This is a simple interface to the EBOP lightcurve model that is useful for
finding starting parameters for a full lightcurve model fit with jktebop.
- Download and unpack the alcfit_1.0.tar.gz
- If you do not have pgplot available through a starlink installation
(i.e., /star/lib/libpgplot.a is not on your system) then you will need
to install pgplot.
- Edit the file Makefile to your requirements
- INSTALL is the location of the executable.
- FC is your fortran compiler
- FFLAGS is flags for the fortran compilation - can be blank
- PGPLOT is the commands to link the PGPLOT directory, e.g., -L
/usr/local/pgplot/ -lpgplot -lpng -L/usr/X11R6/ -lX11
- $ make
Instructions for use
lightcurve model is based on the EBOP code written by Paul B Etzel. You should
cite Popper & Etzel (1981AJ.....86..102P) and Etzel (1981psbs.conf..111E) for EBOP. The following subset of parameters
from the lightcurve model available to the user. (Star 1 is the star eclipsed
at phase 0).
Surface brightness ratio Surface
brightness at the centre of the stellar disc for star 2 compared to star 1.
The surface brightness is related to the effective temperature of the star.
Sum of fractional radii
(R1+R2)/a where R 1,2 are
the radii of the stars and a is the
semi-major axis of the orbit. For a circular orbit, a is the separation of the stars.
Ratio of the
between the normal to the orbital plane and the line of sight in degrees,
i.e., i=90 for an edge-on orbit.
e.cos(ω), e.sin(ω) The eccentricity of the orbit is given by
e (=0 for a circular orbit). The
orientation of an eccentric orbit is given by the angle ω (longitude of
periastron). Rather than using these parameters in the lightcurve model, we
use e.cos(ω), e.sin(ω) because these are directly related
to the phase and width of the secondary eclipse compared to the primary
In addition, the program will
automatically adjust the mean magnitude of the lightcurve and apply a phase
shift to produce the best match to the observed lightcurve. There are a few
other parameters that have a small effect on the lightcurve model so they are
hidden from the user, e.g., limb darkening is fixed at 0.5 for both stars.
The program starts by prompting the user for the input file of
the data to be fitted and some parameters used to model and display the data,
e.g., the width of the eclipses. The input file is a text file with three
columns containing the time of observation, the observed magnitude and its
standard error. The program produces two output text files, a fit file that repeats the input data plus
an extra column with the lightcurve model, and a model file that contains the lightcurve model tabulated as a
function of phase.
The user is then prompted for the
lightcurve model parameters. The data and model for these parameters is
displayed on the selected PGPLOT device and the prompt Re-try? appears on the command line. The
user should reply Yes to this prompt
(or just hit return) and try new lightcurve parameters until the model
lightcurve gives a reasonable match to the observed lightcurve. The default
value for the parameters is the last value entered, so the user only needs to
enter the new value for parameters to be adjusted, for unchanged parameters
the user can hit return at the prompt.
Once the user
has a reasonable match to the observed lightcurve they enter "N" at
the Re-try? prompt. The program then uses the Numerical Recipes
amoeba implementation of the simplex
algorithm to optimize the fit the observed lightcurve (this can take some
time). The new values of the lightcurve parameters and the χ2
value for the fit are reported and the new fit displayed. The user is then
prompted with Re-fit?, which enables
them to repeat the process of entering parameters and re-fitting. Otherwise,
the fit can be re-plotted to a new pgplot device (e.g., a postscript file),
and the program then ends.
Last updated 30 Sep 2011