4 & & & & 9.295 & 1.6\\
f5 & & & & 8.345 & 1.3\\
f6 & & & & 7.925 & 1.4\\
\noalign{\smallskip}
\hline
\end{tabular}
\end{center}
\caption{Table of derived frequencies, amplitudes and epoch of maximum light. We use the techniques of Breger et al. (1999) to derive the uncertainties in amplitude and epoch of maximum light. We assume therefore that the errors of the data points are not correlated in time.}
\end{table}

\IBVSTack{This investigation has been supported by the Austrian Fonds zur F\"{o}rderung
der wissenschaftlichen Forschung under project number P14546-PHY.}

\clearpage

\IBVSfig{14cm}{5430-f2.eps}{Amplitude spectrum of G117-B15A derived from Fourier analysis
with the Period98 package (Sperl, 1998). Three of the six previously
detected frequencies could be resolved. We show only a part of the
spectra in the upper half of the figure to be able to resolve the spectral window completely.}
%%\IBVSfigKey{5430-f2.eps}{G117-B15A}{spectrum}

\references
Breger, M., Stich, J., Garrido, R. et al. 1993, {\it A\&A}, {\bf 271}, 482

Breger, M., Handler, G., Garrido, R. et al. 1999, {\it A\&A}, {\bf 349}, 225

Kepler, S. O., Robinson, E. L., Nather, R. E., \& McGraw, J. T. 1982, {\it ApJ}, {\bf 254}, 676

Sperl, M. 1998, Comm. in Asteroseismology (Vienna), 111, 1

\endreferences
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