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\IBVShead{4900}{8 May 2000}

\IBVStitle{Discovery of \boldmath{$\delta$} Scuti Pulsations in HD 98851}

\IBVSauth{Joshi, S.$^{1}$; Girish, V.$^{2}$; Martinez, P.$^3$; Sagar, R.$^1$; Ashoka, B.N.$^2$; Gupta, S.K.$^1$;\\ \indent Seetha, S.$^2$; Kurtz, D.W.$^4$; Chaubey, U.S.$^1$}

\IBVSinst{Uttar Pradesh State Observatory, Manora Peak-263 129, Naini Tal,
India,  santosh@upso.ernet.in} %email


\IBVSinst{ISRO Satellite Centre, Airport Road, Bangalore-560 034, 
India, girishv@isac.ernet.in} %email


\IBVSinst{South African Astronomical Observatory, P. O. Box 9, South Africa, 
peter@saao.ac.za} %email


\IBVSinst{Department of Astronomy, University of Cape Town, South Africa,
dkurtz@saao.ac.za} %email


\SIMBADobjAlias{HD 98851}{BD+32 2142}

\begintext

We report a new pulsating $\delta$ Scuti variable, HD~98851, discovered
during the ``Naini Tal-Cape Survey for Pulsations in Chemically
Peculiar Stars''. The main aim of the survey is to search for rapidly
oscillating Ap (roAp) stars in the northern hemisphere. Therefore, the
candidates are selected on the basis of Ap and Am spectral
classifications and/or peculiar photometric colours. HD~98851 has
Str\"{o}mgren indices corresponding to high metallicity found in the Am
and Ap stars, {\em viz.}\ $b-y = 0.199$, $m_1 = 0.222$, and $c_1 =
0.766$ (Olsen, 1983). The Johnson colour indices for HD~98851 are
$V=7.41$, $B-V=0.33$ and $U-B=0.12$ (Oja, 1985). Abt (1984) classified
HD 98851 as `Am(F1/F1 IV/F3)' on the basis of its Ca K, hydrogen and
metallic lines. Although the Ca and metallic line types do not differ
by more than 5 subtypes as required by the classical Am definition, the
spectrum has several other indicators of Am character.

\IBVSfig{6cm}{4900-f1.ps}{Light curve of HD~98851 on HJD~2451594.}

On the basis of these peculiar colours we decided to search for rapid
oscillations in HD~98851 on the night of 28 January 2000, JD 2451572.
The data were acquired as continuous 10-s integrations in Johnson $B$
light using a high-speed photometer attached to the 104-cm Sampurnanand
telescope of Uttar Pradesh State Observatory (UPSO), Naini Tal.

These observations revealed a peak-to-peak variation of 0.04~mag on a
time-scale of about 80~min.  Subsequent observations were made on
nights HJD 2451594, 2451596, 2451623 and 2451627 to confirm the presence of
these pulsations and to define better the period.  Figure~1 shows the
light curve obtained on night HJD 2451594.  The data shown here have
been corrected for coincidence counting losses, sky background and
atmospheric extinction, and then binned to 40-s integrations.

\IBVSfig{9cm}{4900-f2.eps}{The amplitude spectrum of HD~98851 on HJD 2451594.}

The reduced data were then Fourier analysed to identify the component
frequencies using Deeming's (1975) discrete Fourier transform. Fig.~2
shows the amplitude spectrum of the HJD 2451594 data.  The amplitude
spectrum peaks strongly at $0.21 \pm 0.02$~mHz (79.4 minutes) and $0.10
\pm 0.03$~mHz (167 minutes). The peak at 0.10~mHz appears in the other
light curves also, but we caution that contamination at low frequences
by sky transparency variations is significant in these single-channel
measurements. In order to confirm this frequency additional two-channel
data or differential data are required. A detailed analysis of the
pulsations in this star will be published elsewhere.

\references

Abt, H.A., 1984, {\it ApJ}, {\bf 285}, 247

Deeming, T.J., 1975, {\it Ap\&SS}, {\bf 36}, 137

Oja, T., 1985, {\it A\&AS}, {\bf 61}, 331

Olsen, E.H., 1983, {\it A\&AS}, {\bf 54}, 55

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