Query : 2009A&A...499..503L

2009A&A...499..503L - Astronomy and Astrophysics, volume 499, 503-513 (2009/5-4)

Imaging galactic diffuse clouds: CO emission, reddening and turbulent flow in the gas around ζ Ophiuchi.


Abstract (from CDS):

Most diffuse clouds are only known as kinematic features in absorption spectra, but those with appreciable H2 content may be visible in the emission of such small molecules as CH, OH, and CO. We interpret in greater detail the extensive observations of 12CO emission from diffuse gas seen around the archetypical line of sight to ζ Oph. The 12CO emission is imaged in position and position-velocity space, analyzed statistically, and then compared with maps of total reddening EB–V and with models of the C+-CO transition in H2-bearing diffuse clouds. Around ζ Oph, 12CO emission appears in two distinct intervals of reddening centered near EB–V≃0.4 and 0.65mag, of which ≲0.2mag is background material. Within either interval, the integrated 12CO intensity varies up to 6-12K.km/s, compared to 1.5K.km/s toward ζ Oph. Nearly 80% of the individual profiles have velocity dispersions σv<0.6km/s, which are subsonic at the kinetic temperature derived from H2 toward ζ Oph, 55 K. Partly as a result, 12CO emission exposes the internal, turbulent, supersonic (1-3km/s) gas flows with especial clarity in the cores of strong lines. The flows are manifested as resolved velocity gradients in narrow, subsonically-broadened line cores. The scatter between N(CO) and EB–V in global, CO absorption line surveys toward bright stars is present in the gas seen around ζ Oph, reflecting the extreme sensitivity of N(12CO) to ambient conditions. The two-component nature of the optical absorption toward ζ Oph is coincidental and the star is occulted by a single body of gas with a complex internal structure, not by two distinct clouds. The very bright 12CO lines in diffuse gas arise at N(H2)≃1021cm–2 in regions of modest density n(H)≃ 200-500cm–3 and somewhat more complete C+-CO conversion. Given the variety of structure in the foreground gas, it is apparent that only large surveys of absorption sightlines can hope to capture the intrinsic behavior of diffuse gas.

Abstract Copyright:

Journal keyword(s): astrochemistry - ISM: molecules - ISM: clouds

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 * zet Oph Be* 16 37 09.5390545 -10 34 01.529471 1.73 2.58 2.56 2.46 2.50 O9.2IVnn 1806 2
2 LDN 121 DNe 16 39 28.4 -14 05 21           ~ 26 0
3 NAME [BM89] L121 PoC 16 39 30.4 -14 05 12           ~ 23 0
4 LDN 204C DNe 16 47 38.4 -12 08 04           ~ 10 0
5 LDN 204B DNe 16 47 47.1 -11 55 16           ~ 9 0
6 LDN 204 DNe 16 47 47.3 -12 05 16           ~ 54 0

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