starspot is a tool for measuring stellar rotation periods using Lomb-Scargle (LS) periodograms, autocorrelation functions (ACFs), phase dispersion minimization (PDM) and Gaussian processes (GPs). It uses the astropy implementation of Lomb-Scargle periodograms, and the exoplanet implementation of fast celerite Gaussian processes.

starspot is compatible with any light curve with time, flux and flux uncertainty measurements, including Kepler, K2 and TESS light curves. If your light curve is has evenly-spaced (or close to evenly-spaced) observations, all three of these methods: LS periodograms, ACFs and GPs will be applicable. For unevenly spaced light curves like those from the Gaia, or ground-based observatories, LS periodograms and GPs are preferable to ACFs.

Example usage

import numpy as np
import starspot as ss

# Generate some data
time = np.linspace(0, 100, 10000)
period = 10
w = 2*np.pi/period
flux = np.sin(w*time) + np.random.randn(len(time))*1e-2 + \
flux_err = np.ones_like(flux)*.01

rotate = ss.RotationModel(time, flux, flux_err)

# Calculate the Lomb Scargle periodogram period (highest peak in the periodogram).
lomb_scargle_period = rotate.ls_rotation()

# Calculate the autocorrelation function (ACF) period (highest peak in the ACF).
# This is for evenly sampled data only -- time between observations is 'interval'.
acf_period = rotate.acf_rotation(interval=np.diff(time)[0])

# Calculate the phase dispersion minimization period (period of lowest dispersion).
period_grid = np.linspace(5, 20, 1000)
pdm_period = rotate.pdm_rotation(period_grid)

print(lomb_scargle_period, acf_period, pdm_period)
>> 9.99892010582963 10.011001100110011 10.0

# Calculate a Gaussian process rotation period
gp_period = rotate.GP_rotation()

License & attribution

Copyright 2018, Ruth Angus.

The source code is made available under the terms of the MIT license.

If you make use of this code, please cite this package and its dependencies. You can find more information about how and what to cite in the citation documentation.