Physics
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...19713205w&link_type=abstract
American Astronomical Society, 197th AAS Meeting, #132.05; Bulletin of the American Astronomical Society, Vol. 33, p.717
Physics
Scientific paper
The tremendous brightness of water masers make them good tracers of motions in molecular gas on small scales. The Very Large Baseline Array (VLBA) provides beams of about one half milliarcsecond (0.17 AU) in size and can measure proper motions of about 10 km s-1 in the several days to weeks lifetime of a typical maser at a distance of 350 pc, the distance generally employed for NGC1333. Observationally, masers occur within about 100 AU of their driving source, and provide excellent signposts for the source of a flow, as well as good probes of the flow geometry and dynamics. The geometry of a flow and the physics of maser emission (produced along a tangential sight-line through the flow cocoon) conspire to result in a spread of radial velocity in a typical low mass maser source of only a few km s-1. A few Herbig-Haro objects have measured proper motions of as much as a few hundred km s-1; CO also shows very high velocites in this source--can the masers also show such high space velocities? Here we report VLBA observations toward the region of NGC1333 near SSV13, the driving source for the well-known Herbig-Haro objects HH7-11. Maser emission was observed over four epochs spaced interstitially by three weeks during late 1998, SSV13 is associated with the millimeter continuum source SSV13A1. High resolution CO observations have secured the association of the flow with the continuum object on arc-second scales. A 1998 Aug 12 VLA observation places the blueshifted masers within 39 AU (0''.1) of the 2.7 mm position for A1 reported from BIMA. We report observations of two groups of masers, one redshifted by about 6 km s-1 and one blueshifted by about 2-3 km s-1, separated by about 100 AU in projected distance along position angle 21 degrees. Red masers were present only in the latter two epochs. During all epochs, an arclike structure was present with similar morphology; over time this structure moved relative to the southernmost blue maser toward the southeast, roughly along the position angle defined by the Herbig-Haro objects, with a proper motion of about 13 km s-1.
Claussen Mark
Marvel Kevin
Wilking Burkhard
Wootten Al
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