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

TL;DR

This study uses ALMA and VLA observations to analyze recombination lines and continuum emission from the dense ionized gas around the Becklin-Neugebauer object in Orion, revealing its physical conditions and kinematics.

Contribution

First detailed millimeter and centimeter recombination line and continuum observations of BN, providing insights into its ionized gas properties and dynamics.

Findings

Ionized gas is dense with Ne=8.4x10^6 cm^-3.

Electron temperature is below 4900 K.

Line-of-sight velocity of BN is 26.3 km/s.

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 (H30alpha at 231.9 GHz, 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 (Ne=8.4x10^6 cm^-3) base of the ionized envelope around BN. This ionized gas has a relatively low electron temperature (Te<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 H30alpha line, the central line-of-sight LSR velocity of BN is 26.3 km s^-1.