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Known keywords

HISTORY
Some ``History'' comments. Whether this information should be given with specific keywords or in an History record is still an open question. This information is not really needed for further data reduction, but it helps bookkeeping.
MAXIS
Number of axes.
MAXISi
Number of elements for axis i. i goes from 1 to MAXIS. The first axis is usually used to define effectively the spectrum. Thus MAXIS1 corresponds to the number of channels. The second and third one can be used to define the coordinates of the spectra when storing a full spectra cube.
CTYPEi
The type of physical coordinate on axis i: frequency, velocity, right ascension, time... The unit of the values of CRVALi and CRPIXi are conventionnally defined by the value of the CTYPEi keyword. The authorized values and associated units are
FREQ or FREQUENCY
Frequency axis. Unit: [Hz]. Frequency for channel number n is defined by: F(n) = RESTFREQ + CRVALi + ( n - CRPIXi ) * CDELTi
LAMBDA or WAVELENG
wavelength axis. Unit: [m$^{-1}$].
VELO or FELO
Velocity axis. Unit: [m.s$^{-1}$]. VELO corresponds to the radio convention while FELO implies channels regularly gridded in frequency but expressed as velocity in the optical convention. CLASS will process VELO and FELO in the same way *** JP. The referential is defined by the second part of the keyword:
  • -LSR or CITY or empty second part: Local Standart Rest velocity.
  • -HEL Heliocentric (barycentric) velocity.
  • -OBS or -TOP The frame of rest of the observer/telescope (topocentric).
  • -EAR or -GEO Geocentric velocity
The full keyword may thus looks like: FELO, VELOCITY, VELO-GEO...
RA- or RA
Right ascension axis. Unit: [degrees]. Right Ascension RA or galactic longitude GLON: The information as presented here is slightly incomplete, since it would be in general necessary to have an information about the kind of projection used. On most radio telescopes, it is simply assumed that the angular offset in RA is divided by the cosine of Declination to represent ``true'' angular offsets (valid only for a small field). Small telescopes may need more elaborate projection systems. In the current example, the position really observed is
Dec = CRVAL3 + ( 1 - CRPIX3 ) * CDELT3
Ra = CRVAL2 + ( 1 - CRPIX2 ) * CDELT2 / COS(Dec)
DEC- or DEC
Declination axis. Unit: [degrees]. Same caveats as for RA.
GLAT
Galactic latitude axis. Unit: [degrees]. Same caveat as for RA.
GLON
Galactic longitude axis. Unit: [degrees]. Same caveat as for RA.
TIME or UT or UTC
Time axis. Unit: [s]. The time since DATE-OBS.
STOKES
Stokes axis. The Stokes parameter of the data as defined in the basic paper of Wells et al.
CRPIXi
The array location of the reference pixel along axis i. CRPIXi's value may be a fractional number of pixels and/or outside of the limits of the array. This descriptor is optional for degenerated axes (i.e. 0 or 1 element).
CRVALi
The value of the physical coordinate on axis i at the reference pixel.
CDELTi
The increment in physical coordinates along axis i. This descriptor is optional for degenerated axes. Warning: Although there is a difference between the frequency spacing between channels and the frequency resolution of each channel, CLASS currently handles only one value for both.
BSCALE
A value of 1 is assumed when it is undefined. The following formula will be applied to the FITS data: CLASS_spectrum = BZERO + BSCALE * FITS_spectrum
BZERO
A value of 0 is assumed when it is undefined. The following formula will be applied to the FITS data: CLASS_spectrum = BZERO + BSCALE * FITS_spectrum
DATAMIN
Minimum value of your spectrum. Understood by CLASS but unused.
DATAMAX
Maximum value of your spectrum. Understood by CLASS but unused.
BLANK
Blanking value. If not specified, -1e38 assumed. BSCALE and BZERO are applied to the blanking value.
PCOUNT
Usually 0. But if you provide your data as Variable Length arrays, then you will have to tweak this value which specifies the size of the variable length array heap, plus a gap (if any). See THEAP.
GCOUNT
Always 1 in Binary tables.
THEAP
Byte offset of heap area. The heap area is where the Variable Length Array data are stored. They are usually stored just after the binary table. The heap does not need to begin at the end of the main table data. The user may choose to provide a gap between the main table and the beginning of the heap. The size of this gap, in bytes, can be found using the value of the THEAP keyword. If there is no gap, the value of THEAP is NAXIS1 * NAXIS2. If there is, the size of the gap is the difference between the value of THEAP and NAXIS1 * NAXIS2. A value of NAXIS1 * NAXIS2 is assumed when this keyword is not defined.
BEAMEFF
The main-beam efficiency.
FORWEFF or ETAFSS
The forward spillover and scattering efficiency.
GAINIMAG
Ratio Image/Signal.
MH2O
Water vapor content. Unit: [mm].
PRESSURE
The ambiant atmospheric pressure. Unit: [hPa].
TOUTSIDE
The ambient temperature. Unit [K].
NPHASE
Value: from 1 to 8. For multi-phased spectra (i.e. frequency switching) number of phases.
DELTAFj
Frequency offset for phase j. Unit: [Hz].
PTIMEj
Duration of phase j. Unit: [s].
WEIGHTj
Weight of phase j.
TELESCOP
A string value giving the telescope name. CLASS truncates this string to the first 12 characters. There is a CLASS convention about TELESCOP, which is not mandatory: TELESCOP contains the name of the instrument, the name of the backend and the name of the subband (if any). For example: ``HIFI-HRV-02'' for subband 2 of the High Resolution Spectrometer (Vertical polarization) of HIFI (one of the Herschel's instrument).
AZIMUTH
The azimuth at TIME. Unit: [degrees]. If the TIME axis is non-degenerated, then this is the azimuth at the TIME of the first pixel on the TIME axis.
ELEVATIO
The elevation at TIME. Unit: [degrees]. Same caveat as for AZIMUTH.
DATE-OBS
or DATE_OBS A string giving the observation date and optionally the time at the observation start using the new FITS y2k convention. Since CLASS does not handle the TIMESYS keyword yet to indicate the time system, UTC is assumed. Accepted formats are
DATE-RED
or DATE_RED or DATE Same as DATE-OBS, except it is the date at which the data have been reduced.
SCAN or SCAN-NUM
or SCAN_NUM Scan number of the observation, according to the CLASS terminology.
SUBSCAN
Subscan number of the observation, according to the CLASS terminology.
UT or UTC
Universal time of the start of the observation provided as a string or a number. Then the format is
LST
Sideral time of the start of the observation. See UT or UTC for information about the format.
OBSTIME or EXPOSURE
The effective integration time. Unit: [s]. Necessary for some kind of weighting when adding several spectra.
TSYS
The system temperature. Unit: [K]. Necessary for some kind of weighting when adding several spectra.
TAU-ATM
or TAU_ATM The opacity at RESTFREQ. CLASS does not handle the opacity in the image band yet.
EPOCH or EQUINOX
The equinox of coordinates. Possible values are 1950 or 2000.
OBJECT
A string value giving an object name. CLASS truncates this string to the first 12 characters.
LINE
Molecular line name, for bookkeeping. CLASS truncates this string to the first 12 characters.
RESTFREQ
The observed frequency at the reference pixel of the frequency-like axis. Unit: [Hz].
IMAGFREQ
The image sideband frequency corresponding to RESTFREQ for double sideband operation. Unit: [Hz].
VELOCITY
The velocity at the reference channel. The referential frame must be defined by VELDEF.
VELO-LSR or VLSR
The velocity at the reference channel, understood as a velocity in the Local Standard Rest frame. Thus, you don't need to use VELDEF to specify the frame. Unit: [m.s$^{-1}$].
VELO-OBS or VELO-TOP
The velocity at the reference channel, understood as a velocity in the frame of rest of the observer/telescope. Thus, you don't need to use VELDEF to specify the frame. Unit: [m.s$^{-1}$].
VELO-HEL
The velocity at the reference channel, understood as a velocity in the Heliocentric (barycentric) frame. Thus, you don't need to use VELDEF to specify the frame. Unit: [m.s$^{-1}$].
VELO-EAR or VELO-GEO
The velocity at the reference channel, understood as a velocity in the Geocentric frame. Thus, you don't need to use VELDEF to specify the frame. Unit: [m.s$^{-1}$].
DELTAV or DELTAVEL
Velocity spacings of the channels. This information is duplicate with the rest frequency and frequency spacing of channels, but convenient. The velocity of a given channel n is thus given by V(n) = VLSR + (n - CRPIXi) * DELTAV. If DELTAV is not provided, then the velocity resolution will be calculated by DELTAV = -c / RESTFREQ * CDELT1, where CDELT1 is the frequency spacing and c the celerity of light.
VELDEF
The velocity definition and frame (8 characters). The first 4 characters describe the velocity definition. Accepted definitions are CLASS only handles RADI and does not handle OPTI or RELA. If nothing specified, RADI is assumed. This is the list of the values CLASS understands


next up previous contents index
Next: Known columns and data Up: BINTABLE Mode Previous: BINTABLE Mode   Contents   Index
Gildas manager 2018-10-15