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

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.

To appear in Astronomy and Astrophysics as a Letter to the editor. Corrections to mm fluxes. Discussion about flux variability shortened. Physical properties of ionized gas remain the same. Table 1 to main text rather than online only. Language edited

References in corpus (5)

• The Early Evolution of Massive Stars: Radio Recombination Line Spectra
• Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region
• Imaging the Ionized Disk of the High-Mass Protostar Orion-I
• Understanding hydrogen recombination line observations with ALMA and EVLA
• A 3D view of the outflow in the Orion Molecular Cloud 1 (OMC-1)

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• ALMA Imaging of Millimeter/Submillimeter Continuum Emission in Orion KL
• The Ionized Circumstellar Envelopes of Orion Source I and the Becklin Neugebauer Object
• Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster
• Recombination Lines and Molecular Gas from Hypercompact HII regions in W51 A
• High spectral resolution observations toward Orion BN at 6 $\mu$m: no evidence for hot water
• Massive envelopes and filaments in the NGC 3603 star forming region
• The SOFIA Massive (SOMA) Star Formation Q-band Follow-up. II. Hydrogen Recombination Lines Toward High-Mass Protostars