ASTE Observations of Warm Gas in Low-Mass Protostellar Envelopes: Different Kinematics between Submillimeter and Millimeter Lines

With the ASTE telescope, we have made observations of three low-massprotostellar envelopes around L483, B335, and L723 in the submillimeter CS($J$=7--6) and HCN ($J$=4--3) lines. We detected both the CS and HCN linestoward all the targets, and the typical CS intensity ($\sim$ 1.0 K in T$_{B}$)is twice higher than that of the HCN line. Mapping observations of L483 inthese lines have shown that the submillimeter emissions in the low-massprotostellar envelope are resolved, exhibit a western extension from thecentral protostar, and that the deconvolved size is $\sim$ 5500 AU $\times$3700 AU (P.A. = 78$^{\circ}$) in the HCN emission. The extent of thesubmillimeter emissions in L483 implies the presence of higher-temperature($\gtrsim$ 40 K) gas at 4000 AU away from the central protostar, which suggeststhat we need to take 2-dimensional radiative transfer models with a flatteneddisklike envelope and bipolar cavity into account to explain the temperaturestructure inside the low-mass protostellar envelope. The position-velocitydiagrams of these submillimeter lines in L483 and B335 exhibit differentvelocity gradients from those found in the previous millimeter observations. Inparticular, along the axis of the associated molecular outflow the sense of thevelocity gradient traced by the submillimeter lines is opposite to that of themillimeter observations or the associated molecular outflow, both in L483 andB335. We suggest that expanding gas motions at the surface of the flatteneddisklike envelope around the protostar, which is irradiated from the centralstar directly, are the origin of the observed submillimeter velocity structure.Comment: 20 pages, 11 figure