\documentstyle[twoside, epsf]{article}

\input ibvs2.sty

\begin{document}

\IBVShead{5054}{30 March 2001}

\IBVStitletl{New Observations of the Possible High Amplitude}{ {\boldmath $\delta$} Scuti variable V854 Scorpii}

\IBVSauth{Van Cauteren, P.$^1$; Vanmunster, T.$^2$; Lampens, P.$^3$}

\IBVSinst{Beersel Hills Observatory, Laarheidestraat 166, B--1650 Beersel, Belgium,\\
\indent email: Paul.Vancauteren@advalvas.be}

\IBVSinst{Center for Backyard Astrophysics (CBA Belgium), Walhostraat 1A, B--3401 Landen, Belgium,\\ \indent email: Tonny.Vanmunster@advalvas.be} 

\IBVSinst{Koninklijke Sterrenwacht van Belgi\"e, B--1180 Brussel, Belgium, 
email: Patricia.Lampens@oma.be}

\SIMBADobjAlias{V854 Sco}{GSC 5617-730}

\IBVSkey{Delta Scuti stars - photometry}
\IBVSabs{CCD differential photometry of the high amplitude} 
\IBVSabs{delta Scuti star V854 Sco has been performed.}
\IBVSabs{Analysis of the data indicates a periodicity unchanged} 
\IBVSabs{since almost 60 years and a strong variation in amplitude at}
\IBVSabs{the phase of maximum light between two successive cycles,}
\IBVSabs{probably caused by a beat phenomenon.}

\begintext

The variability of V854 Sco (= CSV 2614 = HV 10535 = GSC 5617-00730)
was discovered by E. Hughes Boyce (1942) who classified the star as an
eclipsing variable of type W UMa, varying between magnitudes 13.9 and
14.5, but gave no elements. Robinson (1967) estimated the magnitude of
V854 Sco on 200 plates of the Harvard Observatory collection, taken
between JD 2427900 and JD 2430133, with exposure times of 45 minutes. A
period of $0.1024012\pm 0.0000001$ day was found, with a mean
variation between photographic magnitudes 13.05 and 13.41. He also
noted a larger dispersion of the data at maximum, compared to the
minimum, and attributed this to a cycle-to-cycle variation of the
amplitude. Due to the long exposure times, the mean amplitude could be
underestimated. The characteristics of V854 Sco compiled by
Rodr\'{\i}guez et al.\ (1994) are based on these data. Kinman (1998)
refers to V854 Sco as a possible high amplitude $\delta$ Scuti star
(HADS) located high above the galactic plane. To our knowledge there
exists no colour information for this object.

\IBVSfoot{MIRA AP is distributed by Axiom Research,
Inc.}
We observed V854 Sco in the spring of 2000 with the 0.35-m telescope of
CBA Belgium and the 0.4-m telescope of Beersel Hills Observatory (see
Vanmunster et al.\ (2000) for a complete description of the CBA Belgium
Observatory equipment and software). Both telescopes are equipped with
an ST7 CCD-camera. We used a $2\times2$ binning mode. Due to the
faintness of the star and the low altitude above the horizon, no filter
was used.  Exposure times varied between 120 and 200 seconds.
Observations were made on five nights from JD 2451673 to 2451704,
spanning a total time base of 31 days (see Table~1).  Respectively 288
(CBA) and 47 (BHO) data points were obtained, with a total observing
time amounting to 14 hours. The CBA frames were calibrated and reduced
using the profile fitting algorithm of the software package MIPS (Buil
et al.\ 1993). The frames taken at BHO were reduced with the aperture
photometry procedure of the Mira AP software
package\IBVSfm. The comparison star was GSC 5617-00683 (14\fmm0). The standard
deviation of the measurements check minus comparison star was 0\fmm02
on JD 2451679 ($n=47$). An offset in mean magnitude for the latter data
with respect to the rest of the data was applied on a
telescope-to-telescope basis. All differential magnitudes were computed
with respect to the same comparison star. They are available on
request.

\IBVSfig{12.0cm}{5054-f1.eps}{The V854 Sco data phased against the
frequency of 9.7644123 c/d:  filled diamonds represent the data on JD
2451679.428--2451679.521 ($n=39$), 2451693, 2451704 while open
triangles are used for JD 2451673, 2451679.525--2451679.544 ($n=8$),
2451690}

\begin{table}
\caption{Log of observations}
\begin{center}
\begin{tabular}{lccl}
\hline
Date   &  JD+  &  No.\ data & Telescope\\
\hline
May 8/9, 2000 & 673  &  29 & CBA \\
May 14/15 & 679 &  47 & BHO \\
May 25/26 & 690  & 74 & CBA \\
May 28/29 & 693 & 104 & CBA \\
June 8/9 & 704 & 81 & CBA \\
\hline
\multicolumn4c{\normalsize `JD\,+' stands for 'JD 2451000\,+'} \\
\end{tabular}
\end{center}
\end{table}

\clearpage

The data were frequency-analysed with Period98 (Sperl, 1998). We
obtained the same period as reported by Robinson (1967): $0.102413\pm
0.000002$ days, corresponding to the frequency of $9.7644\pm 0.0002$
cycles per day (c/d). Fig.~1 shows the mean light curve phased against
the best fitting frequency of 9.7644123 c/d. The mean peak-to-peak
amplitude in white light is 0\fmm34 in good agreement with the range
in photographic magnitude (Robinson, 1967). The error in frequency
means that we believe that a shift in phase of 0.07 or larger between
the first and the last timing of maximum light can be detected in the
data string ($\Delta \phi = \Delta f \times {\rm number\ of\ cycles}$).  With
a full amplitude of 0\fmm34, such a phase shift corresponds to a
deviation of 0\fmm023, which is of order of the estimated noise level.
This error in frequency is thus an upper limit.  However the
peak-to-peak amplitude varies by as much as 0\fmm15. The shape of the
light curve varies strongly within two subsequent cycles, as can been
seen in Fig.~1 (see different symbols for different sets of data). The
skewness of the light curve is strongest at maximum amplitude.  We have
applied a fit to all the data taking the first harmonic into
consideration, giving:
\begin{center}
\begin{tabular}{lll}
$f= 9.7644$ c/d; & $a_{1}=0\fmm162$; & $\phi_{1}=0.969$; \\
$2f=19.5288$ c/d; & $a_{2}=0\fmm049$; & $\phi_{2}=0.338$; \\
$t_{0}={\rm JD}~2451673.4793$; & \multicolumn2l{mean difference${}=0\fmm703$} \\
\end{tabular}
\end{center}
and a residual standard deviation equal to 0\fmm045 (0\fmm057 without
the harmonic term).  The residual dispersion in amplitude is
concentrated mainly around the phase of maximum light.  The parameters
characterizing the shape of the light curve in a Fourier decomposition
give $R_{21}=0.33$ and $\Phi_{21}=2.51$. The latter value is a bit low
compared to other $\delta$ Scuti stars (Poretti et al., 1990).

In conclusion we report the constancy of the period for this high
amplitude $\delta$ Scuti star over a time range of almost 60 years. In
addition we confirm that the mean peak-to-peak amplitude fluctuates by
as much as 0\fmm15. From the re-occurrence of a similar light curve
shape on a time scale of several days, one can expect beating between
two closely spaced frequencies. We searched but found no indication for
a second frequency in our data.  However this does not argue against
the existence of a second frequency, as it could well be that coverage
with respect to the corresponding beat period is insufficient.

\references

Buil, C., Klotz, A., Prat, G., Szczepaniak, R., Thouvenot, E., 1993, Manual for the Microcomputer Image Processing System, V2.0

Hughes Boyce, E. 1942, {\it HA}, Vol.\ 109, No.\ 2

Kinmann, T., 1998, {\it PASP}, {\bf 110}, 1277

Poretti, E., Antonello, E., Le Borgne, J.F., 1990, {\it A\&A}, {\bf 228}, 350

Robinson, L.J., 1967, {\it IBVS}, No.\ 240

Rodr\'{\i}guez, E., Lop\'ez de Coca, P., Rolland, A., Garrido, R., Costa, V., 1994, {\it A\&AS}, {\bf 106}, 21

Sperl, M., 1998, Manual for Period98 (V1.0.4). A period search-program for Windows and Unix, (http://dsn.astro.univie.ac.at/\~{}period98)

Vanmunster, T., Skillman, D., Fried, R., et al., 2000, {\it IBVS}, No.\ 4940

\endreferences

\end{document}
