Stefi A. Baum

A VLA search for 2-cm continuum radiation from Comet Halley

Abstract We used the VLA2 to search for continuum emission from icy grains in a halo around Comet Halley in mid November 1985. We found the 3σ upper limit to the 2-cm flux density from the comet to be 1 × 10−4 Jy, which is consistent with the detections at 1.3 and 3.5 mm by W.J. Altenhoff et al. (1986, Astron. Astrophys., in press) only if the emission comes from particles which do not radiate efficiently at centimeter wavelengths. These particles could be slightly dirty submillimeter-sized icy grains or small refractory grains.

A search for the millimeter-wave transitions of CO+ in comet P/Halley

Abstract We searched for the N = 2 to 1, J = 5/2 to 3/2, and J = 3/2 to 1/2 millimeter-wave transitions of CO + in Comet P/Halley. No detection was made, but we obtained a 2σ upper limit to the beam averaged column density of CO + in the coma of 8 × 10 11 cm −2 . We compare this upper limit to predictions from models which vary parameters such as the chemical composition and ionization mechanisms and conclude that: (1) H 2 O is likely to be main constituent of the nucleus of Comet Halley, (2) if photodissociative ionization is active in the coma of Comet Halley, then most of the CO + probably originates in CO 2 , rather than CO, and (3) the effective radius for outgassing of the nucleus of Comet Halley was less than 10 km at the time of our observations.

Detailed Spectroscopic Investigation of Emission-Line Nebulae Associated with Cooling Flows

High resolution longslit spectra have been used to study the dynamical, physical, and chemical properties of the emission-line nebulae associated with seven cluster cooling flows. We find that the gas is much more centrally concentrated than implied by the radial accretion profile inferred from the X-ray data. The kinematics show little evidence for ordered large-scale shears or rotation, but are consistent with infall and/or turbulence. Gas pressures on scales of 1-10 kpc are about 10 times larger than X-ray pressures on larger scales and the radial pressure profiles vary significantly among the different nebulae. We present several lines of evidence favoring shock-heating over photoionization. In particular, we can conclusively rule out photoionization by a dilute nuclear continuum source. Several models for the heating of the nebulae are briefly explored. Two classes of nebulae with different chemical abundances have been identified. Finally, we stress the physical relationship between the nebulae and the coterminous nonthermal radio plasma.