SPIRE Photometer Beam Profiles
Summary of beam profile analysis and solid angle revision ( Bernhard Schulz, September 2012)
SPIRE Photometer Solid Angles
The values in the first line were measured from a very finely sampled observation of Neptune as outlined below. Note that these are only accurate for a source of the same spectral shape. Since SPIRE flux densities for point sources are conventionally quoted for the reference wavelengths 250, 350, and 500 microns, assuming a source spectrum rising proportionally to wavelength (nu*F_nu=const.), we can adopt the same convention for (infinitely) extended sources. In this case the values in the second line apply. For sources of other colors a correction will have to be applied. The radial model beam profile is described in
Griffin et al. 2013
and the data files given below can be used to calculate such beam profiles.
Normalized Beam Profile Products to Download
The beam profile maps are available with all backgrounds subtracted and in a normalized form to the peak.
Radial Beam Profile Model
Datasets to construct the radial beam profile model are available below. These allow to take into account the color dependent FWHM of the true beam profiles.
The radial beam profile model for SPIRE was developed and described by
Griffin et al. 2013. The peak normalized monochromatic flux, depending on the distance from the peak (Theta) can be described as:
A value of -0.85 should be adopted for gamma, which controls the dependence of the FWHM of the variable part of the beam on wavelength. The reference frequency nu_eff is the isophotal frequency for the product of the spectrum of Neptune and the respective SPIRE spectral filter profile.
Solid angles derived from integrating this radial beam profile model over area and frequency were consistent with the numbers above within 1.5%.
Analysis Details
The interested reader can find a
detailed description of the data analysis that led to the data products on this page.
--
BernhardSchulz - 11 Oct 2012
