COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3966 Konkoly Observatory Budapest 27 December 1993 HU ISSN 0374 - 0676 DISCOVERY OF 10.5-MINUTE OSCILLATIONS IN THE Ap SrEu STAR HD 9289 Martinez (1993) has obtained Stromgren photometry for all of the Ap SrCrEu stars in the first four volumes of the Michigan Spectral Catalogue, along with selected stars classified by Bidelman & MacConnell (1973) north of declination -12d. Using this photometry we have been conducting a systematic survey for new rapidly oscillating Ap (roAp) stars. In this note we announce the 11th one found as part of the survey, the 26th now known. Table 1. The 26 rapidly oscillating Ap stars HD y b-y m_1 delta m_1 c_1 delta c_1 beta 6532 8.445 0.088 0.214 -0.014 0.879 -0.051 2.880 9289 9.383 0.138 0.225 -0.018 0.826 -0.012 2.833 12932 10.235 0.179 0.228 -0.024 0.765 -0.035 2.810 19918 9.336 0.169 0.216 -0.010 0.822 -0.058 2.855 24712 6.001 0.191 0.211 -0.023 0.626 -0.074 2.760 42659 6.768 0.124 0.257 -0.050 0.765 -0.076 2.834 60435 8.891 0.136 0.240 -0.034 0.833 -0.047 2.855 80316 7.782 0.118 0.324 -0.118 0.599 -0.283 2.856 83368 6.168 0.159 0.230 -0.024 0.766 -0.062 2.825 84041 9.330 0.177 0.233 -0.026 0.797 -0.061 2.844 101065 7.994 0.431 0.387 -0.204 0.002 -0.370 2.641 119027 10.022 0.257 0.214 -0.034 0.557 -0.076 2.731 128898 3.198 0.152 0.195 0.012 0.760 -0.077 2.831 134214 7.464 0.216 0.223 -0.029 0.620 -0.108 2.774 137949 6.673 0.196 0.311 -0.105 0.580 -0.236 2.818 150562 9.816 0.301 0.212 -0.015 0.659 -0.087 2.783 161459 10.326 0.245 0.246 -0.040 0.679 -0.141 2.820 166473 7.923 0.208 0.321 -0.118 0.514 -0.268 2.801 176232 5.89 0.150 0.208 -0.004 0.829 0.031 2.809 190290 9.912 0.289 0.293 -0.091 0.466 -0.306 2.796 193756 9.195 0.181 0.213 -0.008 0.760 -0.040 2.810 196470 9.721 0.211 0.263 -0.059 0.650 -0.144 2.807 201601 4.68 0.147 0.238 -0.032 0.760 -0.058 2.819 203932 8.820 0.175 0.196 0.004 0.742 -0.020 2.791 217522 7.525 0.289 0.227 -0.056 0.484 -0.015 2.691 218495 9.356 0.114 0.252 -0.049 0.812 -0.098 2.870 HD 9289 was classified by Bidelman & MacConnell (1973) as Ap SrEu. Martinez (1993) measured V = 9.383, b-y = 0.138, m_1 = 0225, c_1 = 0.826 and beta = 2.833. The calculated metallicity and luminosity indices are deltam_1 = -0.018 and deltac_1 = -0.012, both of which indicate strong metallicity and heavy line-blocking in the v band - characteristics we have come to associate with roAp stars. The dereddened Stromgren indices, [m_1 ] = 0.250 and [c_1 ] = 0.798, lead to [delta m_1 ] = -0.043 and [delta c_1 ) = -0.046 which even more strongly suggests to us a roAp star. In Table 1 we list the 26 known roAp stars along with their Stromgren indices. [FIGURE 1] [FIGURE 2] On the night of 27/28 August 1993 we obtained 2 hours of continuous 10-s photometric integrations of HD 9289 through a Johnson B filter using the 1-m telescope of the Sutherland Station of the South African Astronomical Observatory. The observations were corrected for coincidence losses, sky brightness, extinction and reduced to 40-s integrations. Fig. 1 shows the light curve for those two hours and Fig. 2 shows the amplitude spectrum. The 10.5-min oscillations are obvious in both. No comparison star was used, but sky transparency variations, scintillation, and photon statistics produced noise of a maximum amplitude of about 0.7 mmag at the frequencies of interest, as can be seen in the amplitude spectrum. We have continued to observe this star and, as of this writing, have over 70 hours of observations obtained on 17 nights. The amplitude of the light curve is strongly modulated. The star is multiperiodic and may also show rotational amplitude modulation. We will continue to observe it for the rest of this season, then present a complete frequency analysis. HD 9289 appears to be of considerable asteroseismological interest. D. W. Kurtz & Peter Martinez Department of Astronomy University of Cape Town Rondebosch 7700 South Africa References Bidelman, W. P., & MacConnell, D. J., 1973, AJ, 78, 687 [BIBCODE 1973AJ.....78..687B ] Houk, N., 1978, Michigan Spectral Catalogue, vol. 2, Department of Astronomy, University of Michigan, Ann Arbor [BIBCODE 1978mcts.book.....H ] Houk, N., 1982, Michigan Spectral Catalogue, vol. 3, Department of Astronomy, University of Michigan, Ann Arbor [BIBCODE 1982mcts.book.....H ] Houk, N., & Smith-Moore, M., 1988, Michigan Spectral Catalogue, vol. 4, Department of Astronomy, University of Michigan, Ann Arbor [BIBCODE 1988mcts.book.....H ] Houk, N., & Cowley, A. P., 1975, Michigan Spectral Catalogue, vol. 1, Department of Astronomy, University of Michigan, Ann Arbor [BIBCODE 1975mcts.book.....H ] Martinez, P., 1993, Ph. D. Thesis, University of Cape Town [BIBCODE 1993PhDT.......246M ]