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\IBVShead{4849}{14 February 2000}

\IBVStitle{GSC 4778~324: a New Multiperiodic {\boldmath $\delta$} Scuti Star}

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

\IBVSinst{Beersel Hills Observatory, email: Paul.VanCauteren@advalvas.be}

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

\SIMBADobjAlias{V1162 Ori}{BD-07 1108}
\IBVStyp{ CWA }
\IBVSkey{photometry}
\IBVSabs{While participating to the multisite campaign set up by Arentoft and 
Sterken (1999)}
\IBVSabs{a new small-amplitude short-period variable star, very probably a $\delta$ Scuti star,}
\IBVSabs{was found in the field of V1162~Ori.}

\begintext

While observing the high-amplitude $\delta$ Scuti star (HADS) V1162~Ori as part of a international multisite campaign, we found a new short-period variable with small amplitude (about 0.01 mag) on our frames. The star, GSC 4778~324, is probably of $\delta$ Scuti type. 

We observed the field of GSC 4778~324  ($\alpha_{2000} = 05\hr 32\mm 34\fsec462, \delta_{2000} =-7\deg 12\arcm 40\farcs116$) on 3 nights in December 1999 and on 4 nights in January 2000. A total of 20.3 hours of CCD-photometry, resulting in 637 datapoints was obtained.

We used a 0.4-m telescope equipped with a ST7 camera and V-filter (according to the Bessel specifications). The frames, made in $2\times2$ binning mode, were dark-framed and flat-fielded. Aperture photometry was performed using MIRA-AP software package\IBVSfm.  

We refer to Fig.~1 for the identification of the stars that we analyzed:

star 0 = GSC 4778 019, our principal comparison star, following the instructions
for the multisite observations of V1162~Ori (Arentoft and Sterken, 1999).

star 1 = V1162~Ori, a high-amplitude $\delta$ Scuti star;

star 2 = GSC 4778 285 (11\fmm8);

star 3 = GSC 4778 324 = the new variable star (10\fmm4);

star 4 = GSC 4778 001 (12\fmm7).

All differential magnitudes were computed with respect to our principal comparison star, labelled star 0. Stars 2 and 4 were used as check stars and remained constant. The differences between check star 2 and comparison star show a standard deviation of about 0.005~mag.  

\IBVSfoot{The MIRA AP software is distributed by Axiom Research, Inc.}

Our first two datasets (of length about 0\fday07) showed respectively a maximum and  a minimum. The next datasets showed barely any variation (Fig.~2), whereas our last dataset (of length about 0\fday14) showed one maximum and two minima (Fig.~3). This leads us to conclude that the star is very probably a multiperiodic variable. We used Period98 (Sperl, 1998) to perform a preliminary period analysis and obtained a provisional frequency of 13.693 c/d, i.e.\ a point of 0\fday073. The peak-to peak amplitude associated to this frequency is only 0.014 magnitude. The (preliminary) phase diagram, that combines four datasets, is illustrated in Fig.~4.

\IBVSfig{10.0cm}{4849-f1.ps}{CCD field-of-view for GSC 4778 324 with star labels as discussed in the text. The dimensions are 8\arcm\ by 12\arcm. The field is rotated to avoid reflections by a bright neighbouring star.}
\IBVSfig{10.0cm}{4849-f2.eps}{Light curve of GSC 4778 324 on 24/01/2000}
\IBVSfig{10.0cm}{4849-f3.eps}{Light curve of GSC 4778 324 on 27/01/2000}
\IBVSfig{10.0cm}{4849-f4.eps}{Phase diagram of four datasets against the (preliminary) frequency of 13.693 c/d}

\vskip-44pt
G. Handler showed interest in our new variable and performed Str\"omgren photometry with the 0.5-m telescope at S.A.A.O\@. He obtained the following colour indices: $V = 10.26$, $b-y = 0.202$, $m1 = 0.168$, $c1 = 0.894$, $\beta = 2.797$ (Handler, 2000). These values put the new variable star right in the middle of the $\delta$ Scuti instability strip.

The small amplitudes and short-period variations we observed as well as the colours obtained by Handler (2000) lead us to state that GSC 4778~324 is a new $\delta$ Scuti variable. The fact that these variations could be detected on some days only and hardly to no longer on some other days, indicates that it is a multiperiodic variable. Further observations are encouraged for trying to solve the complete frequency spectrum.

{\it Acknowledgements:} This research was supported by project G.0265.97 of the Fund for Scientific Research (FWO) --- Flanders (Belgium). Dr.~Sperl is kindly acknowledged for making the programme Period98 available for this application. We made use of the Simbad database, operated at CDS, Strasbourg, France. 

\references

Arentoft, T., Sterken, C., 1999, http://homepages.vub.ac.be/$^\sim$tarentof/welcome.html

Handler, G., 2000, {\it Inf.\ Bull.\ Var.\ Stars}, No.\ 4817 

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

\endreferences

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