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arXiv · 2511.03543

Radiative transfer modeling of the low-mass proto-binary system, IRAS 4A1 and 4A2

Bratati Bhat·Ankan Das·Prasanta Gorai·Dipen Sahu
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Abstract

NGC 1333 IRAS4A is a well-studied low-mass sun-like proto-binary system. It has two components, A1 and A2, which are diverse according to their physical and chemical properties. We modeled this hot corino using the RATRAN radiative transfer code and explained different spectral signatures observed towards A1 and A2, specifically for CH3OH and H2CO. Our main goal is to understand the kinematical and chemical differences between A1 and A2 and to classify their dust emission and absorption properties. We considered a simple 1D spherical infalling envelope consisting of collimated outflow in the source. Recent high-resolution interferometric observations of ALMA shed new light on why the same molecular transitions towards A1 and A2 show different spectral profiles. The significant difference between spectral profiles observed towards A1 and A2 is mainly due to the dust opacity effect. Dust continuum emission toward A1 is optically thick, causing the transitions observed in absorption. Meanwhile, A2 is optically thin, leading to the observed emission profiles, and an inverse P-Cygni profile suggests the presence of an infalling envelope. Using high-resolution observations from ALMA and VLA, we expanded our model from the millimeter wavelength range to the centimeter wavelength range. This expansion demonstrates the opacity effect, which is reduced in the centimeter wavelength range, causing us to observe the lines in emission. Using our model, we reproduced the population inversion causing maser emission of methanol 44 GHz and 95 GHz transitions.

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Bratati Bhat, Ankan Das, Prasanta Gorai, Dipen Sahu. 2025-11-05. Radiative transfer modeling of the low-mass proto-binary system, IRAS 4A1 and 4A2. https://arxiv.org/abs/2511.03543

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