2000A&A...359..967T

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(2_k-1_k) lines in L483 do not show strong high velocity wings, although there is a small (∼0.3km/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^–1 and r^–1.5 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 2x10^–6M_☉/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.