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Line profiles of molecular ions toward the pre-stellar core LDN 1544 | | F. F. S. van der Tak
; P. Caselli
; C. Ceccarelli
; | | Date: |
4 May 2005 | | Subject: | astro-ph | | Affiliation: | MPIfR, Bonn), P. Caselli (Osservatorio di Arcetri), C. Ceccarelli (Observatoire de Grenoble | | 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. | | Source: | arXiv, astro-ph/0505072 | | Services: | Forum | Review | PDF | Favorites | |
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