Star

The star container hosts star-related common objects. Its main entry is star_parameters, which stores stellar quantities shared across models such as transits, Rossiter-McLaughlin effects, and stellar-activity regressions.

Note

Only the parameters required by the selected models need to be defined in the YAML file. PyORBIT will use the default bounds, priors, spaces, and fixed values declared in the source code for any parameter that is not explicitly overridden.

Model definition

• container name: star

• common object name: star_parameters

• source class: CommonStarParameters

In a configuration file the object is defined as:

common:
  star:
    star_parameters:
      ...

Parameters

Name	Parameter	Unit
radius	Stellar radius	Solar radii
mass	Stellar mass	Solar masses
density	Stellar density	Solar density
i_star	Stellar inclination	degrees
cosi_star	Cosine of the stellar inclination	unitless
v_sini	Projected stellar rotational velocity	km/s
rotation_period	Stellar rotation period	days
activity_decay	Decay timescale of active regions	days
temperature	Effective temperature of the photosphere	K
line_contrast	CCF line contrast	percent
line_fwhm	CCF line full width at half maximum	km/s
rv_center	CCF line centroid	km/s
veq_star	Equatorial stellar rotational velocity	km/s
alpha_rotation	Differential-rotation coefficient	unitless
convective_c1	First convective-polynomial coefficient	unitless
convective_c2	Second convective-polynomial coefficient	unitless
convective_c3	Third convective-polynomial coefficient	unitless

Keywords

The default keyword is highlighted in boldface.

use_stellar_rotation_period

• accepted values: True | False

• if True, the stellar rotation is parametrized through rotation_period, radius, and stellar inclination rather than through veq_star or v_sini. In this setup veq_star and v_sini are derived quantities.

use_equatorial_velocity

• accepted values: True | False

• forces the use of veq_star as a sampled parameter.

use_stellar_inclination

• accepted values: True | False

• includes i_star among the sampled parameters.

use_cosine_stellar_inclination

• accepted values: True | False

• samples cosi_star instead of i_star; i_star is then derived from cosi_star.

use_projected_velocity

• accepted values: True | False

• includes v_sini as a direct parameter. This is the default behaviour when no rotation-period-based parametrization is requested.

use_differential_rotation

• accepted values: True | False

• activates the differential-rotation parametrization through alpha_rotation. When enabled without use_stellar_rotation_period, the code also requires veq_star and stellar inclination.

compute_mass

• accepted values: True | False

• when mass and radius are sampled, density is derived from them by default.

compute_radius

• accepted values: True | False

• makes radius a derived quantity from mass and density.

compute_density

• accepted values: True | False

• makes density a derived quantity from mass and radius.

Warning

Only one of compute_mass, compute_radius, or compute_density should be active at a time. If all three are set to False, PyORBIT falls back to compute_mass: True.

convective_order

• accepted values: integer, usually 0 to 3

• enables the convective polynomial terms convective_c1, convective_c2, and convective_c3 up to the requested order in Rossiter-McLaughlin-like models.

Derived quantities

Depending on the selected keywords, PyORBIT can derive:

• i_star from cosi_star

• veq_star from rotation_period and radius

• v_sini from veq_star plus i_star or cosi_star

• rotation_period from veq_star and radius

• one among mass, radius, and density from the other two

This lets you choose the parametrization that is most natural for the dataset being modelled while keeping the physically linked stellar quantities consistent.

Examples

The most common use is to provide informative priors on the stellar bulk properties:

common:
  star:
    star_parameters:
      priors:
        mass: ['Gaussian', 0.806, 0.048]
        radius: ['Gaussian', 0.756, 0.018]
        density: ['Gaussian', 1.864, 0.175]

When the stellar rotation period is known and you want PyORBIT to derive the projected and equatorial velocities consistently, you can switch to the rotation-based parametrization:

common:
  star:
    star_parameters:
      use_stellar_rotation_period: True
      use_cosine_stellar_inclination: True
      boundaries:
        rotation_period: [10.0, 20.0]
        radius: [0.60, 0.90]
        cosi_star: [0.0, 1.0]
      priors:
        rotation_period: ['Gaussian', 14.0, 0.5]
        radius: ['Gaussian', 0.68, 0.02]

For Rossiter-McLaughlin analyses that need differential rotation and a simple convective polynomial:

common:
  star:
    star_parameters:
      use_equatorial_velocity: True
      use_stellar_inclination: True
      use_differential_rotation: True
      convective_order: 2
      boundaries:
        veq_star: [1.0, 20.0]
        i_star: [0.0, 180.0]
        alpha_rotation: [0.0, 1.0]
        convective_c1: [0.0, 2.0]
        convective_c2: [-2.0, 0.0]