Roberto Galvan-Madrid, Ciriaco Goddi, Luis F. Rodriguez
Compared to their centimeter-wavelength counterparts, millimeter recombination lines (RLs) are intrinsically brighter and are free from pressure broadening. We report observations of RLs (H30alpha at 231.9 GHz and H53alpha at 42.9 GHz) and the millimeter and centimeter continuum toward the Becklin-Neugebauer (BN) object in Orion, obtained from the Atacama Large Millimeter/submillimeter Array (ALMA) Science Verification archive and the Very Large Array (VLA). The RL emission appears to be arising from the slowly-moving, dense (N_e=8.4x10^6 cm^-3) base of the ionized envelope around BN. This ionized gas has a relatively low electron temperature (T_e<4900 K) and small (<<10 km s^-1) bulk motions. Comparing our continuum measurements with previous (non)detections, we find evidence that BN could have large flux variations in the mm, but only mild (<30 %) variations in the cm. This could be understood if the free-free continuum of BN arises in an unresolved, unconfined ionized region that preserves its size after sudden recombination events. From the H30alpha line, the central line-of-sight LSR velocity of BN is 26.3 km s^-1.
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http://arxiv.org/abs/1210.1413
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