J/ApJ/783/131 Kinematic of stars in Galactic center (Yelda+, 2014)
Properties of the remnant clockwise disk of young stars in the Galactic Center.
Yelda S., Ghez A.M., Lu J.R., Do T., Meyer L., Morris M.R., Matthews K.
<Astrophys. J., 783, 131 (2014)>
=2014ApJ...783..131Y 2014ApJ...783..131Y (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Associations, stellar ; Radial velocities ;
Proper motions ; Positional data ; Stars, standard
Keywords: astrometry - Galaxy: center - infrared: stars -
techniques: high angular resolution
Abstract:
We present new kinematic measurements and modeling of a sample of 116
young stars in the central parsec of the Galaxy in order to
investigate the properties of the young stellar disk. The measurements
were derived from a combination of speckle and laser guide star
adaptive optics imaging and integral field spectroscopy from the Keck
telescopes. Compared to earlier disk studies, the most important
kinematic measurement improvement is in the precision of the
accelerations in the plane of the sky, which have a factor of six
smaller uncertainties (σ∼10µas/yr2). We have also added the
first radial velocity measurements for eight young stars, increasing
the sample at the largest radii (6''-12'') by 25%. We derive the
ensemble properties of the observed stars using Monte Carlo
simulations of mock data. There is one highly significant kinematic
feature (∼20σ), corresponding to the well-known clockwise disk,
and no significant feature is detected at the location of the
previously claimed counterclockwise disk. The true disk fraction is
estimated to be ∼20%, a factor of ∼2.5 lower than previous claims,
suggesting that we may be observing the remnant of what used to be a
more densely populated stellar disk. The similarity in the kinematic
properties of the B stars and the O/WR stars suggests a common star
formation event. The intrinsic eccentricity distribution of the disk
stars is unimodal, with an average value of =0.27±0.07, which we
show can be achieved through dynamical relaxation in an initially
circular disk with a moderately top-heavy mass function.
Description:
There are 116 stars that form the sample of this study. The
astrometric measurements are based on three types of high-angular
resolution 2µm imaging observations (speckle imaging, narrow-field
adaptive optics imaging, wide-field mosaic AO imaging), which have
been obtained at the W. M. Keck observatory over a 16yr time period.
The earliest data sets were obtained with K-band (2.2µm) speckle
imaging between 1995 and 2005 (1995 Jun 9-12, 1996 Jun 26-27, 1997 May
14, 1998 Apr 2-3, 1998 May 14-15, 1998 Jul 3-5, 1998 Aug 4-6, 1998 Oct
9, 1999 May 2-4, 1999 Jul 24-25, 2000 May 19-20, 2000 Jul 19-20, 2000
Oct 18, 2001 May 7-9, 2001 Jul 28-29, 2002 Apr 23-24, 2002 May 23-24,
2002 Jul 19-20, 2003 Apr 21-22, 2003 Jul 22-23, 2003 Sep 7-8, 2004 Apr
29-30, 2004 Jul 25-26, 2004 Aug 29, 2005 Apr 24-25, 2005 Jul 26-27)
using the Near Infrared Camera (NIRC), which has a ∼5''*5'' FOV.
Since 2004, we have utilized the Keck II Adaptive Optics (AO) system
in conjunction with the facility near infrared camera NIRC2 (PI: K.
Matthews) in its narrow-field mode, which has a plate scale of
9.952mas/pix and a 10'' FOV (∼0.4pc at the 8kpc distance to the
Galactic center). Here we include all existing Keck AO observations
through 2011, which includes 19 epochs (2004 Jul 26, 2005 Jun 30, 2005
Jul 31, 2006 May 2-3, 2006 Jun 19-20, 2006 Jul 16, 2007 May 17, 2007
Aug 11-12, 2008 May 15, 2008 Jul 24, 2009 May 4, 2009 Jul 24, 2009 Sep
9, 2010 May 5, 2010 Jul 6, 2010 Aug 15, 2011 May 27, 2011 Jul 18, 2011
Aug 23) and a time baseline of seven years.
To measure the proper motions of the young stars at larger radii from
Sgr A* (R≳7''), we obtained three epochs of K'-band Laser Guide Star
Adaptive Optics (LGSAO) mosaics with the NIRC2 narrow camera that
cover 27''*27'' (∼1.1pc*1.1pc). These observations were taken on 2006
May 3, 2008 May 20, and 2010 June 5.
To spectroscopically identify young stars and measure their
line-of-sight motions, high angular resolution spectroscopic
observations were obtained with the integral field spectrograph OSIRIS
in conjunction with the LGSAO system on Keck II. The central 4'' have
been observed since 2006 with the Kn3 narrowband filter centered on
the Brγ line (λ=2.1661µm) and using the 35mas plate
scale. In 2010, we began the Galactic Center OSIRIS Wide-field Survey
(GCOWS), in which observations were taken along the eastern portion of
the CW disk in order to maximize the number of young star
identifications (Do et al. 2013, cat. J/ApJ/764/154). These
observations reached a radial extent of R∼14'' east of Sgr A* and used
the 50mas plate scale. The details of our OSIRIS observations are
presented in Ghez et al. (2008ApJ...689.1044G 2008ApJ...689.1044G) and Do et al. 2009
(cat. J/ApJ/703/1323), 2013 (cat. J/ApJ/764/154).
We present the positions, proper motions, and accelerations for our
sample in Table4. Updated astrometry for the secondary standards
originally presented in Yelda et al. 2010 (cat. J/ApJ/725/331) is
shown in Table8.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 113 116 Kinematic data of Galactic center young stars
table8.dat 70 1210 Galactic center secondary infrared astrometric
standards
table9.dat 23 116 Disk membership sample
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See also:
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/ApJ/725/331 : Astrometry in the Galactic Center (Yelda+, 2010)
J/A+A/502/91 : Proper motions of stars near SgrA* (Schoedel+, 2009)
J/A+A/499/483 : NIR observations of sources in GC (Buchholz+, 2009)
J/ApJ/703/1323 : Spectroscopy of stars in Galaxy's nuclear cluster (Do+ 2009)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
J/ApJ/659/1241 : Stellar variability in Galactic Center (Rafelski+, 2007)
J/ApJ/643/1011 : Early-type stars in the center of the Galaxy (Paumard+, 2006)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Group Category of star based on the information
content contained in the acceleration
measurement (Det, Const, or LMS) (1)
7- 15 A9 --- Name Star name
17- 20 F4.1 mag Kmag [9.1/15.9] The K-band magnitude
22- 23 I2 --- Ne [3/45] Number of epochs
25- 30 F6.1 yr Epoch [2001.3/2010.2] Epoch (2)
32- 37 F6.3 arcsec oRA [-9.7/11.9] Offset in Right Ascension ΔRA
39- 43 F5.3 mas e_oRA [0.038/0.85] 1σ error in oRA
45- 50 F6.3 arcsec oDE [-8.2/11.7] Offset in Declination ΔDecl
52- 56 F5.3 mas e_oDE [0.044/1.4] 1σ error in oDE
58- 63 F6.2 mas/yr pmRA [-13.7/13.1] Right Ascension proper motion vRA
65- 68 F4.2 mas/yr e_pmRA [0.02/0.56] 1σ error in pmRA
70- 75 F6.2 mas/yr pmDE [-10.9/9.7] Proper motion in Declination vDecl
77- 80 F4.2 mas/yr e_pmDE [0.02/0.74] 1σ error in pmDE
82- 85 I4 km/s RV [-597/536] Radial velocity vz (3)
87- 89 I3 km/s e_RV [6/150] 1σ error in RV
91- 93 A3 --- r_RV Reference for RV (4)
95 A1 --- l_ddpm [>] Lower limit flag on ddpm
96-101 F6.3 mas/yr2 ddpm [-0.3/-0.02]? Radial acceleration aR (5)
103-107 F5.3 mas/yr2 e_ddpm [0.007/0.015]? 1σ error in ddpm
109-113 F5.3 --- Prob [0/1] Disk membership probability calculated
following Lu et al. (2009ApJ...690.1463L 2009ApJ...690.1463L)
(1-Lnon-disk) (6)
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Note (1): Star type defined as:
Det = Star with significant acceleration detection;
Const = Linearly moving star with acceleration constraints (stars with
acceleration upper limits below or equivalent to the nominal
theoretical maximum acceleration and for which a lower limit to the
line-of-sight distance can be estimated (i.e., inferred from the
lack of acceleration));
LMS = Linearly moving star.
Note (2): Epoch taken as the mean of the imaging observations, weighted by
positional uncertainties for each star.
Note (3): While the spectroscopic identification of young stars using OSIRIS
has been reported elsewhere (Do et al. 2009, cat. J/ApJ/703/1323; Do et al.
2013, cat. J/ApJ/764/154), we report the radial velocities for 38 stars
from this instrument for the first time here. For eight of these stars,
this is the first report of an radial velocity measurement in the
literature.
Note (4): Radial velocity data obtained from the following data:
1 = New measurement based on OSIRIS spectroscopic data reported in Do et
al. 2009 (cat. J/ApJ/703/1323), 2013 (cat. J/ApJ/764/154);
2 = Existing measurement from Very Large Telescope (VLT; Bartko et al.
2009 (cat. J/ApJ/697/1741)). Note that some radial velocity
measurements reported in Bartko et al. 2009 (cat. J/ApJ/697/1741) were
first reported in Paumard et al. 2006 (cat. J/ApJ/643/1011);
3 = Existing measurement from Very Large Telescope (VLT; Paumard et al.
2006 (cat. J/ApJ/643/1011)).
Note (5): Accelerations were fit for stars falling within the central 10'' field
of view only. For stars with acceleration limits, the positions and
velocities are from the linear fits and the acceleration limits are from
the acceleration fits.
Note (6): Where Lnon-disk is the likelihood that the star is not part of the
disk, and is computed as:
Lnon-disk=1-[∫diskPDF(i,Ω)dSA/∫peakPDF(i,Ω)dSA]
(Eq. 10), and ∫diskdSA=∫peakdSA (Eq. 11),
where SA is the solid angle measured as the contour at which the density
drops to 50% of its peak value (∼0.2sr or FWHM=15.2°).
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Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Source identifier (1)
11- 14 F4.1 mag Kpmag [7.4/16.3] K' band magnitude
16- 22 F7.2 yr EpIR [2006.53/2009.52] Average time of infrared
positional measurements (T0,IR)
24- 28 F5.2 arcsec Rad [0.36/18.7] Radius from Sgr A*
30- 36 F7.4 arcsec oRA [-6.6/15.6] Offset in Right Ascension from
Sgr A* (ΔRA) (2)
38- 40 F3.1 mas e_oRA [1/2.2] Uncertainty in oRA (σRA) (3)
42- 48 F7.4 arcsec oDE [-9.6/12.4] Offset in Declination from
Sgr A* (ΔDecl) (2)
50- 52 F3.1 mas e_oDE [1/2.2] Uncertainty in oDE (σDecl) (3)
54- 57 F4.1 mas/yr pmRA [-9.5/9.5] Right Ascension proper motion vRA
59- 61 F3.1 mas/yr e_pmRA [0.1/1.4] Uncertainty in pmRA (4)
63- 66 F4.1 mas/yr pmDE [-9.7/9.7] Declination proper motion vDecl
68- 70 F3.1 mas/yr e_pmDE [0.2/1.5] Uncertainty in pmDE (4)
--------------------------------------------------------------------------------
Note (1): We present 1210 astrometric standards here, slightly fewer than Yelda
et al. 2010 (cat. J/ApJ/725/331), which had 1279 stars. This discrepancy is
a result of the higher signal-to-noise ratio in the overlapping regions of
mosaicked images as compared to mosaicked star lists. See Appendix D for
more details.
Note (2): Positional measurements are differential. Sgr A* SIMBAD position is
RA=17:45:40.03599 (J2000), DE=-29:00:28.1699 (J2000).
Note (3): Does not includes centroiding, alignment, and residual distortion
(1mas) errors, but do not include error in position of Sgr A*.
Note (4): Does not include error in velocity of Sgr A* (0.09mas/yr, 0.14mas/yr
in RA and Dec, respectively).
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Byte-by-byte Description of file: table9.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Source identifier
11- 14 F4.1 deg oPA [1/90] Position angle offset from the line of
nodes of the clockwise disk (Ω=96.3°),
with a range of 0°-90°
16- 23 A8 --- Sample The level above which the star's disk
membership probability falls for its
respective angular offset bin (see Figure 22)
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 28-Apr-2016