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A. Wootten, J. G. Mangum (NRAO), J. Wiseman (Johns Hopkins University), G. A. Fuller (UMIST)
IRAM 04191+1522 numbers among the least evolved low mass protostars known. Belloche, André, Despois, and Blinder (Astronomy and Astrophysics, v393, 927, 2002) found the envelope to lie in a transition stage, with one portion showing constant rotational velocity mediated by magnetic braking and another inner region showing conserved angular momentum suggestive of protostellar collapse. Imaging of the interior 10000 AU in the ammonia lines (Wootten, Wiseman, and Fuller 2001, BAAS v33, 1394) revealed a 2100 AU region devoid of ammonia emission centered on the star. Here we present images made on similar scales with the OVRO Millimeter Array in the 1arrow0 lines of the molecular ions N2H+ and H13CO+. The former shows a ringlike structure coincident with the hole in the ammonia distribution. The latter shows only amorphous structure more distant from the central protostar.
A sufficient explanation of these morphologies is that the nitrogen-bearing molecules vanish owing to depletion onto grains in the cold (13K) central region of high (n>1.5 \times 106 cm-3) density. We expected that N2H+ should survive depletion to higher densities. If N2 is also depleted, as seems likely, kinematics of the central portion of this young protostar will be extremely difficult to measure.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Observations at the OVRO Millimeter Array are supported by the National Science Foundation under Grant No.9981546
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.