Contact Binary with Spots

Setup

IMPORTANT NOTE: if using spots on contact systems or single stars, make sure to use 2.1.15 or later as the 2.1.15 release fixed a bug affecting spots in these systems.

Let's first make sure we have the latest version of PHOEBE 2.1 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).



In [ ]:

    
!pip install -I "phoebe>=2.1,<2.2"



In [1]:

    
%matplotlib inline

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



In [1]:

    
import phoebe
from phoebe import u # units

logger = phoebe.logger()

b = phoebe.default_binary(contact_binary=True)

Model without Spots



In [2]:

    
b.add_dataset('lc', times=phoebe.linspace(0,0.5,101))









    Out[2]:





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



In [3]:

    
b.run_compute(irrad_method='none', model='no_spot')









    Out[3]:





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

Adding Spots

Let's add a spot to the primary component in our binary. Note that if you attempt to attach to the 'contact_envelope' component, an error will be raised. Spots can only be attached to star components.

The 'colat' parameter defines the latitude on the star measured from its North (spin) Pole. The 'long' parameter measures the longitude of the spot - with longitude = 0 being defined as pointing towards the other star at t0. See to spots tutorial for more details.



In [4]:

    
b.add_feature('spot', component='primary', feature='spot01', relteff=0.9, radius=20, colat=90, long=-45)









    



Wed, 19 Jun 2019 09:17 PARAMETERS   WARNING wrapping value of long to 315.0 deg






    Out[4]:





<ParameterSet: 4 parameters | qualifiers: colat, radius, long, relteff>



In [5]:

    
b.run_compute(irrad_method='none', model='with_spot')









    Out[5]:





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

Comparing Light Curves



In [6]:

    
afig, mplfig = b.plot(show=True, legend=True)

Spots near the "neck"

Since the spots are still defined with the coordinate system of the individual star components, this can result in spots that are distorted and even "cropped" at the neck. Furthermore, spots with long=0 could be completely "hidden" by the neck or result in a ring around the neck.

To see this, let's plot our mesh with teff as the facecolor.



In [7]:

    
b.remove_dataset(kind='lc')



In [8]:

    
b.add_dataset('mesh', times=b.to_time(0.25), columns='teffs')









    Out[8]:





<ParameterSet: 4 parameters | contexts: compute, dataset>



In [9]:

    
b.run_compute(irrad_method='none', model='with_spot')









    Out[9]:





<ParameterSet: 8 parameters | components: primary, secondary>



In [10]:

    
afig, mplfig = b.plot(fc='teffs', ec='none', fcmap='plasma', show=True)

Now if we set the long closer to the neck, we'll see it get cropped by the boundary between the two components. If we need a spot that crosses between the two "halves" of the contact, we'd have to add separate spots to each component, with each getting cropped at the boundary.



In [11]:

    
b.set_value('long', value=-30)









    



Wed, 19 Jun 2019 09:18 PARAMETERS   WARNING wrapping value of long to 330.0 deg



In [12]:

    
b.run_compute(irrad_method='none', model='with_spot')









    



Wed, 19 Jun 2019 09:18 BUNDLE       WARNING overwriting model: with_spot






    Out[12]:





<ParameterSet: 8 parameters | components: primary, secondary>



In [13]:

    
afig, mplfig = b.plot(fc='teffs', ec='none', fcmap='plasma', show=True)

If we set long to zero, the spot completely disappears (as there is nowhere in the neck that is still on the surface.



In [14]:

    
b.set_value('long', value=0.0)



In [15]:

    
b.run_compute(irrad_method='none', model='with_spot')









    



Wed, 19 Jun 2019 09:18 BUNDLE       WARNING overwriting model: with_spot






    Out[15]:





<ParameterSet: 8 parameters | components: primary, secondary>



In [16]:

    
afig, mplfig = b.plot(fc='teffs', ec='none', fcmap='plasma', show=True)

But if we increase the radius large enough, we'll get a ring.



In [17]:

    
b.set_value('radius', value=40)



In [18]:

    
b.run_compute(irrad_method='none', model='with_spot')









    



Wed, 19 Jun 2019 09:18 BUNDLE       WARNING overwriting model: with_spot






    Out[18]:





<ParameterSet: 8 parameters | components: primary, secondary>



In [19]:

    
afig, mplfig = b.plot(fc='teffs', ec='none', fcmap='plasma', show=True)