ALMA band 8 continuum emission from Orion Source I

TL;DR

This study uses ALMA band 8 observations to analyze the continuum emission from Orion Source I, revealing an elongated, optically thick dust structure consistent with a circumstellar disk with temperatures around 700-800 K.

Contribution

First high-resolution ALMA band 8 measurements of Orion Source I's continuum emission, confirming the dust emission origin and disk-like structure at sub-100 au scales.

Findings

Continuum emission is elongated perpendicular to outflow.

Brightness temperature is 700-800 K, lower than free-free emission.

Results support the circumstellar disk hypothesis.

Abstract

We have measured continuum flux densities of a high-mass protostar candidate, a radio source I in the Orion KL region (Orion Source I) using the Atacama Large Millimeter/Submillimeter Array (ALMA) at band 8 with an angular resolution of 0.1". The continuum emission at 430, 460, and 490 GHz associated with Source I shows an elongated structure along the northwest-southeast direction perpendicular to the so-called low-velocity bipolar outflow. The deconvolved size of the continuum source, 90 au times 20 au, is consistent with those reported previously at other millimeter/submillimeter wavelength. The flux density can be well fitted to the optically thick black-body spectral energy distribution (SED), and the brightness temperature is evaluated to be 700-800 K. It is much lower than that in the case of proton-electron or H- free-free radiations. Our data are consistent with the latest ALMA results by Plambeck & Wright (2016), in which the continuum emission have been proposed to arise from the edge-on circumstellar disk via thermal dust emission, unless the continuum source consists of an unresolved structure with the smaller beam filling factor.