Cross-matching the Hubble Legacy Archive
22 July 2010
Nathan Cole (JHU)Tamas Budavari (JHU)
Steve Lubow (STScI)Alex Szalay (JHU)
Brian McLean (STScI) Rick White (STScI)
2010 STScI Calibration Workshop
HLA examplesHST_10503_13_ACS_WFC_F606W HST_10503_18_ACS_WFC_F606W
HLA examples
Absolute astrometry of an image ~0.3” Relative astrometry between images
~0.1” Different guide stars Time lapse Etc…
Many overlapping images Link sources? Improve relative astrometry?
Crossmatch and Correction Crossmatch
Probabilistic algorithm all matches and probabilities Budavari and Szalay. 2008, ApJ, 679, 301
3-Dimensional rotation Describes both translation and rotation,
locally
Astrometric Correction
Assuming infinitesimal rotation, ω
▪ r = source position, c = current “best guess” position
Solution is linear !FAST!
▪ Sum a 3x3 matrix▪ Sum a vector▪ Solve!
ProcedureImage 1 Image 2
Take all objects with Flag = 0 (Stellar Sources)
Match ListCalculate probs,Matches with prob>0.95,Best guess position (c) as weighted avg
Trimmed Match List
Transformation (ω1)Transformation (ω2)
Image 1 positions (r1),Best guess positions (c)
Image 2 positions (r2),Best guess positions (c)
Updated source list 1Updated source list 2
r1’ = r1 – r1 x ω1 r2’ = r2 – r2 x ω2
IF: Max change in position > 1e-17
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 0
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 1
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 2
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 3
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 4
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 5
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 6
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Step 7
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Relaxed by Golden Ratio
0 0.05 0.1 0.15 0.2 0.250
100
200
300
400
500
600
700
Step 0Step 1Step 2Step 3Step 4Step 5Step 6Step 7
|r1-r2| (arcseconds)
Co
un
t
-0.00999999999999997 0.01 0.03 0.05 0.070
100
200
300
400
500
600
700
Step 0Step 1Step 2Step 3Step 4Step 5Step 6Step 7
|r1-r2| (arcseconds)
Co
un
t
0.0034”
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F606W
Relaxed by Golden RatioZoom
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 0
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 1
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 2
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 3
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 4
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 5
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 6
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 7
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Step 8
3.8835 3.8836 3.8837 3.8838 3.8839 3.884 3.8841-32.1766
-32.1765
-32.1764
-32.1763
-32.1762
-32.1761
-32.176
-32.1759
Right Ascension (deg)
Declinati
on (
deg)
0 0.05 0.1 0.15 0.2 0.250
100
200
300
400
500
600
700
800
900
1000
Step 0Step 1Step 2Step 3Step 4Step 5Step 6Step 7Step 8
|r1-r2| (arcseconds)
Co
un
tHST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Relaxed by Golden Ratio
0 0.01 0.02 0.03 0.04 0.05 0.06 0.070
100
200
300
400
500
600
700
800
900
1000
Step 0Step 1Step 2Step 3Step 4Step 5Step 6Step 7Step 8
|r1-r2| (arcseconds)
Co
un
t
0.0020”
HST_10503_13_ACS_WFC_F606W -- HST_10503_18_ACS_WFC_F814W
Relaxed by Golden RatioZoom
Upcoming…
Improved astrometry Milli-arcsec (sub-pixel) precision Corrections calculated for complete HLA
catalog
New catalog Link sources between pointings Link sources between instruments
Cross-matching Algorithm
where when
where
Budavari and Szalay. 2008, ApJ, 679, 301
Astrometric Correction Solution
Assuming small rotation,
where
