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WMAP

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Product Name
Intensity Masks
Mission
WMAP
Coord. System
Galactic
Projection Type
HEALPix, nested, res 9 (Nside=512)

Description

A number of WMAP data analysis applications have been aided by the use of pixel intensity masks which exclude 'bright' portions of the sky from use. These masks were used in the generation of maps and CMB angular power spectra. The 3 masks provided allow for the selective exclusion of portions of the sky at different flux levels. The masks are based on the K band map and include a 0.6 degree radius exclusion area around known point sources.

Mask % of pix cut,
including sources
Kp0 23.2
Kp2 15.0
Kp12 5.8

Mask values for each map pixel are provided in the N_obs field of the data file (the 'Temperature' field is set to zero for all pixels and not used). A mask value of zero means that the pixel is excluded; a value of 1 means that the pixel is accepted.

In addition to the above single mask files, we also provide several intensity masks bundled into one file with a bit-coded N_obs field. This "composite mask" file defines the sky pixels excluded by the WMAP intensity masks Kp0, Kp2, Kp4, Kp12, the map-making (data processing) mask, and the point source mask. If a pixel is excluded by a mask, then a unique bit value is set. Bit values are set as follows:

  bit0 not used.
  bit1 set if excluded by Kp0; bit value = 2
  bit2 set if excluded by Kp2; bit value = 4
  bit3 set if excluded by Kp4; bit value = 8
  bit4 set if excluded by Kp12; bit value = 16
  bit5 set if excluded by processing mask; bit value = 32
  bit6 set if excluded by source mask; bit value = 64

The exclusion zone corresponding to a particular mask may be reconstructed by performing a logical AND of the N_obs field (treated as a byte variable) and the bit value set for that mask. For example, point source exclusion zones may be obtained using src = (BYTE(N_obs) AND 64)/64. To combine e.g. the Kp2 cut with the point source cuts, first reconstruct the individual masks using the logical AND described above, then perform a logical OR of the two in order to obtain a composite exclusion map. Note that these exclusion zone masks set an excluded pixel's value to 1 whereas the convention used for the intensity masks products is to set excluded pixels to 0.

More details can be found in:

"First Year Wilkinson Microwave Anisotropy Probe (WMAP) Results:
Foreground Emission", Bennett, et al., 2003

WMAP Explanatory Supplement

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