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

We present line observations of different molecular species toward the dens e core in L483 and its bipolar outflow powered by the Class 0 object IRAS 1 8148-0440. (CO)-C-12(2-1) maps show that the outflow is well collimated and asymmetric, and that its gas is warmer than the surrounding cloud by at le ast 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 (similar to 0.3 km s(-1)) velocity shift approx imately along the outflow direction. We do not find evidence for a CH3OH ab undance enhancement in the flow, and the CH3OH lines trace a centrally conc entrated core which Lye model, assuming optically thin emission, as having a density gradient between r(-1) and r(-1.5) for radii between 15 " and 100 ". H2CO(2(12)-1(11)) lines show strong high-velocity wings with the same d istribution as the outflow, and evidence for a H2CO abundance enhancement o f a factor of 20 with respect to the ambient cloud. At ambient velocities a nd 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 x 10(-6) M -circle dot 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 out flow presents some characteristics common to other outflows from Class 0 so urces, like high degree of collimation, gas heating, and H2CO abundance enh ancement. However, other characteristics, like its low velocity, the lack o f bright SiO or CH3OH outflow wings, and the association with a NIR scatter ing 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 i ts spectral energy distribution, we propose that it is more evolved than ot her objects in its class, probably in transition from Class 0 to Class I.