2023/08/24 by Lin, Yuxin, Spezzano, Silvia, Pineda, Jaime E. +5
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.2308.12835
Pre-stellar cores represent a critical evolutionary phase in low-mass star formation. We aim to unveil the detailed thermal structure and density distribution of three early-stage cores, starless core L1517B, and prestellar core L694-2 and L429, with the high angular resolution observations of the NH3 (1,1) and (2,2) inversion transitions obtained with VLA and GBT. In addition, we explore where/if NH3 depletes in the central regions. Applying the mid-infrared extinction method to the Spitzer 8~μm map we obtain a high angular resolution hydrogen column density map, and derive the gas density profile to assess the variation of NH3 abundance as a function of gas volume density. The measured temperature profiles of L429 and L1517B show a minor decrease towards the core center, dropping from ∼9K to below 8K, and ∼11 K to 10 K, while L694-2 has a rather uniform temperature distribution around ∼9 K. Among the three cores, L429 has the highest central gas density, close to sonic velocity line-width, and largest localised velocity gradient, all indicative of an advanced evolutionary stage. We resolve that the abundance of NH3 becomes two times lower in the central region of L429, occurring around a gas density of 4.4×104~cm-3. Compared to Ophiuchus/H-MM1 which shows an even stronger drop of the NH3 abundance at 2×105~cm-3, the abundance variations of the three cores plus Ophiuchus/H-MM1 suggest a progressive NH3 depletion with increasing central density of the core.