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Synthetic test data

These synthetic data were generated from the scope package, to simulate Target Pixel Files (TPFs) with known levels of spacecraft-induced roll motion.

synthetic-k2-flat.targ.fits.gz a simulated flat (featureless) lightcurve.

synthetic-k2-planet.targ.fits.gz a simulated planet host star with the following properties:

  • Transit period 5.0 days
  • Rp/R_star 0.044
  • Planet semi-major axis in units of R_star 12.3108
  • Starry limb darkening coefficients (0.40, 0.26)

synthetic-k2-sinusoid.targ.fits.gz a simulated sine wave with:

  • Rotation period 5.0 days
  • Sine fractional amplitude 0.001 (i.e. 0.1% or 1000 ppm), so peak-to-valley 0.002.

The level of roll motion was mimicked from the K2 source EPIC 205998445, for a hypothetical 12th magnitude star. 1000 cadences were simulated.

The noise-free signals are housed in the HDU extension 3 "SIMULATED_SIGNAL", with a single data vector "NOISELESS_INPUT".

The SIMULATED_SIGNAL HDU header has additional header cards listing the values of the planet and sine wave parameters.

Python code to generate this synthetic data with scope

You will need these dependencies:

import scope
import lightkurve as lk
import numpy as np
import starry
from astropy.io import fits
import copy

target = scope.generate_target(ncadences=500)

Sine wave signal

target_sine = copy.copy(target)

rot_period = 5.0 # days
lc_amp = 0.001 # percent amplitude
injected_sine_lc = 1.0+ lc_amp * np.sin(2.0*np.pi*target.t/rot_period)

target_sine.add_variability(custom_variability=injected_sine_lc)

sine_tpf = target_sine.to_lightkurve_tpf(target_id="simulated_sine_P5days_Amp0p001")

genuine_tpf = lk.search_targetpixelfile(205998445, mission='K2').download()
col = genuine_tpf.get_keyword('1CRV5P', hdu=1, default=0)
row = genuine_tpf.get_keyword('2CRV5P', hdu=1, default=0)

sine_tpf.hdu[1].header.set('1CRV5P', value=col)
sine_tpf.hdu[1].header.set('2CRV5P', value=row)

extra_hdu = fits.BinTableHDU.from_columns([fits.Column(name='NOISELESS_INPUT', format='E',
                                 array=injected_sine_lc)])

extra_hdu.name = 'SIMULATED_SIGNAL'

sine_tpf.hdu.append(extra_hdu)

sine_tpf.hdu[3].header.set('PERIOD', value=rot_period, comment='Period of noiseless input sine wave')
sine_tpf.hdu[3].header.set('SINE_AMP', value=lc_amp, comment='Amplitude of noiseless input sine wave')

sine_tpf.to_fits(output_fn='synthetic-k2-sinusoid.targ.fits', overwrite=True)

Transiting exoplanet signal

star = starry.kepler.Primary()

star[1] = 0.40
star[2] = 0.26

planet = starry.kepler.Secondary(lmax=5)

planet.tref = 2144.3

planet.r = 0.044 # Rp/R_star, reverse-engineering a nearly 2000 ppm transit without limb darkening
planet.porb = 5.0 # 5 day period
planet.a = 12.3108 # Semi-major axis, assuming 1 solar mass star

rprs = np.sqrt(2000/1.0e6)

system = starry.kepler.System(star, planet)

time = target.t
system.compute(time)

target_planet = copy.copy(target)

target_planet.add_variability(custom_variability=system.lightcurve)

plan_tpf = target_planet.to_lightkurve_tpf(target_id="simulated_planet_P5days")
plan_tpf.hdu[1].header.set('1CRV5P', value=col)
plan_tpf.hdu[1].header.set('2CRV5P', value=row)

extra_hdu = fits.BinTableHDU.from_columns([fits.Column(name='NOISELESS_INPUT', format='E',
                                 array=system.lightcurve)])
extra_hdu.name = 'SIMULATED_SIGNAL'
plan_tpf.hdu.append(extra_hdu)
plan_tpf.hdu[3].header.set('PERIOD', value=5.0, comment='Period of noiseless input transit')
plan_tpf.hdu[3].header.set('RPRS', value=0.044, comment='Rp/Rstar ')
plan_tpf.hdu[3].header.set('PLANA', value=12.3108, comment='Planet semi-major axis in R star')
plan_tpf.hdu[3].header.set('STARLD1', value=0.40, comment='Starry limb darkening 1')
plan_tpf.hdu[3].header.set('STARLD2', value=0.26, comment='Starry limb darkening 2')
plan_tpf.hdu[3].header.set('PLANTREF', value=2144.3, comment='Planet transit reference time')

plan_tpf.to_fits(output_fn='synthetic-k2-planet.targ.fits', overwrite=True)

Default, flat lightcurve

flat_tpf = target.to_lightkurve_tpf(target_id="simulated_flat_star")
flat_tpf.hdu[1].header.set('1CRV5P', value=col)
flat_tpf.hdu[1].header.set('2CRV5P', value=row)

extra_hdu = fits.BinTableHDU.from_columns([fits.Column(name='NOISELESS_INPUT', format='E',
                                 array=np.ones(500))])
extra_hdu.name = 'SIMULATED_SIGNAL'
flat_tpf.hdu.append(extra_hdu)

flat_tpf.to_fits(output_fn='synthetic-k2-flat.targ.fits', overwrite=True)