[ADVANCED OPTIONS]

[Asynchroneous rotation]

	<Synchroneous> rotation means that both stars rotate 
	with their orbital period, and thus always face each 
	other with the same side (like the moon does towards 
	the earth). <Asynchroneous> rotation thus means that 
	the star rotates faster or slower than the orbital 
	period. The asynchroneous rotation rate <F_Ratio> is 
	defined relative to the orbital period, i.e. a value 
	of 1.0 is equivalent to synchroneous rotation.
	<Note:> the critical radius of a star depends on <F_Ratio>.
	For values larger 1.0 it shrinks, thus stars with
	a filling factor of 1.0 (both) are not in physical
	contact anymore.
	For values smaller 1.0 it expands, thus stars might
	'intersect' even with filling factors smaller 1.0.
	(This condition is tested.)

[Eccentric orbit]

	According to Keplers laws, the shape of the orbit is 
	an ellipse. Often, it is close to a special case of 
	an ellipse - a circle. However, sometimes
	binary orbits are markedly eccentric, i.e. non-circular. 
	To define a non-circular elliptical orbit, 
	two parameters are required:
	<Eccentricity> is defined as (r2 - r1)/(r2 + r1), 
	where r1 is the smallest and r2 the largest distance.
	Obviously, an eccentricity of 0.0 corresponds
	to a circular orbit. The upper limit in Nightfall 
	is 0.95 (somewhat arbitrary).
	<Periastron length> is the length (in degree) of the 
	Periastron, i.e. the point of closest approach 
	during the orbit.

[Fractional Visibility]

	Calculate frational visibility (fractional eclipse)
	for individual surface elements on the shadow limb.
	Will yield a smoother lightcurve in case of problems
	('spikes' in the curve during the eclipse).

[Model Atmosphere]

	Use tabulated fluxes from model atmosphere calculations
	instead of the blackbody approximation for light fluxes.

[Detailed reflection]

	By default, the irradiation by the companion star is 
	treated by assuming that the companion is a point 
	source. This may lead to incorrect results if the 
	star(s) fill out a large fraction of the Roche 
	lobe(s).
	With <detailed reflection>, the mutual irradiation of 
	all pairs of surface elements is calculated. By 
	iterating a few (2-3) times, the accuracy can be 
	further improved.
	As this is an <N^2> algorithm, it is somewhat slow.

[Limb darkening]

        The limb of a star is darker than its centre. This 
	effect can be accounted for by various approximations,
	which express the <limb darkening> as a
	function of the angular distance to the limb. Options
	include a simple linear law as well as quadratic and 
	square root functions.

[Lightcurve steps]

	This option determines the number of steps, for which
	the lightcurve is computed. 

[Line profile]

	This option will compute the profile of an absorption
	line in the star's spectrum at each step in orpital phase.
	You can use the <Profiler> (in the <Output> menue) to view
	the result.