One puzzle in understanding how stars form in clusters is the source of mass -is all of the mass in place before the first stars are born, or is there an extended period when the cluster accretes material which can continuously fuel the star formation process? We use a multi-line spectral survey of the southern filament associated with the Serpens South embedded cluster-forming region in order to determine if mass is accreting from the filament onto the cluster, and whether the accretion rate is significant. Our analysis suggests that material is flowing along the filament's long axis at a rate of ∼ 30 M ⊙ Myr −1 (inferred from the N 2 H + velocity gradient along the filament), and radially contracting onto the filament at ∼ 130 M ⊙ Myr −1 (inferred from HNC self-absorption). These accretion rates are sufficient to supply mass to the central cluster at a similar rate to the current star formation rate in the cluster. Filamentary accretion flows may therefore be very important in the ongoing evolution of this cluster.

A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken with the Submillimeter Array. Although not yet completed, it has already yielded a fairly large sample of narrow molecular emission lines with line-widths indicating expansion velocities of ∼4 km s −1 , less than 3 times the well-known value of the terminal expansion velocity (14.5 km s −1 ) of the outer envelope. Five of these narrow lines have now been identified as rotational transitions in vibrationally excited states of previously detected molecules: the v=1, J=17-16 and J=19-18 lines of Si 34 S and 29 SiS and the v=2, J=7-6 line of CS. Maps of these lines show that the emission is confined to a region within ∼60 AU of the star, indicating that the narrow-line emission is probing the region of dust-formation where the stellar wind is still being accelerated.

We have used the Arecibo telescope to measure the H i absorption spectra of eight pulsars. We show how kinematic distance measurements depend on the values of the Galactic constants R 0 and  0 , and we select our preferred current values from the literature. We then derive kinematic distances for the low-latitude pulsars in our sample and electron densities along their lines of sight. We combine these measurements with all others in the inner Galactic plane visible from Arecibo to study the electron density in this region. The electron density in the interarm range 48 < l < 70 is 0:017 þ0:012 À0:007 (68% c:l:) cm À3 . This is 0:75 þ0:49 À0:22 (68% c:l:) of the value calculated by the Galactic electron density model of Cordes & Lazio. The model agrees more closely with electron density measurements toward Arecibo pulsars lying closer to the Galactic center, at 30 < l < 48 . Our analysis leads to the best current estimate of the distance of the relativistic binary pulsar B1913+16: d ¼ 9:0 AE 3 kpc. We use the high-latitude pulsars to search for small-scale structure in the interstellar hydrogen observed in absorption over multiple epochs. PSR B0301+19 exhibited significant changes in its absorption spectrum over 22 yr, indicating H i structure on a $500 AU scale.

We have searched for OH absorption against seven pulsars using the Arecibo telescope. In both OH mainlines (at 1665 and 1667 MHz), deep and narrow absorption features were detected toward PSR B1849+00. In addition, we have detected several absorption and emission features against B33.6+0.1, a nearby supernova remnant (SNR). The most interesting result of this study is that a pencil-sharp absorption sample against the PSR differs greatly from the large-angle absorption sample observed against the SNR. If both the PSR and the SNR probe the same molecular cloud then this finding has important implications for absorption studies of the molecular medium, as it shows that the statistics of absorbing OH depends on the size of the background source. We also show that the OH absorption against the PSR most likely originates from a small (< 30 arcsec) and dense (> 10 5 cm −3 ) molecular clump.