Spitzer Documentation & Tools
MIPS Instrument Handbook

 

4.3.4        Aperture Correction

For aperture corrections, you should also consider constructing your own PSF from your own data, because aperture corrections may vary for different source colors. In Figure 4.5, there is a source of 0.5 Jy from the Extragalactic First-Look Survey (XFLS) main field (at 17:23:44.1 +59:05:18, J2000); there are three radii (1.35, 2, 3 times the FWHM, 5.9 arcsec) in white; the black circle is a 100 arcsec radius.  Figure 4.6 shows the ''curve of growth'' to indicate the fraction of the total flux enclosed by smaller apertures. 

 

The Instrument Support Team (IST) at the SSC and the Instrument Team (IT) at the University of Arizona as part of a large project to better understand and to improve the MIPS photometric calibration, have determined different aperture corrections for the current MIPS Photometric modes (24 um, 70 um, 70 um fine scale and 160 um) plus Spectral Energy Distribution (SED).  The tables below (Table 4.13, Table 4.14, and Table 4.15) summarize these efforts.

 

These example corrections should be good to ~5%, but we emphasize again the importance of deriving this yourself for your own targets and data.  Even if you don´t have enough point sources in your own data to generate your very own PSF, we strongly suggest deriving your own aperture corrections using the copious public data or STINYTIM, or the observed PSFs provided on the web.

 

Figure 4.5: Example source from 24 micron Extragalactic First-Look Survey (XFLS) for example aperture corrections.

 

 

Table 4.13: 24 micron aperture corrections for 10,000 K Blackbody.

 

Description

Aperture radius (arcsec)

Background annulus (arcsec)

6-8 7-13 20-32 40-50 None
Half first dark ring 3.5 2.78 2.80 2.57 2.56 2.56
Center of first dark ring 7.0 n/a 2.05 1.61 1.61 1.61
Outside first bright ring 13.0 n/a n/a 1.17 1.16 1.16
Center of second dark ring 20.0 n/a n/a 1.15 1.13 1.12
Outside second bright ring 35.0 n/a n/a n/a 1.08 1.06

 

Table 4.14: Aperture corrections for 70 microns.

Aperture description Aperture radius in arcsec Background annulus in arcsec Coarse-Scale Correction Fine-Scale Correction
T=10,000 K
2 x HWHM 16 18-39 2.04 1.93
Outside 1st Airy ring 35 39-65 1.22 1.21
Outside 2nd Airy ring 100 120-140 1.10 1.10
T=60K
2 x HWHM           16 18-39 2.07 1.94
Outside 1st Airy ring 35 39-65 1.24 1.22
Outside 2nd Airy ring 100 120-140 1.10 1.10
T=10 K
2 x HWHM 16 18-39 2.30 2.16
Outside 1st Airy ring 35 39-65 1.48 1.47
Outside 2nd Airy ring 100 120-140 1.13 1.13

 

 

 

Table 4.15: Aperture corrections for 160 microns.

Aperture Radius
Temp (K) 16'' 24'' 32'' 40'' 48'' 64''
No Sky Annulus
10 4.761 2.657 2.011 1.776 1.634 1.402
30 4.677 2.610 1.976 1.745 1.605 1.355
50 4.665 2.603 1.971 1.740 1.601 1.348
150 4.651 2.595 1.965 1.735 1.596 1.341
250 4.648 2.593 1.963 1.734 1.595 1.340
500 4.648 2.593 1.963 1.734 1.595 1.339
2000a 4.645 2.592 1.962 1.733 1.594 1.339
With Sky Annulusb
10 4.785 2.670 2.021 1.785 1.642 1.406
30 4.697 2.621 1.984 1.752 1.612 1.361
50 4.683 2.613 1.978 1.747 1.607 1.354
150 4.668 2.605 1.972 1.741 1.602 1.348
250 4.665 2.603 1.971 1.740 1.601 1.347
500 4.662 2.602 1.970 1.739 1.600 1.346
2000 a 4.662 2.602 1.970 1.739 1.600 1.345

Note that sources with near-IR 160μm color temperatures >2000 K are subject to additional, large photometric uncertainty due to contribution from the near-IR ghost image.

b The sky annulus radius was 64-128´´ for apertures up to 48´´, and was 80-160´´, for the 64´´ aperture.

 

Figure 4.6: Example aperture corrections for 24 micron data (see text). The FWHM is 5.9 arcsec