The MODIFY FREQUENCY command
Keywords: class-spectral-axis-v12

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The `MODIFY FREQUENCY` command

This command is used to assign a new rest frequency to the current spectrum. The velocity axis is thus recomputed to set the source systemic velocity at this new rest frequency (see Section ). For consistency the description of the image frequency axis must also be changed.

This command exists because the line rest frequency is sometimes more uncertain than the spectrometer resolution, implying that the line appeared at velocity different from the source systemic velocity. Nowdays, the bandwidth of the receivers is moreover so large that many lines appear in the same spectrum. For this latter use case, the only way to associate the right velocity to different line rest frequency is to use this command.

Subsections

- Signal frequency axis
- Image frequency axis
- Velocity axis