NAME:
  equtemp
 PURPOSE:   (one line only)
  Compute a simple thermal equilibrium temperature for an asteroidal surface
 DESCRIPTION:
  This is a very simplistic calculation that is based on a simple radiative
    balance and does not include any physics for surface and sub-surface
    effects.
 CATEGORY:
  Asteroids
 CALLING SEQUENCE:
  temp=equtemp(r,alb,emvty)
 INPUTS:
  r     - helicentric distance, AU
  alb   - Bond albedo (should be bolometric)
  emvty - emissivity (default 1.0)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  fast  - if set, do fast-rotator model, otherwise do slow-rotator
  iso   - if set, do isothermal model (Trafton-like frost or conducting sphere)
  inc   - if set, the incidence angle (for fast=0) or latitude for
            zero subsolar latitude (for fast=1), in radians, otherwise 
            assume normal incidence
 OUTPUTS:
   return value is the estimated temperature
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2016/01/21, Written by Marc W. Buie, Southwest Research Institute