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TwitterA&A 394, 459-478 (2002)
DOI: 10.1051/0004-6361:20021118
The mass function of the Arches cluster from Gemini adaptive optics data
A. Stolte1, 2, E. K. Grebel1, W. Brandner2 and D. F. Figer31 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: stolte@mpia-hd.mpg.de; grebel@mpia-hd.mpg.de
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: wbrandne@eso.org
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
e-mail: figer@stsci.edu
(Received 8 March 2002 / Accepted 30 July 2002 )
Abstract
We have analysed high resolution adaptive optics (AO) science demonstration data
of the young, massive stellar cluster Arches near the Galactic Center,
obtained with the Gemini North telescope
in combination with the University of Hawai'i AO system Hokupa'a.
The AO
H and
K' photometry is calibrated using HST/NICMOS observations
in the equivalent filters
F160W and
F205W obtained by Figer et al. (1999).
The calibration procedure allows a detailed comparison of the
ground-based adaptive optics observations against
diffraction limited space-based photometry. The spatial resolution as
well as the overall signal-to-noise ratio of the Gemini/Hokupa'a data
is comparable to the HST/NICMOS data.
The low Strehl ratio of only a few percent is
the dominant limiting factor in the Gemini AO
science demonstration data as opposed to space-based observations. After a thorough
technical comparison, the Gemini and HST data are used in combination to
study the spatial distribution of stellar masses in the Arches cluster.
Arches is one of the densest young clusters known in the Milky Way, with
a central density of ~
and a total
mass of about
.
A strong colour gradient is observed over the cluster field.
The visual extinction increases by
mag over a distance of
15´´ from the cluster core.
Extinction maps reveal a low-extinction cavity in the densest parts of
Arches (
), indicating the depletion of dust due to stellar winds
or photo-evaporation. We correct for the change in extinction over the field
and show that the slope of the mass function is strongly influenced by
the effects of differential extinction.
We obtain present-day mass function
slopes of
in the mass range
from both data sets. The spatial analysis reveals a steepening of
the mass function slope from close to zero in the cluster center to
at
, in accordance
with a Salpeter slope (
).
The bias in the mass function towards high-mass stars in the Arches
center is a strong indication for mass segregation. The dynamical and relaxation timescales
for Arches are estimated, and possible mass segregation effects are discussed
with respect to cluster formation models.
Key words: open clusters and associations: individual: Arches -- stars: luminosity function, mass function -- stars: early-type -- stars: formation -- ISM: dust, extinction -- instrumentation: adaptive optics
Offprint request: A. Stolte, stolte@mpia-hd.mpg.de
© ESO 2002