Letter to the Editor

Herschel/HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region ^*,**

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, Giessenbachstrasse 1, 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
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA
⁵ Department of Physics and Astronomy, Denison University, Granville, OH, 43023, USA
⁶ Institute of Astronomy, ETH Zurich, 8093 Zurich, Switzerland
⁷ Observatorio Astronómico Nacional (IGN), Calle Alfonso XII 3, 28014 Madrid, Spain
⁸ Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, France; CNRS/INSU, UMR 5804, Floirac, France
⁹ INAF - Istituto di Fisica dello Spazio Interplanetario, Area di Ricerca di Tor Vergata, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁰ Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
¹¹ Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
¹² California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
¹³ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
¹⁴ INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁵ Centro de Astrobiología. Departamento de Astrofísica. CSIC-INTA. Carretera de Ajalvir, Km 4, Torrejón de Ardoz., 28850 Madrid, Spain
¹⁶ Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
¹⁷ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁸ LERMA and UMR 8112 du CNRS, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
¹⁹ University of Waterloo, Department of Physics and Astronomy, Waterloo, Ontario, Canada
²⁰ Observatorio Astronómico Nacional, Apartado 112, 28803 Alcalá de Henares, Spain
²¹ INAF - Osservatorio Astronomico di Roma, 00040 Monte Porzio catone, Italy
²² SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
²³ National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
²⁴ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 1A1, Canada
²⁵ Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
²⁶ California Institute of Technology, Cahill Center for Astronomy and Astrophysics, MS 301-17, Pasadena, CA 91125, USA
²⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
²⁸ the University of Western Ontario, Department of Physics and Astronomy, London, Ontario, N6A 3K7, Canada
²⁹ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
³⁰ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³¹ Department of Physics and Astronomy, University of Calgary, Calgary, T2N 1N4, AB, Canada
³² Instituto de Radioastronomía Milimétrica (IRAM), Avenida Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
³³ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
³⁴ KOSMA, I. Physik. Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany

Received: 31 May 2010
Accepted: 2 August 2010

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, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are complemented by ground-based observations of lower-J CO and isotopologue lines. The ¹²CO 10–9 profiles are dominated by broad (FWHM 25–30 km s^-1) emission. Radiative transfer models are used to constrain the temperature of this shocked gas to 100–200 K. Several CO and ¹³CO line profiles also reveal a medium-broad component (FWHM5–10 km s^-1), seen prominently in H₂O lines. Column densities for both components are presented, providing a reference for determining abundances of other molecules in the same gas. The narrow C¹⁸O 9–8 lines probe the warmer part of the quiescent envelope. Their intensities require a jump in the CO abundance at an evaporation temperature around 25 K, thus providing new direct evidence for a CO ice evaporation zone around low-mass protostars.