Isochrones for "Know thy Star" 2017

An open-source tool

for stellar model fitting

isochrones

Timothy Morton (Princeton)

#knowthystar

Your local spectroscopist hands you some parameters, but you want to know stellar mass/radius. What do you do next?

Ask your adviser, who vaguely recommends that you "interpolate onto some model isochrones."
Download some model isochrone grids.
Wonder what you should do next…

Option A

~$ pip install isochrones

Option B

~$ ipython
In [1]: from isochrones.dartmouth import Dartmouth_Isochrone
In [2]: from isochrones import StarModel
In [3]: dar = Dartmouth_Isochrone()
In [4]: model = StarModel(dar, Teff=(5700, 100), 
                          logg=(4.5, 0.1), feh=(0.0, 0.1))
In [5]: model.fit()

from python terminal/script:

Teff = 5700, 100
logg = 4.5, 0.1
feh = 0.0, 0.1

mystar/star.ini

$ starfit mystar

From command line:

mystar/star.ini

$ starfit mystar

Also:

Teff = 5700, 100
logg = 4.5, 0.1
feh = 0.0, 0.1

J = 8.71, 0.03
H = 8.39, 0.03
K = 8.34, 0.03

broadband

photometry --->

mass, age, feh, distance, A_V

spectroscopic properties, broadband photometry,

parallax (mas), stellar density, nu_max/delta_nu, ...

Fits for:

Observables:

In [1]: from isochrones.mist import MIST_Isochrone

In [2]: mist = MIST_Isochrone()

In [3]: mass, age, feh = (1.0, 9.6, 0.0)

In [4]: mist.radius(mass, age, feh)
Out[4]: 1.0021006303717472

In [5]: mist.density(mass, age, feh)
Out[5]: 1.4009789196927942

In [6]: mist.delta_nu(mass, age, feh)
Out[6]: 134.45611369338567

In [7]: distance, AV = (100, 0.1)

In [8]: mist.mag['J'](mass, age, feh, distance, AV)
Out[8]: 8.659777868892867

mystar/star.ini

$ starfit mystar --binary

Teff = 5700, 100
logg = 4.5, 0.1
feh = 0.0, 0.1

J = 8.71, 0.03
H = 8.39, 0.03
K = 8.34, 0.03

Multiple Star Systems

In [1]: from isochrones import StarModel, get_ichrone
In [2]: dar = get_ichrone('dartmouth')
In [3]: props = dict(Teff=(5700, 100),
                     logg=(4.5, 0.1),
                     feh=(0.0, 0.1),
                     J=(8.72, 0.03),
                     H=(8.39, 0.03),
                     K=(8.34, 0.03))
In [4]: binary_model = BinaryStarModel(dar, **props)
In [5]: binary_model.fit()

In[7]: binary_model.print_ascii()
root
 ╚═  J=(8.72, 0.03) @(0.00, 0 [99.00])
    ╚═  H=(8.39, 0.03) @(0.00, 0 [99.00])
       ╚═  K=(8.34, 0.03) @(0.00, 0 [99.00])
          ╠═ 0_0, Teff=(5700, 100), logg=(4.5, 0.1), feh=(0.0, 0.1)
          ╚═ 0_1

What if you take an AO image and

resolve a binary system?

maxAV = 1.216
RA = 299.268036
dec = 45.227428
Teff = 4135, 98.0
feh = -0.46, 0.16
logg = 4.711, 0.1

[twomass]
J = 13.513, 0.02
H = 12.845, 0.02
K = 12.693, 0.02

[NIRC2]
resolution = 0.1
separation_1 = 0.6
PA_1 = 100
K_1 = 3.66, 0.05
H_1 = 3.77, 0.03
J_1 = 3.74, 0.05

my_binary/star.ini

In[1]: from isochrones import StarModel, get_ichrone
In[2]: mist = get_ichrone('mist')
In[3]: mod = StarModel.from_ini(mist, 'my_binary')
In[4]: mod.print_ascii()
root
 ╚═ twomass H=(12.85, 0.02) @(0.00, 0 [4.00])
    ╚═ twomass J=(13.51, 0.02) @(0.00, 0 [4.00])
       ╚═ twomass K=(12.69, 0.02) @(0.00, 0 [4.00])
          ╠═ NIRC2 delta-H=(0.00, 0.01) @(0.00, 0 [0.10])
          ║  ╚═ NIRC2 delta-J=(0.00, 0.01) @(0.00, 0 [0.10])
          ║     ╚═ NIRC2 delta-K=(0.00, 0.01) @(0.00, 0 [0.10])
          ║        ╚═ 0_0, Teff=[4135.0, 98.0], feh=[-0.46, 0.16], logg=[4.711, 0.1]
          ╚═ NIRC2 delta-H=(3.77, 0.03) @(0.60, 100 [0.10])
             ╚═ NIRC2 delta-J=(3.74, 0.05) @(0.60, 100 [0.10])
                ╚═ NIRC2 delta-K=(3.66, 0.05) @(0.60, 100 [0.10])
                   ╚═ 0_1

In[5]: mod.param_names
['mass_0_0', 'mass_0_1', 'age_0', 'feh_0', 'distance_0', 'AV_0']

Modeling resolved binaries

maxAV = 1.216
RA = 299.268036
dec = 45.227428
Teff = 4135, 98.0
feh = -0.46, 0.16
logg = 4.711, 0.1

[twomass]
J = 13.513, 0.02
H = 12.845, 0.02
K = 12.693, 0.02

[NIRC2]
resolution = 0.1
separation_1 = 0.6
PA_1 = 100
K_1 = 3.66, 0.05
H_1 = 3.77, 0.03
J_1 = 3.74, 0.05

my_binary/star.ini

In[6]: mod2 = StarModel.from_ini(mist, 'my_binary', index=[0,1])

In[7]: mod2.param_names
['mass_0_0','age_0','feh_0','distance_0','AV_0',
 'mass_1_0','age_1','feh_1','distance_1','AV_1']

In[8]: mod2.print_ascii()
root
 ╚═ twomass H=(12.85, 0.02) @(0.00, 0 [4.00])
    ╚═ twomass J=(13.51, 0.02) @(0.00, 0 [4.00])
       ╚═ twomass K=(12.69, 0.02) @(0.00, 0 [4.00])
          ╠═ NIRC2 delta-H=(0.00, 0.01) @(0.00, 0 [0.10])
          ║  ╚═ NIRC2 delta-J=(0.00, 0.01) @(0.00, 0 [0.10])
          ║     ╚═ NIRC2 delta-K=(0.00, 0.01) @(0.00, 0 [0.10])
          ║        ╚═ 0_0, Teff=[4135.0, 98.0], feh=[-0.46, 0.16], logg=[4.711, 0.1]
          ╚═ NIRC2 delta-H=(3.77, 0.03) @(0.60, 100 [0.10])
             ╚═ NIRC2 delta-J=(3.74, 0.05) @(0.60, 100 [0.10])
                ╚═ NIRC2 delta-K=(3.66, 0.05) @(0.60, 100 [0.10])
                   ╚═ 1_0

Modeling resolved binaries

Goal: widely-used, robust, community-supported tool

Transparent and reproducible model-fitting methodology using principled probabilistic inference
Minimize "re-inventing the wheel"
Easily swap in/out model grids to test model dependence (Dartmouth & MIST currently available)

Caveats

Model dependent (duh.)
Built-in MCMC fitting currently not very robust. Use MultiNest fitting backend for now.
No goodness-of-fit metric—beware of poor fits! (check diagnostic plots)
Linear interpolation may give unreliable results for signficiantly evolved stars.
Treatment of extinction will not be correct for high levels of extinction or very broad bands (e.g. Gaia G)

Version 1.1 is released!

(quick-fix for some nagging issues; stay tuned for more)

~$ pip install --upgrade isochrones

Please contribute!

https://github.com/timothydmorton/isochrones

I have a transit signal.

What is the probability it's an astrophysical false positive?

~$ pip install vespa

name = myplanet
ra = 296.003693
dec = 44.277561
rprs = 0.012585031528
period = 384.845905
photfile = myphotometry.csv

[constraints]
maxrad = 1.26
secthresh = 0.000120176767205

g = 13.8735234, 0.05
r = 13.3370844, 0.05
i = 13.1663488, 0.05
z = 13.1029807, 0.05
J = 12.263, 0.02
H = 11.919, 0.02
K = 11.852, 0.02
Kepler = 13.426

myplanet/star.ini

myplanet/fpp.ini

~$ calcfpp myplanet

What happened here?