# Substructures in the Keplerian disc around the O-type (proto)star G17.64+0.16

## TL;DR

This study uses high-resolution ALMA observations to reveal a rotating, potentially fragmenting disc around a massive proto-O star, G17.64+0.16, showing ring-like dust structures and Keplerian motion, with implications for star formation.

## Contribution

First high-resolution ALMA imaging of a proto-O star's disc, revealing detailed substructures and Keplerian rotation, advancing understanding of massive star formation processes.

## Key findings

- Disc exhibits ring-like dust enhancements and arc structures.
- Keplerian rotation confirmed via vibrationally excited water line.
- Disc stability depends on temperature, with potential for fragmentation.

## Abstract

We present the highest angular resolution (20x15mas - 44x33au) Atacama Large Millimeter/sub-millimeter Array (ALMA) observations currently possible of the proto-O-star G17.64+0.16 in Band 6. The Cycle 5 observations with baselines out to 16km probes scales <50au and reveal the rotating disc around G17.64+0.16, a massive forming O-type star. The disc has a ring-like enhancement in the dust emission, especially visible as arc structures to the north and south. The Keplerian kinematics are most prominently seen in the vibrationally excited water line, H2O (Eu=3461.9K). The mass of the central source found by modelling the Keplerian rotation is consistent with 45+/-10Mo. The H30alpha (231.9GHz) radio-recombination line and the SiO (5-4) molecular line were detected at up to the 10 sigma$ level. The estimated disc mass is 0.6-2.6Mo under the optically thin assumption. Analysis of the Toomre Q parameter, in the optically thin regime, indicates that the disc stability is highly dependent on temperature. The disc currently appears stable for temperatures >150K, this does not preclude that the substructures formed earlier through disc fragmentation.