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

Astronomy & Astrophysics manuscript no. discs_astro_11feb2014 February 13, 2015 c ESO Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters ? A. Stolte 1 , B. Husmann 1 , C. Olczak 2 , W. Brandner 3 , M. Habibi 1 , A. M. Ghez 4, 5 , M. R. Morris 4 , J. R. Lu 6 , W. I. Clarkson 7 , J. Anderson 8 arXiv:1502.03681v1 [astro-ph.SR] 12 Feb 2015 Argelander Institut fur Astronomie, Universitat Bonn, Auf dem Hugel 71, 53121 Bonn, Germany Astronomisches Recheninstitut, Universitat Heidelberg, Monchhofstr. 12-14, 69120 Heidelberg, Germany Max-Planck-Institut fur Astronomie, Konigstuhl 17, 69117 Heidelberg, Germany Division of Astronomy and Astrophysics, UCLA, Los Angeles, CA 90095-1547, USA Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095, USA Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA Department of Natural Sciences, University of Michigan-Dearborn, 125 Science Building, 4901 Evergreen Road, Dearborn, MI 48128, USA Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA February 13, 2015 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 sources with L-band excesses 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 could be 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 M , 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. Key words. open clusters and associations: individual (Quintuplet,Arches)–Galaxy: centre– stars: circumstellar matter–techniques: high angular resolution 1. Introduction In view of the short lifetimes of primordial circumstellar discs around B-type stars in dense environments, the detection of cir- cumstellar discs in the UV-rich environment of the Galactic cen- tre Arches cluster came as a surprise (Stolte et al. 2010). This detection raised the question of whether discs can also be found in the more evolved Quintuplet cluster, and whether these discs can have their origin in massive primordial discs sustained over the clusters’ lifetimes of several million years (Myr). In partic- ular, the nature of the disc sources in the Arches cluster has re- mained unsolved (see the discussion in Stolte et al. 2010). In the past five years, we have extended our disc search to larger radii in the Arches cluster and have encompassed the Quintu- plet cluster. With the aim of shedding light on the nature of the L-band excess sources found in both starburst clusters, we com- Based on data obtained at the ESO VLT under programme IDs 085.D-0446, 089.D-0121 (PI: Stolte), 081.D-0572 (PI: Brandner), 087.D-0720, 089.D-0430 (PI: Olzcak), 071.C-0344 (PI: Eisenhauer), 60.A-9026 (NAOS/CONICA science verification), as well as Hubble Space Telescope observations under programmes 11671 (PI:Ghez). pare their physical properties to pre-transitional discs and dis- cuss secondary mass transfer discs as a possible origin of the circumstellar material. 1.1. Circumstellar disc survival The survival of primordial circumstellar discs in young star clus- ters is known to be a steep function of cluster age (Haisch et al. 2001, Hernandez et al. 2005). For discs around low-mass stars, M ∼ 1 M , planet formation theories suggest that dust ag- glomeration causes a period of grain growth, while at the same time the dense gas of the primordial disc is evaporated by the central star (Cieza et al. 2012, Williams & Cieza 2011, Owen et al. 2011). In consequence, the thermal excess of evolved discs is dominated by increasingly longer wavelength emission, while the near-infrared contribution decreases and vanishes with time (e.g. Espaillat et al. 2012). The disc survival timescale in young stellar clusters is observed to be 3-10 Myr for intermediate-mass stars, 2 < M < 10 M (Hernandez et al. 2005), albeit with lower disc fractions at any given age as compared to clusters dominated by their lower-mass T Tauri counterparts (see Stolte Article number, page 1 of 47