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All data were processed with version 2.50 of the DAT, turning off the electronic nonlinearity correction and using the calibration files specific to campaign X1.
The calibration factor (in units of µJy/arcsec2/(MIPS160 unit)) was calculated from four sources, as follows:
The campaign V observations of HD131873 were compared to the observations of HD10647 (AOR key 7865856), a star with an unresolved debris disk, to determine the relative fluxes of the true 160um source and the ghost from the filter "leak". Since HD10647 is dominated by the cold, unresolved disk, it is a red point source with no leak. I subtracted scaled versions of HD10647 from HD131873 at matching array positions, and chose the largest scaling factor which left no negative residual. This technique demonstrated that the ghost is 4.5±0.5 times brighter than the true 160µm source. Using photometric measurements from the campaign Q data, I could then derive a calibration factor (CF) for HD131873, which should be 0.656 Jy at 160µm:
CF = 0.656 Jy * 1e6 µJy/Jy / 22.4 MIPS160Unit / (16 arcsec)2 * 5.5 = 629 µJy/arcsec2/MIPS160Unit
I also derived calibration factors using the sky background measurements from HD131873 in campaign Q and Mrk 279 in campaign V. I compared the average background measurements to the predictions from SPOT:
HD131873 sky CF = 4.6 MJy/sr * 1e12 µJy/MJy / 0.21 MIPS160Unit * 2.35e-11 sr/arcsec2 = 515 µJy/arcsec2/MIPS160Unit
Mrk 279 sky CF = 3.8 MJy/sr * 1e12 µJy/MJy / 0.16 MIPS160Unit * 2.35e-11 sr/arcsec2 = 558 µJy/arcsec2/MIPS160Unit
Finally, I estimated a flux for the Mrk 279 (measured in campaign V) by extrapolating the power-law fit to shorter-wavelength data, found in the MIPS-353 analysis for campaign P. The estimated 160µm flux is 2.2 Jy. I then computed the counts on the galaxy using the same aperture (and 1.47 aperture correction) as used for all the stellar standards, after first subtracting the companion galaxy (see MIPS-924R analysis for an image):
CF = 2.2 Jy * 1e6 µJy/Jy / (2.45 * 1.47) MIPS160Unit / (16 arcsec)2 = 2.39e3 µJy/arcsec2/MIPS160Unit
The standard star and background measurements imply consistent calibration factors, while the Mrk 279 factor differs by a factor of 4. Due to the contaminating galaxy and uncertain predicted flux, I have chosen to discard this measurement and average the remaining 3 to derive a calibration factor of 567 µJy/arcsec2/MIPS160Unit. Multiplying your data by this factor should put it in units of µJy/arcsec2.
The calibration factor was calculated using estimated stellar flux, sky backgrounds, and a galaxy. The star and sky measurements matched well, and imply an average calibration factor of 567µJy/arcsec2/(MIPS160 unit)
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