VLT/Flames observations of the star forming region NGC 6530 ^*

¹ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: loredana@astropa.inaf.it
² Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

Received: 17 May 2006
Accepted: 3 October 2006

Abstract

Context. Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530.

Aims. We select cluster members using different membership criteria, to study the properties of pre-main sequence stars with or without circumstellar disks.

Methods.We use intermediate resolution spectra including the Li I 6707.8  line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray data to study the cluster membership. Optical-IR data and Hα spectra, these latter available for a subsample of our targets, are used to classify CTTS and WTTS and to compare the properties of stars with and without disks.

Results.We find a total of 237 certain members including 53 binaries. The rotational velocity distributions of stars with IR excesses are statistically different from that of stars without IR excesses, while the fraction of binaries with disks is significantly smaller than that of single stars. Stars with evidence of accretion show circumstellar disks; youth of cluster members is confirmed by the lithium abundance consistent with the initial content.

Conclusions.As indicated by the disk-locking picture, stars with disks in general have rotational velocities lower than stars without disks. Binaries in NGC 6530 seem have undergone significant disk evolution.