COMMISSION 27 OF THE I. A. U.
                  INFORMATION BULLETIN ON VARIABLE STARS
                              Number 3510

                                                         Konkoly Observatory
                                                         Budapest
                                                         27 August 1990

                                                         HU ISSN 0374 - 0676


           HD 190290 - ASTEROSEISMOLOGY IN ONE NIGHT

The Southern (Dec.=-79deg) 10th mag star HD 190290 classified as Ap EuSr by
Houk & Cowley (1975) was recently placed on our program to search for rapid
oscillations in cool southern Ap stars. On the night of 4/5 August 1990 (JD
2448108) we observed this star photometrically for 8.85 hr in high-speed mode
with the University of Cape Town Photometer attached to the 1.0-m Elizabeth
telescope of the South African Astronomical Observatory (SAAO). We acquired
continuous 10-s integrations through a Johnson B filter and a 30-arcsec
aperture. The data were corrected for coincidence counting losses, sky
background, mean extinction and some long period trends which almost certainly
arose from sky transparency variations. We then binned the data to 40-s
integrations and computed an amplitude spectrum using Kurtz (1985) recursive
coding of Deeming's (1975) widely used Discrete Fourier Transform for unequally
spaced data.
   In Figure 1 (a) we present the amplitude spectrum of these observations
out to the Nyquist frequency of 12.5 mHz for 40-s integrations. We include
the sky transparency variations in Fig. 1(a) so that the reader may form a
value judgement of the data. The photometric quality of that night was
excellent; one must bear in mind that the lowest airmass attained by this
Dec.=-79d star at SAAO is 1.4.
   The prominent peak in Fig 1(a) is at nu_1=2.27 mHz with an amplitude 1.13
mmag. In order to test for further frequencies in the data we subtracted a
sinusoid of frequency nu_1 from the data. The resulting amplitude spectrum in
Fig. 1(b) clearly indicates the presence of another frequency at nu_2 =2.23 mHz
with an amplitude of 0.55 mmag. On prewhitening both nu_1 and nu_2 from the
data, we are left with the spectrum shown in Fig. 1(c) which suggests the
presence of further frequencies but we cannot meaningfully pursue the
identification of further frequencies with these data.
   The frequency separation between nu_1 and nu_2 is 40 microHz. This cannot be a
rotation frequency because it would correspond to a rotation period of 6.9 hr,
improbably short for an A star. We thus interpret this spacing as a crude
measurement of the asymptotic p-mode spacing in HD 190290 consistent with
values observed in other roAp stars. Of course, a thorough frequency analysis
is required in order to refine our frequency determinations and to find the
other frequencies which probably exist in this star.


                               [FIGURE 1]



                                                PETER MARTINEZ
                                                D.W. KURTZ

                                                Dept. of Astronomy
                                                University of Cape Town
                                                Rondebosch, 7700
                                                South Africa



References

Houk, N & Cowley, A.P., 1975. Michigan Spectral Catalogue of
   Two-Dimensional Spectral Types for the HD Stars Volume 1, Dept of
   Astronomy, University of Michigan. [BIBCODE 1975mcts.book.....H ]
Deeming, T.J., 1975. Astrophys. Space Sci., 36,137. [BIBCODE 1975Ap&SS..36..137D ]
Kurtz, D.W., 1985. Mon. Not. R. astr. Soc., 213, 773. [BIBCODE 1985MNRAS.213..773K ]