COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3621    

                                             Konkoly Observatory
                                             Budapest
                                             10 June 1991

                                             HU ISSN 0374 - 0676


      DISCOVERY OF RAPID OSCILLATIONS IN THE Ap STAR HD 84041


The rapidly oscillating Ap (roAp) stars are magnetic Ap SrCrEu stars which
exhibit low-amplitude (A<=8 mmag semi-amplitude) rapid broadband light
oscillations with periods in the range P=4-16 min. These light oscillations
are interpreted as low degree (l<=3), high overtone (n>>l) p-mode pulsations.
The most comprehensive recent review of these variables is that of Kurtz
(1990). Shortly after Kurtz's review was written, we commended a systematic
survey of the roAp phenomenon in the Southern sky. The Cape Rapidly
Oscillating Ap Star Survey has already led to the discovery of six new roAp
stars (Martinez el al. 1991, Martinez & Kurtz 1991). We present here the
seventh roAp star to be discovered in our survey, HD 84041.

On the night JD2448335 we acquired 1.02 hr of high-speed photometry of HD84041
which suggested the presence of rapid oscillations with a frequency of 1.1 mHz
and an amplitude of about 1.2 mmag. To confirm our detection of rapid
oscillations, we observed this star again on the nights JD2448354, 8355, 8358,
8359, 8362 and 8377. The observations were acquired with various 0.5-m, 0.75-m
and 1.0-m telescope/photometer combinations at the Sutherland site of the South
African Astronomical Observatory. All observations consisted of continuous
10-s integrations through a Johnson B filter. Our usual observing and
reduction procedures are described in detail by Martinez et al. (1991). The
data were all Fourier analyzed in individual nights, in groups of closely
spaced nights, and as a whole. There are reasonably convincing indications of
amplitude modulation among the nightly data sets, and even on a time-scale
shorter than a night, but space does not permit us to present these frequency
analyses here. These analyses suggest that the oscillations in HD 84041 are
multi-periodic.


                            [FIGURE 1]
                            [FIGURE 2]


In Fig. 1 we present light curve acquired on night JD2448377. The amplitude
spectrum of this light curve is shown in Fig. 2, in which the peak of interest
is the one labeled nu_1 at 1.14 mHz. The solid line in Fig. 1 is a fit of a
sinusoid of frequency nu_1=1.14 mHz to the data. The peaks to the left of nu_1
in Fig. 2 are caused by sky transparency variations during the observations.
These sky transparency variations have been removed in Fig. 1 to facilitate
the reader's perception of the oscillations. There arc several non-cosmetic
reasons why these peaks must be removed in the frequency analyses, but we have
left them in Fig. 2 so that the reader may judge the data. The noise at
frequencies nu_1>=0.8 mHz, the scintillation noise, is quite high in Fig. 1
because these observations were acquired using an 0.5-m telescope. Ironically,
these are some of the best signal-to-noise data we have!  As Fig. 2 shows, at
nu_1=1.1 mHz, the oscillations are not clearly in the frequency regime
dominated by scintillation noise and this complicates the study of the rapid
oscillations in this star. A more detailed analysis of the rapid oscillations
of HD 84041 will be presented in a future publication.


PETER MARTINEZ
Dept of Astronomy
University of Cape Town
Rondebosch,7700
South Africa
PETER @ UCTVAX.UCT.AC.ZA
PETER.UCTVAX @ F4.N494.Z5.FIDONET.ORG

References

Kurtz, D.W., 1990. Annual Reviews of Astronomy & Astrophysics, 28, 607. [BIBCODE 1990ARA&A..28..607K ]
Martinez, P., Kurtz, D.W. & Kauffmann, G., 1991. Mon. Not. R. astr. Soc., in
   press. [BIBCODE 1991MNRAS.250..666M ]
Martinez, P. & Kurtz, D.W., 1991. Inf. Bull. Var. Stars, 3553.