Rømer and Light Travel Time Effects (ltte)

Setup

Let's first make sure we have the latest version of PHOEBE 2.0 installed. (You can comment out this line if you don't use pip for your installation or don't want to update to the latest release).



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!pip install -I "phoebe>=2.0,<2.1"

As always, let's do imports and initialize a logger and a new Bundle. See Building a System for more details.



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%matplotlib inline



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import phoebe
from phoebe import u # units
import numpy as np
import matplotlib.pyplot as plt

logger = phoebe.logger('error')

b = phoebe.default_binary()









    



/usr/lib/python2.7/dist-packages/matplotlib/cbook/deprecation.py:106: MatplotlibDeprecationWarning: The mpl_toolkits.axes_grid module was deprecated in version 2.1. Use mpl_toolkits.axes_grid1 and mpl_toolkits.axisartist provies the same functionality instead.
  warnings.warn(message, mplDeprecation, stacklevel=1)

Now let's add a light curve dataset to see how ltte affects the timings of eclipses.



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b.add_dataset('lc', times=np.linspace(-0.05, 0.05, 51), dataset='lc01')









    Out[3]:





<ParameterSet: 15 parameters | contexts: compute, dataset>

Relevant Parameters

The 'ltte' parameter in context='compute' defines whether light travel time effects are taken into account or not.



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print b['ltte@compute']









    



Parameter: ltte@phoebe01@compute
                       Qualifier: ltte
                     Description: Correct for light travel time effects
                           Value: False

Comparing with and without ltte

In order to have a binary system with any noticeable ltte effects, we'll set a somewhat extreme mass-ratio and semi-major axis.



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b['sma@binary'] = 100



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b['q'] = 0.1

We'll just ignore the fact that this will be a completely unphysical system since we'll leave the radii and temperatures alone despite somewhat ridiculous masses - but since the masses and radii disagree so much, we'll have to abandon atmospheres and use blackbody.



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b.set_value_all('atm', 'blackbody')
b.set_value_all('ld_func', 'logarithmic')



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b.run_compute(irrad_method='none', ltte=False, model='ltte_off')









    Out[8]:





<ParameterSet: 2 parameters | qualifiers: fluxes, times>



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b.run_compute(irrad_method='none', ltte=True, model='ltte_on')









    Out[9]:





<ParameterSet: 2 parameters | qualifiers: fluxes, times>



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fig, axes = b.plot(show=True)



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