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A pair of close YSOs with strikingly different outflow ejection geometry

Published online by Cambridge University Press:  08 November 2005

José M. Torrelles
Affiliation:
Instituto de Ciencias del Espacio (CSIC) and Institut d'Estudis Espacials de Catalunya, Gran Capità, 2-4, 08034 Barcelona, Spain. On sabbatical leave at the UK Astronomy Technology Centre, Royal Observatory Edinburgh
Nimesh A. Patel
Affiliation:
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Guillem Anglada
Affiliation:
Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain
José F. Gómez
Affiliation:
Laboratorio de Astrofísica Espacial y Física Fundamental (INTA), Ap. 50727, 28080 Madrid, Spain
Paul T. P. Ho
Affiliation:
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Lucas Lara
Affiliation:
Departamento de Física Teórica y del Cosmos, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
Antonio Alberdi
Affiliation:
Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain
Jorge Cantó
Affiliation:
Instituto de Astronomía (UNAM), Ap. 70-264, DF 04510, México
Salvador Curiel
Affiliation:
Instituto de Astronomía (UNAM), Ap. 70-264, DF 04510, México
Guido Garay
Affiliation:
Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
Luis F. Rodríguez
Affiliation:
Centro de Radioastronomía y Astrofísica (UNAM), Ap. 72-3, 58089 Morelia, Michoacán, México
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Abstract

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We present Very Long Baseline Array (VLBA) proper motion observations of water masers toward two young stellar objects (YSOs) of the W75N(B) high-mass star forming region. These observations (Torrelles et al. 2003) show two objects having a similar spectral type (early-B stars), separated in the sky by 0$0^''$7 (corresponding to 1400 AU at the source distance), sharing the same molecular gas environment, but presenting a strikingly different outflow ejection geometry. One of these YSOs, W75N(B)-VLA 1, has a jet-like outflow at 2000 AU scale, with the water masers moving at velocities of ${\simeq}$20 km s$^{-1}$ along the major axis of the thermal radio continuum jet, while the other YSO has a water maser shell outflow of 160 AU radius expanding at ${\simeq}$30 km s$^{-1}$ in multiple directions with respect to the central compact radio continuum source W75N(B)-VLA 2. Given the small dynamical time obtained for the water maser shell (${\simeq}$13 yr), we propose that in the very early stages of the star-formation process there may exist short lived, possibly repetitive, events associated with very poorly collimated outflows. All these results suggest that outflow collimation is not only a consequence of ambient conditions, but something intrinsic to the evolution of the individual stars, opening the important question of how and when these non-collimated wind ejection events occur in the evolution of YSOs. Although we argue in this paper that W75N(B)-VLA 2 could be in an earlier stage of evolution than W75N(B)-VLA 1, we think that observations at (sub)millimeter wavelengths with angular resolutions of ${\simeq}0^''1$ can provide the key for determining the relative stage of evolution of these two remarkable YSOs.

Type
Contributed Papers
Copyright
© 2005 International Astronomical Union