#### Description:

This attribute identifies the standard of rest to which the spectral axis values of a SpecFrame refer, and may take any of the values listed in the `"` Standards of Rest`"` section (below).

The default StdOfRest value is `"` Helio`"` .

Type:

  String.

#### Applicability

##### SpecFrame

All SpecFrames have this attribute.

#### Standards of Rest

The SpecFrame class supports the following StdOfRest values (all are case-insensitive):

- `"` Topocentric`"` , `"` Topocent`"` or `"` Topo`"` : The observers rest-frame (assumed to be on the surface of the earth). Spectra recorded in this standard of rest suffer a Doppler shift which varies over the course of a day because of the rotation of the observer around the axis of the earth. This standard of rest must be qualified using the ObsLat, ObsLon, ObsAlt, Epoch, RefRA and RefDec attributes.

- `"` Geocentric`"` , `"` Geocentr`"` or `"` Geo`"` : The rest-frame of the earth centre. Spectra recorded in this standard of rest suffer a Doppler shift which varies over the course of a year because of the rotation of the earth around the Sun. This standard of rest must be qualified using the Epoch, RefRA and RefDec attributes.

- `"` Barycentric`"` , `"` Barycent`"` or `"` Bary`"` : The rest-frame of the solar-system barycentre. Spectra recorded in this standard of rest suffer a Doppler shift which depends both on the velocity of the Sun through the Local Standard of Rest, and on the movement of the planets through the solar system. This standard of rest must be qualified using the Epoch, RefRA and RefDec attributes.

- `"` Heliocentric`"` , `"` Heliocen`"` or `"` Helio`"` : The rest-frame of the Sun. Spectra recorded in this standard of rest suffer a Doppler shift which depends on the velocity of the Sun through the Local Standard of Rest. This standard of rest must be qualified using the RefRA and RefDec attributes.

- `"` LSRK`"` , `"` LSR`"` : The rest-frame of the kinematical Local Standard of Rest. Spectra recorded in this standard of rest suffer a Doppler shift which depends on the velocity of the kinematical Local Standard of Rest through the galaxy. This standard of rest must be qualified using the RefRA and RefDec attributes.

- `"` LSRD`"` : The rest-frame of the dynamical Local Standard of Rest. Spectra recorded in this standard of rest suffer a Doppler shift which depends on the velocity of the dynamical Local Standard of Rest through the galaxy. This standard of rest must be qualified using the RefRA and RefDec attributes.

- `"` Galactic`"` , `"` Galactoc`"` or `"` Gal`"` : The rest-frame of the galactic centre. Spectra recorded in this standard of rest suffer a Doppler shift which depends on the velocity of the galactic centre through the local group. This standard of rest must be qualified using the RefRA and RefDec attributes.

- `"` Local_group`"` , `"` Localgrp`"` or `"` LG`"` : The rest-frame of the local group. This standard of rest must be qualified using the RefRA and RefDec attributes.

- `"` Source`"` , or `"` src`"` : The rest-frame of the source. This standard of rest must be qualified using the RefRA, RefDec and SourceVel attributes.

Where more than one alternative System value is shown above, the first of these will be returned when an enquiry is made.

Copyright (C) 2021 East Asian Observatory