6 Data Products

This section describes the basic data products the observer will receive from the Spitzer Heritage Archive. The available data products consist of Level 0 (raw) data, Level 1 (BCD) data, calibration files, log files, and Level 2 (post-BCD) data. IRAC data are supplied as standard FITS files.

6.1 File Characteristics

Each file consists of a single data collection event (i.e., a single exposure), and contains one image corresponding to one of the four IRAC arrays (the exception being post-BCD products, described below). The FITS headers are populated with keywords including (but not limited to) physical sky coordinates and dimensions, a photometric solution, details of the instrument and spacecraft, including telemetry when the data were taken, and the steps taken during pipeline processing.

Note that because of the “first-frame effect,” the first frame of every Astronomical Observation Request (AOR ) has a different delay time and it cannot be calibrated perfectly. Therefore, the first frame of every AOR with a frame time greater than 2 seconds is taken in HDR mode which causes the first frame to be 0.6 seconds or 1.2 seconds in duration instead of the full frame time. This first frame usually has a name such as SPITZER_I1_11111111_0000_0000_2_bcd.fits (see Section 6.3 for explanation of the various parts of the file name) and has no associated cosmic ray mask (brmsk file). The observer is encouraged not to use this first short frame. The pipeline mosaicker does not use it either when building the mosaic.

6.2 File-Naming Conventions

Table 6.1 lists the IRAC data files produced by the IRAC data reduction pipelines, together with brief descriptions of these files. The Basic Calibrated Data (BCD) are the calibrated, individual images. These are in array orientation and have a size of 256 pixels × 256 pixels for the full array images, and 64 planes times 32 pixels × 32 pixels for the subarray images. These data are fully calibrated and have detailed file headers. The Post-BCD pipeline combines the BCD images into mosaics (per wavelength and per frame time). Calibration observations designated as darks or flats go through a similar but separate pipeline that generates the products listed in the last section of Table 6.1.

Please note that all of the calibration products (specifically: skydarks, skyflats, and linearity curves) are in the raw reference frame. In the raw images the subarrays are located at pixel range (x₁:x₂,y₁:y₂) coordinates (9:40, 9:40). In the BCDs, the subarrays are located in (x₁:x₂,y₁:y₂) coordinates (9:40, 9:40) in channels 3 and 4, and in (x₁:x₂,y₁:y₂) coordinates (9:40, 217:248) in channels 1 and 2. Also note that those coordinates are for the case in which the first pixel is indexed as 1,1 (i.e., IRAF convention). By contrast, IDL pixel indices start from 0,0.

Diagram

Description automatically generated

Figure 6.1: The orientation of the (C)BCDs on the sky.

Table 6.1: Sample IRAC file names.

Brief Description
Basic Calibrated Data (BCD)
SPITZER_I1_0008845056_0031_0000_01 dce.fits	Raw data (in units of DN)
SPITZER_I1_8845056_0031_0000_1_bcd.fits	BCD data (in units of MJy/sr)
SPITZER_I1_8845056_0031_0000_1_bcd.log	BCD pipeline log
SPITZER_I1_8845056_0031_0000_1_bunc.fits	BCD uncertainty file
SPITZER_I1_8845056_0031_0000_1_bimsk.fits	BCD imask file
SPITZER_I1_8845056_0031_0000_1_brmsk.fits	rmask image
SPITZER_I1_8845056_0031_0000_1_ptn.log	BCD Pointing log
SPITZER_I1_8845056_0031_0000_1_sub2d.fits	2D BCD image (subarray only)
SPITZER_I1_8845056_0031_0000_1_unc2d.fits	2D BCD uncertainty file (subarray only)
SPITZER_I1_8845056_0031_0000_1_msk2d.fits	2D BCD imask file (subarray only)
SPITZER_I1_8845056_0031_0000_1_cov2d.fits	2D BCD coverage file (subarray only)
Artifact-Corrected BCD Processing (CBCD)
SPITZER_I1_8845056_0031_0000_1_cbcd.fits	Artifact-corrected BCD data
SPITZER_I1_8845056_0031_0000_1_cbunc.fits	Artifact-corrected BCD uncertainty file
Post-BCD Processing
SPITZER_I1_8845056_0000_1_E123458_maic.fits	Mosaic
SPITZER_I1_8845056_0000_1_A2987651_munc.fits	Mosaic uncertainty file
SPITZER_I1_8845056_0000_1_A2987653_mcov.fits	Mosaic coverage file
SPITZER_I1_8845056_0000_1_A2987653_mmsk.fits	Mosaic mask file
SPITZER_I1_8845056_0000_1_A2987654_maicm.fits	HDR intermediate frame time mosaic
SPITZER_I1_8845056_0000_1_A2987655_muncm.fits	HDR intermediate frame time mosaic uncertainty file
SPITZER_I1_8845056_0000_1_A2987656_mcovm.fits	HDR intermediate frame time mosaic coverage file
SPITZER_I1_8845056_0000_1_A2987657_mmskm.fits	HDR intermediate frame time mosaic mask file
SPITZER_I1_8845056_0000_1_A2987658_maics.fits	HDR short frame time mosaic
SPITZER_I1_8845056_0000_1_A2987659_muncs.fits	HDR short frame time mosaic uncertainty file
SPITZER_I1_8845056_0000_1_A2987660_mcovs.fits	HDR short frame time mosaic coverage file
SPITZER_I1_8845056_0000_1_A2987653_mmsks.fits	HDR short frame time mosaic mask file
SPITZER_I1_8845056_0000_1_A26871875_irsa.tbl	List of 2MASS stars for pointing refinement
SPITZER_I1_8845056_0000_1_A26871873_refptg.tbl	Table of pointing refinement information
Calibration pipeline data files
SPITZER I1_13450853_0000_1_C92523_ sdark.fits	Skydark
SPITZER I1_13450853_0000_1_A210654_ scmsk.fits	Skydark mask file
FUL_2s_2sf4d1r1_ch[1–4]_v1.2.0_dark.fits	IRAC labdark image (full array)
FUL_2s_2sf4d1r1_ch[1-4]_v1.2.0_dark_noise.fits	IRAC labdark noise image
HDR_30s_1.2sf1d1r_ ch[1–4]_v1.2.0_dark.fits	IRAC labdark image (HDR short frame)
HDR_30s_30sf16d1r_ ch[1–4]_v1.2.0_dark.fits	IRAC labdark image (HDR long frame)
SUB_0.1s_0.1sf2d1r1_ch[1–4]_v1.2.0_dark.fits	IRAC labdark image (subarray)
irac_b[1–4]_[fa/sa]_superskyflat_finalcryo_091004.fits	IRAC superskyflat image
irac_b[1–4]_ [fa/sa]_superskyflat_finalcryo_091004_cmask.fits	IRAC superskyflat mask file
irac_b[1–4]_[fa/sa]_20020921_lincal.fits	linearization calibration image
irac_b[1–4]_[fa/sa]_20020921_lincal_cmask.fits	linearization calibration mask
irac_b[1–4]_[fa/sa]_cdelt12_distort.tbl	Array distortion table
irac_b[1–4]_[fa/sa]_16_118_muxbleed_coeff_112003	Muxbleed correction coefficients
irac_b[1–4]_[fa/sa]_16_118_muxbleed_lut_100102	Muxbleed correction look-up table
[month][year]_ch[1–4]_pmask_[subarray].fits	Pmask (nearest in time)
[month][year]_ch[1–4]_fa_pmask[subarray]_flip.fits	Flipped pmask (nearest in time; not in use)
irac_b[1–4]_fa_slmodel_v1.0.1.fits	Subtracted scattered light model
irac_b[1–4_ fluxconv_10112010.tbl	Flux conversion file used
instrument_FOV.tbl	IRAC array locations in Spitzer FOV
irac_b[1–4]_mosaicPRF.fits	PRF file used for pointing refinement
irac_b[1–4]_PRF.tbl	PRF table used for the four quadrants of the image
SPITZER_I1_21752576_0000_5_A41882936_avg.fits	Average image of all BCDs in an AOR
SPITZER_I1_21752576_0000_5_A41882938_avmed.fits	Average image of all HDR intermediate frames
SPITZER_I1_21752576_0000_5_A41882937_ashrt.fits	Average image of all HDR short frames
SPITZER_I1_21752576_0000_5_C8232029_mdn.fits	Median image of all BCDs in an AOR
SPITZER_I1_21752576_0000_5_A41882940_mdmed.fits	Median image of all HDR intermediate frames
SPITZER_I1_21752576_0000_5_A41882939_mshrt.fits	Median image of all HDR short frames