;+
; NAME:
;	ThomsonUBVConst
; PURPOSE:
;	Defines apparent solar magnitudes and limb darkening
;	constants to be used for the Helios UBV system
; CALLING SEQUENCE:
	FUNCTION ThomsonUBVConst, C
; INPUTS:
;	C			scalar; type: integer
;					1,2,3 for U,B,V light, resp.
; OUTPUTS:
;	R			array[2]; type: float
;					R[0]:	limb darkening constant
;					R[1]:	apparent magnitude of the Sun
; INCLUDE:
	@compile_opt.pro		; On error, return to caller
; RESTRICTIONS:
;	1<=C<=3; if C out of range then C=1 is used
; PROCEDURE:
; >	UHOS(LT) is the limb darkening coefficient for Helios photometer
;	light from the U/B/V filter (C=1,2,3). From a graph in
;	RAUMFAHRTFORSCHUNG by LEINERT et al. LAMBDA=3650,4300,5250 A for U,B,V
;	light. From Allen (1985), p. 171, U=0.80,0.77,0.62 by linear
;	interpolation.
; >	LUM is the luminosity of the solar disk in E14 S10 units:
;	LUM = LSUN/LS10 = 10**((10-MSUN)/2.5), with MSUN (from Allen)
;	-25.96,-26.09,-26.73 for U,B and V light respectively.
; MODIFICATION HISTORY:
;	JUL-1996, Paul Hick (UCSD)
;-

APMHOS = [-25.96,-26.09,-26.73]
UHOS   = [  0.8 ,  0.77,  0.62]

I = ((C-1) > 0) < (n_elements(UHOS)-1)

RETURN, [UHOS[I],APMHOS[I]]  &  END