1. BATMAN & SPIDERMAN: Saving the World One Exoplanet Light Curve at a Time
talk about two open-source Python package for modeling transits, eclipses, and phase curves of exoplanets
we have some extraordinarly precise light curves coming from JWST and we want to be prepared to model them.
community resource – we don’t all need to write our own codes!
Laura Kreidberg
Junior Fellow, Harvard Society of Fellows
Enabling Transiting Exoplanets with JWST, 7/11/17

2. BATMAN: Bad-Ass Transit Model cAlculatioN
Python package for transit modeling
(Kreidberg 2015, PASP, 127, 1161)
determines planet position based on orbital parameters
calculates drop in stellar flux for any radially symmetric stellar limb darkening law
first: BATMAN
BATMAN does two things:
calculate planets position
calculates how much stellar flux the planet blocks, based on where it is. can do this for any radially symmetric stellar limb darkening law

3. Calculating Planet Position
input parameters:
period, time of inferior conjunction, longitude of periastron, inclination, a/Rs, eccentricity
solves Kepler’s equation with the Newton-Raphson method
outputs separation of centers in the plane of the sky
this is the easy part!
Murray & Correia, 2011, Exoplanets (ed. Seager)

4. Why is modeling transits hard?
limb darkening!

5. Limb Darkening Laws
Espinoza & Jordàn 2015
uniform, linear, quadratic, square-root, logarithmic, exponential, nonlinear, power2…
some have analytic transit solutions, others must be solved numerically
(Mandel & Agol 2002)

6. Limb Darkening Matters
imperfect limb darkening law can significantly bias transit depths, and stellar models may be wrong (Espinoza & Jordàn 2015)
stellar photospheres may contain same species as planetary atmospheres (e.g. H2O, Kreidberg et al. 2014)
Water absorption features in the limb darkening coefficients for GJ 1214
designed BATMAN to be as flexible as possible in how it treats limb darkening
Kreidberg et al. 2014
Nature, 505, 69

7. BATMAN numeric integration scheme
In addition to the standard analytic LD laws, BATMAN can also handle any radially symmetric LD parameterization
Kreidberg 2015, PASP

8. Users can specify the error tolerance:
1 ppm

9. BATMAN specs in active development on github installs with pip(
installs with pip
written in Python with C extensions
now compatible with GPUs! (thanks Michael Zhang)
handles any radially symmetric limb darkening law, supersampling, simple eclipses
speed: ~1e5 models/min at 10 ppm precision
(on my ancient laptop)

10. SPIDERMAN: [backronym pending)
Python package for eclipse mapping and phase curves for any planet brightness distribution (Louden & Kreidberg, in prep)
as you can see, SAVING the world is SERIOUS business

12. SPIDERMAN integration scheme
planet
figures c/o Tom Louden

13. SPIDERMAN integration scheme
figures c/o Tom Louden

14. SPIDERMAN integration scheme
can calculate area of triangles and area between chord and circle perimeter
figures c/o Tom Louden

15. Brightness Models Zhang & Showman 2017 offset hotspot
physically motivated analytic model
radiative/advective timescale
nightside temperature
day/night temperature contrast
offset hotspot
spot parameterized by:
latitude & longitude
size
temperature
Other models:
two temperature, Lambertian, spherical harmonics, forward model (from GCM)
Stellar brightness model: blackbody or Phoenix

16. input: temperature or brightness model for the planet
output: planet-to-star flux ratio at any orbital phase
GCM temperature map for WASP-43b
(Vivien Parmentier)
Infrared phase curves for a range of pressures
figures c/o Tom Louden

17. Eclipse Mapping zoom in on secondary eclipse
(simulated MIRI observations from PandExo)
deviation from a uniform dayside brightness model
figures c/o Tom Louden

18. SPIDERMAN specs in active development on github(
written in Python with C extensions
speed: fast enough for MCMC
brightness models: Zhang & Showman, hot spot, Lambertian, spherical harmonics, forward
stellar models: blackbody or Phoenix
check back for a paper very soon!

19. Conclusion Check out BATMAN and SPIDERMAN
Open-source development is awesome –
your contributions are welcome!
great thing about open source – the whole community can work to make the best possible models and it’s the opposite of a black box
community has really improved the package
because it’s open source, you can see inner workings and not have black box