WFPC2 Associations Pipeline Products

BEWARE! While in the old times users might have encountered two different types of wfpc2 products, since June 2003 only the Artificial Skepticism pipeline products are supported; the old method that used imshift & imcombine has been withdrawn.

Both the regular HST archive interface, and the specialised WFPC2 Association interface are making use of the same pipeline to calibrate and stack together the observations.

For a overall description of the pipeline, the Artificial Skepticism algorithm, the astrometric corrections, and the quality verification process, please refer to "WFPC2 Association Science Products Pipeline at CADC and ST-ECF" (PDF).

In the following we describe the user's options and the pipeline output products.

Table of Contents

User's Options Products Description An Example

User's Options

1. Raw data (uncalibrated) only
2. Re-calibrate HST datasets NOW with best reference files (OTFC)
3. Apply the stacking pipeline to the selected members of an association, to generate a co-added, and cosmic ray clean product (mosaic).

Option 1: Raw Data

All the raw data files belonging to each dataset in the association are generated (OTFR) from a set of telemetry data files (PODs) stored in a on-line jukebox of DVDs. For a description of the raw files contained in a WFPC2 dataset, please refer to the Wide Field / Planetary Camera 2 dataset description.

No further processing is applied to the data.

Option 2: Recalibrated Data (OTFC)

1. All the raw data files belonging to each dataset in the association are generated (OTFR) from a set of telemetry data files (PODs);
2. The most up-to-date CALWP2 (standard STSCI calibration program) and the best calibration reference files are used to on-the-fly calibrate (OTFC) the raw datasets. Typically the OTFC produces two files, named:
   • datset_name.c0.fits
   • datset_name.c1.fits
   Also these calibrated data files are described in the Wide Field / Planetary Camera 2 dataset description.

Option 3: Mosaic of the Association(s)

WFPC2 Association File {[dataset root]b.asn} An ASCII file for each of the selected associations is created. The association file describes the association (proposal id, filter, total exposure time) and the its members (dataset name, ra, dec, roll, gain, member jflag, exposure time, target name, and, most importantly, the shifts from the leader of the association).
The name of the ASCII file is composed of the dataset root (first 8 characters of the dataset name) concatenated to the string 'b.asn'.
An example:

u23g5103b.asn
u581x101b.asn

Note: Each association file actually contains two tables; the first one (header/body separator is a string composed of dots '....') is for internal archive usage; the second one (header and body are separated by a string of dashes '---') is relevant for the user.

Artificial Skepticism Products Driven by the association file produced in the previous step, the pipeline generates the following products:

• [dataset root]b.c0.fits (eg, u23g5103b.c0.fits) the regular WFPC2 product
  this file, for user convenience, is split into the four individual chips;

• [dataset root]b_1.fits (eg, u23g5103b_1.fits) chip 1 (PC Camera) only
• [dataset root]b_2.fits (eg, u23g5103b_2.fits) chip 2 (WF2 Camera) only
• [dataset root]b_3.fits (eg, u23g5103b_3.fits) chip 3 (WF3 Camera) only
• [dataset root]b_4.fits (eg, u23g5103b_4.fits) chip 4 (WF4 Camera) only

• [dataset root]b_var_1.fits (eg, u23g5103b_var_1.fits) weight map for chip 1
• [dataset root]b_var_2.fits (eg, u23g5103b_var_2.fits) weight map for chip 2
• [dataset root]b_var_3.fits (eg, u23g5103b_var_3.fits) weight map for chip 3
• [dataset root]b_var_4.fits (eg, u23g5103b_var_4.fits) weight map for chip 4

README {readme.wfpc2_B.log} After all associations are processed, and immediately before closing the request, a readme file is created. Such readme describes which WFPC2 association products were created for the given request (only the c0 products are listed).
An example:

     Product name    Exptime #Members Proposal       Filter Target name
----------------- ---------- -------- -------- ------------ --------------------
u23g5103b.c0.fits       2000        2     5248        F502N NGC188
u581x101b.c0.fits       1600        2     8090        F606W ANY
----------------- ---------- -------- -------- ------------ --------------------

Let's suppose to have submitted a request for the association U23G5103B. That association is composed of 2 datasets (U23G5103T and U23G5104T). Hence, the OTFC calibration will produce:

• u23g5103t.c0.fits & u23g5103t.c1.fits
• u23g5104t.c0.fits & u23g5104t.c1.fits

The association file is named u23g5103b.asn (Follow the link to see the association file contents).

The cosmic ray free mosaic product (basically a co-addition without shifts in this specific case) is going to be named: u23g5103b.c0.fits

Each individual chip gets extracted from the cosmic ray free mosaic product; Hence the following four files are equivalent to the c0.fits file:

• u23g5103b_1.fits
• u23g5103b_2.fits
• u23g5103b_3.fits
• u23g5103b_4.fits

The weight maps for each of the chips are also generated:

• u23g5103b_var_1.fits
• u23g5103b_var_2.fits
• u23g5103b_var_3.fits
• u23g5103b_var_4.fits

The readme.wfpc2_B.log is generated.