     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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     NIGHTFALL(1)                                                   NIGHTFALL(1)
     Nightfall manual                                           Nightfall manual

                                  28 December 1999

          -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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     NIGHTFALL(1)                                                   NIGHTFALL(1)
     Nightfall manual                                           Nightfall manual

                                  28 December 1999

               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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