L 483 : a protostar in transition from Class 0 to Class I

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 181480440. CO(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(2k–1k) lines in L483 do not show strong high velocity wings, although there is a small (∼ 0.3 km s) 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 r and r for radii between 15 and 100. 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 40, 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 2× 10 M⊙ yr . 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. Send offprint requests to: M. Tafalla