TTVFast

Author:	Simon Walker <[email protected]>

A Python wrapper around Katherine Deck's TTVFast C program (https://github.com/kdeck/TTVFast)

For the latest changes, see the CHANGELOG.

Installation

For contributing to the package, see the Development instructions.

Install from pypi:

pip install ttvfast

For the latest development version, install with pip:

pip install git+https://github.com/mindriot101/ttvfast.git

Development instructions

To contribute to ttvfast, clone the repository and fetch the submodule:

git clone https://github.com/mindriot101/ttvfast-python.git
cd ttvfast-python
git submodule init
git submodule update # grabs code from TTVFast

install the package, in "development mode" into the current python environment:

pip install -e .

This way any python code changes made to the current directory will be reflected in the package. Note: any changes to the C code require recompilation by reinstalling the package with pip install -e . (see the editable install documentation documentation for more information).

Once the package is installed, test that everything built properly using:

$ py.test
============================== test session starts ===============================
testing/test_lweiss.py .
testing/test_models.py ...
testing/test_python_api.py ...
testing/test_ttvfast.py ...

Usage

To compute the TTV properties for one or more planets:

• build a ttvfast.models.Planet instance (see the class documentation for required parameters)
• pass a list of the planets in the system to ttvfast.ttvfast along with:
  • the stellar mass in units of solar mass,
  • the start point of the integration in days,
  • the time step for the integration in days,
  • and the end point for integration in days.

The function ttvfast.ttvfast returns a dictionary containing positions and rv. The positions entry is a tuple of:

1. a list of integer indices for which values correspond to which planet,
2. a list of integers defining the epoch,
3. a list of times,
4. a list of rsky values, and
5. a list of vsky values.

The optional rv_times parameter takes a list of RV times on which the RV is to be calculated. If so the rv entry in the output dictionary is populated with a list of RV values, and otherwise None.

For example:

from ttvfast import models


gravity = 0.000295994511                        # AU^3/day^2/M_sun
stellar_mass = 0.95573417954                    # M_sun


planet1 = models.Planet(
    mass=0.00002878248,                         # M_sun
    period=1.0917340278625494e+01,              # days
    eccentricity=5.6159310042858110e-02,
    inclination=9.0921164935951211e+01,         # degrees
    longnode=-1.1729336712101943e-18,           # degrees
    argument=1.8094838714599581e+02,            # degrees
    mean_anomaly=-8.7093652691581923e+01,       # degrees
)

planet2 = models.Planet(
    mass=0.00061895914,
    period=2.2266898036209028e+01,
    eccentricity=5.6691301931178648e-02,
    inclination=8.7598285693573246e+01,
    longnode=4.6220554014026838e-01,
    argument=1.6437004273382669e+00,
    mean_anomaly=-1.9584857031843157e+01,
)

planets = [planet1, planet2]
Time = -1045                                    # days
dt = 0.54                                       # days
Total = 1700                                    # days

results = ttvfast.ttvfast(planets, stellar_mass, Time, dt, Total)

For more details, see the original C module's documentation: https://github.com/kdeck/TTVFast/blob/master/c_version/README

Citations

If you use this code, please cite Deck, Agol, Holman, & Nesvorny (2014), ApJ, 787, 132, arXiv:1403.1895.

-Katherine Deck, Eric Agol, Matt Holman, & David Nesvorny