Common jitter

Common jitter#

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The common_jitter model replaces the local jitter parameters defined by the jitter flags in the dataset file with a single jitter parameter shared by all datasets using the same common model.

The jitter is added in quadrature to the formal uncertainties and is useful when the measurement errors underestimate additional white-noise contributions. A common jitter is useful when several datasets should share the same extra white-noise term, for example observations from the same instrument split across different files.

Note

When common_jitter is applied to a dataset, the local jitter flags of that dataset are deactivated internally. This avoids fitting both a local jitter and a shared jitter for the same data.

Model definition and requirements#

  • model name: common_jitter

  • required common object: common_jitter

The jitter boundaries are estimated automatically from the formal uncertainties of the datasets using the model. If more than one dataset shares the same common jitter, the default boundary is expanded to include the uncertainty ranges of all of them.

Keywords#

There are no model-wide keywords.

Examples#

In the following example, two RV datasets share the same jitter parameter even if they are stored in different files.

 1inputs:
 2  RV_HARPS_s01:
 3    file: datasets/HARPS_s01_PyORBIT.dat
 4    kind: RV
 5    models:
 6      - radial_velocities
 7      - common_jitter_RV
 8  RV_HARPS_s02:
 9    file: datasets/HARPS_s02_PyORBIT.dat
10    kind: RV
11    models:
12      - radial_velocities
13      - common_jitter_RV
14common:
15  planets:
16    b:
17      orbit: circular
18      use_time_inferior_conjunction: True
19      boundaries:
20        P: [2.0, 3.0]
21        K: [0.0, 20.0]
22        Tc: [59000.0, 59001.0]
23  common_jitter_RV:
24    model: common_jitter
25models:
26  radial_velocities:
27    planets:
28      - b

If needed, the prior or boundaries can be specified directly in the common object:

1common:
2  common_jitter_RV:
3    model: common_jitter
4    boundaries:
5      jitter: [0.0, 20.0]
6    priors:
7      jitter: ['Gaussian', 5.0, 2.0]

It is also possible to use independent common jitters for different observables:

1common:
2  common_jitter_RV:
3    model: common_jitter
4  common_jitter_BIS:
5    model: common_jitter
6  common_jitter_Sindex:
7    model: common_jitter

Model parameters#

The following parameters will be inherited from the common model.

Name

Parameter

Common?

Definition

Notes

jitter

Extra white-noise term added in quadrature to the dataset errors

common

common_jitter

Same units as the dataset errors