Physical properties of molecular envelopes in low-mass star-forming regions

We have carried out interferometric observations of preprotostellar and protostellar envelopes in Taurus. Protostellar envelopes are dense gaseous condensations with young stellar objects or protostars, while pre-protostellar envelopes are those without any known young stellar objects. Five pre-protostellar envelopes have been observed in CCS J(N)=3(2)-2(1), showing flattened and clumpy structures of the envelopes. The observed CCS spectra show moderately narrow line widths, similar to0.1 to similar to0.35 km s(-1). One pre-protostellar envelope, L1544, shows a remarkable velocity pattern, which can be explained in terms of infall and rotation. Our (CO)-O-18 J=1-0 observations of 8 protostellar envelopes show that they have also flattened structures like pre-protostellar envelopes but no clumpy structures. Four out the eight envelopes show velocity patterns that can be explained by motions of infall (and rotation). Physical properties of pre-protostellar and protostellar envelopes are discussed in detail.