This program ignores references to being in a Barycenric, Heliocentric or LSR frame. See comments below in the CASA and MIRIAD sections.
fitsccd Ha.cube.fits - | ccdmom - - mom=3 | ccd2vel - Ha-3.vel opt rel 6562.80and here an optical velocity field into a relativistic
NGC2347.VoptFromHa.fits - | ccd2vel - NGC2347.VrelFromHa.ccd opt rel
Velocity type (radio, z, ratio, beta, gamma, optical) For start and/or width specified in velocity, specifies the velocity definition
Options: ’radio’,’optical’,’z’,’beta’,’gamma’
NOTE: the viewer always defaults to displaying the ’radio’ frame, but that can be changed in the position tracking pull down.
The different types
(with F = f/f0, the frequency ratio), are:
Z = (-1 + 1/F)
RATIO = (F) *
RADIO = (1 - F)
OPTICAL == Z
BETA = ((1 - F2)/(1 + F2))
GAMMA = ((1 + F2)/2F) *
RELATIVISTIC == BETA (== v/c)
DEFAULT == RADIO
Note that the ones with an ’*’ have no real interpretation
(although the calculation will proceed) if given
as a velocity.
VELSW is a Miriad task used to change the type of a spectral axis. For example, a frequency axis could be changed to redshift or relativistic velocity.
The resulting axis may be non-linear. If so, it will be marked by a code, e.g. VOPT-F2W, meaning that it is actually linear in frequency (F) but is labelled as a spectral type that is linear in wavelength (W). Such non-linear axes are handled properly by the coordinate routines. However, when plotted, non-linear axes are only correct to first-order at the reference point.
Switching between velocity and other spectral types, via the Doppler formula, is only possible if a rest frequency is recorded in the header. It is also possible to change the Doppler reference frame to barycentric or LSRK (only).
Note that velocity axes labelled as {VELO,FELO}-{HEL,LSR} in Miriad have been Doppler-shifted to the specified frame (barycentric or LSRK) as would be expected. However, frequency axes labelled as FREQ-{HEL,LSR} are actually topocentric, the Doppler frame here refers only to the value of vobs recorded in the header. This convention also applies to FITS images written and read by Miriad - the presence of vobs with FREQ-{HEL,LSR} in the header of a Miriad image read from such a FITS file is indicative. However, there is a potential inconsistency when FITS files generated by other packages are read into Miriad. See option altspc below.
Keyword: axis
The spectral type to change to:
FREQ: frequency,
ENER: photon energy (linear with frequency),
WAVN: wavenumber (linear with frequency),
VRAD: radio velocity (linear with frequency),
WAVE: wavelength,
VOPT: optical velocity (linear with wavelength),
ZOPT: redshift (linear with wavelength),
AWAV: air wavelength (applicable to optical regime only),
VELO: apparent radial velocity (relativistic),
BETA: relativistic beta factor (= VELO/c).
Note that there is no minimum-match on these four-letter spectral types. For backwards compatibility, ’frequency’, ’radio’, and ’optical’ (with min-match) are understood as synonyms for ’FREQ’, ’VRAD’, and ’VOPT’.
AIPS-convention types, {FREQ,VELO,FELO}-{HEL,LSR}, are also understood and will be translated. Here VELO means radio velocity (VRAD), and FELO is optical velocity (VOPT-F2W). However, these types are deprecated, and there is no way to switch to them explicitly.
An optional second value defines the Doppler frame to transform
to (min-match applies):
BARYCENT: Solar System barycentre (aka BARYCENT{RE,ER,RIC}, or HEL),
LSRK: Kinematic Local Standard of Rest.
The default for both the spectral type and the Doppler frame is to leave
them as is, performing only required translations.
27-Apr-17 V0.3 Created PJT