Estudo químico do jato/outflow associado com a proto-estrela NGC 1333 IRAS 2A

Abstract

The process of low-mass star formation occurs in embedded regions, called molecular clouds. Due to the high extinction in optical wavelengths, the study of star formation takes place in the infrared (IR) and (sub-)millimeter (mm) wavelengths, since larger wavelengths are less extincted by dust. The presence of a disk and a jet/outflow associated with the protostar is inherent to the star-forming process. In particular, molecular outflows remove angular momentum from the material that is collapsing, induce turbulence in the progenitor cloud and heat the gas to a few hundred K, disturbing the cloud chemistry. Therefore, the knowledge of the physical properties of the outflow help us to better understand the star formation process. CO is the tracer often used in outflows, as it is the most abundant observable molecule. However, by having a low dipole moment, CO is an optically thick tracer and is not sensitive to the dense gas(nH2 ∼1x105cm−3) along the line of sight. Other molecules, like HCN, are significantly more sensitive to dense gas, indicating shocked regions. In this work we used interferometric data of high angular resolution (∼ 1��) of the star forming region NGC 1333 IRAS 2A, taken with the Sub-Millimeter Array (SMA). The calibration, visualization and data analysis were performed using the CASA package. We calculate the physical parameters of the outflow and analyze the emission lines of CO 3-2 and HCN 4-3 by studying a particular region. We compared our values with a shock model taken from the literature, and used a rotational diagram in order to determine the temperatures. The region of interest may be related to a shocked region, where a dissociative shock heated the gas and destroyed molecules. After the passage of the shock the gas is cooling and the HCN molecule is reformed, with temperatures of ∼ 500 K. The CO emission presents two temperature components, a warm one with 196 K indicating regions slightly away from the impact point, and a cold component of 51 K, showing regions less affected by the shock. The selected protostar is a prototype, well studied in the literature, but still shows some unexpected results. In this work, with the detection of a shocked region next to the source possition, we propose that the jet is atomic, dissociating molecules that, after the passage of the shock, reform as the gas begins to cool. This means that despite of having a general idea of how low-mass stars form, the details are unknown. With this work, we intend to contribute to the understanding of the generation of outflows in the low-mass star formation process.