The best conversion factors between instrumental units and MJy/sr to use for any given data set are included within the headers of the data themselves; grep on BUNIT and FLUXCONV. The factors are listed in Table 4.10. The MIPS-24 instrumental units are DN/s, but note that the instrumental MIPS-Ge units are dimensionless after the stimflash response calibration. Uncertainties in the conversion values are often limited by our astrophysical understanding of stars in the far infrared, and thus the uncertainties are likely to decrease with time. We include a history of the changes to the conversion factor of the various MIPS observation modes in Table 4.11.
This conversion factor at 24 microns was derived from 3 sec exposures. The difference in the conversion factor for scan mode and 10 and 30 sec exposure should not be more than 2-8% different.
Table 4.10: Conversion from instrumental units to MJy/sr.
Array
Conversion factor
Uncertaintya
24
0.0447
4%
70
702.
7%
70 fine scale
2808.
15%
SED
20572.7
10%
160
41.7
12%
a For optimal data reduction and flux density extraction of single sources in photometric mode, the uncertainties can be as small as 2%/5%/10% for 24/70/70fine.
Table 4.11: Changes in Conversion Factor with Pipeline.
Pipeline Versiona
24 micron
70 micron
70 micron Fine
70 micron SED
160 micron
S10
0.04391
634.
---
---
42
S11
0.04391
634.
2536.
27093
42
S12
0.04391
634.
2536.
21835
42
S13
0.04391
702.
2808.
20572.7
44.7
S16
0.0447
702.
2808.
20572.7
44.7
S17
0.0447
702.
2808.
20572.7
41.7
a This history is meant to be suggestive of what changes occurred and when. The process of pipeline updates was complicated, with multiple versions and versions that were replaced before significant data was run through them. The data header will always contain the correct conversion factor used.
4.3.3 Magnitude Zero Points
Dr. C. Engelbracht has computed MIPS magnitude zero points using the Kurucz (1993) Vega model, which has then been scaled to the Rieke et al. (2008) 10.6 micron zero point of 35.03 ± 0.3 Jy. He has further assumed that Vega is 0 magnitudes in all MIPS bands, and has computed fluxes at 23.68, 71.42, and 155.9 micron. The resultant zero points are in Table 4.12.
