COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3424 Konkoly Observatory Budapest 24 January 1990 HU ISSN 0374 - 0676 RAPID SHELL LINE VARIATIONS IN THE Be STAR omega Ori The Be star omega Ori (HD 37490, according to Slettebak, 1982: B2 IIIe, v sin i = 160 km/sec), has a long history of irregular variability in Balmer line emissions (Dachs et al., 1977, 1981; Slettebak and Reynolds, 1978; Hubert-Delplace and Hubert, 1979; Andrillat and Fehrenbach, 1982). In the framework of our interest in short-period variability of Be stars, we performed 36 spectroscopic Reticon observations of this object during two nights (Dec. 11 and Dec.. 12, 1986), using a B and C mod. 31523 grating spectrograph combined with the 182 cm telescope of the Osservatorio Astronomico di Asiago. We chose a spectral range including H-alpha and the HeI 6678 A line, and an inverse dispersion of about 18 A/mm. In H-alpha the shell components covered the photospheric one, while only two faint emission features affected the HeI line wings. Anyway, both in H-alpha and in HeI line, the shell profiles showed unequivocal variations during our observational period. Figure 1 and Figure 2 represent the evolution of H-alpha and HeI line profiles respectively during our second observation night (for reasons of graphic clearness, we include in these pictures only 10 spectrograms out of 23). The behaviour of some line parameters is also shown in Table I (the wavelength difference between emission component and shell absorption, with the respective equivalent widths, for H-alpha: the absorption equivalent width and the V/R ratio of the emission features for the HeI line). Typical error bars are about 0.015 A for lambda-e - lambda-a , 0.05 A for E.W.e (H-alpha), 0.025 A for E.W.a (H-alpha), 0.015 A for E.W.a (HeI) and 0.08 for V/R: all the detected variations have to be considered real. Moreover, all the patterns shown in Table I are consistent with the probable 1-day photometric period proposed by Balona et al. (1987). The detection of possible rapid shell variations in Be stars is not a novelty: we can consider, for instance, the case of Zeta Tau (Bossi et al., 1987). Nevertheless, our good signal-to-noise ratio allows us, perhaps for the first time, to be sure about the reality of this phenomenon. The time scales of this kind of variability are consistent with the hypothesis of high order pulsations only. On the other hand, if we consider again Zeta Tau, only high order shell pulsations can explain the H-alpha profiles shown by Hanuschik et al. (1988). [FIGURE 1] [FIGURE 2] Table I H-alpha He I 6678 JD lambda_e-lambda_a EW_e EW_a EW_a V/R 2440000+ (A) (A) (A) (A) 6776.4227 0.009 9.963 1.621 0.724 1.07 6776.4331 0.000 9.983 1.631 0.675 0.86 6776.4387 0.004 9.925 1.632 0.670 0.91 6776.4491 0.004 9.992 1.622 0.674 1.01 6776.4553 -0.003 9.994 1.603 0.690 0.83 6776.4651 -0.004 9.973 1.572 0.643 0.86 6776.4713 -0.003 9.951 1.579 0.661 0.83 6776.4984 0.002 10.021 1.591 0.647 0.97 6776.5081 0.001 10.065 1.621 0.645 0.92 6776.5144 0.002 10.047 1.600 0.645 0.79 6776.5248 0.005 10.029 1.642 0.719 0.78 6776.5303 0.005 10.013 1.631 0.672 1.24 6776.5408 0.000 10.048 1.665 0.626 1.15 6777.3102 -0.029 9.906 1.748 0.539 0.61 6777.3206 -0.032 9.929 1.739 0.515 0.75 6777.3276 -0.030 9.954 1.719 0.514 0.70 6777.3380 -0.028 9.918 1.743 0.537 0.73 6777.3442 -0.029 9.946 1.769 0.530 0.61 6777.3546 -0.022 9.965 1.764 0.517 0.82 6777.3616 -0.017 9.979 1.762 0.517 0.67 6777.3720 -0.018 9.964 1.765 0.508 0.62 6777.3776 -0.017 9.973 1.774 0.515 0.68 6777.3880 -0.014 9.988 1.763 0.526 0.72 6777.4116 -0.006 9.967 1.757 0.580 0.79 6777.4220 -0.005 9.997 1.771 0.585 0.81 6777.4276 -0.006 10.020 1.784 0.600 0.85 6777.4380 -0.003 10.021 1.766 0.599 0.88 6777.4498 -0.002 10.046 1.772 0.644 0.88 6777.4602 0.001 10.086 1.822 0.638 1.08 6777.4658 -0.003 10.088 1.814 0.664 1.00 6777.4762 0.005 10.100 1.811 0.646 0.91 6777.4824 0.010 10.135 1.825 0.700 1.04 6777.4935 0.019 10.136 1.809 0.700 1.01 6777.5067 0.021 10.174 1.847 0.688 1.08 6777.5171 0.024 10.158 1.839 0.704 1.10 6777.5234 0.027 10.178 1.859 0.755 1.12 M. BOSSI, G. GUERRERO, M. SCARDIA and A. STASI Osservatorio Astronomico di Brera, Via Bianchi 46, I-22055 Merate CO, Italy References: Andrillat, Y., Fehrenbach, C.: 1982, Astron. Astrophys. Suppl. 48, 93. [BIBCODE 1982A&AS...48...93A ] Balona, L.A., Marang, F., Monderen, P., Reitermann, A., Zickgraf, F.-J.: 1987, Astron. Astrophys. Suppl. 71, 11. [BIBCODE 1987A&AS...71...11B ] Bossi, M., Guerrero, G., Scardia, M.: 1987, "Physics of Be Stars" Proceedings of the 92nd IAU Colloquium, A. Slettebak and T.P. Snow ed., Cambridge University Press. [BIBCODE 1987pbes.coll...99B ] Dachs, J. Maitzen., H.-M. Moffat, A.F.J., Sherwood, W.A., Stift, M.: 1977, Astron. Astrophys. 56, 417. [BIBCODE 1977A&A....56..417D ] Dachs, J., Eichendorf, W., Schleicher, H., Schmidt-Kaler T., Stift, M., Tug, H.: 1981, Astron. Astrophys. Suppl. 43, 427. [BIBCODE 1981A&AS...43..427D ] Hanuschik, R.W., Kozok, J.R., Kaiser, D.: 1988, Astron. Astrophys. 189, 147. [BIBCODE 1988A&A...189..147H ] Hubert-Delplace, A.M., Hubert, H.: 1979, "An. Atlas of Be Stars", Paris, Observatoire de Meudon. [BIBCODE 1979aabs.book.....H ] Slettebak, A., Reynolds, R.C.: 1978, Astrophys. J. Suppl. 38, 205. [BIBCODE 1978ApJS...38..205S ] Slettebak, A.: 1982, Astrophys. J. Suppl. 55, 50. [BIBCODE 1982ApJS...50...55S ]