COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3651 Konkoly Observatory Budapest 26 August 1991 HU ISSN 0374 - 0676 RAPID SPECTROSCOPIC VARIABILITY IN BE STARS The advent of high signal-to-noise solid state detectors has led to the discovery of short timescale variability (~tens of minutes) in absorption line profiles of a wide variety of stars (e.g. Smith, 1991 and references therein). The variability consists of weak (less than 1% of continuum) absorption features moving from blue to red across the line profiles ("moving bumps"). The phenomenon was first detected in a Be star (zeta Oph) by Walker et al. (1979). The bumps are often variable in intensity: a bump sometimes disappears or a new one appears were none existed. They are not evenly spaced across the line profile and different bumps may have different rates of travel ("accelerations"). The visibility of the bumps varies from time to time and in Be stars may be correlated with veiling by circumstellar matter (Smith et al., 1991). The moving bump phenomenon is generally interpreted as the photospheric manifestation of high-order (|m| > 4) sectorial modes of nonradial pulsations (NRP). Recently, Balona (1990) proposed another explanation in terms of rotational modulation (RM) of spots colder than the surrounding photosphere. The two models are virtually observationally undistinguishable: they fit equally well non-simultaneous spectroscopic and photometric data. In any case, it seems quite probable that some kind of surface magnetic activity is involved in Be variations of timescale < day (Smith, 1991). The NRP vs. RM controversy can only be decided with the help of simultaneous (or, at least contemporary) multi-technique observations (e.g. Balona, 1991). We have started in 1990 a search for moving in the HeI lambda 667.8 nm of (mainly) southern, bright Be stars. The objects of our sample have been selected on the basis of confirmed or suspected photometric variability (Cuypers at al., 1889; Balona, 1991). High resolution (R >= 30,000), high signal-to-noise ratio (S/N >= 300) spectroscopic observations have been performed at the Brazilian Laboratorio Nacional de Astrofisica with a CCD camera attached to the coudé spectrograph of the 1.6 m telescope. Ten stars have been observed in various epochs (Table 1). [FIGURE 1] Moving bumps have been detected for the first time in eta Cen (Janot-Pacheco et al., 1990). Figure 1 shows the residuals (individual minus average spectra sequence) for this star obtained March 12, 1990. Some bumps are indicated. Moving subfeatures were also seen in zeta Oph and eta Cen, and possibly in gamma Arae and zeta Ori. From the average spacing and acceleration of the bumps one can derive the order of the spectral NRP mode supposed to be responsible for the variations (e.g. Yang et al. 1988). TABLE I EPOCH OF STAR OBSERVATIONS BUMPS alpha Eri June 1990 A lambda Eri Nov 1990 ? zeta Ori Apr 1991 D? kappa Ori Apr 1991 A? alpha Col Apr 1991 ? kappa CMa Mar 1990 ? mu Cen June 1990 C eta Cen Mar,Jun 1990 Apr 1991* D zeta Oph June 1990 C gamma Arae June 1990 D? A=Absent ; D= Detected ; C=Confirmed ; * International campaign For eta Cen and zeta Oph, our observations are consistent with order l=|m|~20. Janot-Pacheco et al. (1991) have shown that the photometric behaviour of eta Cen in 1988 can only be reproduced with the RM model by a judicious sequence of dark and bright spots, which is incidentally reminiscent the sectorial type. Anyone who has photometric or other data of the stars in Table 1 in 1990 or 1991, or who are interested in the problem exposed here is welcome to join us in a collaboration. A better understanding of the physics behind the rapid variations shown by Be stars will also throw light over the "Be phenomenon" problem. E. JANOT-PACHECO and N.V. LEISTER Instituto Astronomico e Geofisico Universidade de Sao Paulo C. Postal 9638 CEP 01065 Sao Paulo SP/Brasil A.M. HUBERT, M. FLOQUET and H. HUBERT Observatoire de Paris - Meudon 92145 Meudon - France References Balona, L.A., 1990, M.N.R.A.S. 245, 92 [BIBCODE 1990MNRAS.245...92B ] Balona, L.A., 1991, Be Stars Newsletter 24, 5 (ESO) [BIBCODE 1991BeSN...24....5B ] Cuypers, J., Balona, L.A. and Marang, F., 1989, Astron. Astrophys. 81, 151 [BIBCODE 1989A&AS...81..151C ] Janot-Pacheco, E., Leister, N.V., Torres, C.A.P.C.O., Quast, G.R. and Campos, R.P. 1990, IAU Circular no. 5048 [BIBCODE 1990IAUC.5048....2J ] Janot-Pacheco, E., Leister, N.V., Quast, G.R., and Torres, C.A.P.C.O., 1991, in ESO Workshop "Rapid variability of OB- Stars: Nature and Diagnostic Value", D. Baade (Ed.) p. 45 [BIBCODE 1991ESOC...36...45J ] Smith, M.A., 1991, Be Stars Newsletter 24, 8 (ESO) [BIBCODE 1991BeSN...24....8S ] Smith, M.A., Peters, G.J. and Grady, C.A., 1991, Ap. J. 367, 784 Walker, G.A.H., Yang, S. and Fahlman, G.G., 1979, Ap. J. 233, 199 [BIBCODE 1979ApJ...233..199W ] Yang, S., Ninkov, Z. and Walker, G.A.H., 1988, P.A.S.P. 100, 233 [BIBCODE 1988PASP..100..233Y ]