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\IBVShead{4566}{10 March 1998}

\IBVStitle{HD\,84800: A new $\delta$ Scuti variable}
\IBVSauth{E. Paunzen, K.G. Strassmeier, W.W. Weiss}
\IBVSinsto{Institut f\"ur Astronomie der Universit\"at Wien
T\"urkenschanzstr. 17 A-1180 Wien}
\vskip -2mm
\IBVSinsto{e-mail: paunzen@astro.ast.univie.ac.at}

\SIMBADobj{HD 84800}

\begintext

We present photometric data for HD\,84800 establishing
$\delta$ Scuti type variability for this star. 
Furthermore we solve the previous
discrepancy of different spectral classifications (A4\,V or A2\,II) in the
literature by using the Hipparcos parallax. As a result of the analysis
the found periodicity is likely to be a high overtone f-mode.

HD\,84800 (HIP~48129, V\,=\,7.79) was originally used as one of the
comparison stars for HD\,84123 (HIP~47792, $\lambda$ Boo spectral type,
V\,=\,6.81) during a
photometric survey of pulsating $\lambda$ Bootis stars (Paunzen et al.
1998). Our program star HD\,84123 as well as the second comparison star
HD\,84388 (HIP~47934, F2 spectral type, V\,=\,7.10) turned out to be constant.

Photometric observations were performed with one of the University of 
Vienna automatic photometric telescopes (APT) in the night of
06/07.02.1997 with an integration time of 30 seconds. 
For a detailed description
of the APT see Strassmeier et al. (1997). Figure 1 shows
the differential light curves for all three stars in Str\"omgren $b$. A
preliminary Fourier analysis of these data results in a frequency of
42\,d$^{-1}$ (=\,486\,$\mu$Hz), P\,=\,34\,min and a peak-to-peak amplitude of 
6.3\,mmag (Figure 2).

Using the Hipparcos parallax $\pi$\,=\,6.66$\pm$0.95\,mas, 
and assuming $E(B-V)$\,=\,0 (Bartke\-vi\-\v{c}ius et al. 1992) we estimate an absolute magnitude
$M_{\rm V}$\,=\,+1.91$\pm$0.32\,mag for HD\,84800. This result confirms 
the spectral type A4\,V (Bartkevi\v{c}ius et al. 1992) and rejects the A2\,II classification by Bartaya (1979). Note that for an  A2\,II star the corresponding M$_v$ is about $-$3\,mag.

In order to estimate a Q-value for the detected pulsation, typical
astrophysical quantities for an A4\,V star were adopted from
Schmidt-Kaler (1982) since neither Str\"omgren nor Geneva photometry
is available: log\,$g$\,=\,4.3, $T_{\rm eff}$\,=\,8500\,K and
$B.C.$\,=\,$-$0.16\,mag. These parameters give a Q-value of 0.015\,days based
on L\'{o}pez de Coca et al. (1990):
$$log\,Q = -6.456 + log\,T_{\rm eff} + 0.5\,log\,g + 0.1\,M_{\rm bol} + log\,P$$
A comparison with theoretical Q-values listed in Stellingwerf (1979) results
in the exclusion of the fundamental and the first overtone mode for the detected
variability. However, this conclusion remains preliminary since 
``tabulated'' values for a ``standard`` A4\,V-type star have been used. 


\IBVSfig{20cm}{4566-f1.ps}{The differential APT light curves for HD\,84123, HD\,84388 and HD\,84800 in Str\"omgren $b$}
\eject
\vskip -10cm
\IBVSfig{15cm}{4566-f2.ps}{Amplitude spectra for all three stars}

{\it Acknowledgements}: This research was carried out within the working group
{\it Astero\-seis\-mology-AMS} with funding from the Fonds zur
F\"orderung der wissenschaftlichen Forschung (FWF) project {\em S7303-AST}.
KGS acknowledges support by the FWF, project {\em S7301-AST}.
Use was made of the SIMBAD database, operated at CDS, Strasbourg, France.


\references

Bartaya R.A., 1979, {\it Bull. Abastumani Obs.}, No.\,51

Bartkevi\v{c}ius A., Lazauskait\`e R., Tautvai\v{s}ien\`e G., 1992,
{\it Baltic Astronomy}, {\bf 1}, 216
% Original: {\it Baltic Astronomy}, Vol.\,1, 216
% Corrected: Mon Aug 11 13:23:43 MET DST 2003

L\'{o}pez de Coca P., Rolland A., Rodr\'{\i}guez E., Garrido R.,
1990, {\it A\&AS}, {\bf 83}, 51

Paunzen E., Weiss W.W., Kuschnig R., et al., 1998, {\it A\&A} (in press)

Schmidt-Kaler Th., 1982, in: Landolt-B\"ornstein New Series,
group VI, vol. 2b, p. 453

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

Strassmeier K.G., Boyd L.J., Epand D.H., Granzer Th., 1997,
{\it PASP}, {\bf 109}, 697

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