ALMA and VLA observations of recombination lines and continuum toward the Becklin-Neugebauer object in Orion^⋆

¹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: rgalvan@eso.org
² Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de Mexico, 58090 Morelia, Mexico
³ Astronomy Department, Faculty of Science, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia

Received: 3 September 2012
Accepted: 4 October 2012

Abstract

Compared to their centimeter-wavelength counterparts, millimeter recombination lines (RLs) are intrinsically brighter and are free of pressure broadening. We report observations of RLs (H30α at 231.9 GHz, H53α 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 = 8.4 × 10⁶ 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, it is possible that BN has large flux variations in the millimeter. However, dedicated observations with a uniform setup are needed to confirm this. From the H30α line, the central line-of-sight LSR velocity of BN is 26.3 km s^-1.