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

L. T. Maud, R. Cesaroni, M. S. N. Kumar, V. M. Rivilla, A. Ginsburg, P. D. Klaassen, D. Harsono, Á. Sánchez-Monge, A. Ahmadi, V. Allen, M. T. Beltrán, H. Beuther, R. Galván-Madrid, C. Goddi, M. G Hoare, M. R. Hogerheijde, K. G. Johnston, R. Kuiper, L. Moscadelli, T. Peters, L. Testi, F. F. S. van der Tak, W.-J. de Wit

Abstract
We present the highest angular resolution (∼20 × 15 mas–44 × 33 au) Atacama Large Millimeter/sub-millimeter Array (ALMA) observations that are currently possible of the proto-O-star G17.64+0.16 in Band 6. The Cycle 5 observations with baselines out to 16 km probe scales < 50 au 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 that is especially visible as arc structures to the north and south. The Keplerian kinematics are most prominently seen in the vibrationally excited water line, H2O 55, 0−64, 3 ν2 = 1 (Eu = 3461.9 K). The mass of the central source found by modelling the Keplerian rotation is consistent with 45 ± 10 M. The H30α (231.9 GHz) radio-recombination line and the SiO (5-4) molecular line were detected at up to the ∼10σ level. The estimated disc mass is 0.6 − 2.6 M⊙ 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 > 150 K; this does not preclude that the substructures formed earlier through disc fragmentation.

Keywords
stars: formation / stars: protostars / stars: massive / stars: winds / outflows / stars: pre-main sequence / submillimeter: stars

Notes
Data cubes of the source are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/L6.

Astronomy and Astrophysics
Volume 627, Article Number L6, Number of pages 7
2019 July

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia