Transit models

PyTransit implements a family of exoplanet transit light curve models, each with model-specific optimisations that make it efficient for the cases it was designed for. They all share the interface described in the User guide; this section describes what each model computes, when to reach for it, and its full API.

Choosing a model

Situation	Model
Anything, unless something below applies	RoadRunnerModel
Spectroscopic transit time series	TransmissionSpectroscopyModel
Secondary eclipse	EclipseModel
Spectroscopic eclipse time series	EclipseSpectroscopyModel
Planet with a measurably oblate projection	OblatePlanetModel
Fast-rotating, gravity-darkened host star	GravityDarkenedModel
Transit over a chromosphere in an emission line	ChromosphereModel
Reproducing a published Mandel & Agol analysis	QuadraticModel
Transit search, or limb darkening genuinely irrelevant	UniformModel
GPU acceleration	the OpenCL models

Start with RoadRunner. It supports any radially symmetric limb darkening law, is fast, and is accurate to a few ppm with its default settings for typical radius ratios. The specialised models above exist because they model something RoadRunner does not (an oblate planet, a gravity-darkened star, an eclipse) or because they exploit structure RoadRunner cannot (the shared geometry of a spectroscopic time series).

The remaining classical models – QuadraticModel, QPower2Model, and GeneralModel – are analytic solutions for one specific limb darkening law each. They are kept because they are well tested, widely used, and directly comparable to the literature, but for new work RoadRunner does what they do with more flexibility. In particular, GeneralModel is superseded by RoadRunner with the 'general' limb darkening law, which is both faster and more flexible.

Note

This guidance reflects the general design of the package rather than a benchmark of your particular problem. If model evaluation is the bottleneck in your analysis, time the candidates on your own data and hardware.

The catalogue

Model	Limb darkening	Reference
RoadRunnerModel	Any	Parviainen (MNRAS 499, 1633, 2020)
TransmissionSpectroscopyModel	Any	Parviainen (MNRAS 499, 1633, 2020)
OblatePlanetModel	Any	Seager & Hui (2002); Barnes & Fortney (2003)
QuadraticModel	Quadratic	Mandel & Agol (ApJ 580, L171, 2002)
UniformModel	None	Mandel & Agol (ApJ 580, L171, 2002)
QPower2Model	Power-2	Maxted & Gill (A&A 622, A33, 2019)
GeneralModel	General	Giménez (A&A 450, 1231, 2006)
ChromosphereModel	None	Schlawin et al. (ApJL 722, L75, 2010)
EclipseModel	None	Mandel & Agol (ApJ 580, L171, 2002)
EclipseSpectroscopyModel	None	Parviainen (MNRAS 499, 1633, 2020)
GravityDarkenedModel	Any	Barnes (ApJ 705, 683, 2009)

RoadRunner family

• RoadRunner model
  • What makes it different
  • Usage
  • Performance options
  • How it works
  • Accuracy
  • Speed against the quadratic model
  • Examples
  • API
• Transmission spectroscopy model
  • The problem it solves
  • Differences from the other models
  • Usage
  • How it works
  • Accuracy
  • API
• Oblate planet model
  • Why oblateness matters
  • Accuracy levels
  • Usage
  • API

Eclipse models

• Eclipse models
  • EclipseModel
  • EclipseSpectroscopyModel

Classical models

• Quadratic model
  • Usage
  • Interpolation
  • Converting to OpenCL
  • Examples
  • API
• Power-2 model
  • Why the power-2 law
  • Usage
  • API
• General model
  • Usage
  • Transmission spectroscopy mode
  • API
• Uniform model
  • When to use it
  • API
• Chromosphere model
  • Limb brightening
  • Usage
  • API

Specialised models

• Gravity-darkened model
  • The physics
  • Parameters
  • Usage
  • Accuracy and resolution
  • Visualisation
  • API

GPU models

• OpenCL models
  • Uniform model
  • Quadratic model
  • Power-2 model
  • RoadRunner model