IRAS 16293–2422 FROM CENTIMETER TO FAR INFRARED WAVELENGTHS AND THE DETERMINATION OF ITS THREE-DIMENSIONAL STRUCTURE

In this thesis we present a multi-frequency observational study of the properties of IRAS 16293-2422 (I16293), a very-well studied low-mass solar-type multiple stellar system located within the Ophiuchus complex. Because I16293 is the prototype source for astrochemistry due to its wealth of molecular lines, it provides a suitable laboratory to study not only the physics of clustered star-formation but also the chemistry in early stages of this process. In this thesis, we will place special emphasis on nitrogen-bearing molecules present in I16293since these species are known to be powerful tools to derive chemical, kinematic and dynamic properties of star-forming regions over a wide range of conditions. The first part of this work is based on the analysis of the individual components of I16293 from interferometric centimeter -and millimeter- wavelength continuum observations. Since the correct interpretation of the observations and their corresponding modelling strongly depend on the accurate measurement of its distance, we have measured the parallax to its H2O maser emission at 22.2 GHz based on archival Very Large Baseline Array (VLBA) observations, obtaining a precise estimation of the distance of 141(+30,-21)pc. From high angular resolution observations with the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA), we followed the astrometry of the individual objects in the system for almost 30 years. We have seen that the properties of source B are remarkable because its spectrum indicates that its emission is dominated by thermal dust radiation. We present a full radiative transfer modelling of the structure of this source. The density and temperature profiles needed to explain the observational properties of source B resemble those expected for first hydrostatic cores. This fact, combined with the lack of free- free centimeter emission, might indicate that source B is just entering the protostellar phase. In the second part of the thesis we focus on the chemistry of I16293 based on single-dish observations of nitrogen-bearing molecules obtained with the radiotelescopes IRAM-30m, APEX, JCMT and the HIFI instrument on-board the Herschel Space Observatory over a wide frequency range from 80 GHz to 1 THz. We have extracted the rotational transitions of isocyanic acid (HNCO) from the observations and used a radiative transfer model out of Local Thermodynamical Equilibrium (non-LTE) to reproduce the observed line profiles. We conclude that I16293 can be modelled considering three regions: a dense, compact and warm component related with the hot corino, a warm and extended component associated with the innermost part of the envelope and a more extended and cold layer associated with the outermost part of the envelope. It is important to emphasize that the emission produced by these regions interacts one with another. As a consequence, our analysis not only constraints the properties of the different regions, but also establishes their relative positions along the line of sight. An HNCO abundance profile for the envelope of I16293 computed with the chemical code Nautilus shows a good agreement with the abundances derived from our radiative transfer model. On the other hand, the lines of cyanide (CN) have much more complex profiles since they show hyperfine structure and present deep absorptions. Indeed, since we detect the CN rotational transitions from J = 1 - 0 to J = 5 - 4 level, we have used an LTE model in CASSIS and defined a separate model for each transition. We noted that an extended emission larger than the envelope of I16293 is needed to correctly model the line profiles. We also derived the abundance ratio between CN and its isotopes 13CN and C15N.Taken together, the results presented here enabled us to constrain the structure of IRAS 16293- 2422 from the scale of its individual protostars (~ 10 AU) up to the scale of its extended envelope (~ 10,000 AU).