Astron. Astrophys. 359, 967-976 (2000)

L483: a protostar in transition from Class 0 to Class I

M. Tafalla ¹, P.C. Myers ², D. Mardones ³ and R. Bachiller <sup>1

1</sup> Observatorio Astronómico Nacional, Apartado 1143, 28800 Alcalá de Henares, Spain (tafalla,bachiller@oan.es)
² Harvard-Smithsonian Center for Astrophysics, MS 42, 60 Garden St., Cambridge, MA 02138, USA (pmyers@cfa.harvard.edu)
³ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile (mardones@das.uchile.cl)

Received 13 October 1999 / Accepted 23 May 2000

Abstract

We present line observations of different molecular species toward the dense core in L483 and its bipolar outflow powered by the Class 0 object IRAS 18148-0440. ¹²CO(2-1) maps show that the outflow is well collimated and asymmetric, and that its gas is warmer than the surrounding cloud by at least a factor of 2. In contrast with the outflows from other Class 0 objects, the CH₃OH(-) lines in L483 do not show strong high velocity wings, although there is a small ( km s^-1) velocity shift approximately along the outflow direction. We do not find evidence for a CH₃OH abundance enhancement in the flow, and the CH₃OH lines trace a centrally concentrated core which we model, assuming optically thin emission, as having a density gradient between and for radii between and . H₂CO(2₁₂-1₁₁) lines show strong high-velocity wings with the same distribution as the outflow, and evidence for a H₂CO abundance enhancement of a factor of 20 with respect to the ambient cloud. At ambient velocities and over the central , this line presents a strong self absorption and a brighter blue peak, a characteristic signature of inward motions. A simple analysis of the H₂CO line profiles suggests an infall rate of   yr^-1.

Combining the results from our observations with previous work, we discuss the evolutionary status of IRAS 18148-0440 and its outflow. The bipolar outflow presents some characteristics common to other outflows from Class 0 sources, like high degree of collimation, gas heating, and H₂CO abundance enhancement. However, other characteristics, like its low velocity, the lack of bright SiO or CH₃OH outflow wings, and the association with a NIR scattering nebula (optically invisible) seem more common to outflows from the more evolved Class I sources. As IRAS 18148-0440 is a Class 0 object based on its spectral energy distribution, we propose that it is more evolved than other objects in its class, probably in transition from Class 0 to Class I.

Key words: stars: formation ISM: clouds ISM: individual objects: L 134N ISM: jets and outflows ISM: molecules

Send offprint requests to: M. Tafalla

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000

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