Validation of HLA Source Lists

Feb. 4, 2008

Brad Whitmore

1. Overview

2. Plots

3. Summary

Overview

A number of validation checks have been made of the

the HLA DAOPHOT source lists.

Fewer validation checks have been made of the SExtractor

source lists, hence they have been designated as Beta products.

This document collects plots and tables from various

presentations that have been made during the past several months

(e.g., to the STScI Users Committee).

A more formal set of documents will be available in the future

(e.g., PASP paper, Instrument Science Reports)

Comparison of four different visits

47TUC - Stellar Field

NOTE: The offset at the bright end is due to saturation in the HST image.

• DAOPHOT and SExtractor match to better than 0.02 mag when comparing aperture photometry for F435W image.

• 4 different visits (fields A - D) match to better than 0.02 mag.

• Only 1 star is not saturated in F555W observations, but that matches with Stetson to -0.008 mag.

Comparison with M31 Catalog

M31 Halo (Tom Brown) vs. HLA_9453_33

Bottom Panel• Circled points predicted by HLA

to be saturated. Good prediction.• Offsets and RMS within design

goals.(i.e., 0.1 offset, 0.3 RMS)Middle Panel• Find correlations between

residuals and Concentration Index (CI)

Top Panel• Use correlation to select small CI

and improve offset and RMS

NOTE • Tom Brown adds ~ 100 orbits to

get to 31 mag• HLA is single orbit so only

reaches 27 mag

Comparison with M31 Catalog - deeper

M31 Halo (Tom Brown) vs. HLA_9453_33

.

Middle Panel

• Correlations between residuals and CI less well defined since lower S/N

• Smaller residuals for small CI, as might expect

Bottom and Top Panels

• Similar to brighter comparison with RMS increasing for fainter objects, as expect.

• Offsets and RMS still well within design goals even for faintest objects in HLA catalog.

Comparison between HRC and WFC for slightly Resolved

Star Clusters

HRC in crowded part of Antennae vs. WFC

Conclusions• Good photometric offset

and RMS comparisons, especially for bright objects

• Astrometry for HRC is not very good (i.e. 0.789 arcsec offset) as expected since small field of view and crowded region means no standard stars to compare with.

Comparison with SDSS

Comparison of random HLA source list vs. Sloan Digital Sky Survey (SDSS) catalog

Conclude• Photometric offset and

RMS well within design goals for stellar like sources

• Astrometry well within design goal (< 0.3 arcsec)

• Not many objects to compare with generally

• Several other comparisons give similar results.

Comparison of SExtractor source list with SDSS

Random HLA field vs. SDSS - extended objects

Conclusions • Photometric offsets and

RMS barely within design goals.

Several reasons likely :1. Extended nature of

objects.2. SDSS phot is ground-

based, so some mismatch due to how things look from space and from the ground (i.e., different resolution).

3. Transformations from SDSS filters to HLA.

Comparisons for stellar field, slightly

extended objects, and faint galaxies

47 TUC - stellar field

• Comparison with Stetson ground-based B is excellent

• Shows multidrizzle maintains photometric integrity for ACS images

M87 - slightly extended, globular clusters• Extended objects have offset since using stellar aperture corrections.

• Correction made in top panel, but not general, so flag extended sources with 999 for “total mag” in data files

UDF - faint galaxies • SExtractor source lists look promising, but very limiting testing so far.

DAOPHOT Source List Artifacts (Early Data Release, Data Release 1)

Image Edge effects

Blank Cosmic Rays

Saturated (“swarm”)

Misc Total

col 1-3

Antennae

10188_10_color

0.05 % 0.00%

4.8 % 0.0%

2.8 % 0.0%

0%

0.0%

0% 0.0%

7.6% 0.0%

M101

9490_01_color

0.3% 0.0001%

0%

0.0%

1.2 % 0.5%

0 %

0.0%

2.1%

0.2%

3.3% 0.7%

A1689

9289_51_850

4.3 % 0.00%

0 %

0.0%

0 % 0.0%

40%

0.00%

0 % 0.0%

4.3 % 0.0%

SBS1415

9361_01_606

0.9 % 0.00%

0 %

0.0%

0 % 0.0%

33 %

0.00%

0 % 0.3%

0.9 % 0.3 %

47 Tuc (no cr-split)

10048_a2_color

0 % 0 % 16.7 %

NA

10 %

NA

3.3 %

NA

20 % NA

NOTE: 1. Conclude: The Data Release 1 (Feb. 2008) source lists are much improved over Early Data Release (July 2007)

2. The HLA design goal is < 20 % artifacts. These source lists have room to spare. Some observing strategies (e.g., N=2 hence impossible to remove all cosmic rays) result in poorer quality source lists, hence the 20 % is still relevant.

3. No longer make source list for 47_tuc WFC, since all N=1. The HRC catalog is quality=1 .

Summary1. All tests of the DAOphot source list to date have shown them to be well

within the design goals of 0.10 absolute astrometry, and 0.3 mag RMS.

2. The existing tests of the Sextractor source lists are also promising, but have not been as extensive, hence we are defining these as BETA products for now.

3. The number of artifacts has been improved dramatically since the Early Data Release, but there will always be artifacts at some level since some observing strategies make it difficult to remove cosmic rays (e.g., N= 2), hot pixels (undithered), or impose other limitations (e.g., saturated, very crowded, …). We have defined < 20 % artifacts as our design goal.

4. It should be kept in mind that these are meant to be “general use” source lists. In most cases it will be necessary to make your own source lists focused on your specific science goals (e.g., going as deep as possible).