Circular No. 4273 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Postal Address: Central Bureau for Astronomical Telegrams Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. TWX 710-320-6842 ASTROGRAM CAM Telephone 617-495-7244/7440/7444 PERIODIC COMET HALLEY (1982i) Z. Sekanina, Jet Propulsion Laboratory, California Institute of Technology, writes: "The approximation of P/Halley's nucleus by a torque-free rigid spheroid, which is homogeneous and has axial ratios of 1.9:1.0:1.0, reconciles the two reported recurrence periods as follows. The 2.2-day period (IAUC 4151; also Sekanina 1986, Adv. Space Res. 5, No. 12, 307) is the precession period of the long axis about a fixed direction. The 7.4-day period (Millis and Schleicher 1986, Nature, in press) is identified with the rotation period about this axis. The moments of inertia require that the precession angle (the semiamplitude of the precessional motion) be 77 deg, implying a 26 deg full-amplitude wobble for what had been interpreted as the 'spin axis'. This model offers attractive explanations for various aspects of the observed phenomena ( including the jet evolution) that had been rather puzzling, but it involves an element of instability (a prolate spheroid). The possibility was investigated that the 7.4-day period is a composite of the 2.2-day period and an intrinsic period of rotation about the long axis, but no satisfactory solution was found. A more detailed study is being submitted to Nature." LSI +65 010 E. Faverey, M. H. van Kerkwyk and E. P. J. van den Heuvel, Astronomical Institute, University of Amsterdam, telex: "Reticon spectra (dispersion 6 nm/mm, wavelength range 380-540 nm) obtained with the Calar Alto 1.2-m telescope show that strong Balmer absorption lines suddenly appeared in the spectrum of LSI +65 010 (2S 0114+650, spectral type B0IIIe) from Nov. 4 onwards. During Oct. 31-Nov. 3, the same lines were weak, as usual (cf. Crampton et al. 1985, Ap.J. 299, 839), with central depths not exceeding 15 percent at our resolution. On Nov. 4.91, 5.08, 5.10 and 5.89 UT the relative central depths were larger than 30 percent, and the equivalent widths had increased by a factor of ~ 3 with respect to those of the previous week. As this strongly suggests that the Be component of this x-ray binary has entered a mass-ejection (shell) phase, x-ray astronomers are urged to observe this source, for an increase of the x-ray intensity of the neutron-star component is expected. Photometric observations are also needed." 1986 November 17 (4273) Brian G. Marsden
Our Web policy. Index to the CBAT/MPC/ICQ pages.