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\IBVShead{4507}{13 August 1997} 
 
\IBVStitle{HD~213637 IS A RAPIDLY OSCILLATING A\lowercase{p} STAR} 
 
\IBVSauth{Peter Martinez$^1$, P.\ J.\ Meintjes$^2$, S.\ J.\ Ratcliff$^2$} 
 
\IBVSinst{South African Astronomical Observatory, P.O.\ Box 9, 
Observatory 7935, South Africa, email: peter@saao.ac.za} 
 
\IBVSinst{Department of Physics \& Astronomy, University of the Free 
State, Bloemfontein 9300, South Africa} 

\IBVSabs{Discovery of a new RoAP star HD 213637 is reported.}

\SIMBADobj{HD213637}
\IBVStyp{ ACVO }
\IBVSkey{photometry, RoAP}
 
 
\begintext 
 
The rapidly oscillating Ap (roAp) stars are cool, magnetic, chemically 
peculiar A-type stars that pulsate with periods in the range 6--16 
minutes and Johnson $B$ semi-amplitudes $\le 0.008$ mag.  The observed 
characteristics of the roAp phenomenon have been reviewed by Martinez 
and Kurtz (1995) for the 28 confirmed roAp stars known at the time of 
that writing.  This Bulletin announces the discovery of the 29th roAp 
star, HD~213637. 

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\IBVSfig{11cm}{4507-f1.ps}
 
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HD~213637 is classified by Houk \& Smith-Moore (1988) as A(p EuSrCr). 
Martinez (1993) determined its Str\"omgren indices to be $V$=9.611, 
$b-y=0.298$, $m_1=0.206$, $c_1=0.411$ and $\beta=2.670$.  Our 
attention was particularly drawn to the calculated metallicity and 
luminosity indices, $\delta m_1=-0.035$ and $\delta c_1 = -0.031$, 
both of which indicate strong metallicity and line blocking in the $v$ 
band.  As these are characteristics that we associate with the roAp 
stars, we decided to search for rapid oscillations in HD~213637.  Our 
observations comprised continuous 10-s integrations in Johnson $B$ 
light acquired with the Radcliffe Peoples Photometer attached to the 
0.75-m telescope of the South African Astronomical Observatory at 
Sutherland. 
 
Rapid oscillations were discovered in HD~213637 on the night of 26/27 
July 1997, JD~2450656.  Fig.\ 1 shows the discovery light curve (top) 
and its amplitude spectrum (bottom).  The data shown here have been 
corrected for coincidence counting losses, sky background and 
extinction, and were then binned to 40-s integrations.  The 
oscillations, which are barely discernible in the light curve, are 
more evident in the Fourier representation of the data in the lower 
panel.  The amplitude spectrum peaks strongly at a frequency of 
1520$\pm220$~$\mu$Hz, corresponding to a pulsation period of 11 
minutes.  Subsequent to the discovery of these pulsations a number of 
additional confirmatory light curves were acquired.  Inspection of the 
available light curves indicates the presence of amplitude modulation, 
which may be caused by beating among several frequencies and/or 
non-radial pulsations being seen from variable aspect as the star 
rotates.  Further observations and an analysis of those observations 
will be presented in a future publication. 
 
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\references 
 
Houk, N., Smith-Moore, M., 1988, {\em Michigan Spectral Catalogue of 
Two-Dimensional Spectral Types for the HD Stars} - Volume 4, 
Department of Astronomy, University of Michigan, Ann Arbor, Michigan. 
 
Martinez, P., 1993, Ph.D.\ Dissertation, University of Cape Town. 
 
Martinez, P., Kurtz, D.W., 1995, A.S.P.\ Conf.\ Ser.,\ {\bf 83,} 58--69., 
In: Astrophysical Applications of Stellar Pulsation, Eds.\ R.S.\ Stobie, 
P.A.\ Whitelock
%Modified: Wed Sep 28 10:14:35 MEST 2005
 
\endreferences 
 
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