Line profiles of molecular ions toward the pre-stellar core LDN 1544
Abstract
Velocity profiles of ground state lines of H2D+, HC18O+ and N2H+, observed previously with the CSO and IRAM 30m telescopes, are modeled with a Monte Carlo radiative transfer program to study the temperature, density and velocity structure of the pre-stellar core LDN 1544. The H2D+ line is double-peaked like that of the other ions, but previous models that fit the HC18O+ and N2H+ profiles are found not to fit the H2D+ data. Matching the H2D+ observations requires at least three modifications to the model at small radii: (1) the density profile must continue to rise inward and not flatten off toward the center; (2) the gas temperature must be nearly constant and not drop inwards significantly; (3) the infall velocity must increase inward, in a fashion intermediate between `quasi-static' (ambipolar diffusion) and `fully dynamic' (Larson-Penston) collapse. The C18O emission indicates a chemical age of <~0.1 Myr. The effects of a flattened structure and rotation on the line profiles are shown to be unimportant, at least on the scales probed by single-dish telescopes. Alternatively, the H2D+ profile is affected by absorption in the outer layers of the core, if gas motions in these layers are sufficiently small.
Cite
@article{arxiv.astro-ph/0505072,
title = {Line profiles of molecular ions toward the pre-stellar core LDN 1544},
author = {F. F. S. van der Tak and P. Caselli and C. Ceccarelli},
journal= {arXiv preprint arXiv:astro-ph/0505072},
year = {2009}
}
Comments
Accepted by A&A; 10 pages, 10 colour figures