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Analysis pipeline for HST/WFC3 spectroscopic observations of exoplanet transits and eclipses
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Iraclis

Analysis pipeline for HST/WFC3 spectroscopic observations of exoplanet transits and eclipses

A complete package to analyse single-object spatially scanned spectroscopic observations of extrasolar planets obtained with the near-infrared grisms (G102, G141) of the Wide Field Camera 3 on-board the Hubble Space Telescope.

Includes:

  • Reduction of the raw frames.
  • Calibration of the position of the total spectrum and the different spectral elements.
  • Extraction of the total flux and the flux per spectral element.
  • Fitting of the white and the spectral light-curves.

Currently, fitting can be applied only on single-visit light-curves but in the next version it will be updated to fit also multiple visits of the same target simultaneously.

References

License

This work is licensed under the Creative Commons Attribution 4.0 International License.

Copyright (c) 2018 Angelos Tsiaras

Please pay attention to Section 3 of the license and do:

  • retain identification of the creators by including the above listed references in future work and publications,
  • indicate if You modified the Licensed Material and retain an indication of any previous modifications.

To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

Installation

Open a terminal and type: pip install iraclis

Usage

Getting HST/WFC3 data

Each transit or eclipse dataset, obtained with WFC3, includes many spectroscopic images (using one of the two spectroscopic grisms: G102 or G141) and also, at least, one direct (undispersed) image (using one of the 15 WFC3 imaging filters: F098W, F132N, F140W, F126N, F153M, F167N, F139M, F164N, F127M, F160W, F128N, F125W, F130N, F110W, F105W).

To use Iraclis, download all the spectroscopic data in the RAW format and the imaging data in the FLT format from the MAST archive. Keep all your files together in one directory.

Analysing HST/WFC3 data

Within a bash terminal:

  • you can process a dataset using a parameters file by typing: iraclis -p path_to_parameters_fle
  • or using default values for the parameters by typing: iraclis -d path_to_data_directory

Within a python terminal, first import the package: import iraclis

  • you can process a dataset using a parameters file by typing: iraclis.process_visit(parameters_file='path_to_parameters_fle')
  • or using default values for the parameters by typing: iraclis.process_visit(data_directory='path_to_data_directory')

Setting up a parameters file

A parameters file is a simple txt file that contains all the important paramets controlling the data anlaysis process of a WFC3 dataset. Below, you can find the description of such a file (this file is included in the examples).

data_directory iraclis_test_dataset_hatp26b_raw_data
(diectory path) The path of the directory where the dataset is stored.

output_directory_copy False
(diectory name/False) If you wish to copy your results in a new directory, give here its name. The default results are stored in the “results” directory. This is useful if you wish to analyse the same dataset multiple times with different fitting parameters.

reduction True
(True/False) Whether to reduce the data or not. You can set it to False if you wish to re-run the analysis starting from a later stage.

splitting True
(True/False) Whether to split the data or not. In this case the reduced data will be splitted into the differential frames N - N-1, rather than final-initial.

extraction False
(True/False) Whether to extract the light-curves or not. You can set it to False if you wish to re-run the analysis starting from a later stage.

splitting_extraction True
(True/False) Whether to extract the light-curves from the splitted data or not. You can set it to False if you wish to re-run the analysis starting from a later stage. Note: set only one of the extraction or splitting_extraction to true. If you wish to have both, re-run the analysis with different values for these parameters.

fitting_white True
(True/False) Whether to fit the white light-curve or not. You can set it to False if you wish to re-run the analysis starting from a later stage.

fitting_spectrum True
(True/False) Whether to fit the spectral light-curves or not.

target_x_offset 0
target_y_offset 0
(number) In the rare case that in the field of view there is a star brighter that your target, give here the difference in their positions. This is important because the code automatically identifies the brightest star as the target (in 99% of the observations, this is the case).

aperture_lower_extend -20
(number) Vertical starting position of the extraction box. Use negative value. -20 means that the extraction box will start 20 pixels below the spectrum.

aperture_upper_extend 20
(number) Vertical final position of the extraction box. Use positive value. 20 means that the extraction box will stop 20 pixels above the spectrum.

extraction_method gauss
(gauss/integral) There are two available extraction methods: gauss (where the flux extracted is the convolution of the spectrum with a gaussian) or integral (where the flux extracted is calculated as the integral of the spectrum inside the extraction aperture)

extraction_gauss_sigma 47
(number) Useful only in the case of gauss extraction. This is the sigma of the gaussian used, in Angstrom. The default number of 47 is approximately equal to one pixel.

method claret
(claret/linear/quad/sqrt) Limb-darkening method to be used. Choose between: claret, linear, quad, sqrt.

white_lower_wavelength 10880
white_upper_wavelength 16800
(number/default) Right and left edges of the extracted white light curve, in Angstroms.

white_ldc1 0.850033
(number/default) First limb-darkening coefficients for the white light-curve.

white_ldc2 -0.728096
(number/default) Second limb-darkening coefficients for the white light-curve. Will not be used if the linear method is chosen.

white_ldc3 0.908153
(number/default) Third limb-darkening coefficients for the white light-curve. Will not be used if the linear, the quad or the sqrt method is chosen.

white_ldc4 -0.397691
(number/default) Forth limb-darkening coefficients for the white light-curve. Will not be used if the linear, the quad or the sqrt method is chosen.

Comment: You can set the above six parameters to default, if you want to use the pre-calculated limb-darkening coefficients. In this case, the claret limb-darkening method will be used. These coefficients have been calculated for a wavelength range between 10880.0 and 16800.0 Angstroms.

bins_file iraclis_test_dataset_hatp26b_bins.txt
(file path/default_high/default_low/default_vlow) Path to the bins file.

Comment: You can set the above parameter to default_high, default_low or default_vlow. In this case, the claret limb-darkening method will be used. Be careful to avoid conflicts, as the limb-darkening method used between spectral and white light curves should be the same.

planet HAT-P_26 b
(name/auto) Planet name, useful if the system has multiple planets.

star_teff -0.04
(number/auto) Stellar temperature, used if the limb-darkening coefficients are set to auto.

star_logg 5079
(number/auto) Stellar log(g), used if the limb-darkening coefficients are set to auto.

star_meta 4.56
(number/auto) Stellar metallicity, used if the limb-darkening coefficients are set to auto.

rp_over_rs 0.0715
(number/auto) Initial value for the planet-to-star radius ratio. This parameters is always fitted both for the white and the spectral light-curves in cases of transits.

fp_over_fs 0.0001
(number/auto) Initial value for the planet-to-star flux ratio. This parameters is always fitted both for the white and the spectral light-curves in cases of eclipses.

period 4.234515
(number/auto) Period of the planetary orbit in days. Always fixed.

sma_over_rs 13.44
(number/auto) Initial value for the semi-major axis of the planetary orbit.

eccentricity 0.0
(number/auto) Eccentricity of the planetary orbit. Always fixed.

inclination 88.6
(number/auto) Initial value for the inclination of the planetary orbit, in degrees.

periastron 0.0
(number/auto) Periastron of the planetary orbit in degrees. Always fixed.

mid_time 2455304.65118
(number/auto) Initial value for the mid-transit-time of the planetary orbit, in HJD.

Comment: You can set any of the above 12 parameters to auto, to use the data from the Open Exoplanet Catalogue.

apply_up_down_stream_correction False
(True/False) Whether to correct for the up-stream/down-stream effect or not. Useful only in cases of fast scans that cross the line between the upper two and lower two quadrants of the detector.

exclude_initial_orbits 1
(number) Number of HST orbits to be removed from the begging of the visit. Usually set to 1.

exclude_final_orbits 0
(number) Number of HST orbits to be removed from the end of the visit. Usually set to 0.

exclude_initial_orbit_points 0
(number) Number of HST exposures to be removed from the begging of each HST-orbit.

mcmc_iterations 500000
(number) Number of emcee iterations for the white light-curve fitting

mcmc_walkers 200
(number) Number of emcee wakers for the white light-curve fitting

mcmc_burned_iterations 200000
(number) Number of emcee burned iterations for the white light-curve fitting

spectral_mcmc_iterations 50000
(number) Number of emcee iterations for the spectral light-curve fitting

spectral_mcmc_walkers 100
(number) Number of emcee walkers for the spectral light-curve fitting

spectral_mcmc_burned_iterations 20000
(number) Number of emcee burned iterations for the spectral light-curve fitting

first_orbit_ramp True
(True/False) Whether to fit for different ramp coefficients for the first HST orbit in the analysis (after excluding exclude_initial_orbits orbits) or not.

second_order_ramp False
(True/False) Whether to fit for a quadratic visit-long ramp or not.

mid_orbit_ramps True
(True/False) Whether to fit for mid-orbit ramps caused by buffer-dumps or not.

fit_ldc1 False
(True/False) Whether to fit for the first limb-darkening coefficient or not. The same will be applied both for the white and the spectral light-curves.

fit_ldc2 False
(True/False) Whether to fit for the second limb-darkening coefficient or not. The same will be applied both for the white and the spectral light-curves. Will not be used if the linear method is chosen.

fit_ldc3 False
(True/False) Whether to fit for the third limb-darkening coefficient or not. The same will be applied both for the white and the spectral light-curves. Will not be used if the linear, the quad or the sqrt method is chosen.

fit_ldc4 False
(True/False) Whether to fit for the forth limb-darkening coefficient or not. The same will be applied both for the white and the spectral light-curves. Will not be used if the linear, the quad or the sqrt method is chosen.

fit_sma_over_rs False
(True/False) Whether to fit for the semi-major axis of the planetary orbit or not. This is fitted only on the white light-curve.

fit_inclination False
(True/False) Whether to fit for the inclination of the planetary orbit or not. This is fitted only on the white light-curve.

fit_mid_time True
(True/False) Whether to fit for the mid-transit-time of the planetary orbit or not. This is fitted only on the white light-curve.

Setting up a bins file

A bins file is a simple txt file that contains three to six columns, indicating for each spectral light curve: a-b. Right and left edges of the extracted spectral light curve, in Angstroms, c-f. limb-darkening coefficients for the spectral light-curve. Below, you can find the description of such a file (this file is included in the examples).

11108 11416 0.985047 -1.385670 1.781030 -0.7267230
11416 11709 0.949097 -1.266470 1.640630 -0.6754740
11709 11988 0.928715 -1.195690 1.553730 -0.6452910
11988 12257 0.903069 -1.109910 1.456180 -0.6107730
12257 12522 0.878225 -1.023230 1.361070 -0.5780620
12522 12791 0.859841 -0.950740 1.274760 -0.5481460
12791 13058 0.849884 -0.896126 1.203900 -0.5267150
13058 13321 0.832077 -0.833290 1.125660 -0.4941230
13321 13586 0.809188 -0.726211 0.991314 -0.4438480
13586 13860 0.795028 -0.641081 0.872551 -0.3971340
13860 14140 0.788556 -0.586294 0.802106 -0.3739860
14140 14425 0.784454 -0.561833 0.775730 -0.3685690
14425 14719 0.772069 -0.460859 0.627183 -0.3091360
14719 15027 0.772703 -0.404730 0.517165 -0.2597780
15027 15345 0.772846 -0.296638 0.327104 -0.1754390
15345 15682 0.798113 -0.256525 0.198611 -0.1108030
15682 16042 0.848830 -0.376905 0.274511 -0.1251750
16042 16432 0.894871 -0.410984 0.233093 -0.0939863

Testing the code

In the examples you will find a short python script that downloads a test dataset from the MAST archive. There, you can also find the parameters file and the bins file described above. The test dataset is a transit of HATP-26 b from the observing proposal 14260 (PI: Deming Drake).

Products

The final product is a pickle file named "fitting_results.pickle" and can be found in the "results" directory (or the output_directory_copy that you have set in the parameters file. To open the pickle file you will need python installed in your computer and the packages pickle and numpy.

The command to load a pickle file is: database = pickle.load(open(‘database_file.pickle’))

This dictionary contains the three main dictionaries that include all the results for a particular dataset. These are:

database['lightcurves'] extracted light-curves and transit fitting data
database['spectrum'] planetary spectrum

The database['lightcurves'] dictionary contains all the information on the extracted white and spectral light-curves and their fitting, and has the following content:

database['lightcurves']['white'] white light curve and fitting
database['lightcurves']['bin_01'] first wavelength channel
database['lightcurves']['bin_02'] second wavelength channel
etc...

The database['spectra'] dictionary contains the final extracted planetary spectrum, and has the following structure:

database['spectrum']['wavelength'] mean wavelength of the different channels (μm)
database['spectrum']['width'] wavelength width of the different channels (μm)
database['spectrum']['depth'] transit depth in each wavelength channel
database['spectrum']['error'] uncertainty in the transit depth in each wavelength channel

White light curve and fitting

The database['lightcurves']['white'] dictionary has the following structure:

database['lightcurves']['white']['limb_darkening']['method'] limb darkening method used
database['lightcurves']['white']['wavelength']['lambda1'] lower wavelength limit of the band in Angstroms
database['lightcurves']['white']['wavelength']['lambda2'] upper wavelength limit of the band in Angstroms
database['lightcurves']['white']['wavelength']['lambda_mean'] mean wavelength of the band in Angstroms
database['lightcurves']['white']['wavelength']['lambda_width'] width of the band in Angstroms
database['lightcurves']['white']['exposure']['exp_time'] exposure time for each data point in seconds
database['lightcurves']['white']['exposure']['model_resolution'] sub-exposure time used to model each data point in seconds
database['lightcurves']['white']['input_time_series']['x_shift'] horizontal shifts during the observation
database['lightcurves']['white']['input_time_series']['x_shift_error'] uncertainty in the horizontal shifts during the observation
database['lightcurves']['white']['input_time_series']['y_shift'] vertical shifts during the observation
database['lightcurves']['white']['input_time_series']['y_shift_error'] uncertainty in the horizontal shifts during the observation
database['lightcurves']['white']['input_time_series']['sky'] sky background level during the observation
database['lightcurves']['white']['input_time_series']['scan'] scan direction (1 for forward scans, -1 for reverse scans)
database['lightcurves']['white']['input_time_series']['hjd'] heliocentric Julian date during the observation
database['lightcurves']['white']['input_time_series']['raw_lc'] raw white light-curve
database['lightcurves']['white']['input_time_series']['raw_lc_error'] uncertainty in the raw white light-curve
database['lightcurves']['white']['output_time_series']['phase'] orbital phase
database['lightcurves']['white']['output_time_series']['systematics'] best-fit model for the systematics
database['lightcurves']['white']['output_time_series']['detrended_lc'] de-trended white light-curve
database['lightcurves']['white']['output_time_series']['transit'] best-fit model for the transit
database['lightcurves']['white']['output_time_series']['residuals'] fitting residuals
database['lightcurves']['white']['statistics']['res_std'] standard deviation of the residuals
database['lightcurves']['white']['statistics']['res_autocorr'] autocorrelation function of the residuals
database['lightcurves']['white']['statistics']['corr_variables'] fitted variables
database['lightcurves']['white']['statistics']['corr_matrix'] correlation matric of the fitted variables
database['lightcurves']['white']['parameters']['ldc_1'] first limb-darkening coefficient
database['lightcurves']['white']['parameters']['ldc_2'] second limb-darkening coefficient
database['lightcurves']['white']['parameters']['ldc_3'] third limb-darkening coefficient
database['lightcurves']['white']['parameters']['ldc_4'] forth limb-darkening coefficient
database['lightcurves']['white']['parameters']['rp'] planetary radius relative to the stellar radius
database['lightcurves']['white']['parameters']['fp'] planetary flux relative to the stellar flux (useful only for eclipses)
database['lightcurves']['white']['parameters']['P'] orbital period in days
database['lightcurves']['white']['parameters']['a'] orbital semi-major axis relative to the stellar radius
database['lightcurves']['white']['parameters']['e'] orbital eccentricity
database['lightcurves']['white']['parameters']['i'] orbital inclination in degrees
database['lightcurves']['white']['parameters']['omega'] orbital argument of periastron in degrees
database['lightcurves']['white']['parameters']['t_0'] mit-transit time in HJD
database['lightcurves']['white']['parameters']['n_w_for'] normalization factor for the forward scans
database['lightcurves']['white']['parameters']['n_w_rev'] normalization factor for the reverse scans
database['lightcurves']['white']['parameters']['r_a1'] linear term of the long-term ramp
database['lightcurves']['white']['parameters']['r_a2'] quadratic term of the long-term ramp
database['lightcurves']['white']['parameters']['r_b1'] amplitude of the exponential short-term ramp
database['lightcurves']['white']['parameters']['r_b2'] decay of the exponential short-term ramp
database['lightcurves']['white']['parameters']['for_b1'] amplitude of the exponential short-term ramp for the first orbit
database['lightcurves']['white']['parameters']['for_b2'] amplitude of the exponential short-term ramp for the first orbit
database['lightcurves']['white']['parameters']['mor_b1'] amplitude of the exponential short-term ramp after a buffer dump
database['lightcurves']['white']['parameters']['mor_b2'] amplitude of the exponential short-term ramp after a buffer dump

Each database['lightcurves']['white']['parameters']['xx'] element includes also the following keys:

database['lightcurves']['white']['parameters']['xx']['name'] name
database['lightcurves']['white']['parameters']['xx']['initial'] initial value (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['min_allowed'] minimum of the prior (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['max_allowed'] maximum of the prior (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['trace'] mcmc trace (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['trace_bins'] mcmc trace bins (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['trace_counts'] mcmc trace distribution (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['value'] final value
database['lightcurves']['white']['parameters']['xx']['m_error'] final -error (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['p_error'] final +error (None if not fitted)
database['lightcurves']['white']['parameters']['xx']['print_name'] name shown in plots
database['lightcurves']['white']['parameters']['xx']['print_value'] value shown in plots
database['lightcurves']['white']['parameters']['xx']['print_m_error'] -error shown in plots (- if not fitted)
database['lightcurves']['white']['parameters']['xx']['print_p_error'] +error shown in plots (- if not fitted)

Spectral light curves and fitting

Each database['light_curves']['bin_yy'] dictionary has the following structure:

database['lightcurves']['bin_yy']['limb_darkening']['method'] limb darkening method used
database['lightcurves']['bin_yy']['wavelength']['lambda1'] lower wavelength limit of the band in Angstroms
database['lightcurves']['bin_yy']['wavelength']['lambda2'] upper wavelength limit of the band in Angstroms
database['lightcurves']['bin_yy']['wavelength']['lambda_mean'] mean wavelength of the band in Angstroms
database['lightcurves']['bin_yy']['wavelength']['lambda_width'] width of the band in Angstroms
database['lightcurves']['bin_yy']['exposure']['exp_time'] exposure time for each data point in seconds
database['lightcurves']['bin_yy']['exposure']['model_resolution'] sub-exposure time used to model each data point in seconds
database['lightcurves']['bin_yy']['input_time_series']['x_shift'] horizontal shifts during the observation
database['lightcurves']['bin_yy']['input_time_series']['x_shift_error'] uncertainty in the horizontal shifts during the observation
database['lightcurves']['bin_yy']['input_time_series']['y_shift'] vertical shifts during the observation
database['lightcurves']['bin_yy']['input_time_series']['y_shift_error'] uncertainty in the horizontal shifts during the observation
database['lightcurves']['bin_yy']['input_time_series']['sky'] sky background level during the observation
database['lightcurves']['bin_yy']['input_time_series']['scan'] scan direction (1 for forward scans, -1 for reverse scans)
database['lightcurves']['bin_yy']['input_time_series']['hjd'] heliocentric Julian date during the observation
database['lightcurves']['bin_yy']['input_time_series']['raw_lc'] raw spectral light-curve
database['lightcurves']['bin_yy']['input_time_series']['white_raw_lc'] raw white light-curve
database['lightcurves']['bin_yy']['input_time_series']['relative_lc'] relative spectral light-curve (raw relative spectral light-curve divided by the raw white light-curve) database['lightcurves']['bin_yy']['input_time_series']['relative_lc_error'] uncertainty in the relative spectral light-curve database['lightcurves']['bin_yy']['input_time_series']['white_model'] transit model for the white light-curve
database['lightcurves']['bin_yy']['output_time_series']['phase'] orbital phase
database['lightcurves']['bin_yy']['output_time_series']['systematics'] best-fit model for the systematics
database['lightcurves']['bin_yy']['output_time_series']['detrended_lc'] de-trended white light-curve
database['lightcurves']['bin_yy']['output_time_series']['transit'] best-fit model for the transit
database['lightcurves']['bin_yy']['output_time_series']['residuals'] fitting residuals
database['lightcurves']['bin_yy']['statistics']['res_std'] standard deviation of the residuals
database['lightcurves']['bin_yy']['statistics']['res_autocorr'] autocorrelation function of the residuals
database['lightcurves']['bin_yy']['statistics']['corr_variables'] fitted variables
database['lightcurves']['bin_yy']['statistics']['corr_matrix'] correlation matric of the fitted variables
database['lightcurves']['bin_yy']['parameters']['ldc_1'] first limb-darkening coefficient
database['lightcurves']['bin_yy']['parameters']['ldc_2'] second limb-darkening coefficient
database['lightcurves']['bin_yy']['parameters']['ldc_3'] third limb-darkening coefficient
database['lightcurves']['bin_yy']['parameters']['ldc_4'] forth limb-darkening coefficient
database['lightcurves']['bin_yy']['parameters']['rp'] planetary radius relative to the stellar radius
database['lightcurves']['bin_yy']['parameters']['fp'] planetary flux relative to the stellar flux (useful only for eclipses)
database['lightcurves']['bin_yy']['parameters']['P'] orbital period in days
database['lightcurves']['bin_yy']['parameters']['a'] orbital semi-major axis relative to the stellar radius
database['lightcurves']['bin_yy']['parameters']['e'] orbital eccentricity
database['lightcurves']['bin_yy']['parameters']['i'] orbital inclination in degrees
database['lightcurves']['bin_yy']['parameters']['omega'] orbital argument of periastron in degrees
database['lightcurves']['bin_yy']['parameters']['t_0'] mit-transit time in HJD
database['lightcurves']['bin_yy']['parameters']['n_l_for'] normalization factor for the forward scans
database['lightcurves']['bin_yy']['parameters']['n_l_rev'] normalization factor for the reverse scans
database['lightcurves']['bin_yy']['parameters']['r_a1'] linear term of the long-term ramp

Each database['lightcurves']['bin_yy']['parameters']['zz'] element includes also the following keys:

database['lightcurves']['bin_yy']['parameters']['zz']['name'] name
database['lightcurves']['bin_yy']['parameters']['zz']['initial'] initial value (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['min_allowed'] minimum of the prior (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['max_allowed'] maximum of the prior (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['trace'] mcmc trace (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['trace_bins'] mcmc trace bins (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['trace_counts'] mcmc trace distribution (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['value'] final value
database['lightcurves']['bin_yy']['parameters']['zz']['m_error'] final -error (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['p_error'] final +error (None if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['print_name'] name shown in plots
database['lightcurves']['bin_yy']['parameters']['zz']['print_value'] value shown in plots
database['lightcurves']['bin_yy']['parameters']['zz']['print_m_error'] -error shown in plots (- if not fitted)
database['lightcurves']['bin_yy']['parameters']['zz']['print_p_error'] +error shown in plots (- if not fitted)

BUGS!!!

For any issues and bugs please send an E-mail at atsiaras@star.ucl.ac.uk.

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