Spitzer Documentation & Tools
IRS Instrument Handbook


4.3  Peak-Up Acquisition (PUA) Calibration

Data in the peak-up array can be taken in two modes: as part of the target acquisition observations and as part of the imaging mode observations. These data are taken in Double Correlated Sampling (DCS) and Sample-Up-the-Ramp (SUR) formats, respectively, and therefore have different calibration parameters. Here we give the approximate calibration for the acquisition mode.

The blue zeropoint calibration stars were HD163466 (47 mJy, 52 AORs), HD172728 (74 mJy, 32 AORs), and HR5467 (74 mJy, 44 AORs).  Red zeropoint calibration stars were HD163466 (23 mJy, 26 AORs), HD172728 (37 mJy, 34 AORs), HR5467 (37 mJy, 16 AORs), and 29 Vul (89 mJy, 9 AORs). Each AOR consists of 3 images each at the acquisition position and the sweet spot position. All images have SAMPTIME=1.0486 sec, for a total exposure time of 8.32 sec. The bright PUI calibrators (20 Vul: blue; HD173511 and HR6348: red) were not usable because they were just under the saturation limit for 6 second peak-up imaging observations and thus saturated these 8.32 second peak-up acquisition images.

Four DCS mode darks, referred to as S1, S2, and S4, correspond to SAMPTIME=1.0486, 2.0972, and 4.1944, respectively. S1 was used for sources brighter than 1.4 mJy, S2 for sources between 1 and 1.4 mJy, and S4 for sources between 0.75 and 1 mJy. All calibration stars, and the majority of all peak-up acquisition data, use the S1 dark.

For each AOR, the appropriate DCS mode dark was subtracted from each of the six images. The images were then run through the DARKDRIFT pipeline module to remove jailbar artifacts (see Section 5.1.13). The DCS mode flat was then applied to the data. The three DCEs at the same position (acquisition of sweet spot) were coadded in order to mitigate the effects of cosmic rays. The calibration stars were measured using the same procedure as the PUI data (blue: 12 pixel radius aperture, red: 13 pixels). The aperture measurement was corrected ot infinite radius using the standard aperture corrections. The resulting zeropoints are 0.0115 +/- 0.0003 (MJy/sr)(electron/sec) (blue) and 0.0118 +/- 0.0005 (MJy/sr)(electron/sec) (red). This zeropoint is applied in the PUA pipeline.

The results of this pipeline are the *acqb.fits and *acqr.fits calibrated image cutouts in the S18.18 version of the IRS pipeline.