%matplotlib inline
import numpy as np
import matplotlib.pyplot as plt
from isochrones.dartmouth import Dartmouth_Isochrone
dar = Dartmouth_Isochrone()
from isochrones.starmodel import StarModel
Here, I create a stellar model object with observations of $T_{eff}$, $\log g$, and $[Fe/H]$ corresponding to properties in the Huber stellar properties catalog paper, which agree closely with the Borucki (2011) values, if not exactly.
mod = StarModel(dar, Teff=(5642,50), logg=(4.44,0.06), feh=(-0.27,0.08))
I then run an MCMC chain using the Dartmouth isochrone grids, which can predict $T_{eff}$ and $\log g$ (and $[Fe/H]$) as a function of mass, age, and $[Fe/H]$, where the likelihood surface is determined by the observations above. This gives chains of mass, age, and $[Fe/H]$ that can be used to read off distributions of other stellar properties, such as radius.
mod.fit_mcmc()
We can look at the result of these chains, which support the idea of an older, smaller star than the literature values (plotted with red vertical lines) seem to indicate. This discrepancy is pretty severe, and I'm not sure how to explain it.
mod.plot_samples('radius')
plt.axvline(0.979, color='r', ls='--')
mod.plot_samples('mass')
plt.axvline(0.970, color='r', ls='--')
mod.plot_samples('age')
Just for a sanity check, let's look directly at the Dartmouth isochrone grid (the MASTERDF dataframe), query within the literature range of mass and logg, and show the resulting effective temperatures:
from isochrones.dartmouth import MASTERDF
subdf = MASTERDF.query('feh > -0.31 and feh < -0.19 and M > 0.95 and M < 1 and logg > 4.42 and logg < 4.46')
plt.hist(np.array(10**subdf['logTeff']));
Nowhere do we see anything close to 5640 K. What is going on here?
mod.save_hdf('kep22.h5')
mod2 = StarModel.load_hdf('kep22.h5')
mod2.plot_samples('radius')