Heliocentric Correction

Overview

Nearly all analysis of the 1D spectra from astronomical objects will require one to remove the motion of the Earth with respect to the Sun; i.e. perform a heliocentric correction. In addition, one may wish to correct for the Solar System. The default in PypeIt is to impose a heliocentric correction to place the Earth within the Sun’s reference frame.

Algorithm

The basic algorithm may be summarized as follows:

  1. Collect the time, observational RA/DEC, and observatory info from the header

  2. Calculate the correction using geomotion_velocity() (which is based on astropy.coordinates.SkyCoord.radial_velocity_correction)

  3. Apply the correction to calibrated wavelengths of the data after extraction and flexure correction

Details

Time

By default, the code establishes the time of observation from the date read from the header; see Use of Metadata to Identify Instrument Configurations. Note that it currently must be written ISOT format for the code to run successfully.

Observatory info

These are set by the individual telescopes, which source the Earth coordinates of the telescope from astropy.coordinates.EarthLocation.

RA/DEC

By default, these are taken from the header; see Use of Metadata to Identify Instrument Configurations.