NIGHTFALL(1) Nightfall manual NIGHTFALL(1)NAMEnightfall - binary star astronomy
SYNOPSISnightfall-h
nightfall-U [more options] [mass_ratio inclination primary_size sec‐
ondary_size primary_temperature secondary_temperature]
nightfall [-G] [-A] [more options] mass_ratio inclination primary_size
secondary_size primary_temperature secondary_temperature
nightfall [-G | -U] [-A] [more options] -C file
DESCRIPTIONnightfall is an interactive astronomy program for fun, education and
science. It can generate animated views of eclipsing (or non-eclips‐
ing) binary stars, compute light curves and radial velocity curves, and
determine best-fit models for observational data.
In the simplest case, nightfall computes the light curve for a binary
star system with some given mass_ratio (mass of secondary star/mass of
primary star), inclination (0 = plane-on view, 90 = edge-on view of the
orbital plane), stellar sizes primary_size,secondary_size (dimension‐
less, in the range 0 - 1.3), and stellar temperatures primary_tempera‐
ture,secondary_temperature (in Kelvin), and writes the light curve to a
file NightfallCurve.dat.
nightfall is able to show many non-trivial, and sometimes spectacular,
physical effecs in binary stars, as it uses a detailed physical model
rather than simply assuming the stars to be spherical.
The full documentation for nightfall is distributed only in DVI and
HTML format, as it is quite big, and thus not very well suited to
the 'man' page format. It includes some discussion of binary stars (at
a popular science level, hopefully) that you may find helpful in under‐
standing what the program does.
OPTIONS-h Print a usage message on standard output and exit successfully.
-U Run in interactive mode.
-C file
Use binary star parameters from a configuration file instead of
giving them on the command line. Sample configuration files are
in share/nightfall/cfg.
-G[P|S|1|2]
Plot a graph of the lightcurve after its computation (P|S - zoom
on primary/secondary eclipse, 1|2 - plot 1/2 orbits).
-A Generate an animated view of the binary star.
-V[v|i|c|a]
Visualize the geometry of the binary star system (v - view of
the stars, i - image of the potential, c - contour plot of the
potential, a - all of them).
-H Send plot to a postscript file. If the postscript file exists,
it will be overwritten.
-B[U|B|V|I|R|J|H|K|u|v|b|y|1|2]
Select the filter/bandpass for which the lightcurve should be
plotted. U-K range from ultraviolett to infrared, best match to
the human eye is V. u-y are narrow-band filters. 1|2 will
select radial velocity curves instead of a light curve.
-fP/-fS value
By default, nightfall assumes synchroneous rotation, which
means that the stars are rotating with the orbital period, and
thus show each other always the same 'side'. With this option,
you can set the ratio of stellar rotation frequency to orbital
frequency to some value different from one, seperately for the
primary P and the secondary S.
-e eccentricity periastron_length
By default, nightfall assumes the orbit to be circular. With
this option, you can set the eccentricity of the orbit (0 is
circular, maximum is less than 1), and the periastron length,
which is the point of closest approach of the two stars in their
orbit (0 - 360 degree).
-sP/-sS longitude latitude radius dimfactor
Place a spot on the primary (P) or secondary (S). The spot
parameters are the location of the spot (longitude,latitude),
its radius, and the dimfactor by which the temperature is
reduced (or increased) within the spot area.
-tP/-tM/-tD value
Set the absolute value for the orbital period P (in days), the
total mass M (in units of solar masses), and/or the orbital sep‐
aration D (in solar radii) of the system. Any two of these are
independent, the third is then calculated from Kepler's laws
(i.e., you should set only two of these).
-I file
Read in observational data from a data file. Sample data files
are in share/nightfall/data.
-D[vwb]
Diagnostic output (v - verbose, w - warnings, b - status mes‐
sages).
NOTES
The definition of primary/secondary is inverse to the usual convention
in astronomy.
Obviously, the size of a star in a binary system is limited by the
orbital separation of the two stars. Instead of having to calculate the
maximum useful stellar size herself, the user simply gives the desired
stellar size as a fraction (0.001-1.3) of the maximum polar radius of
the star (which is calculated by the program). In the output file
NightfallCurve.dat, you will then find the 'real' size of the star(s).
If no absolute values for total mass and orbital period/separation are
given, the program will use some default values (mass = two solar
masses, orbital separation = distance earth-sun). In this case,
sizes/masses/velocities given in absolute units (e.g. kg, m, m/s, solar
masses/radii) are fictuous only - they would be valid only for a system
with the assumed default values of total mass and orbital separation.
The newest version of nightfall can be found on ftp://meta‐
lab.unc.edu/pub/Linux/science/astronomy, and on the homepage
http://www.lsw.uni-heidelberg.de/~rwichman/Nightfall.html.
To subscribe to the nightfall mailing list, send mail to major‐
domo@seul.org with a body of subscribe nightfall-l.
AUTHOR
Rainer Wichmann (rwichmann@hs.uni-hamburg.de)
BUG REPORTS
If you find a bug in nightfall, please send electronic mail to rwich‐
mann@hs.uni-hamburg.de. Please include your operating system and its
revision, the version of nightfall, what C compiler you used to compile
it, and the output from 'configure'.
28 December 1999 NIGHTFALL(1)
