Stellar Parameter Inference

and

Transit False Positive Probabilities

(isochrones)
(vespa)

Timothy Morton 

(Princeton/UFlorida/Flatiron)

I have X-, Y-, and Z-band photometry of a star.

What kind of star is it?

~$ pip install isochrones 
~$ ipython
In [1]: from isochrones import StarModel, get_ichrone
In [2]: mist = get_ichrone('mist')
In [3]: model = StarModel(mist, X=(12, 0.05), Y=(11, 0.05), Z=(10, 0.05))
In [4]: model.fit()

from python terminal/script:

X = 12, 0.05
Y = 11, 0.05
Z = 10, 0.05

mystar/star.ini

$ starfit mystar

From command line:

X = 12, 0.05
Y = 11, 0.05
Z = 10, 0.05

Teff = 5300, 80 
feh = -0.1, 0.1
logg = 4.6, 0.15

mystar/star.ini

$ starfit mystar

Also:

X = 12, 0.05
Y = 11, 0.05
Z = 10, 0.05

Teff = 5300, 80 
feh = -0.1, 0.1
logg = 4.6, 0.15

mystar/star.ini

$ starfit mystar --binary

Or:

and more... ask!

  • In principle can use arbitrary stellar model grids
  • 3-d linear interpolation in (M, log(age), [Fe/H])
  • Any observable property can be called at any (in-bounds) values of (M, log(age), [Fe/H]); thus any property provided by stellar grids can be used as observed data for conditioning model

  • Uses MultiNest to fit by default;  will use emcee if MultiNest not installed.

  • Uses local [Fe/H] prior based on SDSS

To do / in progress

  • Include other built-in model grids (e.g., PARSEC)
  • Interpolate in EEP rather than mass
  • Improve treatment of extinction
  • Clever tricks to speed up model fitting?
  • Write/publish an overview paper!

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

~$ starfit --all myplanet
~$ calcfpp myplanet

results from Morton+ (2016)

tutorial notebook

github.com/timothydmorton/vespa

Group Projects (Tues/Wed)

  1. How much do different follow-up observations contribute to FPP? (apply to GJ 9827)
  2. Unvalidated Planets I (based on Cabrera+ 2017)
  3. Unvalidated Planets II (based on Shporer+ 2017)

Goal: learn careful, thoughtful use of vespa!

N.B. Stay tuned for TESS-related updates!

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