J/A+A/556/A26 Arches cluster: IR phot., extinction and masses (Habibi+, 2013)
The Arches cluster out to its tidal radius: dynamical mass segregation and the
effect of the extinction law on the stellar mass function.
Habibi M., Stolte A., Brandner W., Hussmann B., Motohara K.
<Astron. Astrophys. 556, A26 (2013)>
=2013A&A...556A..26H 2013A&A...556A..26H
ADC_Keywords: Clusters, open ; Photometry, infrared ; Stars, masses
Keywords: Galaxy: center, open clusters and associations -
individual: Arches cluster, stellar dynamics, extinction map -
stars: mass function, luminosity function - stars: early-type -
infrared: stars - instrumentation: adaptive optics
Abstract:
The Galactic Center is the most active site of star formation in the
Milky Way Galaxy, where particularly high-mass stars have formed very
recently and are still forming today. However, since we are looking at
the Galactic Center through the Galactic disk, knowledge of extinction
is crucial to study this region. The Arches cluster is a young,
massive starburst cluster near the Galactic Center. We observed the
Arches cluster out to its tidal radius using Ks-band imaging obtained
with NAOS/CONICA at the VLT combined with Subaro/Cisco J-band data to
gain a full understanding of the cluster mass distribution. We show
that the determination of the mass of the most massive star in the
Arches cluster, which had been used in previous studies to establish
an upper-mass limit for the star formation process in the Milky Way,
strongly depends on the assumed slope of the extinction law. Assuming
the two regimes of widely used infrared extinction laws, we show that
the difference can reach up to 30% for individually derived stellar
masses and ΔAKs∼1 magnitude in acquired Ks-band extinction,
while the present mass function slope changes by ∼0.17dex. The
present-day mass function slope derived assuming the Nishiyama et al.
(2009) extinction law increases from a flat slope of
α-Nishi=-1.50±0.35 in the core (r<0.2pc) to
α-Nishi=-2.21±0.27 in the intermediate annulus (0.2<r<0.4pc),
where the Salpeter slope is -2.3. The present-day mass function
steepens to α-Nishi=-3.21±0.30 in the outer annulus
(0.4<r<1.5pc), indicating that the outer cluster region is depleted of
high mass stars. This picture is consistent with mass segregation due
to the dynamical evolution of the cluster.
Description:
We observed the Arches cluster out to its tidal radius using Ks-band
and H-band imaging obtained on June 6-10 2008 with NAOS/CONICA at the
VLT combined with Subaro/Cisco J-band data to gain a full
understanding of the cluster mass distribution. The acquired Ks-band
images cover four fields of 27.8*27.8(arcsec) each, provided by the
medium resolution camera (S27) with a pixel scale of 0.027(arcsec).
During the Ks-band observations, the natural visual seeing varied from
0.61" to 0.98". We achieved typical spatial resolutions of
0.081-0.135(arcsec) on individual frames using this AO setup.
Seeing-limited J-band observations, on July 17, 2000, were performed
with the CISCO spectrograph and camera which provided a pixel scale of
0.116(arcsec) and a field of view of 2*2(arcmin). An average seeing of
0.49(arcsec) resulted into a Full Width at Half Maximum (FWHM) of the
point-spread function (PSF) of 0.39(arcsec) on the combined image. The
catalogue includes derived infrared-photometry in J, H and Ks bands as
well as derived individual extinction value and stellar masses.
We used the NAOS-CONICA observations obtained in March 2002 in the
central part of the Arches cluster to cover the whole cluster area.
Objects:
-------------------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------------------
17 45 50.5 -28 49 28 Arches cluster = NAME ARCHES CLUSTER
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 101 3351 Photometry, mass and extinction in Arches cluster
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See also:
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
J/ApJ/581/258 : Infrared photometry in the Arches Cluster (Figer+, 2002)
J/MNRAS/371/38 : X-ray observations of the Galaxy center (Wang+, 2006)
J/ApJ/670/1115 : IRS spectra at 38 positions in GC (Simpson+, 2007)
J/A+A/501/563 : HKs photometry in the Arches cluster (Espinoza+, 2009)
J/ApJ/718/810 : Astrometry & photometry in the Arches cluster (Stolte+, 2010)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq Sequential number
6- 12 F7.3 arcsec oRA Right ascension offset from the reference
star, J2000 (1)
14- 20 F7.3 arcsec oDE Declination offset from the reference
star, J2000 (1)
22- 27 F6.3 mag AKs(RL) ?=-9 Ks-band extinction applying the RL-EL (2)
29- 34 F6.3 mag AKs(N) ?=-9 Ks-band extinction applying the N-EL (2)
36- 43 F8.3 Msun Mi(RL) ?=-999 Initial mass applying the RL-EL (2) (3)
45- 51 F7.3 Msun M(RL) ?=-99 Present mass applying the RL-EL (2) (3)
53- 59 F7.3 Msun Mi(N) ?=-99 Initial mass applying the N-EL (2) (3)
61- 67 F7.3 Msun M(N) ?=-99 Present mass applying the N-EL (2) (3)
69- 75 F7.3 mag Jmag [0/23.1]?=-99 J-band brightness
77- 83 F7.3 mag Hmag [10.9/23.6]?=-99 H-band brightness
85- 90 F6.3 mag Ksmag [0/33.4]? Ks-band brightness
92- 97 F6.3 mag A(Ks) [0/0.442]?=-9.000 estimated Ks-band extinction
99 I1 --- F [1/5] Cluster field in which the source is
located
101 I1 --- Mm [0/1] Cluster members (1), others (0)
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Note (1): Position offsets are calculated with respect to reference star
which is the source with ID 1, at 17:45:50.046-28:49:23.62 (J2000).
Note (2): Masses are derived by comparing our observations against the Geneva
isochrone with solar metallicity located at the GC distance of 8kpc.
Note (3): RL-EL stands for Rieke and Lebofsky (1985ApJ...288..618R 1985ApJ...288..618R) Extinction
Law, and N-EL stands for Nishiyama et al (2009ApJ...696.1407N 2009ApJ...696.1407N) extinction
law.
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Acknowledgements:
Maryam Habibi, mhabibi(at)astro.uni-bonn.de
(End) Maryam Habibi [Bonn Univ., Germany], Patricia Vannier [CDS] 21-May-2013