Eggman

Code for calculating the geometry and transit depths of piecewise ellipsoidal objects.

Installation

Eggman relies on three packages that the user must install themselves before compiling: Cython, NASA's CSPICE library, and the GNU Scientific Library (GSL). See below for instructions on how to do this. The latter two are C libraries so the Python setup script cannot retrieve them itself.

Once the prerequisites are installed, eggman can be compiled and installed from the terminal with pip install . from the eggman directory.

Cython

Cython can be installed in pip with pip install cython.

CSPICE

The CSPICE library can be installed by navigating the terminal to the eggman directory and running the included install script with csh getCSPICE.csh. This requires csh be installed, which it is by default on Mac and can be acquired from the system package manager on Linux (sorry, I'd have used Bash if CSPICE didn't use csh already). Other (Anaconda or system) installations of CSPICE probably work correctly, but please report any errors encountered.

GSL

The GNU Scientific Library (GSL) can be installed through essentially any system package manager: anaconda::gsl for Anaconda, gsl for MacPorts, gsl for Homebrewand libgsl-dev for Linux using apt-get. It can also be installed directly from the GSL website; just make sure you install it such that the compiler can locate it.

Usage

For now the only production ready function is asymmetricTransit, which calculates the transit of a piecewise-ellipsoidal planet consisting of two half-ellipses attached at the location of the planet (diagram TODO). They have the same polar radius unless the polar radius is set to a negative number, which eggman interprets to mean that the two half-circle model of catwoman is to be used, such that the polar radius is rMorning for the morning side and rEvening for the evening side.

import numpy as np
import eggman

eggman.asymmetricTransit(
    rMorning=.12,                   # Relative to stellar radius
    rEvening=.1,
    rPole=.11,
    t=np.linspace(-.05,.05,100),    # In any unit, so long as it's the same as t0 and period.
    t0=0,
    period=1.,
    semimajor=10.,                  # Relative to the stellar radius
    inclination=89.,                # In degrees
    limbType='quadratic',           # Must be one of 'quadratic', 'nonlinear'
    limb=[.3, .2]                   # Two parameters for quadratic, 4 for nonlinear
)

Limb Darkening Settings

The limb darkening of the star is set by the limbType and limb parameters. limbType is the name of the darkening formula to use and limb is the parameters of that formula. limb must have exactly the correct number of parameters for that limbType. Currently, the options for limb darkening types are:

1. quadratic, 2 parameters, $I(\mu)/N = 1 - \gamma_0 (1-\mu) - \gamma_1 (1-\mu)^2$
2. nonlinear, 4 parameters, $I(\mu)/N = 1 - \gamma_0 (1 - \sqrt{\mu}) - \gamma_1 (1-\mu) - \gamma_2 (1-\mu^{3/2}) - \gamma_3 (1-\mu^2)$

where $N$ is a normalization factor, $\gamma$ are model parameters (specified in limb), $\mu$ is the cosine of the angle between the viewer-star vector and the star center-to-surface-point vector. See Mandel & Agol (2002) for more information.