Issue |
A&A
Volume 427, Number 2, November IV 2004
|
|
---|---|---|
Page(s) | 485 - 494 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20040453 | |
Published online | 28 October 2004 |
NGC 2180: A disrupting open cluster?
Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil e-mail: charles@if.ufrgs.br
Received:
16
March
2004
Accepted:
18
July
2004
The spatial dependence of luminosity and mass functions of evolved open
clusters is discussed in this work using J and H 2MASS photometry, which allows a wide
spatial coverage and proper background determination. The target objects are the
intermediate-age open cluster NGC 3680 ( and
),
which has been reported as being in an advanced state of dissolution, and NGC 2180
(
,
), a possible dynamically evolved open cluster.
At the
level, NGC 2180 presents a radial distribution of stars that can
be represented by a King law. We conclude that, although in an advanced dynamical state
(mass segregated), NGC 3680 does not present strong signs of dissolution, having
luminosity and mass functions very similar to those of the
Gyr open
cluster M 67. On the other hand, NGC 2180 appears to have flat, eroded luminosity
functions throughout its structure, suggesting that in addition to mass segregation,
Galactic tidal stripping has been effective in depleting this object. Accordingly,
NGC 2180 may be the missing link between evolved open clusters and remnants. For
NGC 2180 we infer a distance to the Sun
± 0.15 kpc, an age
Myr and an observed stellar mass of
. For NGC 3680
we derive an age
Gyr,
and
± 0.09 kpc, confirming
previous estimates. The observed stellar mass
agrees with previous
values. We study both clusters in the context of dynamical states estimated from
diagnostic diagrams involving photometric and structural parameters. Both objects appear
to be dynamically evolved systems. In particular, NGC 2180 is closer to open cluster
remnants than NGC 3680.
Key words: Galaxy: open clusters and associations: general / stars: luminosity function, mass function
© ESO, 2004
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