cross-matching the hubble legacy archive

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