J/ApJ/751/132 Keck observations of the Arches cluster (Clarkson+, 2012)
Proper motions of the Arches cluster with Keck Laser Guide Star Adaptive Optics:
the first kinematic mass measurement of the Arches.
Clarkson W.I., Ghez A.M., Morris M.R., Lu J.R., Stolte A., McCrady N.,
Do T., Yelda S.
<Astrophys. J., 751, 132 (2012)>
=2012ApJ...751..132C 2012ApJ...751..132C
ADC_Keywords: Proper motions ; Photometry, infrared ; Clusters, open
Keywords: astrometry - galaxies: clusters: individual: Arches -
Galaxy: kinematics and dynamics -
open clusters and associations: individual: Arches -
stars: kinematics and dynamics - techniques: high angular resolution
Abstract:
We report the first detection of the intrinsic velocity dispersion of
the Arches cluster - a young (∼2Myr), massive (104M☉)
starburst cluster located only 26pc in projection from the Galactic
center. This was accomplished using proper motion measurements within
the central 10"x10" of the cluster, obtained with the laser guide star
adaptive optics system at Keck Observatory over a three-year time
baseline (2006-2009). This uniform data set results in proper motion
measurements that are improved by a factor ∼5 over previous
measurements from heterogeneous instruments. By careful, simultaneous
accounting of the cluster and field contaminant distributions as well
as the possible sources of measurement uncertainties, we estimate the
internal velocity dispersion to be 0.15±0.01mas/yr, which
corresponds to 5.4±0.4km/s at a distance of 8.4kpc. Collateral
benefits of our data and analysis include: (1) cluster membership
probabilities, which may be used to extract a clean-cluster sample for
future photometric work; (2) a refined estimate of the bulk motion of
the Arches cluster with respect to the field, which we find to be
172±15km/s, which is slightly slower than suggested by previous
measurements using one epoch each with the Very Large Telescope and
the Keck telescope; and (3) a velocity dispersion estimate for the
field itself, which is likely dominated by the inner Galactic bulge
and the nuclear disk.
Description:
Observations of the central 10"x10" of the Arches cluster were
obtained between 2006 May and 2009 May with the Keck NIRC2 (PI: K.
Matthews), behind the LGSAO (Laser Guide Star Adaptive Optics) system
on the W. M. Keck II 10m telescope. Observations were taken in the K'
filter (Δλ=0.35um, λ0=2.12um).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table5.dat 67 432 Membership table for objects in the Arches
Central field
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See also:
J/A+A/556/A26 : Arches cluster: IR phot., extinction and masses (Habibi+, 2013)
J/ApJ/718/810 : Astrometry and Photometry in the Arches cluster (Stolte+, 2010)
J/A+A/501/563 : HKs photometry in the Arches cluster (Espinoza+, 2009)
J/ApJ/581/258 : Infrared photometry in the Arches Cluster (Figer+, 2002)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/432] Sequential star number
5- 9 F5.2 mag K'mag [10/20] Keck/NIRC2 K-prime apparent magnitude
11- 16 F6.3 arcsec DelX [-4.1/6.4] Position offset from reference star,
East to West (1)
18- 23 F6.3 arcsec DelY [-6.9/3.4] Position offset from reference star,
South to North (1)
25- 30 F6.3 mas/yr pmX [-4.3/8.5] East to West proper motion
32- 36 F5.3 mas/yr e_pmX [0.06/0.5] The 1σ error in pmX
38- 43 F6.3 mas/yr pmY [-9.9/5.4] South to North proper motion
45- 49 F5.3 mas/yr e_pmY The 1σ error in pmY
51- 57 F7.5 --- CMem [0/1] Cluster membership probability
59- 65 F7.5 --- FMem [0/1] Field membership probability
67 I1 --- R [0/1] PSF reference star flag (2)
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Note (1): See PSF reference stars (indicated by circles) and the reference
star (indicated by the square) in Figure 1.
Note (2):
1 = PSF (point-spread function) star used in the analysis.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Jan-2014