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CCM_UNRED

CCM_UNRED

Name


    CCM_UNRED

Purpose


    Deredden a flux vector using the CCM 1989 parameterization

Explanation


    The reddening curve is that of Cardelli, Clayton, and Mathis (1989 ApJ.
    345, 245), including the update for the near-UV given by O'Donnell
    (1994, ApJ, 422, 158). Parameterization is valid from the IR to the
    far-UV (3.5 microns to 0.1 microns).
    Users might wish to consider using the alternate procedure FM_UNRED
    which uses the extinction curve of Fitzpatrick (1999).

Calling Sequence


    CCM_UNRED, wave, flux, ebv, funred, [ R_V = ]
            or
    CCM_UNRED, wave, flux, ebv, [ R_V = ]

Input


    WAVE - wavelength vector (Angstroms)
    FLUX - calibrated flux vector, same number of elements as WAVE
            If only 3 parameters are supplied, then this vector will
            updated on output to contain the dereddened flux.
    EBV - color excess E(B-V), scalar. If a negative EBV is supplied,
            then fluxes will be reddened rather than deredenned.

Output


    FUNRED - unreddened flux vector, same units and number of elements
            as FLUX

Optional Input Keyword


    R_V - scalar specifying the ratio of total selective extinction
            R(V) = A(V) / E(B - V). If not specified, then R_V = 3.1
            Extreme values of R(V) range from 2.75 to 5.3

Example


    Determine how a flat spectrum (in wavelength) between 1200 A and 3200 A
    is altered by a reddening of E(B-V) = 0.1. Assume an "average"
    reddening for the diffuse interstellar medium (R(V) = 3.1)
      IDL> w = 1200 + findgen(40)*50 ;Create a wavelength vector
      IDL> f = w*0 + 1 ;Create a "flat" flux vector
      IDL> ccm_unred, w, f, -0.1, fnew ;Redden (negative E(B-V)) flux vector
      IDL> plot,w,fnew

Notes


    (1) The CCM curve shows good agreement with the Savage & Mathis (1979)
            ultraviolet curve shortward of 1400 A, but is probably
            preferable between 1200 and 1400 A.
    (2) Many sightlines with peculiar ultraviolet interstellar extinction
            can be represented with a CCM curve, if the proper value of
            R(V) is supplied.
    (3) Curve is extrapolated between 912 and 1000 A as suggested by
            Longo et al. (1989, ApJ, 339,474)
    (4) Use the 4 parameter calling sequence if you wish to save the
              original flux vector.
    (5) Valencic et al. (2004, ApJ, 616, 912) revise the ultraviolet CCM
            curve (3.3 -- 8.0 um-1). But since their revised curve does
            not connect smoothly with longer and shorter wavelengths, it is
            not included here.

Revision History


      Written W. Landsman Hughes/STX January, 1992
      Extrapolate curve for wavelengths between 900 and 1000 A Dec. 1993
      Use updated coefficients for near-UV from O'Donnell Feb 1994
      Allow 3 parameter calling sequence April 1998
      Converted to IDLV5.0 April 1998



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