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 NGC6530 with ages from ~1 Myr up to 10 Myrs. 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 NGC6530. We used low-resolution
spectra taken with VIMOS@VLT and literature spectra of standard stars to derive
spectral types of a subsample of 94 candidate members of this cluster. 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. The cluster members studied in this work have
masses between 0.4 and 4 M⊙ and ages between 1-2 Myrs and 6-7 Myrs. 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 Myrs. This is
consistent with the scenario of sequential star formation suggested in
literature.Comment: 23 pages, 16 Postscript figures, 5 tables. Accepted for publication
in Astronomy and Astrophysic