Name

---

      PLANCK()

Purpose

---

      To calculate the Planck function in units of ergs/cm2/s/A

Calling Sequence

---

      bbflux = PLANCK( wave, temp)

Input Parameters

---

      WAVE Scalar or vector giving the wavelength(s) in **Angstroms**
              at which the Planck function is to be evaluated.
      TEMP Scalar giving the temperature of the planck function in degree K

Output Parameters

---

      BBFLUX - Scalar or vector giving the blackbody flux (i.e. !pi*Intensity)
              in erg/cm^2/s/A in at the specified wavelength points.

Examples

---

      To calculate the blackbody flux at 30,000 K every 100 Angstroms between
      2000A and 2900 A
 
      IDL> wave = 2000 + findgen(10)*100
      IDL> bbflux = planck(wave,30000)
      If a star with a blackbody spectrum has a radius R, and distance,d, then
      the flux at Earth in erg/cm^2/s/A will be bbflux*R^2/d^2

Procedure

---

      The wavelength data are converted to cm, and the Planck function
      is calculated for each wavelength point. See Allen (1973), Astrophysical
      Quantities, section 44 for more information.

Notes

---

      See the procedure planck_radiance.pro in
      ftp://origin.ssec.wisc.edu/pub/paulv/idl/Radiance/planck_radiance.pro
      for computation of Planck radiance given wavenumber in cm-1 or
      wavelength in microns

Modification History

---

      Adapted from the IUE RDAF August, 1989
      Converted to IDL V5.0 W. Landsman September 1997
      Improve precision of constants W. Landsman January 2002