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\centerline{\ft MULTIPERIODIC PHOTOMETRIC VARIATIONS OF HD\,210111}
\centerline{\ft AND SUSPECTED VARIABILITY OF  HD\,210049}
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We present time series of our observations of a new variable $\lambda$\,Boo star, HD\,210111
($m_V$ = 6.4), which is classified as kA2hA7mA2V\,$\lambda$\,Boo by Gray and Corbally 
(1993). $\lambda$\,Bootis stars are a group of metal poor Population\,I stars
(Weiss et al. 1994) with broad and often shallow hydrogen lines, which are
probably caused by a gas shell.
There are indications for such a gas shell also for HD\,210111 (St\"urenburg 1993).
An abundance analysis for that star (St\"urenburg 1993) gave a metal deficiency
of about a factor of 10 compared to the Sun.

Our observations were part of a survey for pulsation among $\lambda$\,Boo stars
(Paunzen, Weiss and North 1994, Kuschnig, Paunzen and Weiss 1994a,b), using 
the 70\,cm Swiss-telescope at ESO, La Silla with the Geneva photometer.
When variability of HD\,210111 became evident in the raw data, it was decided 
to observe this $\lambda$\,Boo type star as frequently as possible. 
PN and EP used HD\,210049 ($m_{V}$ = 4.5, A1\,IVnn) as first comparison star
during 8 nights distributed over 2 weeks, and in addition in one of these nights HD\,210302 
($m_{V}$ = 4.9, F6\,V) as a second comparison. 


{\bf  HD 210111:}
A quick look at the extinction corrected differential instrumental magnitudes (Fig.\,1) indicates 
already multiperiodic variations for this star. An amplitude spectrum computed with
a single-frequency Fourier technique for unequally spaced data (program PERIOD, Breger 1990)
indicates the presence of at least 2 pulsation frequencies (Fig.\,2, second panel). The frequencies
with the largest amplitudes are $f_1$ = 27.99\,c/d and $f_2$ = 17.01\,c/d, which could be 
influenced by a 1\,c/d aliasing. In any case, this solution is rather formal and serves only as 
a guideline for the relevant frequency range. 

A simultaneous 4-frequency fit to the observations of HD\,210111, based on the lowest residuals after 
a step-by-step prewhitening, results in a scatter of 4.0\,mmag, which is almost twice the value for 
the extinction corrected observations of the comparison star HD\,210049. We thus conclude that 
probably several modes may be excited in HD\,210111. A problem for the frequency analysis is
the poor duty cycle of only 7\% of our single-site data. However, it is quite obvious that 
HD\,210111 is a promising candidate for an international photometric observing campaign. 

The calibration (Crawford 1979, Philip \& Relyea 1979, for [Fe/H] = $-$1) of $uvby\beta$ 
photometry applied to the indices listed by Hauck \& Mermilliod (1990) for HD\,210111 results in 
$M_{v}$ = 1.65, $T_{eff}$ = 7900\,K, and log $g$ = 3.95. These parameters give $Q$-values ranging 
from 0.014 to 0.022\,d, based on
	\begin{displaymath}
	\log Q = -6.456 + \log T_{eff} + 0.5 \log g + 0.1 M_{bol} + \log P
	\end{displaymath}
According to pulsation models (Fitch 1981), such $Q$-values indicate pulsation
in the second to fifth overtone. 



{\bf HD 210049:} 
Our present analysis depends on the constancy of the primary comparison, HD\,210049,
except for one night, where a second comparison star has been observed. 
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\centerline{Figure 1. HD\,210111--HD\,210049 in Geneva-V, residuals to night-mean}
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\centerline{Figure 2. Amplitude spectrum (bottom panel) and spectral window of the data of Fig. 1}
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\centerline{3}
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\centerline{Figure 3. Amplitude spectrum of the extinction corrected Geneva-V photometry}
\centerline{of	HD\,210049}

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\noindent In order to demonstrate the 
validity of this assumption we show the amplitude spectrum of our extinction corrected 
instrumental data of HD\,210049 in Fig.\,3. The highest noise peaks for frequencies larger than 
15\,c/d show amplitudes of 0.7\,mmag. However, a peak at 8.9\,c/d with an amplitude of 1.7\,mmag 
clearly exceeds the noise level. This peak also appears in the amplitude spectrum of the
{\em differential}  HD\,210111 -- HD\,210049 data, but {\em not} in the HD\,210111 data alone. 
The differential magnitudes of the two comparison stars HD\,210049 -- HD\,210302 have  
$\sigma$=2.0\,mmag.
%, which corresponds to an upper limit for  semi-amplitude of 2\,mmag on the 2-$\sigma$ level.

We therefore cannot exclude variability of our primary comparison star, HD\,210049, with a period
of about 2.7 hours, but cannot proof this claim with the second comparison star. However, it is quite 
safe to attribute the variability in the differential photometry of our $\lambda$\,Boo star in the 15 to 
30\,c/d frequency domain (Figs. 1 and 2) to HD\,210111, and {\em not} to the comparison star.

Pulsation of HD\,210049 would be remarkable, because effective temperature 
and absolute magnitude ($T_{eff}$ = 9000\,K, $M_v$ = 0.9), based on Str\"omgren photometry, 
locate this star outside
the $\delta$\,Scuti instability strip. On the other hand, the hot border of
this instability strip is not very well defined and a shift towards hotter temperatures 
was recently proposed by Rodriguez et al. (1994). 

{\bf Conclusions:}
We discovered multi-periodic variability in the $\lambda$\,Boo star HD\,210111 and cannot
rule out variability of HD\,210049. The frequency
spectrum of HD\,210111 is complicated and only a sufficiently long multi-site campaign 
(3 weeks or more) will allow a successful resolution.
HD\,210111 is a promising candidate for applying asteroseismic techniques and thus to investigate
the problem of the origin of $\lambda$\,Bootis stars. 
Another interesting case is HD\,111786 (Kuschnig et al. 1994a). We also encourage further 
observations of HD\,210049. 
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\centerline{4}
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Acknowledgement: This research was supported by the Hochschuljubil\"aumsstiftung
der Stadt Wien, and by the Swiss National Foundation for Scientific Research.

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% Call for macros \authors - \authorsrightcol - \endauthors
\beginauthors
E. PAUNZEN
G. HANDLER
W. W. WEISS
Institut f\"ur Astronomie
T\"urkenschanzstr. 17
A-1180 Wien, Austria
E-mail: LAST\_NAME@ASTRO.AST.UNIVIE.AC.AT
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P. NORTH
Institut d'astronomie de l'Universit\'e 
de Lausanne,
CH-1290 Chavannes-des-Bois, Switzerland
E-mail: NORTH@OBS.UNIGE.CH 
\authorsrightcol
\endauthors
% Call for macro \references
\references

Breger, M., 1990, Communications in Asteroseismology 20, 1 (University of Vienna)

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

Fitch, W. S., 1981, {\it ApJ}, {\bf 249}, 218 

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

Hauck, B., Mermilliod, M., 1990, {\it A}\&{\it AS}, {\bf 86}, 107

Kuschnig, R., Paunzen, E., Weiss, W. W., 1994a, {\it IBVS}, No.\, 4069 

Kuschnig, R., Paunzen, E., Weiss, W. W., 1994b, {\it IBVS}, No.\, 4070

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

Philip A. G. D., Relyea L. J., 1979, {\it AJ}, {\bf84}, 1743 

Rodriguez, E., L\'opez de Coca, P., Rolland, A., Garrido, R., Costa, V., 1994,
{\it A}\&{\it AS}, {\bf 106}, 21

St\"urenburg S., 1993, {\it A}\&{\it A}, {\bf 277}, 139 

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

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