; Computes the MMB intensity at wavelength 
; Used by fit_sed.pro
; 
;
function bg, lambda, a, COLOR_C=cc
;
; lambda (I): lambda-grid in microns
; a (I): parameters

  E_bg = a[0]	; Emissivity of Big Grains at 250 microns (lambda_ref)
  T_bg = a[1]   ; Temperature of Big Grains
  beta = a[2]	; Spectral index of Big Grains

  lambda_ref = 2.5d2	; 250 microns
  model = E_bg * (lambda_ref/lambda)^beta * BLACKBODY( lambda, T_bg, unit='w' )  ; nu^beta * lambda*B_lambda

  ; Color-corrections
  if keyword_set(cc ) then model= model*cc

  return, model
end