Query : 2007A&A...470..221C

2007A&A...470..221C - Astronomy and Astrophysics, volume 470, 221-230 (2007/7-4)

Observing the gas temperature drop in the high-density nucleus of L 1544.


Abstract (from CDS):

The thermal structure of a starless core is crucial for our understanding of the physics in these objects and hence for our understanding of star formation. Theory predicts a gas temperature drop in the inner ∼5000AU of the pre-stellar core L 1544, but there has been no observational proof of this. We performed VLA observations of the NH3 (1,1) and (2,2) transitions towards L 1544 in order to measure the temperature gradient between the high density core nucleus and the surrounding core envelope. Our VLA observation for the first time provide measurements of gas temperature in a core with a resolution smaller than 1000AU. We have also obtained high resolution Plateau de Bure observations of the 110 GHz 111-101 para-NH2D line in order to further constrain the physical parameters of the high density nucleus. We combine our interferometric NH3 and NH2D observations with available single dish measurements in order to estimate the effects of flux loss from extended components upon our data. We have estimated the temperature gradient using a model of the source to fit our data in the u,v plane. As the NH3(1, 1) line is extremely optically thick, this also involved fitting a gradient in the NH3 abundance. In this way, we also measure the [NH2D]/[NH3] abundance ratio in the inner nucleus. We find that indeed the temperature decreases toward the core nucleus from 12K down to 5.5K resulting in an increase of a factor of 50% in the estimated density of the core from the dust continuum if compared with the estimates done with constant temperature of 8.75 K. Current models of the thermal equilibrium can describe consistently the observed temperature and density in this object, simultaneously fitting our temperature profile and the continuum emission. We also found a remarkably high abundance of deuterated ammonia with respect to the ammonia abundance (50%±20%), which proves the persistence of nitrogen bearing molecules at very high densities (2x106cm–3) and shows that high-resolution observations yield higher deuteration values than single-dish observations. The NH2D observed transition, free of the optical depth problems that affect the NH3 lines in the core center, is a much better probe of the high-density nucleus and, in fact, its map peak at the dust continuum peak. Our analysis of the NH3 and NH2D kinematic fields shows a decrease of specific angular momentum from the large scales to the small scales.

Abstract Copyright:

Journal keyword(s): ISM: clouds - ISM: evolution - ISM: individual objects: L1544 - ISM: molecules - stars: formation - techniques: interferometric

Simbad objects: 7

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Number of rows : 7
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 LDN 1544 DNe 05 04 16.6 +25 10 48           ~ 858 0
2 NAME [BM89] L1544 cor 05 04 22.5 +25 11 36           ~ 437 1
3 3C 273 BLL 12 29 06.6998257176 +02 03 08.597629980   13.05 14.830 14.11   ~ 5771 1
4 3C 286 Sy1 13 31 08.2883506368 +30 30 32.960091564   17.51 17.25     ~ 4312 2
5 LDN 183 MoC 15 54 12.2 -02 49 42           ~ 753 1
6 NAME LDN 1014 IRS Y*O 21 24 07.58 +49 59 08.9           ~ 81 0
7 3C 454.3 Bla 22 53 57.7480438728 +16 08 53.561508864   16.57 16.10 15.22   ~ 2827 2

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