Volume 546, October 2012
|Number of page(s)||22|
|Section||Galactic structure, stellar clusters and populations|
|Published online||27 September 2012|
INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, Italy 1, 90134 Palermo, Italy
Received: 20 June 2012
Accepted: 3 August 2012
Context. Mechanisms involved in the star formation process and in particular the duration of the different phases of the cloud contraction are not yet fully understood. Photometric data alone suggest that objects coexist in the young cluster NGC 6530 with ages from ~1 Myr up to 10 Myr.
Aims. We want to derive accurate stellar parameters and, in particular, stellar ages to be able to constrain a possible age spread in the star-forming region NGC 6530.
Methods. We used low-resolution spectra taken with VLT/VIMOS and literature spectra of standard stars to derive spectral types of a subsample of 94 candidate members of this cluster.
Results. We assign spectral types to 86 of the 88 confirmed cluster members and derive individual reddenings. Our data are better fitted by the anomalous reddening law with RV = 5. We confirm the presence of strong differential reddening in this region. We derive fundamental stellar parameters, such as effective temperatures, photospheric colors, luminosities, masses, and ages for 78 members, while for the remaining 8 YSOs we cannot determine the interstellar absorption, since they are likely accretors, and their V − I colors are bluer than their intrinsic colors.
Conclusions. The cluster members studied in this work have masses between 0.4 and 4 M⊙ and ages between 1 − 2 Myr and 6 − 7 Myr. We find that the SE region is the most recent site of star formation, while the older YSOs are loosely clustered in the N and W regions. The presence of two distint generations of YSOs with different spatial distribution allows us to conclude that in this region there is an age spread of 6 − 7 Myr. This is consistent with the scenario of sequential star formation suggested in literature.
Key words: techniques: spectroscopic / open clusters and associations: individual: NGC 6530 / stars: formation / Hertzsprung-Russell and C-M diagrams / stars: pre-main sequence / stars: fundamental parameters
Based on observations collected at the European Southern Observatory, Paranal, under program ID 077.C-0073B.
Tables 1, 3, and 5 are available in electronic form at http://www.aanda.org
FITS files are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A9
© ESO, 2012
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