COBE DIRBE Color Correction Software

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This is software written in IDL to calculate the color correction factor for DIRBE photometry in a specified DIRBE band for a specified source spectrum.The IDL software is available in dirbe_colorcorr.pro and the DIRBE system response data file that it reads, DIRBE_SYSTEM_SPECTRAL_RESPONSE_TABLE.ASC, is available here. The code and the system response data file can also be downloaded together in this tar file.- recommended download procedure for '.fits' or '.tar.gz' files: right click on the file name and save.

In delivered DIRBE data products, the spectral intensity data are intensity per frequency interval I_𝝂 in MJy sr-1 at the band nominal wavelength assuming that the source spectrum is 𝝂*I_𝝂 = constant across the band. This code uses a user-specified source spectrum and delivered DIRBE system frequency response data to calculate the color correction factor K defined such that I_𝝂0(actual) = I_𝝂0(quoted)/K, where I_𝝂0(actual) is the actual specific intensity of the sky at frequency 𝝂0, I_𝝂0(quoted) is the corresponding value given in a DIRBE data product, and 𝝂0 is the frequency corresponding to the DIRBE band nominal wavelength.

The input source spectrum must cover the full bandpass of the specified band as given below. The thumbnail for each band can be clicked on to see a plot of the delivered system response data.

Band 1: 1.25 µm Range: 1.078 - 1.506 µm	Band 2: 2.2 µm Range: 1.947 - 2.517 µm	Band 3: 3.5 µm Range: 2.963 - 4.206 µm	Band 4: 4.9 µm Range: 4.339 - 5.311 µm	Band 5: 12 µm Range: 7.656 - 17.467 µm

Band 6: 25 µm Range: 15.543 - 29.191 µm	Band 7: 60 µm Range: 30.349 - 81.529 µm	Band 8: 100 µm Range: 65.568 - 134.147 µm	Band 9: 140 µm Range: 99.809 - 263.981 µm	Band 10: 240 µm Range: 162.953 - 451.585 µm

Documentation from the top level routine follows.

;-------------------------------------------------------------------------------
function dirbe_colorcorr, bandnum, I_nu, wavelength, $
         interp_response=interp_response, verbose=verbose, $
         response_dir=response_dir
;+
; NAME:
;    dirbe_colorcorr
;
; PURPOSE:
;
;    This IDL procedure calculates the color correction factor for DIRBE
; photometry in a specified DIRBE band for a specified source spectrum.
; In delivered DIRBE data products, the spectral intensity data are intensity
; per frequency interval I_nu in MJy sr-1 at the band nominal wavelength
; assuming that the source spectrum is nu*I_nu = constant across the band.
; This code uses a user-specified source spectrum and delivered DIRBE
; system frequency response data to calculate the color correction factor K
; defined such that I_nu0(actual) = I_nu0(quoted)/K, where I_nu0(actual) is
; the actual specific intensity of the sky at frequency nu0, I_nu0(quoted)
; is the corresponding value given in a DIRBE data product, and nu0 is the
; frequency corresponding to the DIRBE band nominal wavelength.
;
; CALLING SEQUENCE:
;    K = dirbe_colorcorr (bandnum, I_nu, wavelength [, /interp_response]
;        [, /verbose] [, /response_dir])
;
; INPUTS:
;    bandnum          integer scalar  DIRBE Band Number, from 1 to 10.
;    I_nu             float array     Source intensity spectrum in e.g. Jy sr-1.
;    wavelength       float array     Wavelengths for I_nu in microns.
;    interp_response  keyword         By default, the input source spectrum is
;                                     interpolated to the frequency grid for
;                                     the DIRBE system response. Set
;                                     /interp_response to instead interpolate
;                                     the DIRBE system response to the
;                                     frequencies for the source spectrum.
;    verbose          keyword         Set /verbose to print the color
;                                     correction value. The default is not
;                                     to print.
;    response_dir     keyword         Specifies the directory from which the
;                                     response data file
;                                     DIRBE_SYSTEM_SPECTRAL_RESPONSE_TABLE.ASC
;                                     is to be read. If not specified, the
;                                     current working directory is used.
;
; OUTPUT:
;    K                float           Color correction factor K.
;
; PROCEDURE:
;    Reads the DIRBE system response data for the DIRBE band specified by
;    "bandnum" from the ascii file DIRBE_SYSTEM_SPECTRAL_RESPONSE_TABLE.ASC,
;    which is available at
;    https://lambda.gsfc.nasa.gov/product/cobe/c_spectral_res.html.
;    Then interpolates the input source spectrum to the response frequency
;    grid or interpolates the response to the spectrum frequency grid
;    and performs the appropriate integrals. The value returned is
;
;       K = Integral( (Inu/Inueff) * Rsystem * dnu ) /
;           Integral( (nueff/nu)   * Rsystem * dnu )
;
;    This code calls readcol.pro and associated routines from the IDL
;    Astronomy User's Library, http://idlastro.gsfc.nasa.gov/
;
; EXAMPLE:
;    To produce the DIRBE Band 5 (12 um) color correction for a power law
;    spectrum I_nu ~ nu^2 :
;
;    IDL> wavelength = 7.5 + 0.01*findgen(1050)
;    IDL> I_nu = 1./wavelength^2
;    IDL> K = dirbe_colorcorr(5, I_nu, wavelength, /verbose, response_dir='/home/username/')
;
;    IDL prints:
;      DIRBE um        K
;       12.00        1.189
;
; REFERENCE:
;    See IRAS Explanatory Supplement, pg VI.26-28,
;        DIRBE Explanatory Supplement, section 5.5
;-----------------------------------------------------------------------------