Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters

TL;DR

This study measures the fraction of B-type stars with circumstellar discs in the Galactic centre's Arches and Quintuplet clusters, revealing unexpectedly high disc survival in UV-rich environments and suggesting binary mass transfer as a formation mechanism.

Contribution

First measurement of disc fractions in the Quintuplet cluster and analysis of disc survival in UV intense environments of Galactic centre clusters.

Findings

Disc fractions are 4.0% in Quintuplet and 9.2% in Arches.

Discs are found around late A- to early B-type stars (2-15 Msun).

Discs may form via binary mass transfer in UV-rich environments.

Abstract

We investigate the circumstellar disc fraction as determined from L-band excess observations of the young, massive Arches and Quintuplet clusters residing in the central molecular zone of the Milky Way. The Quintuplet cluster was searched for L-band excess sources for the first time. We find a total of 26 excess sources in the Quintuplet cluster and 21 in the Arches cluster, of which 13 are new detections. With the aid of proper motion membership samples, the disc fraction of the Quintuplet cluster was derived for the first time to be 4.0 +/- 0.7%. There is no evidence for a radially varying disc fraction in this cluster. In the case of the Arches cluster, a disc fraction of 9.2 +/- 1.2% approximately out to the cluster's predicted tidal radius, r < 1.5 pc, is observed. This excess fraction is consistent with our previously found disc fraction in the cluster in the radial range 0.3 < r < 0.8 pc. In both clusters, the host star mass range covers late A- to early B-type stars, 2 < M < 15 Msun, as derived from J-band photospheric magnitudes. We discuss the unexpected finding of dusty circumstellar discs in these UV intense environments in the context of primordial disc survival and formation scenarios of secondary discs. We consider the possibility that the L-band excess sources in the Arches and Quintuplet clusters could be the high-mass counterparts to T Tauri pre-transitional discs. As such a scenario requires a long pre-transitional disc lifetime in a UV intense environment, we suggest that mass transfer discs in binary systems are a likely formation mechanism for the B-star discs observed in these starburst clusters.