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FM_UNRED

FM_UNRED

Name


    FM_UNRED

Purpose


    Deredden a flux vector using the Fitzpatrick (1999) parameterization

Explanation


    The R-dependent Galactic extinction curve is that of Fitzpatrick & Massa
    (Fitzpatrick, 1999, PASP, 111, 63; astro-ph/9809387 ).
    Parameterization is valid from the IR to the far-UV (3.5 microns to 0.1
    microns). UV extinction curve is extrapolated down to 912 Angstroms.

Calling Sequence


    FM_UNRED, wave, flux, ebv, [ funred, R_V = , /LMC2, /AVGLMC, ExtCurve=
                      gamma =, x0=, c1=, c2=, c3=, c4= ]

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 dereddened.

Output


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

Optional Input Keywords


      R_V - scalar specifying the ratio of total to selective extinction
              R(V) = A(V) / E(B - V). If not specified, then R = 3.1
              Extreme values of R(V) range from 2.3 to 5.3
      /AVGLMC - if set, then the default fit parameters c1,c2,c3,c4,gamma,x0
            are set to the average values determined for reddening in the
            general Large Magellanic Cloud (LMC) field by Misselt et al.
            (1999, ApJ, 515, 128)
      /LMC2 - if set, then the fit parameters are set to the values determined
            for the LMC2 field (including 30 Dor) by Misselt et al.
            Note that neither /AVGLMC or /LMC2 will alter the default value
            of R_V which is poorly known for the LMC.
           
      The following five input keyword parameters allow the user to customize
      the adopted extinction curve. For example, see Clayton et al. (2003,
      ApJ, 588, 871) for examples of these parameters in different interstellar
      environments.
      x0 - Centroid of 2200 A bump in microns (default = 4.596)
      gamma - Width of 2200 A bump in microns (default =0.99)
      c3 - Strength of the 2200 A bump (default = 3.23)
      c4 - FUV curvature (default = 0.41)
      c2 - Slope of the linear UV extinction component
          (default = -0.824 + 4.717/R)
      c1 - Intercept of the linear UV extinction component
          (default = 2.030 - 3.007*c2
           

Optional Output Keyword


      ExtCurve - Returns the E(wave-V)/E(B-V) extinction curve, interpolated
                onto the input wavelength vector

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> fm_unred, w, f, -0.1, fnew ;Redden (negative E(B-V)) flux vector
      IDL> plot,w,fnew

Notes


      (1) The following comparisons between the FM curve and that of Cardelli,
          Clayton, & Mathis (1989), (see ccm_unred.pro):
          (a) - In the UV, the FM and CCM curves are similar for R < 4.0, but
                diverge for larger R
          (b) - In the optical region, the FM more closely matches the
                monochromatic extinction, especially near the R band.
      (2) Many sightlines with peculiar ultraviolet interstellar extinction
              can be represented with the FM curve, if the proper value of
              R(V) is supplied.
      (3) Use the 4 parameter calling sequence if you wish to save the
              original flux vector.

Procedure Calls


      CSPLINE(), POLY()

Revision History


      Written W. Landsman Raytheon STX October, 1998
      Based on FMRCurve by E. Fitzpatrick (Villanova)
      Added /LMC2 and /AVGLMC keywords, W. Landsman August 2000
      Added ExtCurve keyword, J. Wm. Parker August 2000
      Assume since V5.4 use COMPLEMENT to WHERE W. Landsman April 2006
      Fix calculation of EXTCurve A. Sarkisyan/W. Landsman Jan 2014



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