Studies of the local interstellar medium. VIII - Morphology and kinematics of the diffuse interstellar clouds toward Orion

• Published in: The Astrophysical journal Vol. 364; no. 2; pp. 540 - 548
• Main Authors: Frisch, P. C., Sembach, K., York, D. G.
• Format: Journal Article
• Language: English
• Published: Legacy CDMS University of Chicago Press 01.12.1990
• Subjects: Astronomy; Astrophysics; Earth, ocean, space; Exact sciences and technology; Interstellar medium (ism) and nebulae in milky way; Molecular clouds, h2 clouds, dense clouds, and dark clouds; Stellar systems. Galactic and extragalactic objects and systems. The universe; Interstellar cloud; Diffuse interstellar cloud; Equivalent width; Orion nebula; Spectral line; Column density; Diffuse source; Spatial distribution; Stellar population; Morphology; Kinematics; Data table; Optical observation; Radial velocity; Interstellar matter
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/169435

Interstellar clouds in the direction of the Orion association show only positive velocities for target stars within 190 pc of the sun, and both positive and negative velocities for more distant target stars, confirming an earlier prediction by Cowie, Songaila, and York (1979). The nearby positive velocity cloud, designated here as Orion-Lepus 70 (OL 70), is a standard diffuse interstellar cloud: it is subject to the ambient galactic radiation field, with properties consistent with T about equal to 100 K and n about equal to 3/cu cm. Combined with a column density log N(H) = 19.8-20.0/sq cm, these values imply a cloud thickness of about 7 pc. The kinematics of OL 70 are consistent with either an origin as part of the expanding Loop I superbubble shell, or as part of Lindbald's expanding ring, or a synthesis of the two models. The negative velocity interstellar components seen in stars at d not less than 200 pc are caused by interstellar matter accelerated by the expanding Ori-Eri superbubble. Relatively dense interstellar gas at positive LSR velocities is also found within the Orion association, so that it is difficult to pick out OL 70 components in the spectra of the distant stars.