J/ApJ/873/65 Keck/NIRC2 obs. of the Galactic Center (Sakai+, 2019)
The Galactic Center: an improved astrometric reference frame for stellar orbits
around the supermassive black hole.
Sakai S., Lu J.R., Ghez A., Jia S., Do T., Witzel G., Gautam A.K., Hees A.,
Becklin E., Matthews K., Hosek M.W.
<Astrophys. J., 873, 65 (2019)>
=2019ApJ...873...65S 2019ApJ...873...65S
ADC_Keywords: Positional data; Photometry, infrared; Galactic center
Keywords: instrumentation: adaptive optics ; astrometry ; black hole physics ;
Galaxy: center
Abstract:
Precision measurements of the stars in short-period orbits around the
supermassive black hole at the Galactic Center are now being used to
constrain general relativistic effects, such as the gravitational
redshift and periapse precession. One of the largest systematic
uncertainties in the measured orbits has been errors in the
astrometric reference frame, which is derived from seven
infrared-bright stars associated with SiO masers that have extremely
accurate radio positions, measured in the Sgr A*-rest frame. We have
improved the astrometric reference frame within 14" of the Galactic
Center by a factor of 2.5 in position and a factor of 5 in proper
motion. In the new reference frame, Sgr A* is localized to within a
position of 0.645mas and proper motion of 0.03mas/yr. We have removed
a substantial rotation (2.25° per decade), that was present in the
previous less-accurate reference frame used to measure stellar orbits
in the field. With our improved methods and continued monitoring of
the masers, we predict that orbital precession predicted by general
relativity will become detectable in the next ∼5yr.
Description:
Maser stars that are detected in both the IR and radio are used to
bring the IR stellar positions into an Sgr A* (radio) rest frame.
Reid+ (2007ApJ...659..378R 2007ApJ...659..378R) presented radio data of masers that were
based on five epochs of observations over the period of 1995-2006.
In this paper, we use radio positions and proper motions from M. Reid
(2018, private communication) that have been updated with two
additional epochs of observations.
All the data for the IR observations of SiO masers in the Galactic
Center region were obtained using the laser guide-star adaptive optics
(LGSAO) facility on the Keck II telescope at the W. M. Keck Observatory.
Images were obtained with a near-infrared facility imager (NIRC2;
PI: K. Matthews) through the K' (λ0=2.12um,
Δλ=0.35um) bandpass between 2005 June 30 and 2017 May 5.
Objects:
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RA (ICRS) DE Designation(s)
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17 45 40.04 -29 00 28.2 Sgr A* = NAME Sgr A*
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 108 742 Galactic Center secondary IR astrometric standard
and point-spread function (PSF) stars
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See also:
J/A+A/470/191 : Mid-IR and radio interferometry of S Ori (Wittkowski+, 2007)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/ApJ/725/331 : Astrometry in the Galactic Center (Yelda+, 2010)
J/A+A/557/A82 : NIR polarimetry of Galactic center sources (Buchholz+, 2013)
J/ApJ/783/131 : Kinematic of stars in Galactic center (Yelda+, 2014)
J/ApJ/830/17 : GC secondary IR astrometric standards (Boehle+, 2016)
J/ApJ/863/15 : Spitzer, VLT and Keck NIR light curves of SgrA* (Witzel+, 2018)
J/A+A/618/L10 : SgrA* orbital motions with GRAVITY (GRAVITY Col., 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Name of the standard
11- 14 F4.1 mag K'mag [7.4/15.7] K' magnitude
16- 22 F7.2 yr T0 [2009.4/2013.8] Average time of the
IR positional measurement
24- 28 F5.2 arcsec Rad [0.36/17.6] Radius
30- 36 F7.4 arcsec dRA [-6.4/15.5] Positional offset in RA (1)
38- 41 F4.2 mas e_dRA [0.05/1.1] Uncertainty in dRA, milli-arcsec (2)
45- 51 F7.4 arcsec dDE [-9.52/12.31] Positional offset in DE (1)
53- 56 F4.2 mas e_dDE [0.06/3.5] Uncertainty in dDE, milli-arcsec (2)
60- 65 F6.3 mas/yr vRA [-9.01/13.4] Velocity fit in RA
67- 71 F5.3 mas/yr e_vRA [0.009/0.4] Uncertainty in vRA (3)
73- 78 F6.3 mas/yr vDE [-9.3/11.2] Velocity fit in DE
80- 84 F5.3 mas/yr e_vDE [0.016/0.9] Uncertainty in vDE (3)
86- 86 A1 --- Std [Y/N] Astrometric Standard (4)
88-108 A21 --- PSF PSF Star (5)
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Note (1): Positional offset from final position of Sgr A*
Note (2): Positional errors include centroiding and alignment but do not include
error in position of Sgr A* (±10mas for epoch 1996).
Note (3): Velocity errors do not include error in velocity of Sgr A*
(0.018mas/yr and 0.026mas/yr in RA and Dec respectively).
Note (4): Indicates whether the star is a secondary astrometric standard.
Note (5): Indicates for which mosaic field the star was used to create a PSF.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 12-Aug-2020