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TMC-1C: an accreting starless core | | S. Schnee
; P. Caselli
; A. Goodman
; H. G. Arce
; J. Ballesteros-Paredes
; K. Kuchibhotla
; | | Date: |
28 Jun 2007 | | Abstract: | We have mapped the starless core TMC-1C in a variety of molecular lines with
the IRAM 30m telescope. High density tracers show clear signs of
self-absorption and sub-sonic infall asymmetries are present in N2H+ (1-0) and
DCO+ (2-1) lines. The inward velocity profile in N2H+ (1-0) is extended over a
region of about 7,000 AU in radius around the dust continuum peak, which is the
most extended ``infalling’’ region observed in a starless core with this
tracer. The kinetic temperature (~12 K) measured from C17O and C18O suggests
that their emission comes from a shell outside the colder interior traced by
the mm continuum dust. The C18O (2-1) excitation temperature drops from 12 K to
~10 K away from the center. This is consistent with a volume density drop of
the gas traced by the C18O lines, from ~4x10^4 cm^-3 towards the dust peak to
~6x10^3 cm^-3 at a projected distance from the dust peak of 80" (or 11,000 AU).
The column density implied by the gas and dust show similar N2H+ and CO
depletion factors (f_D < 6). This can be explained with a simple scenario in
which: (i) the TMC-1C core is embedded in a relatively dense environment (H2
~10^4 cm^-3), where CO is mostly in the gas phase and the N2H+ abundance had
time to reach equilibrium values; (ii) the surrounding material (rich in CO and
N2H+) is accreting onto the dense core nucleus; (iii) TMC-1C is older than
3x10^5 yr, to account for the observed abundance of N2H+ across the core
(~10^-10 w.r.t. H2); and (iv) the core nucleus is either much younger (~10^4
yr) or ``undepleted’’ material from the surrounding envelope has fallen towards
it in the past 10,000 yr. | | Source: | arXiv, arxiv.0706.4115 | | Services: | Forum | Review | PDF | Favorites | |
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