Spatially Extended Evidence for Inward Motions Toward Low Mass Protostars

Details Spatially Extended Evidence for Inward Motions Toward Low Mass Protostars Spatially Extended Evidence for Inward Motions Toward Low Mass Protostars

Nov 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe.185m&link_type=abstract

"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199

Astronomy and Astrophysics

Astronomy

Scientific paper

We present H_2CO (212-101) and (312-201) ,N_2H^+ (1-0), and CS (2-1) single-dish observations toward 12 young stellar objects (YSOs) from the survey of Mardones et al. (1997) having strong H_2CO line asymmetries. The N_2H^+ lines tend be optically thin, as indicated by their line shapes and hyperfine structure fits (0.3< \langle \tau \rangle < 1.7). The N_2H^+ maps define cores having radii ~0.02-0.07pc, and densities 0.1-2.0x10^5 cm^{-3}. The H_2CO line profiles tend to be optically thick, as evidenced by the line profiles which are often self-absorbed at the velocity of the N_2H^+ line peak. The absorption features are concentrated toward the YSOs in all sources, having typical radii ~0.01-0.04pc. Most of the self-absorbed line profiles have a brighter blue peak, indicating a predominance of inward over outward motions of the absorbing gas. We obtain infall speeds of 0.01 to 0.1 km/s at distances of a few times 0.01 pc from the YSOs. We study the spatial distribution of the line asymmetries, correlating the spatial variations of \delta v = (vthick-vthin)/ \Delta vthin with that expected from envelopes dominated by infall, bipolar outflows and differential velocity gradients. We find that infall motions are necessary to explain at least in part the morphology of the \delta v maps toward NGC1333-4, L1527, IRAS 13036-7644, IRAS 16293-2422, L483, SMM5, B335, L1157, and L1251B. The spatial variation of \delta v maps toward Serp SMM9 and Serp SMM1 is dominated by the associated bipolar outflows. Expansion motions dominate in L1448. We find strong radial velocity gradients in the optically thin N_2H^+ and CH_3OH lines located predominantly close to the core integrated intensity half maximum contour in NGC1333-4, L483, Serpens, and most likely also L1527 and L1251B. The radial velocity gradients tend to point either away or toward the core centers. These gradients can not arise from optical depth effects, but most likely originate from a radial velocity difference between the core and the inter-core medium.

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