The ortho and para fractions of molecular hydrogen in protostellar outflows and Herbig-Haro objects

Smith, M.D. and Davis, C.J. and Lioure, A. (1997) The ortho and para fractions of molecular hydrogen in protostellar outflows and Herbig-Haro objects. Astronomy and Astrophysics, 327 (3). pp. 1206-1214. ISSN 0004-6361. (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Abstract

Hydrogen molecules exist in two forms, according to the alignment of the nuclear spins. We present an accurate method for extracting the distributions of the two forms from three K-band infrared transitions. Images of the 1-0 S(0), S(1) and S(2) emission lines yield the ortho and para spatial distributions with negligible extinction and model dependence. The ortho-para ratio from individual pointings to various Herbig-Haro outflows are (re-)calculated using our analytical approach. All accurate determinations yield a value between 2.5 and 3.0. The vibrational temperature remains in the range 2000-2500 K although rotational temperatures vary between 1100-2100 K. Applied to new data for OMC-1, we find no strong evidence for spatial variations in the ortho/para ratio (3.0 ± 0.4) on all scales down to 1″. The vibrationally-excited molecules have either (1) not been modified since their formation in a warm state or (2) have reached equilibrium through conversions within a warm state. Collisional excitation to the first vibrational level dominates, with no fluorescent component. We suggest that collisions with atomic hydrogen in the warm shock layers converts the ortho-para ratio to 3 locally. We also find strong evidence for spatial variations in the rotational excitation in OMC-1: the rotational temperature increases from east to west.

Item Type: Article
Uncontrolled keywords: Infrared: molecular processes, ISM: jets and outflows, ISM: kinematics and dynamics, ISM: lines, ISM: molecules, ISM: OMC 1
Subjects: Q Science > QB Astronomy > QB460 Astrophysics
Divisions: Faculties > Sciences > School of Physical Sciences > Centre for Astrophysics and Planetary Sciences
Depositing User: Giles Tarver
Date Deposited: 11 Aug 2015 10:32 UTC
Last Modified: 12 Aug 2015 16:06 UTC
Resource URI: https://kar.kent.ac.uk/id/eprint/50150 (The current URI for this page, for reference purposes)
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