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\IBVShead{4483}{29 May 1997}

\title{HD\,102541: a pulsating candidate $\lambda$ Bootis star}

\begintext

The candidate $\lambda$ Bootis star HD\,102541 was observed during five
nights 
with the ``modular photometer'' at the 0.5m telescope (observer: R.~Kuschnig), 
operated by
the South African Astronomical Observatory (SAAO). The characteristics of
these nonmagnetic, metal-deficient Population\,I, A- to F-type
dwarfs are described in more detail
by Paunzen et al. (1997). The journal of observations
and the chosen comparison stars are listed in Table 1. The light curve
shown in Fig. 1 reveals the photometric variability of the program star
with respect to both comparison stars. The applied standard time series
analysis (Wei 1990) to the high quality data results in the amplitude
spectrum and spectral window shown in Figure 2. The highest signal (6$\sigma$
detection) appears
at the frequency of 20 d$^{-1}$ (232 $\mu$Hz)
which refers to a period of 72 min and the peak to peak
amplitude is about 30 mmag in Str\"omgren $v$. These values are typical compared
to previous results obtained by our survey for pulsating $\lambda$ Bootis
stars (Paunzen \& Handler 1996). 

In order to establish the membership of HD\,102541 to the $\lambda$ Bootis
group, an intermediate resolution
spectrum (0.9\,\AA/pixel) was obtained in the night of 13./14.06.95
(observer: E.~Paunzen) with the Cassegrain spectrograph of the
1.6m telescope at Itajuba, Brazil. 
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Figure 1. Light curve of HD\,102541 and both comparison stars for the
first night in Str\"omgren $v$
\end{center}
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\centerline{2}
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Figure 2. Amplitude spectrum and spectral window for the merged differential 
data of all five nights [HD\,102541\,--\,HD\,103017] in Str\"omgren $v$
\end{center}

\begin{center}
Table 1. Journal of observations for the program and comparison stars
\vskip 2mm
\begin{tabular}{llccccc}
\hline
Star & Durchm. & JD & hours & $m_{V}$ & Spec. &\\
\hline
HD~102541 & CD~$-$39\degr ~7307 & 2449740 & 2 & 8.0 & ($\lambda$ Boo) &\\
& & 2449741 & 2.5 & & &\\
& & 2449742 & 1.5 & & &\\
& & 2449744 & 2 & & &\\
& & 2449747 & 1 & & &\\
HD~103017 & CD~$-$39\degr ~7339 & & & 7.7 & F3IV/V &\\
HD~103051 & CD~$-$40\degr ~6992 & & & 7.4 & F5V &\\
\hline
\end{tabular}
\end{center}

Houk (1978) classified HD\,102541 as A3 II/III. The Str\"omgen colours
(b\,--\,y\,=\,0.163, m$_{1}$\,=\,0.141, c$_{1}$\,=\,0.810, 
$\beta$\,=\,2.798; Gray \& Olsen 1991), on the other hand, indicate that this
star is actually a metal-deficient dwarf. Using the calibrations of
Crawford (1979) and Napiwotzki et al. (1993), we derive 
T$_{eff}$\,=\,7700(200)\,K, log\,$g$\,=\,4.1(2)
(typical for luminosity class V), $\delta$m$_{0}$\,=\,0.053(10)
and M$_{Bol}$\,=\,2.5(3). The discrepancy between the luminosity classification
given in the Michigan catalogue and a reclassification with higher resolution
spectra, is a common fact for $\lambda$ Bootis stars (Gray 1991).
We classify HD\,102541, based on the spectrum showed in
Figure 3, as kA3hA5mA3\,V\,(LB), please
note that the Mg\,II\,4481-line is normal for A3 and not remarkably weak.
\vskip 3mm

Many similarities of HD\,102541 to the pulsating (P$_{obs}$\,=\,84 min) 
$\lambda$ Bootis star HD\,168947 are obvious (Paunzen et al., 1994). This
star was also classified as A3\,II/III, but turned out to be a
metal-deficient dwarf. Both stars are almost at the same place in the
H-R diagram resulting in a comparable pulsation behaviour (observed period
and amplitude). The observed period for HD\,102541
is very close to the theoretical radial fundamental mode
(P$_{th}$\,=\,67 min) derived by the PLC-relation taken from Stellingwerf 
(1979) making this star to an interesting target for an international
multisite campaign.

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\centerline{3}
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Figure 3. Intermediate resolution (0.9\,\AA/pixel) spectrum of HD\,102541
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{\it Acknowledgement:} This research was carried out within the working group
{\it Asteroseismo\-logy-AMS} with funding from the Fonds zur F\"orderung der 
wissenschaftlichen Forschung (project {\em S7303-AST}). We are indebted to
the scientific committees of LNA/CNPq/MCT and SAAO for granting observing
time. This
research has made use of the Simbad database, operated at CDS, Strasbourg,
France.


\vskip 6mm

\beginauthors
\authorsrightcol
R. KUSCHNIG
E. PAUNZEN
W.W. WEISS
Institut f\"ur Astronomie der
Universit\"at Wien
T\"urkenschanzstr. 17
A-1180 Wien
e-mail: paunzen@astro.ast.univie.ac.at
\endauthors
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\references

Crawford, D.L., 1979, {\it AJ}, {\bf 84}, 1858

Gray, R.O., 1991, in: {\it Precision Photometry}, Davis Philip, A.G.,
Upgren, A.R., Janes, K.A. (eds.), p. 541

Gray, R.O., Olsen, H.H., 1991, {\it A\&AS}, {\bf 87}, 541

Houk, N., 1978, {\it University of Michigan Catalogue of Two-Dimensional
Spectral Types for the HD Stars}, {\bf Volume II}, Astronomy Dept., Univ. Mich.,
Ann Arbor, Michigan

Napiwotzki, R.. Sch\"onberner, D., Wenske, V., 1993, {\it A\&A}, {\bf 268}, 653

Paunzen, E., Weiss, W.W., North, P., 1994, {\it IBVS}, No.\,4068

Paunzen, E., Handler, G., 1996, {\it IBVS}, No.\,4318

Paunzen, E., Weiss, W.W., Heiter, U., North, P., 1997, {\it A\&AS}, {\bf 123}, 93

Stellingwerf, R., 1979, {\it ApJ}, {\bf 227}, 935

Wei, W., 1990, {\it Time Series Analysis}, Addison-Wesley Publishing Company

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