Moderate-Density Regions in the LYNDS 134 Cloud Complex

Details Moderate-Density Regions in the LYNDS 134 Cloud Complex Moderate-Density Regions in the LYNDS 134 Cloud Complex

Nov 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apjs..101...87l&link_type=abstract

Astrophysical Journal Supplement v.101, p.87

Astronomy and Astrophysics

Astronomy

20

Ism: Clouds, Ism: Individual Name: Lynds 134, Infrared: Ism: Continuum, Ism: Molecules

Scientific paper

IRAS images, carbon monoxide observations at 2.7 mm (CO, 13CO, and C18O), and blue extinction from star counts have been used for a large-scale study of the L134 complex of high-latitude clouds. We have correlated the different tracers in order to investigate the range of physical conditions for which these tracers apply. We find tight linear correlations between 13CO and AB and between 13CO and ΔI100. The quantity ΔI100 is the infrared emission of inner cloud regions obtained from the relationship ΔI100 = I100 - I60/Θ, where Θ is the value for I60/I100 in the outer regions of the clouds. We find that ΔI100 probes the same regions as 13CO and can therefore be used to predict the 13CO emission. From the correlation between 13CO and AB and the CO measurements we determine an average 13CO abundance in the complex which does not differ significantly from other studies. However, the abundance in the translucent cloud Ll780 is about a factor of 4 lower than in the opaque clouds L134, L183, and L169.
Using the 13CO observations we have compiled the properties of 18 clumps in the complex. The clumps follow clear luminosity-size and size-line width relationships. The size-line width relationship is consistent with a power law with exponent 0.5. The derived ambient pressure acting on the clumps is of order p/k = 2 × l04 K cm-3.
Both molecular and infrared data show that the UV radiation field in the complex is anisotropic. This is consistent with the presence of the nearby UV sources ζ Oph and the Upper Scorpius OB association. The densest regions in the complex as delineated by the ammonia cores can be found close to the low-illumination edges of the clouds. In addition, a higher density contrast on the shadow side can be observed. These observations support the view that the anisotropic UV field affects the density distribution in the clouds and that the increased strength of the UV field causes a bigger halo on the illuminated side. The influence of the UV field on the appearance of clouds is most evident in the outer layers of a cloud. The inner, denser, and well-shielded parts seem much more similar, judging by the uniform behavior of most tracers. However, the displacement of the ammonia cores with respect to the cloud centers suggests the effects of the anisotropy extend down to the densest layers of the clouds.

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