transit.py - Transit models

These are routines used to generate a transit model, primarily for transit injection/recovery tests. These are wrappers around pysyzygy.Transit(), with the added feature that the transit depth and the transit duration can be specified as input variables (as opposed to the planet-star radius ratio and the stellar density, which pysyzygy expects).

everest.transit.Get_RpRs(d, **kwargs)

Returns the value of the planet radius over the stellar radius for a given depth d, given the everest.pysyzygy transit kwargs.

everest.transit.Get_rhos(dur, **kwargs)

Returns the value of the stellar density for a given transit duration dur, given the everest.pysyzygy transit kwargs.

everest.transit.Transit(time, t0=0.0, dur=0.1, per=3.56789, depth=0.001, **kwargs)

A Mandel-Agol transit model, but with the depth and the duration as primary input variables.

Parameters:

• time (numpy.ndarray) – The time array
• t0 (float) – The time of first transit in units of BJD - 2454833.
• dur (float) – The transit duration in days. Don’t go too crazy on this one – very small or very large values will break the inverter. Default 0.1
• per (float) – The orbital period in days. Default 3.56789
• depth (float) – The fractional transit depth. Default 0.001
• kwargs (dict) – Any additional keyword arguments, passed directly to pysyzygy.Transit()

Returns tmod:

The transit model evaluated at the same times as the time array

class everest.transit.TransitModel(name, single=False, sig_RpRs=0.001, **kwargs)

A transit model for use in regression. Note that the transit model is linear in the transit depth, so the depth (or planet/star radius ratio) is not a free parameter here!

Parameters:

• name (str) – The name of the planet, such as “b”.
• single (bool) – Is this a single transit? Default False (transit is assumed to be periodic at period given by per).
• sig_RpRs (float) – The standard deviation of the prior on the planet/star radius ratio. Used only when the transit model is included in the design matrix. Default 0.001
• kwargs – Any of the pysyzygy.Transit keyword arguments. These include:

• b or bcirc - The (circular) impact parameter. Default 0.
• MpMs - The planet-star mass ratio. Default 0.
• per - The planet orbital period in days. Default 10.

• rhos or aRs - The stellar density in g/cm^3 or the semi-major

  axis-stellar radius ratio. Default is rhos = 1.4, the density of the Sun

• ecc and w or esw and ecw - The eccentricity and the

  longitude of pericenter in radians, or the two eccentricity vectors. Default is ecc = 0. and w = 0.

• t0 or times - The time of first transit, or the time of each

  of the transits (in case they are not periodic) in days. Default is t0 = 0.

• u1 and u2 or q1 and q2 - The quadratic limb darkening

  parameters (u1, u2) or the modified quadratic limb darkening parameters (q1, q2) from Kipping (2013). Default is u1 = 0.40 and u2 = 0.26

• exptime - The exposure time in days for binning the model.

  Default ps.KEPLONGEXP

• fullorbit - Compute the orbital parameters for the entire orbit?

  Only useful if you’re interested in the full arrays of orbital parameters. Default False

• maxpts - Maximum number of points in the model. Increase

  this if you’re getting errors. Default 10,000

• exppts - The number of exposure points per cadence when

  binning the model. Default 50

• keptol - The tolerance of the Kepler solver. Default 1.e-15

• maxkepiter - Maximum number of iterations in the Kepler solver.

  Default 100

class everest.transit.TransitShape(depth=1, dur=0.1, **kwargs)

Return a single transit model used for injection/recovery tests.

A Mandel-Agol transit model, but with the depth and the duration as primary input variables. Note that the time(s) of transit is not an input parameter, nor is the period.

Parameters:

• depth (float) – The transit depth. Set this to 1. for transit injection/recovery tests. Default 1
• dur (float) – The transit duration in days. Default 0.1
• kwargs – Any additional keyword arguments, passed directly to pysyzygy.Transit()