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\IBVShead{4302}{5 March 1996}      % Use it with dummy or empty a

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\centerline{\ft NONVARIABILITY AMONG $\lambda$ Boo STARS I.:} 
\centerline{\ft ESO 1993 AND 1994 DATA}
\vspace{8mm}

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In 1993 we started an extensive survey for pulsation in $\lambda$ Bootis
stars.
The $\lambda$ Bootis
stars are a group of metal poor, population I, A-type stars 
(Weiss et al., 1994) with broad and often shallow hydrogen lines, which
are probably caused by a gas shell. 
Two theories exist concerning the evolutionary status of this group. In
the first case diffusion would be the determining mechanism and the stars are
at the end of the ZAMS phase. In the other hypothesis accretion and/or
mass-loss would be responsible for the low metallicity and the stars would be
just
arriving at the ZAMS (Turcotte \& Charbonneau, 1993). 

Therefore their location in the Hertzsprung--Russell diagram, and hence
their evolutionary status, is still controversial (Iliev \& Barzova, 1995).
Keeping these contradicting theories in mind, it is important 
to discover pulsation among $\lambda$ Bootis stars, because
pulsation allows to derive stellar structure parameter by applying the tools
of asteroseismology. 
We have chosen for our survey candidates from Renson et al. (1990) and
Gray \& Corbally (1993). These stars were observed with the classical
technique, using at least one comparison star and two filters (Str\"omgren
$v$ and $b$). All observations were corrected for the sky background, deadtime and extinction.
Up to now we found 11 new pulsating $\lambda$ Bootis stars
(e.g. Paunzen, 1995). In a series of IBVS notes we want to present data of
all photometrically constant $\lambda$ Bootis candidates. 

In this paper we discuss data observed at the 50 cm ESO telescope 
(observer: E. Paunzen) from June 25th to July 8th 1993 and July 19th to
July 31st 1994. Table 1 lists all observed $\lambda$ Bootis and comparison
stars with the night and duration of the observations. The amplitude spectra and
spectral window (Figures 1 to 5) were calculated with a standard Fourier 
technique (Breger, 1990). 
Due to the limitation of the IBVS format we present in these figures the
amplitude spectra and spectral windows for the differential photometry of the
$\lambda$ Bootis and $one$ comparison star up to the Nyquist frequency. The
other comparison star (if observed) was constant as well.
In case of observations in
more than one night, we merged the data of all nights. The upper level of
nonvariability is typically 4 mmag in Str\"omgren $b$. 

It is evident from Table 1 and the figures that the nights have been of
different quality. Due to the noise and the limitation of the data set we 
cannot exclude variability on a low amplitude level because we can only give
an upper limit for it. However, until proven otherwise, we assume these stars
to be constant. 
The periods of variable $\lambda$ Bootis
stars detected so far range typically from 50 to 140 minutes.
From the PLC-relation
of Stellingwerf (1979) we would expect a fundamental
period of a radial mode for early A-type stars at
the MS of about 45 to 120 minutes (30 to 10 c/d).
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\centerline{2}
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\begin{center}
\centerline{Table 1. Program and comparison stars, $\star$ this comparison
star is used for the figure}
\begin{tabular}{|llcccccc|}
\hline
Star & Durchm. & JD & hours & $m_{V}$ & Spec. &   & Upper level [$b$]\\
\hline
HD\,319 & CD $-$23\degr 13 & 2449166 & 2 & 5.93 & $\lambda$ Boo & & 0.004 \\
HD\,203 & CD $-$3\degr  4 & & & 6.18 & F2IV & $\star$ & \\
\hline
HD\,141851 & CD $-$023\degr  4058 & 2449168 & 4 & 5.10 & $\lambda$ Boo  & & 0.004 \\
& & 2449175 & 5 & & & & \\
HD\,140775 & CD $-$03\degr 3829 & & & 5.52 & A5IV & $\star$ & \\
HD\,140837 & CD $-$01\degr 3092 & & & 5.39 & B8III & & \\
\hline
HD\,143148 & CD $-$31\degr 12442 & 2449560 & 4 & 7.39 & $\lambda$ Boo(?) & & 0.004 \\
HD\,142542 & CD $-$31\degr 12407 & & & 6.29 & F5V & $\star$ & \\
HD\,142851 & CD $-$31\degr 12426 & & & 7.13 & A0V & & \\
\hline
HD\,145782 & CP $-$57\degr 7716 & 2449166 & 4 & 5.71 & $\lambda$ Boo(?) & & 0.006 \\
HD\,144480 & CP $-$57\degr 7613 & & & 5.57 & B9.5V & $\star$ &\\
\hline
HD\,154153 & CD $-$43\degr 11396 & 2449175 & 3 & 6.18 & $\lambda$ Boo(?) & & 0.004 \\
HD\,153234 & CD $-$44\degr 11339 & & & 6.51 & F3V & & \\
HD\,154025 & CD $-$45\degr 11188 & & & 6.28 & A2V & $\star$ & \\
\hline
HD\,179791 & BD +05\degr 4081 & 2449166 & 3 & 6.51 & $\lambda$ Boo(?) & & 0.006 \\
HD\,178596 & BD +05\degr 4040 & & & 5.22 & F0III & $\star$ & \\
HD\,180482 & BD +04\degr 4045 & & & 5.59 & A3IV & & \\
\hline
HD\,188164 & CP $-$69\degr 3073 & 2449173 & 3 & 6.35 & $\lambda$ Boo(?) & & 0.004 \\
& & 2449174 & 6 & & & & \\
HD\,188097 & CP $-$69\degr 3072 & & & 5.75 & Am & $\star$ & \\
\hline
HD\,193256 & CD $-$29\degr 16980 & 2449560 & 5 & 7.70 & $\lambda$ Boo & & 0.002 \\
& & 2449563 & 3 & & & & \\
& & 2449564 & 5 & & & & \\
HD\,193281 & CD $-$29\degr 16981 & 2449563 & 3 & 6.61 & $\lambda$ Boo & & 0.004 \\
& & 2449564 & 5 & & & & \\
HD\,194170 & CD $-$29\degr 17046 & & & 8.27 & A4V & $\star$ & \\
\hline
HD\,204041 & CD $-$00\degr 4215 & 2449568 & 3 & 6.45 & $\lambda$ Boo & & 0.002 \\
HD\,203405 & CD +00\degr 4714 & & & 6.78 & F2 & & \\
HD\,204121 & CD +00\degr 4726 & & & 6.13 & F5V & $\star$ & \\
\hline
\end{tabular}
\end{center}

\vskip 3mm
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\epsffile{4302-f1.ps}
\normalsize
\begin{center}
Figure 1. Amplitude spectrum and spectral window for the differential data of
HD\,319 and HD\,141851 in Str\"omgren $b$.
\end{center}
\large
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\centerline{3}
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\epsffile{4302-f2.ps}
\normalsize
\begin{center}
Figure 2. Amplitude spectrum and spectral window for the differential data of
HD\,143148 and HD\,145782 in Str\"omgren $b$
\end{center}
\large 
\hspace{1.5cm}
\epsfysize=60mm
\epsffile{4302-f3.ps}
\normalsize
\begin{center}
Figure 3. Amplitude spectrum and spectral window for the differential data of
HD\,154153 and HD\,179791 in Str\"omgren $b$.
\end{center}
\large
\hspace{1.5cm}
\epsfysize=60mm
\epsffile{4302-f4.ps}
\normalsize
\begin{center}
Figure 4. Amplitude spectrum and spectral window for the differential data of
HD\,193256 and HD\,193281 in Str\"omgren $b$.
\end{center}
\large

\vfill \eject

\centerline{4}
\vskip 3mm
\hspace{1.3cm}
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\epsffile{4302-f5.ps}
\normalsize
\begin{center}
Figure 5. Amplitude spectrum and spectral window for the differential data of
HD\,188164 and HD\,204041 in Str\"omgren $b$.
\end{center}
\large
\vskip 5mm
{\it Acknowledgement:} This research was done within the working group
{\it Asteroseismology-AMS}. Computing resources and financial support for
this international collaboration were provided by the Fonds zur F\"orderung
der wissenschaftlichen Forschung (project {\it S 8303-AST}) and the 
Hochschuljubil\"aumsstiftung der Stadt Wien ($\lambda$ Bootis Sterne). This
research has made use of the Simbad database, operated at CDS, Strasbourg, 
France.


\vskip 1cm
\beginauthors
\authorsrightcol
E. PAUNZEN
W.W. WEISS
R. KUSCHNIG
Institut f\"ur Astronomie, 
T\"urkenschanzstra\ss e 17,
A-1180 Wien, Austria
e-mail: paunzen@astro.ast.univie.ac.at
\endauthors


\references

Breger, M., 1990, {\it Communications in Asteroseismology}, {\bf 20}, 1

Gray, R.O., Corbally, C.J., 1993, {\it AJ}, {\bf 106}, 632

Iliev, I.K., Barzova, I.S., 1995, {\it A\&A}, {\bf 302}, 735

Paunzen, E., 1995, {\it IBVS}, No.\,4254

Renson, P., Faraggiana, R., B\"ohm, C., 1990, {\it Bull. Inform. CDS}, {\bf 38}, 137

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

Turcotte, S., Charbonneau, P., 1993, {\it ApJ}, {\bf 413}, 376

Weiss, W.W., Paunzen, E., Kuschnig, R., Schneider, H., 1994, {\it A\&A}, {\bf 281}, 797

\vfill\eject
\centerline{5}
\vskip 2cm
\centerline{\bf ERRATUM}
\vskip 1cm
In Table 1 of the IBVS No.\,4302 several cross-identifications have been
erroneously given. The correct version of the Table is given below.
\vskip 1cm

\begin{center}
\centerline{Table 1. Program and comparison stars, $\star$ this comparison
star is used for the figure}
\vskip 1mm
\begin{tabular}{|llcccccc|}
\hline
Star & Durchm. & JD & hours & $m_{V}$ & Spec. &   & Upper level [$b$]\\
\hline
HD\,319 & CD $-23^{\circ}$ 13 & 2449166 & 2 & 5.93 & $\lambda$ Boo & & 0.004 \\
HD\,203 & CD $-23^{\circ}$ 4 & & & 6.18 & F2IV & $\star$ & \\
\hline
HD\,141851 & BD $-02^{\circ}$ 4058 & 2449168 & 4 & 5.10 & $\lambda$ Boo  & & 0.004 \\
& & 2449175 & 5 & & & & \\
HD\,141378 & BD $-03^{\circ}$ 3829 & & & 5.52 & A5IV & $\star$ & \\
HD\,140873 & BD $-01^{\circ}$ 3092 & & & 5.39 & B8III & & \\
\hline
HD\,143148 & CD $-31^{\circ}$ 12442 & 2449560 & 4 & 7.39 & $\lambda$ Boo(?) & & 0.004 \\
HD\,142542 & CD $-31^{\circ}$ 12407 & & & 6.29 & F5V & $\star$ & \\
HD\,142851 & CD $-31^{\circ}$ 12426 & & & 7.13 & A0V & & \\
\hline
HD\,145782 & CP $-57^{\circ}$ 7716 & 2449166 & 4 & 5.71 & $\lambda$ Boo(?) & & 0.006 \\
HD\,144480 & CP $-57^{\circ}$ 7613 & & & 5.57 & B9.5V & $\star$ &\\
\hline
HD\,154153 & CD $-43^{\circ}$ 11396 & 2449175 & 3 & 6.18 & $\lambda$ Boo(?) & & 0.004 \\
HD 153234 & CD $-44^{\circ}$ 11339 & & & 6.51 & F3V & & \\
HD\,154025 & CD $-45^{\circ}$ 11188 & & & 6.28 & A2V & $\star$ & \\
\hline
HD 179791 & BD $+05^{\circ}$ 4081 & 2449166 & 3 & 6.51 & $\lambda$ Boo(?) & & 0.006 \\
HD\,178596 & BD $+05^{\circ}$ 4040 & & & 5.22 & F0III & $\star$ & \\
HD\,180482 & BD $+04^{\circ}$ 4045 & & & 5.59 & A3IV & & \\
\hline
HD\,188164 & CP $-69^{\circ}$ 3073 & 2449173 & 3 & 6.35 & $\lambda$ Boo(?) & & 0.004 \\
& & 2449174 & 6 & & & & \\
HD 188097 & CP $-69^{\circ}$ 3072 & & & 5.75 & Am & $\star$ & \\
\hline
HD\,193256 & CD $-29^{\circ}$ 16980 & 2449560 & 5 & 7.70 & $\lambda$ Boo & & 0.002 \\
& & 2449563 & 3 & & & & \\
& & 2449564 & 5 & & & & \\
HD\,193281 & CD $-29^{\circ}$ 16981 & 2449563 & 3 & 6.61 & $\lambda$ Boo & & 0.004 \\
& & 2449564 & 5 & & & & \\
HD\,194170 & CD $-29^{\circ}$ 17046 & & & 8.27 & A4V & $\star$ & \\
\hline
HD\,204041 & BD $-00^{\circ}$ 4215 & 2449568 & 3 & 6.45 & $\lambda$ Boo & & 0.002 \\
HD\,203405 & BD $+00^{\circ}$ 4714 & & & 6.78 & F2 & & \\
HD\,204121 & BD $+00^{\circ}$ 4726 & & & 6.13 & F5V & $\star$ & \\
\hline
\end{tabular}
\end{center}

\end{document}
