Overview

A false positive probability calculation in vespa is built of two basic components: a TransitSignal and a PopulationSet, joined together in a FPPCalculation object. The TransitSignal holds the data about the transit signal photometry, and the PopulationSet contains a set of simulated populations, one EclipsePopulation for each astrophysical model that is considered as a possible origin for the observed transit-like signal. By default, the populations included will be PlanetPopulation and three astrophysical false positive scenarios: an EBPopulation, an HEBPopulation, and a BEBPopulation.

The EclipsePopulation object derives from the more general vespa.stars.StarPopulation, which is useful beyond false positive calculations, such as for generating a hypothetical population of binary companions for a given star in order to help quantify completeness to stellar companions of an imaging survey.

Installation

To install, you can get the most recently released version from PyPI:

pip install vespa [--user]

Or you can clone the repository:

git clone https://github.com/timothydmorton/vespa.git
cd vespa
python setup.py install [--user]

The --user argument may be necessary if you don’t have root privileges.

Basic Usage

The simplest way to run an FPP calculation straight out of the box is as follows.

1. Make a text file containing the transit photometry in three columns: t_from_midtransit [days], flux [relative, where out-of-transit is normalized to unity], and flux_err. The file should not have a header row (no titles); and can be either whitespace or comma-delimited (will be ingested by np.loadtxt()).

  1. Make a star.ini file that contains the observed properties of the target star (photometric and/or spectroscopic, whatever is available):

    #provide spectroscopic properties if available
#Teff = 3503, 80  #value, uncertainty
#feh = 0.09, 0.09
#logg = 4.89, 0.1

#observed magnitudes of target star
# If uncertainty provided, will be used to fit StarModel
J = 9.763, 0.03
H = 9.135, 0.03
K = 8.899, 0.02
Kepler = 12.473

  2. Make a fpp.ini file containing the following information:

    name = k2oi #anything
ra = 11:30:14.510 #can be decimal form too
dec = +07:35:18.21

period = 32.988 #days
rprs = 0.0534   #Rp/Rstar
photfile = lc_k2oi.csv #contains transit photometry

[constraints]
maxrad = 12  # aperture radius [arcsec]
secthresh = 1e-4 # Maximum allowed depth of potential secondary eclipse

  3. Run the following from the command line (from within the same folder that has star.ini and fpp.ini):

    $  calcfpp -n 1000

This will take a few minutes the first time you run it (note the default simulation size is n=20000, which would take longer but be more reliable), and will output the FPP to the command line, as well as producing diagnostic plots and a results.txt file with the quantitative summary of the calculation. In addition, this will produce a number of data files in the same directory as your fpp.ini file:

  • trsig.pkl: the pickled vespa.TransitSignal object.
  • starfield.h5: the TRILEGAL field star simulation
  • starmodel.h5: the isochrones.StarModel fit
  • popset.h5: the vespa.PopulationSet object representing the model population simulations.

It will also generate the following diagnostic plots:

  • trsig.png: A plot of the transit signal
  • eb.png, heb.png, beb.png, pl.png: plots illustrating the likelihood of each model.
  • FPPsummary.png: A summary figure of the FPP results.
  • Summary plots of the isochrones.StarModel fits.

Once these files have been created, it is faster to re-run the calculation again, even if you change the constraints.