J/ApJ/710/1032 Proper motions in ω Cen (Anderson+, 2010)
New limits on an intermediate-mass black hole in Omega Centauri. I. Hubble Space Telescope photometry and proper motions. Anderson J., van der Marel R.P. <Astrophys. J., 710, 1032-1062 (2010)> =2010ApJ...710.1032A
ADC_Keywords: Clusters, globular ; Photometry, HST ; Photometry, UBVRI ; Proper motions Keywords: catalogs - globular clusters: general - techniques: photometric - globular clusters: individual (Omega Cen) - stars: kinematics and dynamics - techniques: image processing Abstract: We analyze data from the Hubble Space Telescope's (HST) Advanced Camera for Surveys of the globular cluster (GC) Omega Cen. We construct a photometric catalog of 1.2x106 stars over a 10'x10' central field down to below BF435W=25 (M∼0.35M☉). The 2.5 to 4 year baseline between observations yields a catalog of some 105 proper motions over a smaller area, with 53382 "high-quality" measurements in a central R≲2' field. Artificial-star tests characterize the photometric incompleteness. We determine the cluster center to ∼1" accuracy from star counts using two different methods, one based on isodensity contours and the other on "pie slices." We independently confirm the result by determining also the kinematical center of the HST proper motions, as well as the center of unresolved light seen in Two Micron All Sky Survey data. All results agree to within their 1"-2" levels of uncertainty. The proper-motion dispersion of the cluster increases gradually inward, but there is no variation in kinematics with position within the central ∼15": there is no dispersion cusp and no stars with unusually high velocities. We measure for the first time in any GC the variation in internal kinematics along the main sequence. Description: This paper draws on three HST data sets, taken with the Wide-Field Channel (WFC) of the ACS. * The first data set is GO-9442 (PI: Cool), taken over the period between 2002 June 27 and 30 in F435W (B), F625W (R) and F658N (Hα). * The second data set is GO-10252 (PI: Anderson), taken on 2004 December 11, in F606W (V) and F814W (I). * The third data set is GO-10775 (PI: Sarajedini). These observations were taken as a part of a large survey of 65 GCs, on 2006 June 22 in F606W and F814W. Objects: ------------------------------------------------ RA (2000) DE Designation(s) ------------------------------------------------ 13 26 47.28 -47 28 46.1 Omega Cen = NGC 5139 ------------------------------------------------ File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 77 1164317 Star catalog table2b.dat 77 500000 Artificial star catalog (includes 110843 empty rows) table3.dat 41 500000 Parameters for the artificial-star tests table4.dat 89 108507 Proper-motion catalog for the central field table4b.dat 89 61293 Proper-motion catalog for the major-axis field
See also: B/hst : HST Archived Exposures Catalog (STScI, 2007) VII/202 : Globular Clusters in the Milky Way (Harris, 1997) J/AJ/140/631 : HST WFC3/UVIS photometry of omega Cen core (Bellini+, 2010) J/A+A/493/959 : UBV(RI)cHalpha photometry in omega Cen (Bellini+, 2009) J/ApJ/663/1021 : Log of ω Cen scientific images (Castellani+, 2007) J/ApJ/663/296 : UBV(RI)c phot. of omega Cen (NGC5139) subgiants (Villanova+, 2007) J/A+AS/115/297 : BVRI photometry of Central Field of Omega Cen (Lynga+, 1996) J/PASP/106/828 : BVRI photometry of omega Cen (Walker 1994) Byte-by-byte Description of file: table2.dat table2b.dat
Bytes Format Units Label Explanations
1- 9 F9.3 pix XREF ?=0 X position in reference frame (G1) 11- 19 F9.3 pix YREF ?=0 Y position in reference frame (G1) 21- 28 F8.4 mag Bmag ?=0 Instrumental HST F435W band (B) magnitude (1) 30- 37 F8.4 mag Rmag ?=0 Instrumental HST F625W band (R) magnitude (1) 39- 43 F5.3 pix e_XREF ?=9 RMS scatter of single-exposure X position (2) 45- 49 F5.3 pix e_YREF ?=9 RMS scatter of single-exposure Y position (2) 51- 55 F5.3 mag e_Bmag ?=9 RMS scatter of single-exposure F435W observation (2) 57- 61 F5.3 mag e_Rmag ?=9 RMS scatter of single-exposure F625W observation (2) 63- 65 I3 --- NBc [1/9]?=0 Number of B images where star could be found 67- 69 I3 --- NBf [1/9]?=0 Number of B images where star was found 71- 73 I3 --- NRc [1/9]?=0 Number of R images where star could be found 75- 77 I3 --- NRf [1/9]?=0 Number of R images where star was found
Note (1): Where ZPVEGA(F435W)=32.043 and ZPVEGA(F625W)=31.991. Stars brighter than about 13.75 are saturated in the deep exposures, and therefore have larger systematic errors. Note (2): In principle, the errors in columns 1 through 4 can be constructed by dividing these RMSs by the square root of the number of observations (columns 10, 12 or their sum). However, not all errors are random, so this may underestimate the errors. The RMS can be used to help select stars with good measurement consistency.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 8 F8.2 pix pXREF Parameter X position in reference frame (G1) 10- 17 F8.2 pix pYREF Parameter Y position in reference frame (G1) 19- 26 F8.4 mag Bimag Instrumental HST F435W band (B) magnitude 27- 34 F8.4 mag Rimag Instrumental HST F625W band (R) magnitude 35 I1 --- NdB Number of deep F435W images star could have been found in 37 I1 --- NdR Number of deep F625W images star could have been found in 39 I1 --- NsB Number of short F435W images star could have been found in 41 I1 --- NsR Number of short F625W images star could have been found in
Byte-by-byte Description of file: table4.dat table4b.dat
Bytes Format Units Label Explanations
1- 7 F7.2 pix XREF X position in master frame (G1) 9- 15 F7.2 pix YREF Y position in master frame (G1) 17- 23 F7.3 mag Bmag Calibrated VEGAMAG HST BF435W band magnitude 25- 31 F7.3 mag Rmag Calibrated VEGAMAG HST RF625W band magnitude 33- 40 F8.4 mas/yr mux Proper motion in X; x along -RA 42- 49 F8.4 mas/yr muy Proper motion in Y; y along DEC 51- 56 F6.4 mas/yr e_mux Error in mux (1) 58- 63 F6.4 mas/yr e_muy Error in muy (1) 65- 72 F8.4 mas/yr muMaj Proper motion projected along major axis (2) 74- 81 F8.4 mas/yr muMin Proper motion projected along minor axis (2) 83- 84 I2 --- n1u Number of 1st epoch observations in proper motion calculation 86- 87 I2 --- n2u Number of 2nd epoch observations in proper motion calculation 89 I1 --- Q [0/1]? The "good" flag (1: small internal errors) (3)
Note (1): Based on multiple independent estimates. Errors are determined by adding the errors in the average for each epoch in quadrature, assuming no inter-epoch transformation error. Note (2): The major/minor axis projections were made assuming the major axis to be 100 degrees East of North. Note (3): The "good" flag refers to the 53382 stars that are part of the high-quality subset defined in Section 3.6.2. Within this sample, the typical proper-motion error is better than 0.1mas/yr in each coordinate, corresponding to 0.008 pixel over the four-year baseline.
Global notes: Note (G1): The 3 sets of observations are GO-9442 (J2002.49; PI: Cool), GO-10252 (J2004.95; PI: Anderson) and GO 10775 (J2006.56; PI: Sarajedini). The "reference" frame was constructed in a distortion-corrected frame based on the central pointing. To align our frame with R.A. and decl., we found the linear transformation from this frame into the frame constructed in Anderson et al. (2008AJ....135.2055A), based on the GO-10775 Treasury data, which has a pixel scale of 50mas/pixel and was aligned with R.A. and decl., and has the Harris (1996, Cat. VII/195; superseded by Cat. VII/202) cluster center at [3000,3000]. (We will refer to this as the "traditional" center, since it is based on the literature at the time). We conformally transformed our reference frame into this frame and added 4000 to each coordinate, so that our entire field would be contained within the range [1:14000,1:14000], with the center close to [7000,7000]. We refer to this frame as the "master" frame. See section 3.1 for further explanations.
History: From electronic version of the journal References: van der Marel & Anderson, Paper II, 2010ApJ...710.1063V
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 15-Mar-2012
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