Granulation, Oscillation, Rotation kernels

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The celerite2 activity models provide fast semi-separable kernels for stellar rotation, granulation, and oscillations. They are especially useful for long or densely sampled time series where a full covariance matrix would be too expensive.

Note

These models use the celerite2 package. When using them, please cite the relevant celerite/celerite2 references together with PyORBIT.

Model definition and requirements

model name: celerite2_rotation

• required common object: activity

• rotation term only

model name: celerite2_granulation_rotation

• required common object: activity

• one granulation SHO term plus one rotation term

model name: celerite2_granulation_oscillation_rotation

• required common object: activity

• configurable number of granulation and oscillation SHO terms plus one rotation term

Keywords

Model-wide keywords, with the default value in boldface.

use_stellar_rotation_period

• accepted values: True | False

• replaces Prot with rotation_period from star_parameters.

use_shared_hyperparameters

• accepted values: True | False

• for celerite2_rotation, also makes rot_sigma a common parameter.

rotation_kernels

• accepted values: integer | 1

• used by celerite2_granulation_oscillation_rotation. Only one rotation kernel is currently supported.

granulation_kernels

• accepted values: integer | 2

• used by celerite2_granulation_oscillation_rotation. Adds parameters named grn_k0_period, grn_k0_sigma, grn_k1_period, grn_k1_sigma, and so on.

oscillation_kernels

• accepted values: integer | 1

• used by celerite2_granulation_oscillation_rotation. Adds parameters named osc_k0_period, osc_k0_sigma, osc_k0_Q0, and so on.

common_amplitudes

• accepted values: True | False

• used by celerite2_granulation_oscillation_rotation. If activated, the *_sigma amplitudes are common parameters instead of dataset-specific parameters.

Examples

Rotation-only model:

inputs:
  LCdata:
    file: datasets/lightcurve_PyORBIT.dat
    kind: Phot
    models:
      - celerite2_rotation
common:
  activity:
    boundaries:
      Prot: [10.0, 20.0]
      rot_Q0: [0.1, 100.0]
      rot_deltaQ: [0.1, 100.0]
      rot_fmix: [0.01, 1.0]
models:
  celerite2_rotation:
    model: celerite2_rotation
    common: activity
    boundaries:
      rot_sigma: [0.0, 1.0]

Granulation, oscillation, and rotation model:

models:
  celerite2_activity:
    model: celerite2_granulation_oscillation_rotation
    common: activity
    granulation_kernels: 2
    oscillation_kernels: 1
    common_amplitudes: False
    boundaries:
      rot_sigma: [0.0, 1.0]
      grn_k0_sigma: [0.0, 1.0]
      grn_k1_sigma: [0.0, 1.0]
      osc_k0_sigma: [0.0, 1.0]

Model parameters

celerite2_rotation

Name	Parameter	Common?	Definition	Notes
Prot	Primary period of variability	common	activity	Replaced by rotation_period when use_stellar_rotation_period: True
rot_Q0	Base quality factor of the secondary oscillation	common	activity
rot_deltaQ	Difference between the quality factors of the two modes	common	activity
rot_fmix	Fractional amplitude of the secondary mode	common	activity
rot_sigma	Standard deviation of the process	dataset	activity	Common when use_shared_hyperparameters: True

celerite2_granulation_rotation

Name	Parameter	Common?	Definition	Notes
grn_period	Granulation SHO timescale	common	activity
Prot	Primary period of variability	common	activity	Replaced by rotation_period when use_stellar_rotation_period: True
rot_Q0	Base quality factor of the secondary oscillation	common	activity
rot_deltaQ	Difference between the quality factors of the two modes	common	activity
rot_fmix	Fractional amplitude of the secondary mode	common	activity
grn_sigma	Granulation amplitude	dataset	activity
rot_sigma	Rotation amplitude	dataset	activity

celerite2_granulation_oscillation_rotation

Name	Parameter	Common?	Definition	Notes
Prot	Primary period of variability	common	activity	Replaced by rotation_period when use_stellar_rotation_period: True
rot_Q0	Base quality factor of the secondary oscillation	common	activity
rot_deltaQ	Difference between the quality factors of the two modes	common	activity
rot_fmix	Fractional amplitude of the secondary mode	common	activity
rot_sigma	Rotation amplitude	dataset	activity	Common when common_amplitudes: True
grn_k*_period	Timescale of each granulation SHO term	common	activity	* is the kernel index, starting at 0
grn_k*_sigma	Amplitude of each granulation SHO term	dataset	activity	Common when common_amplitudes: True
osc_k*_period	Timescale of each oscillation SHO term	common	activity	* is the kernel index, starting at 0
osc_k*_Q0	Quality factor of each oscillation SHO term	common	activity
osc_k*_sigma	Amplitude of each oscillation SHO term	dataset	activity	Common when common_amplitudes: True