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Methanol in protostellar outflows: Single-dish and interferometric maps of NGC 1333/IRAS2

R. Bachiller tex2html_wrap_inline821 , C. Codella tex2html_wrap_inline821 , F. Colomer tex2html_wrap_inline821 , S. Liechti tex2html_wrap_inline821 , C.M. Walmsley tex2html_wrap_inline829
tex2html_wrap_inline821 Observatorio Astronomico Nacional (IGN), Apartado 1143, E-28800 Alcalá de Henares (Madrid), Spain
tex2html_wrap_inline829 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
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[]Channel maps of the CH tex2html_wrap_inline795 OH 2 tex2html_wrap_inline837 -1 tex2html_wrap_inline837 A tex2html_wrap_inline841 emission detected with the IRAM interferometer, integrated over velocity intervals of 1 km s tex2html_wrap_inline799 wide. The white star stands for the coordinates of the central source IRAS2 as measured by Blake (1996), while the straight line points out the direction of the outflow. The central LSR velocities for each interval, measured with respect to the LSR velocity of the ambient gas, are indicated in the upper left corner of each panel. The contours placed at the south-east of IRAS2 are due to redshifted emission, whereas the contours at the north-west are blueshifted emission. Nevertheless, some overlap of redshifted and blueshifted emission is observed at low velocities in the south-east lobe (the left region in the panels at tex2html_wrap_inline845 0.5 and tex2html_wrap_inline845 1.5 km s tex2html_wrap_inline799 ). The contour levels range from 0.15 to 1.50 Jy km s tex2html_wrap_inline799 /beam by step of 0.15 Jy km s tex2html_wrap_inline799 /beam (1.58 K km s tex2html_wrap_inline799 ).

We report high-resolution mapping observations of the 2 tex2html_wrap_inline857 -1 tex2html_wrap_inline857 , 3 tex2html_wrap_inline857 -2 tex2html_wrap_inline857 , and 5 tex2html_wrap_inline857 -4 tex2html_wrap_inline857 thermal lines of
CH tex2html_wrap_inline795 OH toward the young bipolar outflow driven by the Class 0 object NGC1333/IRAS2 (see Fig. 1). Only weak emission has been detected towards the position of the central object, while strong methanol lines have been observed towards the endpoints of the outflow lobes, where the CH tex2html_wrap_inline795 OH abundance is enhanced by a factor tex2html_wrap_inline873 300. The methanol emission is confined in two jets, with a collimation factor of about 20: redshifted emission comes from the south-east lobe, while blueshifted lines are detected towards the north-west. Statistical equilibrium calculations have been used to fit the relative intensities of the observed transitions. These lead us to the conclusion that the ambient gas surrounding the protostar has a density similar to that of the high velocity gas in the shocked regions ( tex2html_wrap_inline873 10 tex2html_wrap_inline877 cm tex2html_wrap_inline879 ).

Interferometric maps with a resolution of 3 tex2html_wrap_inline881 show that the blueshifted lobe consists of several ``bullets'' indicating that episodic mass loss has occurred. The age estimate is tex2html_wrap_inline883 2-5 10 tex2html_wrap_inline885 yr. The high-velocity redshifted emission comes from a structure which becomes ``V-like'' at velocities close to that of the ambient gas. These results fit nicely with recent magnetohydrodynamical models where a working surface with a cone-like shape creates elongated naked jets containing bullets in their interior.

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