The Perseus B5 molecular cloud halo: Measurements of pressure, temperature, and composition

Citation
P. Wannier et al., The Perseus B5 molecular cloud halo: Measurements of pressure, temperature, and composition, ASTROPHYS J, 510(1), 1999, pp. 291-304
Citations number
50
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004637X → ACNP
Volume
510
Issue
1
Year of publication
1999
Part
1
Pages
291 - 304
Database
ISI
SICI code
0004-637X(19990101)510:1<291:TPBMCH>2.0.ZU;2-G
Abstract
We present GHRS observations of interstellar C I and CO toward three stars located in the direction of the Perseus region near the B5 molecular cloud and discuss these together with published results from a fourth sight line. The column densities of the three fine-structure levels of C I are used to gether with ground-based optical data and published ultraviolet data to yie ld several properties of the gas along the stellar sight lines. The selecte d stars probe gas located in the neutral envelope surrounding the dense mol ecular cloud. The gas pressure is tightly constrained by our observations, yielding a value of approximate to 2200 K cm(-3) in the vicinity of B5, som ewhat higher than in the surrounding interstellar medium. We also present e stimates of the kinetic temperature, based on observations of H-2 and C-2, yielding 20-60 K in the vicinity of B5. Together with the pressure determin ation, this implies a local gas density of 35-100 cm(-3), very close to tha t which would be implied by the observed H-2 column density assuming a fill ing factor of unity. This result provides additional support to the notion that the gas is part of an extensive, uniform gaseous halo surrounding the B5 cloud. The combination of temperature and pressure suggests that the dif fuse gas may be part of a general outflow from the dense molecular cloud.