Energetic processes revealed by spectrally resolved high-J CO lines in low-mass star-forming regions with Herschel-HIFI

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands ;
e-mail: yildiz@strw.leidenuniv.nl
² Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching, Germany
³ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K., Denmark

Abstract

Herschel-HIFI observations of high-J lines (up to J_u = 10) of ¹²CO, ¹³CO and C¹⁸O are presented toward three deeply embedded low-mass protostars in NGC 1333. The observations show several energetic components including shocked and quiescent gas. Radiative transfer models are used to quantify the C¹⁸O envelope abundance which require a jump in the abundance at an evaporation temperature, T_ev ~ 25 K, providing new direct evidence of a CO ice evaporation zone around protostars. The abundance in the outermost part of the envelope, X₀, is within the canonical value of 2 × 10^-4; however the inner abundance, X_in, is found around a factor of 3–5 lower than X₀.