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The WFPC2 Association Project Version 2

This page provides access to Version 2 of the WFPC2 Association Project, the complete stacks of all public WFPC2 observations obtained with the Hubble Space Telescope up to April 2006. The WFPC2 Association Project is a collaboration between the NRC's Canadian Astronomy Data Centre (CADC), Victoria and the Space Telescope European Coordinating Facility, ST-ECF, Munich and the Space Telescope Science Institute (STScI), Baltimore.

The Canadian Astronomical Data Center (CADC), the Space Telescope European Coordination Facility (ST-ECF) and the Multimission Archive at STScI (MAST) are pleased to make available combined images from the Wide Field Planetary Camera 2 of the Hubble Space Telescope. These combined images are the products of the basic registration and averaging of related sets of WFPC2 images, referred to as associations, that is otherwise usually performed by archival researchers after the retrieval of individual images. As of December 2006, over 26,866 combined images have been created from associations of nearly 90,000 individual WFPC2 images. The product of many person-years of development at CADC and ST-ECF, these combined images form an important new set of high-quality astronomical data that should be useful for a wide range of investigations. Also, they provide better preview images of a given field than the individual WFPC2 images.

Association Example: U92C4201B
U92C4201B

Contents:

Association members definition
- Caveat: Unsupported filter bands
Generating association products
1. Members RAW file production
2. Members offset determination: Cross correlation, Jitter, WCS
3. Stacking members into a cleaner and deeper product (IMSTACK)
4. Product astrometric correction
5. Source extraction (for preview)
6. Statistical image classification
7. Characterisation and header augmentation
8. WFPC2 Association Version 2: The filenames

Association members definition

Aim

Description

Recipe

Once a week, ST-ECF runs an association identification and maintenance software. Various database tables containing the observation log and other metadata are used as input to the process that assembles WFPC2 individual observations into groups. The criteria used for this are here indicated. Members of an association have to have:

Same proposal identifier
Same filter
Same aperture (hence same reference pixel and pixel scale)
Same position (within 100 WF4 pixels)
Same roll angle (within 0.03 degrees)

Such groups are stored in the asn_maint and asn_maint_mem tables.
Being WFPC2 an active instrument, versioning of associations was implemented from the beginning: potential new members of an already existing association are considered for inclusion, hence augmenting the original association; changes in the input data or metadata of existing associations trigger the creation of new versions, making the old associations obsolete.

Main outcome & file names

The main outcome is the maintenance of the association tables stored at ST-ECF and replicated (via the SYBASE Replication Server) at CADC.

Header keywords

Precision

Caveat

For the production of WFPC2 Association Project Version2, we have limited ourselves to the observations acquired with calibrated filters, that is, for which photometric zeropoint exists. Here are the list of filters which have been rejected from the processing list. This is not stopping users to get the participating members and stack them by themselves. It is just that, without proper calibration parameters, we were not able to produce fully characterised and calibrated final images from those associations.

Excluded filters:

%POL%
%F160AW%
%FR%
%LP
%BN%
%BW%
%FQ%

Also, the CADC has decided not to generate products for those observations which are used mainly for calibration purposes, and which are filtered out from the CADC science table.
Here some statistics (December 2006)

Number of associations in table: 31738
Number of associations in valid filters: 27096
Number of associations which are public: 26866
Number of processed associations:

Hence the difference between the number of associations identified by the ST-ECF software and the data products actually available.

Supported filters

F1042M F122M F170W F185W F218W F255W F300W F336W F343N F375N F380W F390N F410M F437N F439W F450W F467M F469N F487N F502N F547M F555W F569W F588N F606W F622W F631N F656N F658N F673N F675W F702W F791W F814W F953N

Generating association products

Members RAW file production

Aim

Generating and caching the RAW files.

Description

The very first step is to produce all the necessary RAW files from the STScI delivered telemetry (POD) files.

The POD files are translated into usable RAW files using the Solaris based software suite called OTFR (or on the fly reprocessing) developed at STScI following the ideas which were implemented at CADC a few years before. These files are in integer format, thus highly compressible. Keeping only the POD files for the HST archive has drastically reduced the need for storage space but requires more compute power in order to get to a calibrated science file.

Thus for the WFPC2 Associations project V2, the CADC has cached all the RAW files needed to produce the final associations.

The following tables gives some idea of the number of files involved. As an example, let's look at the following association: U92C4201B

Metadata on U92C4201B
ASSOC_ID	Number of Members	Total Exptime	STATUS	MIXGAIN	Public Date	Creation Date	Validation Date	Filter
U92C4201B	42	44600.000000	Done	N	Nov 14 2005 6:18AM	Oct 22 2004 12:01PM	Mar 30 2006 11:08PM	F606W

The members of this associations, 42, are the following:

Members of U92C4201B
Dataset	exptime	gain	Member creation
U92C2801M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C2802M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C2803M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C2804M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3001M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3002M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C3003M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3004M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3201M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3202M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C3203M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3204M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3401M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3402M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C3403M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3404M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3601M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3602M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C3603M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3604M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C3801M	800.000000	7.000000	Oct 22 2004 12:01PM
U92C3802M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C3803M	900.000000	7.000000	Oct 22 2004 12:01PM
U92C3804M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4001M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4002M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C4003M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4004M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4201M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4202M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C4203M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4204M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4401M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4402M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C4403M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4404M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4601M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4602M	1000.000000	7.000000	Oct 22 2004 12:01PM
U92C4603M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4604M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4801M	1100.000000	7.000000	Oct 22 2004 12:01PM
U92C4802M	1000.000000	7.000000	Oct 22 2004 12:01PM

And for each of those members, the CADC had cached the following files

Raw files for U92C4802M
File name	Size (bytes)
U92C4802M.D0F	File size: 5175360
U92C4802M.DGR	File size: 31680
U92C4802M.LOG	File size: 1373
U92C4802M.Q0F	File size: 5175360
U92C4802M.Q1F	File size: 103680
U92C4802M.SHF	File size: 37440
U92C4802M.TRL	File size: 8640
U92C4802M.X0F	File size: 103680

Recipe

As this software has been distributed from STScI, please refer to the STScI OTFR for its documentation. It is delivered as binary applications to CADC and ST-ECF.

Main outcome & file names

For each original WFPC2 observation, member of the given association, the standard RAW set of files is produced, including extensions d0, q0, q1, sh, x0, input to the calibration pipeline (see Par. 2). Here is a file with the description of each extension.

Header keywords

The OTFR software, regularly maintained and installed at all three sites, reconstructs the header keywords according to the best knowledge available at the time of the request.

Calibration of each of the members

Aim

Calibrating each member to obtain the necessary input files (CALWP2 output extensions: c0,c1).

Description

The input files to the WFPC2 association pipeline are the calibrated products generated with the standard STSDAS CALWP2 task.

Recipe

We are calibrating each WFPC2 RAW files using the standard calwfp2 from stsdas. This is identical to what STScI and ST-ECF is doing. We are running the same version of each elements of the pipeline. Please refer to WFPC2 standard calibration pipeline (CALWP2).
Main outcome & file names

The pipeline generates the *.c0.fits (calibrated science data) and *.c1.fits (data quality flag image) files for each (member) observation.

Header keywords

The calibration process is adding all the necessary keywords and history to the calibrated files.
Members offset determination: Cross Correlation, Jitter, WCS

Aim

Determining and assigning to each member its offset with respect to the first and deepest member of the association (named the association leader).

Description

Three types of offsets are measured or computed using the following methods:
- measured via cross correlation
- computed from the observatory monitoring system information (aka, jitter)
- computed from the World Coordinate System in the header of the observation fits
Recipe
1. Shifts measured via cross-correlation
  The cross-correlation method, is supposed to offer the most reliable offsets.
  
  It actually measures the shifts onto the images providing also the error on the measurement. To ensure the correctness of the measurements two things are taken into consideration:
  1. The provided error
  2. Since the shifts of each individual WFPC2 chip are computed separately, a voting system is introduced to make sure that the intra-chip shifts agree.
2. Shifts computed using the jitter information (Observatory Monitoring System)
  For each observation, RA, DEC, ROLL measurements (averages and standard deviations) are extracted, along with some of the telemetry keywords; the comparison of RA and DEC with those of the association leader provides the jitter offsets.
  
  The quality of the jitter is also evaluated, see the "jitter flag" and the jitter table.
  These offsets were used in the previous associations (associations of type "A").
3. Shifts computed using the WCS information (science headers)
  Each association member's WCS is compared with the WCS of the association leader (defined to be the deepest first observation in the group).
Of the three methods, the cross-correlation algorithm is preferred
In those cases where the cross-correlation method fails (not enough signal, typically in blue filters), the jitter information is used.
In case the jitter information is missing or provides non-reliable offsets, the World Coordinate System (WCS) information is used.

Stacking members into a cleaner and deeper product (IMSTACK)

Aim

Optimising the stacking algorithm

Description

The algorithm used to stack the images are describe in this document. Also, please refer to the description of the stacking algorithm.

Recipe

Image shifting, scaling, zeropoint: We adopted a shift-and-add approach for combining the individual members of the association. Images are shifted to a common reference frame using fractional pixel shifts normally accurate to 0.015 arcseconds or better and then combined using a weighted average. The frames are scaled to the average exposure time and a zeropoint offset is added to correct for background differences between the images. Artificial Skepticism (AS) (Stetson 1989, V Advanced School of Astrophysics [Univerisidade de Sao Paulo], p.1.) is a method of computing a robust average image using a continuous weighting scheme that is derived from the data themselves.

The adaptive weights are given by the equation:
weight formula

where w_i is the weight of the i-th pixel, is the sigma of the i-th pixel in the stack as derived from the read noise and gain. The "natural" pixel weights are therefore modified by a Lorentzian-like function that puts decreasing weight on increasingly suspicious values such as cosmic rays without fully clipping any value. The ri term, which is the residual between the current average pixel value and the value of the ith pixel, is recomputed at each iteration. Convergence is achieved quickly, and the weights only need to be iterated a few times (we adopt five iterations).

Weight Maps: After the first pass through the AS stacking is complete the resulting stack is used to back-predict the variance in each pixel yielding an improved, more robust estimate that is free of cosmic rays. The AS stacking is then repeated with this improved weight map. An output weight map is produced for the stack by propagating the AS weights for the final image.

Main outcome & file names

The generated stacked image is packaged by the chip in 8 files (example dataset name: u5351005b):

u5351005b_1.fits	Science stacked image chip 1
u5351005b_2.fits	Science stacked image chip 2
u5351005b_3.fits	Science stacked image chip 3
u5351005b_4.fits	Science stacked image chip 4
u5351005b_var_1.fits	Variance weight map for chip 1
u5351005b_var_2.fits	Variance weight map for chip 2
u5351005b_var_3.fits	Variance weight map for chip 3
u5351005b_var_4.fits	Variance weight map for chip 4

where each science chip image is expressed as a weighted average of the input images, and it is not background subtracted.

Header keywords

The header keywords of these products obviously reflect the processing applied to the data:

NCOMBINE	Number of input images
EXPTIME	Average exposure time (seconds)	It is the appropriate exposure time for the actual level of counts in the output images.
TEXPTIME	Total exposure time (seconds)	It would correspond to the count levels of the output image if multiplied by NCOMBINE.
MEXPTIME	Average exposure time (seconds)
ATODGAIN	Equivalent gain for stack (e^-/DN).	It equals the original gain multiplied by the value of the NCOMBINE keyword.

Precision

Astrometric correction

Aim

Correcting the CRVAL1 and CRVAL2 (right ascension and declination of the reference pixel in the World Coordinate System header keywords) according to USNO2B (and 2MASS) sources available within the field of view of the observation.

Description

The absolute pointing accuracy of HST is immediately related to the accuracy with which the position of the guide stars is known. So far, the HST has relied onto the GSC catalogue version 1, which is known to have an uncertainty of about 1-2 seconds of arc. To pinpoint with higher accuracy the association products onto the sky, we setup a task in the pipeline named astrom_corr. Such task matches a reference list of stars with the stars extracted from the association products. We use 2 different source catalogues: USNO2B and 2MASS. Solutions using both catalogues independently are found and stored in the header of each products. The actual WCS is updated using the USNO2B solution if proved robust (enough stars were found). When no solutions (or bad matches) are found, the original pointing solution is retained, still USNO2B and 2MASS information will be found in the header.

Please note that we are correcting only the zero point of the WCS solution and are not correcting any scale nor rotation for the stacks.

Recipe

Main outcome & file names

The outcome is given by the augmented astrometric metadata available in the header. A few files are also produced in order to judge the quality of the astrometric correction. Since the entire pipeline is been executed without intervention, it is important that we produce some graphs representing the quality of the correction to let the user decide if he/she want to revert to the original solution. This is done simply in inverting the OCRVALn keywords with the CRVALn. The correction applies a shift only, with no rotation or no scale changes.

Astrometric correction Files
u96g0402b_2mass_astrom_corr_shiftarray.txt
u96g0402b_2mass_astrom_corr_summary.txt
u96g0402b_astrom_2mass.png	Difference Map of 2MASS stars against found sources
u96g0402b_astrom_usno.png	Difference Map of USNO stars against found sources
u96g0402b_usno_astrom_corr_shiftarray.txt	Shifts
u96g0402b_usno_astrom_corr_summary.txt	Shifts

Header keywords

For each astrom_corr pass, we store various parameters within the header of the science images as well as within the CADC WFPC2 databases. Since the correction is performed unattended we save the original CRVAL parameters in the header as well the the CRVAL values for the second catalogue correction. So a user can always revert to the original WCS, or use the second catalogue.

We refer to the USNO2B catalog as the PRIMARY one, and to 2MASS as the SECONDARY one.

ASTROM CORR INFO
ASTCOV	Version of the pipeline step
ASTCOS	Execution date for this step
ASTFLAG	Step completion status flag
ASTDETH	SExtractor detection threshold
ASTCOMM	Overall comment
ASTFLAG	Overall status, one of the following: complete := successfully completed; omitted := if not enough sources were found; failed := necessary files were not produced for any reason; rejected := the standard deviation of the solution is too high,or undetermined.
ASTNSEX	ASTROM number of SExtracted sources used
CRVAL1	[deg] ASTROM new/old? CRVAL1 value
CRVAL2	[deg] ASTROM new/old? CRVAL2 value
OCRVAL1	[deg] ASTROM Original CRVAL1 value
OCRVAL2	[deg] ASTROM Original CRVAL2 value
CATALOGUE 1 (USNO)
PCRVAL1	[deg] ASTROM primary CRVAL1 value
PCRVAL2	[deg] ASTROM primary CRVAL2 value
RA_OFF1	[deg] ASTROM Primary Shift applied to CRVAL1 (if any)
DEC_OFF1	[deg] ASTROM Primary Shift applied to CRVAL2 (if any)
astrefc1	Reference to the Primary catalogue (USNO2B)
astflag1	Primary catalogue corr. status. One of: complete, failed, rejected, omitted. See ASTFLAG above.
astcomm1	Primary catalogue corr. comment
astocat1	Num primary catalog sources found
astncat1	Num primary catalog sources used
astnbst1	Num best sources for primary corr catalogue
astxoff1	delta_ra * cos(delta) in arcsec
astyoff1	delta_dec in arcsec
astxsig1	sigma_ra * cos(delta) in arcsec
astysig1	sigma_dec in arcsec
ra_off1
dec_off1
CATALOGUE 2 (2MASS)
SCRVAL1	[deg] ASTROM secondary CRVAL1 value
SCRVAL2	[deg] ASTROM secondary CRVAL2 value
RA_OFF2	[deg] ASTROM Secondary shift with respect to original CRVAL1
DEC_OFF2	[deg] ASTROM Secondary Shift with respect to original CRVAL2
astrefc2	Reference to the Secondary catalogue (2MASS)
astflag2	Secondary catalogue correction status. One of: complete, failed, rejected, omitted. See ASTFLAG above.
astcomm2	secondary catalogue corr. comment
astocat2	num secondary catalog sources found
astncat2	num secondary catalog sources used
astnbst2	num best sources for secondary corr catalogue<
astxoff2	delta_ra * cos(delta) in arcsec
astyoff2	delta_dec in arcsec
astxsig2	sigma_ra * cos(delta) in arcsec
astysig2	sigma_dec in arcsec

Precision

Precision is quite hard to address here. Essentially we are limited to the internal precision of the external sources catalogue which is typically not better than 0.3 arcsec RMS for USNO and 0.2 arcsec for 2MASS.

Plot of XY sigmas for USNO

Using USNO

Plot of XY sigmas for 2MASS

Using 2MASS

Plot of XY offsets for USNO

Using USNO

Plot of XY offsets for 2MASS

Using 2MASS

Examples

Astrometric correction example 2: U94D0108B 2MASS
Using 2MASS

Astrometric correction example 1: U96E3902B 2MASS
Using 2MASS

Astrometric correction example 1: U96E3902B USNO2B
Using USNO

Astrometric correction example 2: U94D0108B 2MASS
Using 2MASS

Astrometric correction example 2: U94D0108B USNO
Using USNO

Astrometric correction example 3: U4P70105B 2MASS
Using 2MASS

Astrometric correction example 3: U4P70105B USNO
Using USNO

Source extraction (for preview)

Aim

An augmented preview capability providing an extracted catalogue of sources.

Description

At the end of the main body of the WFPC2 association pipeline, we detect and extract, using SExtractor, the sources present on each science image. The sources are extracted using the inverse weight map. Sources are then stored into a SExtractor output file as well as within a VOTABLE format for VO and for Aladin overlay.

The SExtractor parameters used for the extraction are the following

SExtractor Parameters
ParametersValue
PIXEL_SCALE	str(pixscale)
WEIGHT_TYPE	MAP_VAR
CATALOG_NAME	assoc_id_sex_chip.cat
CATALOG_TYPE	ASCII_HEAD
MAG_ZEROPOINT	str(mag_zero)
GAIN	str(real_gain)
DETECT_TYPE	CCD
DETECT_MINAREA	5
DETECT_THRESH	3.0
ANALYSIS_THRESH	1.5
THRESH_TYPE	RELATIVE
FILTER	Y
FILTER_NAME	wfpc2_cat.conv
DEBLEND_NTHRESH	32
DEBLEND_MINCONT	0.01
CLEAN	Y
CLEAN_PARAM	1.0
MASK_TYPE	CORRECT
PHOT_APERTURES	aperture_pc or aperture_wf
PHOT_AUTOPARAMS	2.5, 3.5
SATUR_LEVEL	50000.0
MAG_GAMMA	4.0
SEEING_FWHM	str(seeing_fwhm)
STARNNW_NAME	wfpc2_cat.nnw
BACK_SIZE	64
BACK_FILTERSIZE	11
BACK_TYPE	AUTO
BACKPHOTO_TYPE	LOCAL
BACKPHOTO_THICK	24
WEIGHT_IMAGE	assoc_id_var_chip.fits

Where aperture is:
aperture_wf     = "10.05,20.10,30.15,40.20,50.25,60.30"
aperture_pc     = "21.98,43.96,65.93,87.91,109.89,131.87"

seeing_fwhm = 1.22 * (photplam / 24000000000.0 ) * 206264.806247

Catalogue extraction for U90R0701B
Catalogue overlay for U90R0701B

Recipe

Main outcome & file names

Catalogue files
u96g0402b_sex_1.cat	Extracted catalogue in SExtractor format for PC1
u96g0402b_sex_2.cat	Extracted catalogue in SExtractor format for WF2
u96g0402b_sex_3.cat	Extracted catalogue in SExtractor format for WF3
u96g0402b_sex_4.cat	Extracted catalogue in SExtractor format for WF4
u96g0402b_segment_1	Segmentation image for PC1
u96g0402b_segment_2	Segmentation image for WF2
u96g0402b_segment_3	Segmentation image for WF3
u96g0402b_segment_4	Segmentation image for WF4
u96g0402b_background_1	Background image for PC1
u96g0402b_background_2	Background image for WF2
u96g0402b_background_3	Background image for WF3
u96g0402b_background_4	Background image for WF4
u96g0402b_ap_1	Aperture image for PC1
u96g0402b_ap_2	Aperture image for WF2
u96g0402b_ap_3	Aperture image for WF3
u96g0402b_ap_4	Aperture image for WF4
u96g0402b_sex_1.vot	Extracted catalogue in VO table format for PC1
u96g0402b_sex_2.vot	Extracted catalogue in VO table format for WF2
u96g0402b_sex_3.vot	Extracted catalogue in VO table format for WF3
u96g0402b_sex_4.vot	Extracted catalogue in VO table format for WF4
u96g0402b_sex_1.stats	Basic statistics on sectracted parameters output for PC1
u96g0402b_sex_2.stats	Basic statistics on sectracted parameters output for WF2
u96g0402b_sex_3.stats	Basic statistics on sectracted parameters output for WF3
u96g0402b_sex_4.stats	Basic statistics on sectracted parameters output for WF4
u96g0402b_sex_1_his_g.png	Histogram of Extended sources against Magnitude for PC1
u96g0402b_sex_1_his_s.png	Histogram of Point sources against Magnitude for PC1
u96g0402b_sex_1_his_t.png	Histogram of All sources against Magnitude for PC1
u96g0402b_sex_1_mag_err.png	Histogram of Error on Magnitude against Magnitude for PC1
u96g0402b_sex_1_sgs.png	Histogram of Stars/Galaxies separation against Magnitude for PC1
u96g0402b_sex_2_his_g.png	Histogram of Extended sources against Magnitude for WF2
u96g0402b_sex_2_his_s.png	Histogram of Point sources against Magnitude for WF2
u96g0402b_sex_2_his_t.png	Histogram of All sources against Magnitude for WF2
u96g0402b_sex_2_mag_err.png	Histogram of Error on Magnitude against Magnitude for WF2
u96g0402b_sex_2_sgs.png	Histogram of Stars/Galaxies separation against Magnitude for WF2
u96g0402b_sex_3_his_g.png	Histogram of Extended sources against Magnitude for WF3
u96g0402b_sex_3_his_s.png	Histogram of Point sources against Magnitude for WF3
u96g0402b_sex_3_his_t.png	Histogram of All sources against Magnitude for WF3
u96g0402b_sex_3_mag_err.png	Histogram of Error on Magnitude against Magnitude for WF3
u96g0402b_sex_3_sgs.png	Histogram of Stars/Galaxies separation against Magnitude for WF3
u96g0402b_sex_4_his_g.png	Histogram of Extended sources against Magnitude for WF4
u96g0402b_sex_4_his_s.png	Histogram of Point sources against Magnitude for WF4
u96g0402b_sex_4_his_t.png	Histogram of All sources against Magnitude for WF4
u96g0402b_sex_4_mag_err.png	Histogram of Error on Magnitude against Magnitude for WF4
u96g0402b_sex_4_sgs.png	Histogram of Stars/Galaxies separation against Magnitude for WF4

Header keywords

CATALOGUE EXTRACTION
SEXCV	step_version
SEXCB	Execution Date for this step
pipeline_version	Overall pipeline version
SEXFLAG	Step completion status flag
SEXNEXT	Number of sextracted sources
SEXNFIL	Number of filtered sources
SEXMAMI	Brightest magnitude detected by SExtractor. SExtractor value is MAG_AUTO
SEXMAMA	Faintest magnitude detected by SExtractor. SExtractor value is MAG_AUTO
SEXMAME	Mean magnitude detected by SExtractor. SExtractor value is MAG_AUTO
SEXMAMS	Sigma magnitude detected by SExtractor. SExtractor value is MAG_AUTO
SEXBAMI	Maximum value of background values used by SExtractor
SEXBAMA	Maximum value of background values used by SExtractor
SEXBAME	Mean value of background values used by SExtractor
SEXBAMS	Sigma of background values used by SExtractor
SEXSSMI	Minimum value of the STAR/Galaxy separation parameter as measured by SExtractor (CLASS_STAR)
SEXSSMA	Maximum value of the STAR/Galaxy separation parameter as measured by SExtractor (CLASS_STAR)
SEXSSME	Mean value of the STAR/Galaxy separation parameter as measured by SExtractor (CLASS_STAR)
SEXSSMS	Sigma value of the STAR/Galaxy separation parameter as measured by SExtractor (CLASS_STAR)
SEXFAMI	Minimum value of the FLUX_AUTO parameters from the SExtractor output
SEXFAMA	Maximum value of the FLUX_AUTO parameters from the SExtractor output
SEXFAME	Mean value of the FLUX_AUTO parameters from the SExtractor output
SEXFAMS	Sigma value of the FLUX_AUTO parameters from the SExtractor output
SEXFEMI	Minimum flux error from the SExtractor parameter FLUXERR_AUTO
SEXFEMA	Maximum flux error from the SExtractor parameter FLUXERR_AUTO
SEXFEME	Mean flux error from the SExtractor parameter FLUXERR_AUTO
SEXFEMS	Sigma flux error from the SExtractor parameter FLUXERR_AUTO
SEXFWMI	Minimum value of the FWHM_IMAGE as measured by SExtractor
SEXFWMA	Maximum value of the FWHM_IMAGE as measured by SExtractor
SEXFWME	Mean value of the FWHM_IMAGE as measured by SExtractor
SEXFWMS	Sigma of the FWHM_IMAGE value as measured by SExtractor
SEXNFIL	Number of filtered sources
SEXNPOI	Number of point sources
SEXNEXX	Number of filtered extended sources
SEXSO	Number of sources
SEXSN10	Number of sources with SN>10
SEXMA10	AB Magnitude with S/N >10
SEXFL10	Flux where S/N > 10
SEXJS10	Flux(mjansky) where S/N > 10
SEXSN5	Number of sources with SN>5
SEXMA5	AB Magnitude with S/N >5
SEXFL5	Flux where S/N > 5
SEXJS5	Flux(mjansky) where S/N > 5
SEXSN2	Number of sources with SN> 2
SEXMA2	AB Magnitude with S/N > 2
SEXFL2	Flux where S/N >2
SEXJS2	Flux(mjansky) where S/N > 2

Precision

Statistical image classification

Aim

Detecting and extracting sources for image characterisation and to provide an augmented preview

Description

One of the pipeline tasks is the so-called image_type characterisation step which extracts some statistical parameters from a catalogue of sources extracted using the SExtractor astronomical software. This step is our first attempt to try to characterise the content of a given science image. For this purpose we are measuring the amount of energy stored into the large scale and the small scale component.

Although not used yet within the next steps of the pipeline, this might be useful one day if one want to try to tune up some source extraction parameters to a specific image type. Might also be useful for users who want to get "star free" images.

Example:

            IMATYF  = 'complete'           / IMAGE_TYPE: complete
            IMATYB  = '20/03/2006 13:15:48' / IMAGE_TYPE: start time
            IMATYV  =                  4.1 / IMAGE_TYPE: version
            IRATYI  = 'IRAF V2.12.2 January 2004 release:2.12.2' / IMAGE_TYPE: IRAF version
            SGSEP   =                 0.85 / IMAGE_TYPE: Star-Galaxy separation limit
            MAXMERR =                 0.05 / IMAGE_TYPE: Maximum mag_error acceptable
            FR_LOWF =  0.02400447472982964 / IMAGE_TYPE: Flux ratio for low frequency (per c
            FR_STAR =                  0.0 / IMAGE_TYPE: Flux ratio in point sources (per ch
            FR_GAL  =   0.9759955252701703 / IMAGE_TYPE: Flux ratio in extended sources (per
            F_LOWF  = 7.980762385539072E-05 / [Jy]IMAGE_TYPE:Flux for low frequency(per chip
            F_STAR  =                  0.0 / [Jy]IMAGE_TYPE:Flux for point sources component
            F_GAL   = 0.003244890156605357 / [Jy]IMAGE_TYPE:Flux for extended sources(per ch
            F_TOTAL = 0.003324697780460747 / [Jy]IMAGE_TYPE:Total flux per chip
            IMATYE  = '20/03/2006 13:16:18' / IMAGE_TYPE stop time

Recipe

Main outcome & file names

Header keywords

IMAGE TYPE INFO
IMATYF	Step completion status message
IMATYV	Version of the pipeline step
IMATYB	Execution Date for this step
pipeline_version	Overall pipeline version
SGSEP	Star-Galaxy separation limit
MAXMERR	Maximum mag_error acceptable
FR_LOWF	Flux ratio for low frequency (per chip)
FR_STAR	Flux ratio in point sources (per chip)
FR_GAL	Flux ratio in extended sources (per chip)
F_LOWF	[Jy]IMAGE_TYPE:Flux for low frequency(per chip)
F_STAR	[Jy]IMAGE_TYPE:Flux for point sources component(per chip)
F_GAL	[Jy]IMAGE_TYPE:Flux for extended sources(per chip)
F_TOTAL	[Jy]IMAGE_TYPE:Total flux per chip

Precision

Characterisation and header augmentation

Aim

Characterising the science products for enhanced metadata, and scientific queries.

Description

As a last step of the pipeline, we extract or compute some parameters useful to characterise the n-dimensional parameters the science images occupy, including coverage, sampling and resolution on the spatial, spectral and temporal axes. Each of these parameters are to be found in the header of each science image in addition of being stored into the CADC VO database for VO type query.

Recipe

the recipe is quite simple. For each science files, we are computing and/or reading from the headers the exact values for the 3 main physical axis: spatial, temporal and energy. The characteristics has to follow the Common Archive Observation Model (CAOM) which is used within CADC to migrate from an existing archive to the mode stringent VO models. This way the operation of migrating any archive observations to the ever changing VO characterisation is greatly simplify.

Header keywords

We choose to use the FITS header as the vehicle for our characterisation as well as inserting the characterisation information within the CAOM database.

TIME VALUES
CVOEQUI	[yr]Equinox in proper format for SExtractor
CVOTMIN	Time min (mjd)
CVOTMAX	Time max (mjd)
CVOTUNIT	Time unit
CVOTERR	Time error
CVOTFILL	Time filling factor
CVOTFILE	Time filling factor error
CVOTSPAN	Time span
CVOTSPAE	Time span error
CVOTSAMP	Time sampling
CVOTSAME	Time sampling error
SPATIAL VALUES
CVOSUNIT	Unit for spatial coordinates values
CVOSERR	Spatial typical error
CVOSFILL	Spatial Filling Factor
CVOSFILE	Spatial filling factor error
CVOSSPAN	Spatial Span (deg)
CVOSSPAE	Spatial Span error (deg)
CVOSSAMP	Spatial Sampling (deg)
CVOSSAME	Spatial Sampling error (deg)
CVOSRES	Spatial Resolution
CVOPSFW	Spatial PSFW
CVOSNYQR	Nyquist value
SPECTRAL VALUES
CVOWMIN	Wave min (nm)
CVOWMAX	Wave max (nm)
CVOWUNIT	Wave unit
CVOWERR	Wave err (nm)
CVOWFILL	Wave filling factor
CVOWFILE	Wave filling factor error
CVOWSPAN	Wave span (nm)
CVOWSPAE	Wave span error (nm)
CVOWSAME	Wave sampling error (nm)

The Hubble Space Telescope Archive at CADC (Subscribe to new public observations)

The WFPC2 Association Project Version 2

Contents:

Association members definition

Aim

Description

Recipe

Main outcome & file names

Header keywords

Precision

Caveat

Generating association products

Members RAW file production

Aim

Description

Recipe

Main outcome & file names

Header keywords

Calibration of each of the members

Aim

Description

Recipe

Main outcome & file names

Header keywords

Members offset determination: Cross Correlation, Jitter, WCS

Aim

Description

Recipe

Stacking members into a cleaner and deeper product (IMSTACK)

Aim

Description

Recipe

Main outcome & file names

Header keywords

Precision

Astrometric correction

Aim

Description

Recipe

Main outcome & file names

Header keywords

Precision

Examples

Source extraction (for preview)

Aim

Description

Recipe

Main outcome & file names

Header keywords

Precision

Statistical image classification

Aim

Description

Recipe

Main outcome & file names

Header keywords

Precision

Characterisation and header augmentation

Aim

Description

Recipe

Header keywords