Secondary eclipse and phase curve

The batman_transit_eclipse_phasecurve model combines the primary transit, the secondary eclipse and a sinusoidal orbital phase curve. It is a photometric model for systems where the same linear ephemeris must describe both the transit and the occultation.

The alias batman_transit_secondary_phasecurve is also accepted.

When to use it

Use this model when the light curve contains the primary transit and enough out-of-transit orbital coverage to constrain the planet-to-star flux ratio. The model uses the same orbital parameters as the standard transit model, then adds dataset-level parameters for the eclipse depth and the phase-curve amplitude.

For a pure transit model, use Transit light-curve models. For independent mid-transit times, use Transit models for TTV measurements.

Parameters

Parameter	Scope	Meaning
P	planet common	Orbital period.
Tc	planet common	Reference time of inferior conjunction.
R_Rs	planet common	Planet-to-star radius ratio.
e, omega	planet common	Eccentricity and argument of periastron, or the selected parametrization.
phase_off	planet common	Phase offset in degrees, included when phase_offset: True.
phase_amp	dataset	Phase-curve semi-amplitude.
delta_occ	dataset	Secondary-eclipse depth, included when nightside_emission: True.
limb-darkening coefficients	limb-darkening common	Coefficients used by the transit part of the batman model.

The model also uses the transit geometry prepared by the abstract transit machinery: b or i, and either a_Rs or the stellar density, depending on the common-object configuration.

Model keywords

Keyword	Default	Meaning
planets	required	Planet common objects included in the model.
limb_darkening	required	Limb-darkening common object.
supersample_factor	1	Number of sub-exposures used to integrate finite exposure times.
exposure_time	dataset cadence	Exposure time used with supersample_factor.
nthreads	1	Number of threads passed to batman.
nightside_emission	True	If false, delta_occ is removed and the occulted flux is tied to phase_amp.
phase_offset	True	If false, phase_off is removed and the phase maximum is fixed to the default phase.

Example

planet_b:
  common: planets
  orbit: circular
  parametrization: Eastman2013
  use_time_inferior_conjunction: True

phasecurve_model:
  model: batman_transit_eclipse_phasecurve
  planets: [b]
  limb_darkening: ld_quadratic
  supersample_factor: 5
  exposure_time: 0.02043365
  nightside_emission: True
  phase_offset: True

input:
  LCdata:
    file: full_orbit_lightcurve.dat
    kind: Phot
    models:
      - phasecurve_model

When nightside_emission is enabled, delta_occ represents the flux blocked during the secondary eclipse. The phase curve is normalized internally with phase_amp and delta_occ, so the priors on these two parameters should be chosen consistently with the flux units of the photometric dataset.