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Validation of HLA Source Lists

This document presents plots and tables from various presentations validating the HLA DAOPHOT and SExtractor source lists. It compares different visits, catalogs, and instruments to assess photometric and astrometric accuracy. The results show that the source lists are well within the design goals, with improvements made over time. However, for specific science goals, it may be necessary to create custom source lists.

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Validation of HLA Source Lists

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  1. Validation of HLA Source Lists Overview Plots Summary Feb. 4, 2008 Brad Whitmore

  2. 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)

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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 : • Extended nature of objects. • SDSS phot is ground- based, so some mismatch due to how things look from space and from the ground (i.e., different resolution). • Transformations from SDSS filters to HLA.

  9. 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.

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

  11. Summary 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. 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. 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. 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).

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