A wide-area photometric and astrometric (Gaia DR2) study of the young cluster NGC 6530

Abstract

(abridged) NGC6530 is a young cluster with a complex morphology and star-formation history. We present a statistical study of its global properties using a new large list of candidate members down to masses of 0.2-0.4 Msun and Gaia DR2 astrometry. We consider a wider sky region compared to previous studies, to investigate the whole cluster and its neighborhood. We study the distribution of extinction and age across the different regions, and obtain constraints on the star-formation history. Cluster membership is determined on the basis of X-ray data, H-alpha emission, near-IR and UV excesses from VPHAS+, UKIDSS and other surveys, and Gaia DR2 astrometry; we also use a novel method for photometric selection of M-type pre-main-sequence cluster members. The list of candidates includes nearly 3700 stars, of which we estimate ~2700 genuine NGC6530 members. Using Gaia parallaxes, the cluster distance is found to be 1325 pc, with errors of 0.5% (statistical) and 8.5% (systematic), in agreement with previous determinations. The cluster morphology and boundaries are established with great confidence, from members selected using different criteria. There is no diffuse population of members around the cluster, but there are minor member subgroups (associated with the stars 7 Sgr (F2II-III) and HD 164536 (O7.5V)) in addition to the two main groups in the cluster core and in the Hourglass nebula. We find a pattern of sequential star formation, between ages of <0.5 Myr and ~5 Myr. Extinction is spatially non-uniform, with part of the population still obscured by thick dust. The precise Gaia proper motion data indicate that the NGC6530 parent cloud collided with the Galactic plane ~4 Myr ago, and we suggest that event as the trigger of the bulk of star formation in NGC6530. The internal cluster dynamics is also partially resolved by the Gaia data, indicating expansion of the main cluster population.

21 pages, 22 figures, accepted for publication on Astronomy and Astrophysics

References in corpus (10)

• The Gaia mission
• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The VST Photometric Halpha Survey of the Southern Galactic Plane and Bulge (VPHAS+)
• The Spatial Structure of Young Stellar Clusters. I. Subclusters
• Correlation between the spatial distribution of the circumstellar disks and the massive stars in the open cluster NGC 6611. Compiled catalog and cluster parameters
• The Spatial Structure of Young Stellar Clusters. II. Total Young Stellar Populations
• VLT/Flames observations of the star forming region NGC 6530
• A Chandra X-ray study of the young star cluster NGC 6231: low-mass population and initial mass function
• The Gaia-ESO Survey: dynamics of ionized and neutral gas in the Lagoon nebula (M8)

Cited by in corpus (13)

• The Gaia-ESO Survey: age spread in the star forming region NGC6530 from the HR diagram and gravity indicators
• Multicolor Variability of Young Stars in the Lagoon Nebula: Driving Causes and Intrinsic Timescales
• Unveiling the traits of massive young stellar objects through a multi-scale survey
• The influence of metallicity on a combined stellar and disk evolution
• Surveying the Giant HII Regions of the Milky Way with SOFIA: IV. Sgr D, W42, and a Reassessment of the Giant HII Region Census
• Unbound stars hold the key to young star cluster history
• Studying the effects and cause of the massive star formation in Messier 8 East
• Tying the geometrical traits of massive young stellar objects and their discs to a potential evolutionary sequence using infrared observations
• Circumstellar disk accretion across the Lagoon Nebula: the influence of environment and stellar mass
• The effects of stellar feedback on molecular clumps in the Lagoon Nebula (M8)
• On the nature of VX Sagitarii: Is it a TZO, a RSG or a high-mass AGB star?
• Revisiting rotationally excited CH at radio wavelengths: A case study towards W51
• Investigating star formation scenarios in the Milky Way using YSO distributions -- A pilot study