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\IBVShead{4550}{28 January 1998}

\IBVStitletl{HD\,17892, a new Delta Scuti star}

\IBVSauth{G. Handler}
\IBVSinsto{Institut f\"ur Astronomie, Universit\"at Wien, 
T\"urkenschanzstra\ss e 17, A-1180 Wien, Austria}
\IBVSinsto{e-mail: gerald@dsn.astro.univie.ac.at}

\SIMBADobj{HD17892}
\IBVStyp{ DSCT, ROAP }

\begintext

We are currently undertaking a large multisite campaign for the main-sequence
$\delta$~Scuti star XX Pyx (Handler \& Breger 1997). Since this star is not
available all night from Northern Hemisphere observatories, we selected a
backup program for the rest of the nights. We decided to undertake a search
for rapidly oscillating Ap (roAp) stars in the Northern Hemisphere. Our
candidates were carefully selected from Str\"omgren and Geneva photometry as
well as spectral classification. 

The observations were carried out with a two-channel photometer attached to the 
0.9m telescope at McDonald Observatory, Fort Davis, Texas. We acquired 
continuous 10-second integrations through a Johnson B filter in both channels, 
only interrupted by sky background measurements.

As our first target, we chose BD+39\deg 654. It has been classified as SrCrEu by
Bidelman (1983). Schneider's (1986) Str\"omgren photometry yields $(b-y)_0$ =
0.136, $\delta$m$_1$ = $-$0.095 and $\delta$m$_1$ = $-$0.267, while Geneva 
photometry (Burki et al. 1998) results in $[\Delta]$ = 0.163 and $[g]$ = 0.162.
All these features are typical for roAp stars.

We tested BD+39\deg 654 for rapid light variations in the night of January 16/17,
1998. We chose HD\,17892 as our channel 2 comparison star. While our roAp
candidate did not show indications of variability, we noticed light variations
of the comparison star and continued the observations. The
reduced light curve of HD 17892, where the integrations have been summed
into 2-minute bins, is shown in Figure~1 together with an amplitude spectrum
for both stars.

\IBVSfig{10cm}{4550-f1.ps}{Upper panel: reduced light curve of HD\,17892
together with a single-frequency fit (see text). Lower panel: amplitude 
spectrum of this run for HD\,17892 (full line) and BD+39\deg 654 (dashed line)}

A frequency analysis of this run yields a period of 71.2 $\pm$ 1.3 minutes
with a B amplitude of 4.1 $\pm$ 0.4~mmag. The error bars have been determined 
following Kov\'acs (1981) and should be taken only as formal values; the real 
errors may be higher by up to a factor of 2.
From an inspection of Figure~1 it can be suspected that the light curve of
HD\,17892 is multiperiodic, but our data set is to small to prove this.

The HD spectral type of HD\,17892 is A5. From this and from the period and
amplitude we derived for the star we conclude that it is a $\delta$ Scuti
pulsator. Mode stability considerations allow us to estimate that this
object is near the middle of its main sequence evolution. Str\"omgren
photometry would allow to support this conclusion, but no optical photometric 
indices of HD\,17892 have been determined up to now.

\references

Bidelman, W. P., 1983, {\it AJ}, {\bf 88}, 1182

Burki, G., et al., 1998, in preparation

Handler, G., Breger, M., 1997, Delta Scuti Star Newsletter 11, 10 (University
of Vienna)

Kov\'acs, G., 1981, {\it Ap\&SS}, {\bf 78}, 175

Schneider, H., 1986, A\&A 161, 203

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