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- 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].
- VELO or FELO
- Velocity axis. Unit: [m.s]. 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
- 'dd/mm/yy' (1900 is added to yy)
- 'yyyy/mm/dd'
- 'yyyy/mm/ddThh:mm:ss.s', where 'T' stands for the letter 'T'
and has no meaning except as a separator between date and time. The
trailing time is ignored, you have to provide it through UT, UTC or LST.
- 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
- 'hh:mm:ss.s', when this keyword contains a string.
- The number of seconds after midnight, when this keyword contains a
number.
- 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 epoch 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].
- 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].
- 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].
- 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].
- 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
- RADI Radio convention.
- OPTI Optical convention.
- RELA Relativistic convention.
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
- LSR or RADI-LSR Local Standart Rest frame.
- HEL or RADI-HEL Heliocentric (barycentric) frame.
- OBS or RADI-OBS Frame of rest of the
observer/telescope. Note that TOP is not handled here.
- EAR or RADI-EAR Geocentric frame.
Next: Known columns and data
Up: BINTABLE Mode
Previous: BINTABLE Mode
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Gildas manager
2014-07-01