Common offset

Common offset#

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

This is useful when several files represent the same instrumental zero point, or when datasets of the same observable have been split into seasons but should still share the same baseline. For example, radial velocities from the same instrument can be split into different observing seasons for the stellar-activity model while still using one common systemic velocity.

Note

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

Model definition and requirements#

  • model name: common_offset

  • required common object: common_offset

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

Keywords#

There are no model-wide keywords.

Examples#

In the following example, two RV datasets share the same offset parameter even if they are stored in different files. The two datasets can still have independent models for other effects, such as seasonal Gaussian processes.

 1inputs:
 2  RV_HARPS_s01:
 3    file: datasets/HARPS_s01_PyORBIT.dat
 4    kind: RV
 5    models:
 6      - radial_velocities
 7      - common_offset_RV
 8  RV_HARPS_s02:
 9    file: datasets/HARPS_s02_PyORBIT.dat
10    kind: RV
11    models:
12      - radial_velocities
13      - common_offset_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_offset_RV:
24    model: common_offset
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_offset_RV:
3    model: common_offset
4    boundaries:
5      offset: [-100.0, 100.0]
6    priors:
7      offset: ['Gaussian', 0.0, 20.0]

The same pattern can be repeated for different observables:

1common:
2  common_offset_RV:
3    model: common_offset
4  common_offset_BIS:
5    model: common_offset
6  common_offset_Sindex:
7    model: common_offset

Model parameters#

The following parameters will be inherited from the common model.

Name

Parameter

Common?

Definition

Notes

offset

Additive zero point of the dataset

common

common_offset

Same units as the dataset values