Issue |
A&A
Volume 430, Number 3, February II 2005
|
|
---|---|---|
Page(s) | 941 - 957 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20040432 | |
Published online | 26 January 2005 |
The star formation region NGC 6530: Distance, ages and initial mass function *,**
1
Dipartimento di Scienze Fisiche ed Astronomiche, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: loredana@astropa.unipa.it
2
INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
Received:
12
March
2004
Accepted:
28
September
2004
We present astrometry and BVI photometry, down to ,
of the very young open cluster
NGC 6530, obtained from
observations taken with the Wide Field Imager camera at the MPG/ESO 2.2 m
Telescope. Both the V vs.
and the V vs.
color-magnitude
diagrams (CMD) show that the upper main sequence is dominated by very bright cluster
stars,
while, because of the high obscuration of the giant molecular
cloud surrounding the cluster, the blue envelopes of the diagrams at
are limited to
the main sequence stars at the distance of NGC 6530. This particular
structure of the NGC 6530 CMD allows us to conclude that its distance
is about
pc, significantly lower than the previous
determination of
pc.
We have positionally matched our optical catalog with the list of X-ray
sources found in a Chandra-ACIS observation,
finding a total of 828 common stars,
90% of which are pre-main sequence stars in NGC 6530.
Using evolutionary tracks of [CITE], mass
and age values are inferred for these stars. The median age of the cluster
is about 2.3 Myr; in the mass range (0.6-4.0)
,
the Initial Mass Function (IMF) shows a power law
index
, consistent with both the Salpeter index (1.35),
and with
the index derived for other young clusters;
towards smaller masses the IMF shows a peak and then
it starts to decrease.
Key words: Galaxy: open clusters and association: individual: NGC 6530 / techniques: photometric / astrometry / stars: pre-main sequence stars / stars: Hertzprung-Russel (HR) and C-M diagrams
© ESO, 2005
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