NIGHTFALL(1) NIGHTFALL(1)
Nightfall manual Nightfall manual
28 December 1999
NAME
nightfall - binary star astronomy
SYNOPSIS
nightfall -h
nightfall -U [more options] [mass_ratio inclination primary_size
secondary_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
DESCRIPTION
nightfall is an interactive astronomy program for fun, education and
science. It can generate animated views of eclipsing (or non-
eclipsing) 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
(dimensionless, in the range 0 - 1.3), and stellar temperatures
primary_temperature,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
understanding 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|
Plot a graph of the lightcurve after its computation (P|S - zoom
on primary/secondary eclipse, 1|2 - plot 1/2 orbits).
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-A Generate an animated view of the binary star.
-V[v|i|
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
separation 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]
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Diagnostic output (v - verbose, w - warnings, b - status
messages).
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://metalab.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
majordomo@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
rwichmann@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'.
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