Chemical constraints and microstructure in TMC-1 Core D

Details Chemical constraints and microstructure in TMC-1 Core D Chemical constraints and microstructure in TMC-1 Core D

Apr 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001a%26a...369..605h&link_type=abstract

Astronomy and Astrophysics, v.369, p.605-610 (2001)

Astronomy and Astrophysics

Astrophysics

16

Ism: Clouds, Ism: Tmc-1, Ism: Molecules

Scientific paper

Microstructure has been detected in Core D of TMC-1. Unless it is confined or replenished by an as yet unexamined mechanism, this microstructure will dissipate on the sound-crossing timescale, which is less than 105 yr. We reconsider the large number of models that have been proposed to explain chemical variations in TMC-1 in an ffort to determine whether chemical constraints require the microstructure to be confined or replenished for times much longer than the sound crossing timescale. We explore here a chemical model which, though consistent with the assumption of an age of 6 104 yr and a number density of H nuclei of 2 105 cm-3, shows the richness in both molecular variety and abundances observed in Core D. In particular, the computed HC3N fractional abundance relative to H2 is 6 10-8, in agreement with the latest observations of Ohishi & Kaifu (\cite{ohi98}). Apparently, the chemistry of TMC-1 cannot be used to discard the possibility that TMC-1 Core D is young. This model has the following characteristics: the cosmic ray ionization rate is consistently larger than that usually assumed for dark regions; carbon atoms and hydrocarbons that strike grains are rapidly hydrogenated and promptly returned to the gas phase as methane; CO and N2 striking grains are immediately returned to the gas phase unaltered; other chemical species containing at least one atom more massive than helium colliding with dust grains remain frozen on their surfaces; and the material other than hydrogen was initially in atomic form. For such a model to be viable, collapse of Core D must have been triggered by a stellar wind-driven shock of several km s-1. This speed is low enough that magnetic moderation of the shock would have prevented the activation of a high temperature chemistry. The model results indicate that Core D would have fractional abundances of H2O and O2 at a core age of 6 104 yr consistent with the upper limits placed by very recent observations of Core D made with SWAS. The implications of this study are (1) that hydrogenation of atoms at the surfaces of dust grains may be a significant contributor to the chemistry of dark clouds; (2) that the special chemical nature of TMC-1 is due primarily to the exceptional youth of Core D.

Affiliated with

Also associated with

No associations

Rating

Chemical constraints and microstructure in TMC-1 Core D does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Chemical constraints and microstructure in TMC-1 Core D, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Chemical constraints and microstructure in TMC-1 Core D will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1181801