System

class orbitize.system.System(num_secondary_bodies, data_table, stellar_or_system_mass, plx, mass_err=0, plx_err=0, restrict_angle_ranges=False, tau_ref_epoch=58849, fit_secondary_mass=False, hipparcos_IAD=None, gaia=None, fitting_basis='Standard', use_rebound=False)[source]

A class to store information about a system (data & priors) and calculate model predictions given a set of orbital parameters.

Parameters

  • num_secondary_bodies (int) – number of secondary bodies in the system. Should be at least 1.

  • data_table (astropy.table.Table) – output from orbitize.read_input.read_file()

  • stellar_or_system_mass (float) – mass of the primary star (if fitting for dynamical masses of both components) or total system mass (if fitting using relative astrometry only) [M_sol]

  • plx (float) – mean parallax of the system, in mas

  • mass_err (float, optional) – uncertainty on stellar_or_system_mass, in M_sol

  • plx_err (float, optional) – uncertainty on plx, in mas

  • restrict_angle_ranges (bool, optional) – if True, restrict the ranges of the position angle of nodes to [0,180) to get rid of symmetric double-peaks for imaging-only datasets.

  • tau_ref_epoch (float, optional) – reference epoch for defining tau (MJD). Default is 58849 (Jan 1, 2020).

  • fit_secondary_mass (bool, optional) – if True, include the dynamical mass of the orbiting body as a fitted parameter. If this is set to False, stellar_or_system_mass is taken to be the total mass of the system. (default: False)

  • hipparcos_IAD (orbitize.hipparcos.HipparcosLogProb) – an object containing information & precomputed values relevant to Hipparcos IAD fitting. See hipparcos.py for more details.

  • gaia (orbitize.gaia.GaiaLogProb) – an object containing information & precomputed values relevant to Gaia astrometrry fitting. See gaia.py for more details.

  • fitting_basis (str) – the name of the class corresponding to the fitting basis to be used. See basis.py for a list of implemented fitting bases.

  • use_rebound (bool) – if True, use an n-body backend solver instead of a Keplerian solver.

Priors are initialized as a list of orbitize.priors.Prior objects and stored in the variable System.sys_priors. You should initialize this class, then overwrite priors you wish to customize. You can use the System.param_idx attribute to figure out which indices correspond to which fitting parameters. See the “changing priors” tutorial for more detail.

Written: Sarah Blunt, Henry Ngo, Jason Wang, 2018

compute_all_orbits(params_arr, epochs=None, comp_rebound=False)[source]

Calls orbitize.kepler.calc_orbit and optionally accounts for multi-body interactions. Also computes total quantities like RV (without jitter/gamma)

Parameters

  • params_arr (np.array of float) – RxM array of fitting parameters, where R is the number of parameters being fit, and M is the number of orbits we need model predictions for. Must be in the same order documented in System() above. If M=1, this can be a 1d array.

  • epochs (np.array of float) – epochs (in mjd) at which to compute orbit predictions.

  • comp_rebound (bool, optional) – A secondary optional input for use of N-body solver Rebound; by default, this will be set to false and a Kepler solver will be used instead.

Returns

raoff (np.array of float): N_epochs x N_bodies x N_orbits array of

RA offsets from barycenter at each epoch.

decoff (np.array of float): N_epochs x N_bodies x N_orbits array of

Dec offsets from barycenter at each epoch.

vz (np.array of float): N_epochs x N_bodies x N_orbits array of

radial velocities at each epoch.

Return type

tuple

compute_model(params_arr, use_rebound=False)[source]

Compute model predictions for an array of fitting parameters. Calls the above compute_all_orbits() function, adds jitter/gamma to RV measurements, and propagates these predictions to a model array that can be subtracted from a data array to compute chi2.

Parameters

  • params_arr (np.array of float) – RxM array of fitting parameters, where R is the number of parameters being fit, and M is the number of orbits we need model predictions for. Must be in the same order documented in System() above. If M=1, this can be a 1d array.

  • use_rebound (bool, optional) – A secondary optional input for use of N-body solver Rebound; by default, this will be set to false and a Kepler solver will be used instead.

Returns

np.array of float: Nobsx2xM array model predictions. If M=1, this is

a 2d array, otherwise it is a 3d array.

np.array of float: Nobsx2xM array jitter predictions. If M=1, this is

a 2d array, otherwise it is a 3d array.

Return type

tuple of

convert_data_table_radec2seppa(body_num=1)[source]

Converts rows of self.data_table given in radec to seppa. Note that self.input_table remains unchanged.

Parameters

body_num (int) – which object to convert (1 = first planet)

save(hf)[source]

Saves the current object to an hdf5 file

Parameters

hf (h5py._hl.files.File) – a currently open hdf5 file in which to save the object.

orbitize.system.radec2seppa(ra, dec, mod180=False)[source]

Convenience function for converting from right ascension/declination to separation/ position angle.

Parameters

  • ra (np.array of float) – array of RA values, in mas

  • dec (np.array of float) – array of Dec values, in mas

  • mod180 (Bool) – if True, output PA values will be given in range [180, 540) (useful for plotting short arcs with PAs that cross 360 during observations) (default: False)

Returns

(separation [mas], position angle [deg])

Return type

tuple of float

orbitize.system.seppa2radec(sep, pa)[source]

Convenience function to convert sep/pa to ra/dec

Parameters

  • sep (np.array of float) – array of separation in mas

  • pa (np.array of float) – array of position angles in degrees

Returns

(ra [mas], dec [mas])

Return type

tuple

orbitize.system.transform_errors(x1, x2, x1_err, x2_err, x12_corr, transform_func, nsamps=100000)[source]

Transform errors and covariances from one basis to another using a Monte Carlo apporach

Parameters

  • x1 (float) – planet location in first coordinate (e.g., RA, sep) before transformation

  • x2 (float) – planet location in the second coordinate (e.g., Dec, PA) before transformation)

  • x1_err (float) – error in x1

  • x2_err (float) – error in x2

  • x12_corr (float) – correlation between x1 and x2

  • transform_func (function) – function that transforms between (x1, x2) and (x1p, x2p) (the transformed coordinates). The function signature should look like: x1p, x2p = transform_func(x1, x2)

  • nsamps – number of samples to draw more the Monte Carlo approach. More is slower but more accurate.