A Keplerian disk around Orion Source I, a ~15 Msun YSO

TL;DR

This study uses high-resolution ALMA observations to analyze the disk around Orion Source I, confirming its status as a high-mass protostar and providing insights into its potential binary nature and dynamical history.

Contribution

First high-resolution ALMA imaging of Orion Source I's disk, measuring its mass and revealing possible binarity and its role in Orion's dynamical history.

Findings

Measured the mass of SrcI as approximately 15 solar masses.

Detected a potential hot spot indicating a possible binary system.

Supported the theory of SrcI's ejection from a multiple star system 500 years ago.

Abstract

We report ALMA long-baseline observations of Orion Source I (SrcI) with resolution 0.03-0.06" (12-24 AU) at 1.3 and 3.2 mm. We detect both continuum and spectral line emission from SrcI's disk. We also detect a central weakly resolved source that we interpret as a hot spot in the inner disk, which may indicate the presence of a binary system. The high angular resolution and sensitivity of these observations allow us to measure the outer envelope of the rotation curve of the H$_2$O $5_{5,0}-6_{4,3}$ line, which gives a mass $M_I\approx15\pm2$ Msun. We detected several other lines that more closely trace the disk, but were unable to identify their parent species. Using centroid-of-channel methods on these other lines, we infer a similar mass. These measurements solidify SrcI as a genuine high-mass protostar system and support the theory that SrcI and the Becklin Neugebauer Object were ejected from the dynamical decay of a multiple star system $\sim$500 years ago, an event that also launched the explosive molecular outflow in Orion.