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astro 465
teaching
Astro 465
Computational assignment 1
CA1.1
- To find where a model matches the Sun, you can use the star.plt1 file.
By default it saves every fifth model.
If you want to change that to every model, set the parameter KT4 to 1. This ought to be a short run; you can
monitor the age of the model with tail as discussed before. As soon as you see that the model has passed
the age of the Sun, you can stop the code as discussed here.
- In order to make the code stop when the model reaches a certain age, you can use the parameter UC(2) in the file
init.run (see the manual).
- Remember that the stellar-structure output of the code is saved in the file star.mdl1.
- By default, the code does not save every structure model it computes; for most models the output would take up too much
disc space. The parameter KT1 in init.dat ensures that every KT1-th model gets saved. You
can set it to 1 to save every model.
CA1.2
Abundances
- You need a model with helium abundance Y and metallicity Z. These two numbers determine the hydrogen
abundance X, which can be set in the code as the parameter CH in init.dat (the default value,
-1, tells the code to use the value from the ZAMS model).
- However, to make the code realise you change the abundances at startup, we need to tell it to fully mix the ZAMS model
in order to create a homogeneous composition with the proper abundances. To do so, set JCH in init.dat
to 4.
- The model may not converge when the initial time step is too large. Start the code and see whether it exits
after a few seconds or not. If so, see which time step was used (e.g. in star.out1, first column second
row). The initial time step is specified in init.run by setting the parameter DTY to a positive number
(in years). Try setting it to an order if magnitude lower than what the code tried initially, and keep doing that until
it works. This initial time step may scale with the main-sequence lifetime and hence be shorter for more massive stars.
I would be very surprised though if you'd need an initial time step smaller than 1 yr.
- For some combinations of X, Y, Z and M, especially (it seems) around M=0.75-0.95Mo,
a ZAMS model may never converge. A solution may be to set in init.run ML1 to a value for which the
ZAMS model does converge (e.g. ML1=0.0 if a 1.0Mo does converge) while setting SM to
the desired mass (e.g. SM=0.80).
Isochrones
ZAMS
plotpltn
- To plot more than one evolutionary track (e.g., iso.plt1 and zams.plt1) in one figure,
see the program plotpltn.
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