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

6       nightfall - binary star astronomy
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SYNOPSIS

9       nightfall -h
10       nightfall  -U  [more options] [mass_ratio inclination primary_size sec‐
11       ondary_size primary_temperature secondary_temperature]
12       nightfall [-G] [-A] [more options] mass_ratio inclination  primary_size
13       secondary_size primary_temperature secondary_temperature
14       nightfall [-G | -U] [-A] [more options] -C file
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DESCRIPTION

17       nightfall  is  an  interactive astronomy program for fun, education and
18       science.  It can generate animated views of eclipsing  (or  non-eclips‐
19       ing) binary stars, compute light curves and radial velocity curves, and
20       determine best-fit models for observational data.
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22       In the simplest case, nightfall computes the light curve for  a  binary
23       star  system with some given mass_ratio (mass of secondary star/mass of
24       primary star), inclination (0 = plane-on view, 90 = edge-on view of the
25       orbital  plane),  stellar sizes primary_size,secondary_size (dimension‐
26       less, in the range 0 - 1.3), and stellar temperatures  primary_tempera‐
27       ture,secondary_temperature (in Kelvin), and writes the light curve to a
28       file NightfallCurve.dat.
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30       nightfall is able to show many non-trivial, and sometimes  spectacular,
31       physical  effecs  in binary stars, as it uses a detailed physical model
32       rather than simply assuming the stars to be spherical.
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34       The full documentation  for nightfall is distributed only  in  DVI  and
35       HTML  format,  as  it is quite big,  and  thus  not very well suited to
36       the 'man' page format.  It includes some discussion of binary stars (at
37       a popular science level, hopefully) that you may find helpful in under‐
38       standing what the program does.
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OPTIONS

41       -h     Print a usage message on standard output and exit successfully.
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43       -U     Run in interactive mode.
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45       -C file
46              Use binary star parameters from a configuration file instead  of
47              giving  them on the command line. Sample configuration files are
48              in share/nightfall/cfg.
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50       -G[P|S|1|2]
51              Plot a graph of the lightcurve after its computation (P|S - zoom
52              on primary/secondary eclipse, 1|2 - plot 1/2 orbits).
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54       -A     Generate an animated view of the binary star.
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56       -V[v|i|c|a]
57              Visualize  the  geometry  of the binary star system (v - view of
58              the stars, i - image of the potential, c - contour plot  of  the
59              potential, a - all of them).
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61       -H     Send  plot  to a postscript file. If the postscript file exists,
62              it will be overwritten.
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64       -B[U|B|V|I|R|J|H|K|u|v|b|y|1|2]
65              Select the filter/bandpass for which the  lightcurve  should  be
66              plotted.  U-K range from ultraviolett to infrared, best match to
67              the human eye is V.  u-y  are  narrow-band  filters.   1|2  will
68              select radial velocity curves instead of a light curve.
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70       -fP/-fS value
71              By  default,  nightfall  assumes  synchroneous   rotation, which
72              means that the stars are rotating with the orbital  period,  and
73              thus  show  each other always the same 'side'. With this option,
74              you can set the ratio of stellar rotation frequency  to  orbital
75              frequency  to  some value different from one, seperately for the
76              primary P and the secondary S.
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78       -e eccentricity periastron_length
79              By default, nightfall assumes the orbit  to  be  circular.  With
80              this  option,  you  can  set the eccentricity of the orbit (0 is
81              circular, maximum is less than 1), and  the  periastron  length,
82              which is the point of closest approach of the two stars in their
83              orbit (0 - 360 degree).
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85       -sP/-sS longitude latitude radius dimfactor
86              Place a spot on the primary (P)  or  secondary  (S).   The  spot
87              parameters  are  the  location of the spot (longitude,latitude),
88              its radius, and  the  dimfactor  by  which  the  temperature  is
89              reduced (or increased) within the spot area.
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91       -tP/-tM/-tD value
92              Set  the  absolute value for the orbital period P (in days), the
93              total mass M (in units of solar masses), and/or the orbital sep‐
94              aration  D  (in solar radii) of the system. Any two of these are
95              independent, the third is then  calculated  from  Kepler's  laws
96              (i.e., you should set only two of these).
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98       -I file
99              Read  in observational data from a data file.  Sample data files
100              are in share/nightfall/data.
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102       -D[vwb]
103              Diagnostic output (v - verbose, w - warnings, b  -  status  mes‐
104              sages).
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NOTES

107       The  definition of primary/secondary is inverse to the usual convention
108       in astronomy.
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110       Obviously, the size of a star in a binary  system  is  limited  by  the
111       orbital separation of the two stars. Instead of having to calculate the
112       maximum useful stellar size herself, the user simply gives the  desired
113       stellar  size  as a fraction (0.001-1.3) of the maximum polar radius of
114       the star (which is calculated by the  program).   In  the  output  file
115       NightfallCurve.dat, you will then find the 'real' size of the star(s).
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117       If  no absolute values for total mass and orbital period/separation are
118       given, the program will use some  default  values  (mass  =  two  solar
119       masses,  orbital  separation  =  distance  earth-sun).   In  this case,
120       sizes/masses/velocities given in absolute units (e.g. kg, m, m/s, solar
121       masses/radii) are fictuous only - they would be valid only for a system
122       with the assumed default values of total mass and orbital separation.
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124       The  newest  version  of  nightfall  can  be   found   on   ftp://meta‐
125       lab.unc.edu/pub/Linux/science/astronomy,    and    on    the   homepage
126       http://www.lsw.uni-heidelberg.de/~rwichman/Nightfall.html.
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128       To subscribe to  the  nightfall  mailing  list,  send  mail  to  major‐
129       domo@seul.org with a body of subscribe nightfall-l.
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AUTHOR

132       Rainer Wichmann (rwichmann@hs.uni-hamburg.de)
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BUG REPORTS

135       If  you  find a bug in nightfall, please send electronic mail to rwich‐
136       mann@hs.uni-hamburg.de.  Please include your operating system  and  its
137       revision, the version of nightfall, what C compiler you used to compile
138       it, and the output from 'configure'.
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145                               28 December 1999                   NIGHTFALL(1)
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