platon package

Submodules

platon.abundance_getter module

class platon.abundance_getter.AbundanceGetter(include_condensation=True)

static from_file()

Reads abundances file in the ExoTransmit format (called “EOS” files in ExoTransmit), returning a dictionary mapping species name to an abundance array of dimension

get(logZ, CO_ratio=0.53)

Get an abundance grid at the specified logZ and C/O ratio. This abundance grid can be passed to TransitDepthCalculator, with or without modifications. The end user should not need to call this except in rare cases.

Returns:abundances – A dictionary mapping species name to a 2D abundance array, specifying the number fraction of the species at a certain temperature and pressure. Return type:dict of np.ndarray

is_in_bounds(logZ, CO_ratio, T)

Check to see if a certain metallicity, C/O ratio, and temperature combination is within the supported bounds

platon.constants module

platon.constants.M_earth = 5.97236e+24

Earth mass

platon.constants.M_jup = 1.89819e+27

Jupiter mass

platon.constants.M_sun = 1.98848e+30

Solar mass

platon.constants.R_earth = 6378100.0

Earth radius

platon.constants.R_jup = 71492000.0

Jupiter radius

platon.constants.R_sun = 695700000.0

Solar radius

platon.fit_info module

class platon.fit_info.FitInfo(guesses_dict)

add_gaussian_fit_param(name, std, low_guess=None, high_guess=None)

Fit for the parameter name using a Gaussian prior with standard deviation std. If using emcee, the walkers’ initial values for this parameter are randomly selected to be between low_guess and high_guess. If low_guess is None, it is set to mean-2*std; if high_guess is None, it is set to mean+2*std.

add_uniform_fit_param(name, low_lim, high_lim, low_guess=None, high_guess=None)

Fit for the parameter name using a uniform prior between low_lim and high_lim. If using emcee, the walkers’ initial values for this parameter are randomly selected to be between low_guess and high_guess. If not specified, low_guess is set to low_lim, and similarly with high_guess.

platon.retriever module

class platon.retriever.Retriever

static get_default_fit_info(Mp, Rp, T, logZ=0, CO_ratio=0.53, log_cloudtop_P=inf, log_scatt_factor=0, scatt_slope=4, error_multiple=1, T_star=None)

Get a FitInfo object filled with best guess values. A few parameters are required, but others can be set to default values if you do not want to specify them. All parameters are in SI.

Parameters:

• Rs (float) – Stellar radius
• Mp (float) – Planetary mass
• Rp (float) – Planetary radius
• T (float) – Temperature of the isothermal planetary atmosphere
• logZ (float) – Base-10 logarithm of the metallicity, in solar units
• CO_ratio (float, optional) – C/O atomic ratio in the atmosphere. The solar value is 0.53.
• log_cloudtop_P (float, optional) – Base-10 log of the pressure level (in Pa) below which light cannot penetrate. Use np.inf for a cloudless atmosphere.
• log_scatt_factor (float, optional) – Base-10 logarithm of scattering factoring, which make scattering that many times as strong. If scatt_slope is 4, corresponding to Rayleigh scattering, the absorption coefficients are simply multiplied by scattering_factor. If slope is not 4, scattering_factor is defined such that the absorption coefficient is that many times as strong as Rayleigh scattering at the reference wavelength of 1 um.
• scatt_slope (float, optional) – Wavelength dependence of scattering, with 4 being Rayleigh.
• error_multiple (float, optional) – All error bars are multiplied by this factor.
• T_star (float, optional) – Effective temperature of the star. This is used to make wavelength binning of transit depths more accurate.

Returns:

fit_info – This object is used to indicate which parameters to fit for, which to fix, and what values all parameters should take.

Return type:

FitInfo object

run_emcee(wavelength_bins, depths, errors, fit_info, nwalkers=50, nsteps=10000, include_condensation=True, plot_best=False, max_P_profile=100000.0)

Runs affine-invariant MCMC to retrieve atmospheric parameters.

Parameters:

• wavelength_bins (array_like, shape (N,2)) – Wavelength bins, where wavelength_bins[i][0] is the start wavelength and wavelength_bins[i][1] is the end wavelength for bin i.
• depths (array_like, length N) – Measured transit depths for the specified wavelength bins
• errors (array_like, length N) – Errors on the aforementioned transit depths
• fit_info (FitInfo object) – Tells the method what parameters to freely vary, and in what range those parameters can vary. Also sets default values for the fixed parameters.
• nwalkers (int, optional) – Number of walkers to use
• nsteps (int, optional) – Number of steps that the walkers should walk for
• include_condensation (bool, optional) – When determining atmospheric abundances, whether to include condensation.
• plot_best (bool, optional) – If True, plots the best fit model with the data
• max_P_profile (float, optional) – Maximum pressure at which to calculate radiative transfer. If you change this, the planetary radius will be interpreted as the radius at this max_P_profile

Returns:

result – This returns emcee’s EnsembleSampler object. The most useful attributes in this item are result.chain, which is a (W x S X P) array where W is the number of walkers, S is the number of steps, and P is the number of parameters; and result.lnprobability, a (W x S) array of log probabilities. For your convenience, this object also contains result.flatchain, which is a (WS x P) array where WS = W x S is the number of samples; and result.flatlnprobability, an array of length WS

Return type:

EnsembleSampler object

run_multinest(wavelength_bins, depths, errors, fit_info, maxiter=None, include_condensation=True, plot_best=False, max_P_profile=100000.0)

Runs nested sampling to retrieve atmospheric parameters.

Parameters:

• wavelength_bins (array_like, shape (N,2)) – Wavelength bins, where wavelength_bins[i][0] is the start wavelength and wavelength_bins[i][1] is the end wavelength for bin i.
• depths (array_like, length N) – Measured transit depths for the specified wavelength bins
• errors (array_like, length N) – Errors on the aforementioned transit depths
• fit_info (FitInfo object) – Tells us what parameters to freely vary, and in what range those parameters can vary. Also sets default values for the fixed parameters.
• maxiter (bool, optional) – If not None, run at most this many iterations of nestled sampling
• include_condensation (bool, optional) – When determining atmospheric abundances, whether to include condensation.
• plot_best (bool, optional) – If True, plots the best fit model with the data
• max_P_profile (float, optional) – Maximum pressure at which to calculate radiative transfer. If you change this, the planetary radius will be interpreted as the radius at this max_P_profile.

Returns:

result – This returns the object returned by nestle.sample The object is dictionary-like and has many useful items. For example, result.samples (or alternatively, result[“samples”]) are the parameter values of each sample, result.weights contains the weights, and result.logl contains the log likelihoods. result.logz is the natural logarithm of the evidence.

Return type:

Result object

platon.transit_depth_calculator module

class platon.transit_depth_calculator.TransitDepthCalculator(include_condensation=True, min_P_profile=0.1, max_P_profile=100000.0, num_profile_heights=400)

__init__(include_condensation=True, min_P_profile=0.1, max_P_profile=100000.0, num_profile_heights=400)

All physical parameters are in SI.

Parameters:

• include_condensation (bool) – Whether to use equilibrium abundances that take condensation into account.
• min_P_profile (float) – For the radiative transfer calculation, the atmosphere is divided into zones. This is the pressure at the topmost zone.
• max_P_profile (float) – The pressure at the bottommost zone of the atmosphere
• num_profile_heights (int) – The number of zones the atmosphere is divided into

change_wavelength_bins(bins)

Specify wavelength bins, instead of using the full wavelength grid in self.lambda_grid. This makes the code much faster, as compute_depths will only compute depths at wavelengths that fall within a bin.

Parameters:bins (array_like, shape (N,2)) – Wavelength bins, where bins[i][0] is the start wavelength and bins[i][1] is the end wavelength for bin i. Raises:NotImplementedError – Raised when change_wavelength_bins is called more than once, which is not supported.

compute_depths(star_radius, planet_mass, planet_radius, temperature, logZ=0, CO_ratio=0.53, add_scattering=True, scattering_factor=1, scattering_slope=4, scattering_ref_wavelength=1e-06, add_collisional_absorption=True, cloudtop_pressure=inf, custom_abundances=None, custom_T_profile=None, custom_P_profile=None, T_star=None)

Computes transit depths at a range of wavelengths, assuming an isothermal atmosphere. To choose bins, call change_wavelength_bins().

Parameters:

• star_radius (float) – Radius of the star
• planet_mass (float) – Mass of the planet, in kg
• planet_radius (float) – radius of the planet at self.max_P_profile (by default, 100,000 Pa). Must be in metres.
• temperature (float) – Temperature of the isothermal atmosphere, in Kelvin
• logZ (float) – Base-10 logarithm of the metallicity, in solar units
• CO_ratio (float, optional) – C/O atomic ratio in the atmosphere. The solar value is 0.53.
• add_scattering (bool, optional) – whether Rayleigh scattering is taken into account
• scattering_factor (float, optional) – if add_scattering is True, make scattering this many times as strong. If scattering_slope is 4, corresponding to Rayleigh scattering, the absorption coefficients are simply multiplied by scattering_factor. If slope is not 4, scattering_factor is defined such that the absorption coefficient is that many times as strong as Rayleigh scattering at scattering_ref_wavelength.
• scattering_slope (float, optional) – Wavelength dependence of scattering, with 4 being Rayleigh.
• scattering_ref_wavelength (float, optional) – Scattering is scattering_factor as strong as Rayleigh at this wavelength, expressed in metres.
• add_collisional_absorption (float, optional) – Whether collisionally induced absorption is taken into account
• cloudtop_pressure (float, optional) – Pressure level (in Pa) below which light cannot penetrate. Use np.inf for a cloudless atmosphere.
• custom_abundances (str or dict of np.ndarray, optional) – If specified, overrides logZ and CO_ratio. Can specify a filename, in which case the abundances are read from a file in the format of the EOS/ files. These are identical to ExoTransmit’s EOS files. It is also possible, though highly discouraged, to specify a dictionary mapping species names to numpy arrays, so that custom_abundances[‘Na’][3,4] would mean the fractional number abundance of Na at a pressure of self.P_grid[3] and temperature of self.T_grid[4].
• custom_T_profile (array-like, optional) – If specified and custom_P_profile is also specified, divides the atmosphere into user-specified P/T points, instead of assuming an isothermal atmosphere with T = temperature.
• custom_P_profile (array-like, optional) – Must be specified along with custom_T_profile to use a custom P/T profile. Pressures must be in Pa.
• T_star (float, optional) – Effective temperature of the star. If you specify this and use wavelength binning, the wavelength binning becomes more accurate.

Raises:

ValueError – Raised when invalid parameters are passed to the method

Returns:

• wavelengths (array of float) – Central wavelengths, in metres
• transit_depths (array of float) – Transit depths at wavelengths

Module contents