|
Description
The Hubble Ultra Deep Field (UDF, Principle Investigator: Steven V. W. Beckwith) is a 400-orbit Hubble Space Telescope (HST) Cycle 12 program to image a single field of the Wide Field Camera (WFC) of the Advanced Camera for Surveys (ACS) in four filters: F435W (B), F606W (V), F775W (i), and F850LP (z). The observations took place over 4 months from September 2003 to January 2004 under two program IDs: 9978 and 10086. The observations consist of half-orbit exposures, cycling through each of the filters in a 4-point dither pattern to provide sub-pixel sampling, as well as a larger-scale 3-point line pattern to cover the 2 second of arc gap between the two ACS/WFC chips. The total exposure times are summarized below, with typical exposure times of 1200s for individual images. The AB magnitude zero-points for ACS are current as of March 2004. <pre> Number of Number of Total Exp. AB mag. Orbits Exposures Time (s) zero-point B (F435W): 56 112 134880 25.673 V (F606W): 56 112 135320 26.486 i (F775W): 144 288 347110 25.654 z (F850LP): 144 288 346620 24.862 </pre> This HEASARC Browse table contains the list of sources found in the deepest UDF image, the i-band image. The formal i-band catalog contains a total of 10,040 sources. A visual inspection of all the sources revealed an additional 5 spurious sources (which do not form part of the catalog). Moreover, the deblending algorithms in SExtractor caused an additional 100 sources to be missed, owing to their proximity to brighter sources. These sources were identified manually, and formally added by doing another SExtractor run with considerably different deblending parameters, in order to detect them all. An initial list of 208 sources was produced, which was then reduced to a total of 100 sources after visual inspection and rejection of sources that were clearly part of previously identified sources. These additional sources are denoted by ID numbers 20001 - 20208. Although the i-band image is the deepest image, there remain additional sources that were not detected in i-band, even though they may be detected in one of the other bands. Therefore, the authors produced a second catalog based on detection in the z-band image (not part of the present table), and an additional 39 sources are included from this catalog that were detected at > 10 sigma in the z-band image, but were not in the catalog that was run using the i-band image for detection. These additional sources are denoted by ID numbers above 30000. More details are found in the file <a href="https://cdsarc.cds.unistra.fr/ftp/cats/II/258/intro.txt">https://cdsarc.cds.unistra.fr/ftp/cats/II/258/intro.txt</a> or from the UDF home page at <a href="http://www.stsci.edu/hst/udf/">http://www.stsci.edu/hst/udf/</a>. This table was created by the HEASARC in May 2005 based on CDS table II/258/udf-i.dat. This is a service provided by NASA HEASARC .
|
