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TOPIC: NGC1333-IRAS2A

Blobrana

L

Posts: 131433

Date: Mar 27 03:21 2013

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Title: Hot water in the inner 100 AU of the Class 0 protostar NGC1333 IRAS2A Authors: Ruud Visser (1), Jes K. Jorgensen (2,3), Lars E. Kristensen (4,5), Ewine F. van Dishoeck (4,6), Edwin A. Bergin (1) ((1) Univ. of Michigan, (2) Niels Bohr Inst., (3) StarPlan, (4) Leiden Observatory, (5) CfA, (6) MPE Garching) Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapour abundances of ~10^-4 relative to H2. Observational evidence so far points at abundances of only a few 10^-6. However, these values are based on spherical models, which are known from interferometric studies to be inaccurate on the relevant spatial scales. Are hot cores really that much drier than expected, or are the low abundances an artifact of the inaccurate physical models? We present deep velocity-resolved Herschel-HIFI spectra of the 3(12)-3(03) lines of H2-16O and H2-18O (1097 GHz, Eup/k = 249 K) in the low-mass Class 0 protostar NGC1333 IRAS2A. A spherical radiative transfer model with a power-law density profile is unable to reproduce both the HIFI data and existing interferometric data on the H2-18O 3(13)-2(20) line (203 GHz, Eup/k = 204 K). Instead, the HIFI spectra likely show optically thick emission from a hot core with a radius of about 100 AU. The mass of the hot core is estimated from the C18O J=9-8 and 10-9 lines. We derive a lower limit to the hot water abundance of 2x10^-5, consistent with the theoretical predictions of ~10^-4. The revised HDO/H2O abundance ratio is 1x10^-3, an order of magnitude lower than previously estimated. Read more (135kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: May 31 17:55 2009

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Title: The kinematics of NGC1333-IRAS2A - a true Class 0 protostar Authors: C. Brinch, J. K. J\orgensen, M. R. Hogerheijde Low-mass star formation is described by gravitational collapse of dense cores of gas and dust. At some point during the collapse, a disk is formed around the protostar and the disk will spin up and grow in size as the core contracts because of angular momentum conservation. The question is how early the disk formation process occurs. In this paper we aim to characterize the kinematical state of a deeply embedded, Class 0 young stellar object, NGC1333-IRAS2A, based on high angular resolution (< 1'' ~200 AU) interferometric observations of HCN and H^{13}CN J = 4-3 from the Submillimetre Array, and test whether a circumstellar disk can be detected based on gas kinematic features. We adopt a physical model which has been shown to describe the object well and obtain a fit of a parameterised model of the velocity field, using a two-dimensional axis-symmetric radiation transfer code. The parameterisation and fit to the high angular resolution data characterize the central dynamical mass and the ratio of infall velocity to rotation velocity. We find a large amount of infall and very little rotation on all scales. The central object has a relatively low mass of 0.25 solar masses . As an object with a low stellar mass compared to the envelope mass, we conclude that NGC1333-IRAS2A is consistent with the suggestion that, as a Class 0 object, it represents the earliest stages of star formation. The large amount of infall relative to rotation also suggests that this is a young object. We do however find the need of a central compact component on scales of a few hundred AU based on the continuum data, which suggests that disk formation happens shortly after the initial gravitational collapse. The data do not reveal a distinct velocity field for this 0.1 solar masses component. Read more (200kb, PDF) __________________

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