Deep observations of O-2 toward a low-mass protostar with Herschel-HIFI
Artikel i vetenskaplig tidskrift, 2013

Context. According to traditional gas-phase chemical models, O-2 should be abundant in molecular clouds, but until recently, attempts to detect interstellar O-2 line emission with ground-and space-based observatories have failed. Aims. Following the multi-line detections of O-2 with low abundances in the Orion and. Oph A molecular clouds with Herschel, it is important to investigate other environments, and we here quantify the O-2 abundance near a solar-mass protostar. Methods. Observations of molecular oxygen, O-2, at 487 GHz toward a deeply embedded low-mass Class 0 protostar, NGC 1333IRAS 4A, are presented, using the Heterodyne Instrument for the Far Infrared (HIFI) on the Herschel Space Observatory. Complementary data of the chemically related NO and CO molecules are obtained as well. The high spectral resolution data are analysed using radiative transfer models to infer column densities and abundances, and are tested directly against full gas-grain chemical models.Results. The deep HIFI spectrum fails to show O-2 at the velocity of the dense protostellar envelope, implying one of the lowest abundance upper limits of O-2/H-2 at = 6x 10-9 (3s). The O-2/CO abundance ratio is less than 0.005. However, a tentative (4.5s) detection of O-2 is seen at the velocity of the surrounding NGC 1333 molecular cloud, shifted by 1 km s-1 relative to the protostar. For the protostellar envelope, pure gas-phase models and gas-grain chemical models require a long pre-collapse phase (similar to 0.7-1 x 106 years), during which atomic and molecular oxygen are frozen out onto dust grains and fully converted to H2O, to avoid overproduction of O2 in the dense envelope. The same model also reproduces the limits on the chemically related NO molecule if hydrogenation of NO on the grains to more complex molecules such as NH2OH, found in recent laboratory experiments, is included. The tentative detection of O-2 in the surrounding cloud is consistent with a low-density PDR model with small changes in reaction rates.

ISM: molecules

ISM: individual objects


NGC 1333 IRAS 4A

stars: formation


U. A. Yildiz

Universiteit Leiden

K. Acharyya

S N Bose National Centre for Basic Science

P. F. Goldsmith

Jet Propulsion Laboratory, California Institute of Technology

E. F. van Dishoeck

Max Planck-institutet

Universiteit Leiden

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

R. Snell

University of Massachusetts

René Liseau

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

Jo-Hsin Chen

Jet Propulsion Laboratory, California Institute of Technology

L. Pagani

LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres

E. A. Bergin

University of Michigan

P. Caselli

University of Leeds

Osservatorio Astrofisico di Arcetri

E. Herbst

University of Virginia

L. Kristensen

Harvard-Smithsonian Center for Astrophysics

R. Visser

University of Michigan

D. C. Lis


M. Gerin

CNRS Centre National de la Recherche Scientifique

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 558 A58


Astronomi, astrofysik och kosmologi