Name

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    FLUX2MAG

Purpose

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    Convert from flux (ergs/s/cm^2/A) to magnitudes.

Explanation

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    Use MAG2FLUX() for the opposite direction.

Calling Sequence

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    mag = flux2mag( flux, [ zero_pt, ABwave= ] )

Inputs

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    flux - scalar or vector flux vector, in erg cm-2 s-1 A-1

Optional Input

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    zero_pt - scalar giving the zero point level of the magnitude.
              If not supplied then zero_pt = 21.1 (Code et al 1976)
              Ignored if the ABwave keyword is supplied

Optional Keyword Input

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    ABwave - wavelength scalar or vector in Angstroms. If supplied, then
          FLUX2MAG() returns Oke AB magnitudes (Oke & Gunn 1983, ApJ, 266,
          713).

Output

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    mag - magnitude vector. If the ABwave keyword is set then mag
          is given by the expression
          ABMAG = -2.5*alog10(f) - 5*alog10(ABwave) - 2.406
           
          Otherwise, mag is given by the expression
          mag = -2.5*alog10(flux) - zero_pt

Example

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      Suppose one is given wavelength and flux vectors, w (in Angstroms) and
      f (in erg cm-2 s-1 A-1). Plot the spectrum in AB magnitudes
      IDL> plot, w, flux2mag(f,ABwave = w), /nozero

Revision History

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      Written J. Hill STX Co. 1988
      Converted to IDL V5.0 W. Landsman September 1997
      Added ABwave keyword W. Landsman September 1998