The instrument model
Overview
The RIMOreduced IMO, or Reduced Instrument Model is a FITSFlexible Image Transfer Specification file containing selected instrument characteristics that are needed by users who work with the released data products. It is described in detail in The HFI(Planck) High Frequency Instrument and LFI(Planck) Low Frequency Instrument RIMO ICDInterface Control Document (ref). There will be two RIMOs, one for each instrument, which will follow the same overall structure, but will differ in the details. The type of data in the RIMO can be:
- Parameter
- namely scalars to give properties such as a noise level or a representative beam FWHMFull-Width-at-Half-Maximum
- Table
- to give, e.g., filter transmission profiles or noise power spectra
- Image
- namely 2-D "flat" array, to give, e.g., the beam correlation matrices
The FITSFlexible Image Transfer Specification file begins with primary header that contains some keywords that mainly for internal use and no data. The different types of data are written into different BINTABLE (for parameters and tables) or IMAGE (for 2-D arrays) extensions, as described below.
File Names
- HFI(Planck) High Frequency Instrument
- HFI_RIMO_R1.10.fits
- LFI(Planck) Low Frequency Instrument
- LFI_RIMO_R1.12.fits
Map-level parameter data
The map-level data table contains the effective beam solid angle (total and out to different multiples of the beamFWHM) and noise information. It is written into a BINTABLE extension named MAP_PARAMS whose structure is different for HFI(Planck) High Frequency Instrument and LFI(Planck) Low Frequency Instrument and is as follows. The noise description below is very simplified; a more accurate rendition can be obtained from the half-ring maps. Regarding the characterization of systematics, the user should use the survey differences.
HFI(Planck) High Frequency Instrument
- FREQUENCY (String)
- a 3-digit string giving the reference frequency in GHz, i.e., of the form 217
- OMEGA_F, OMEGA_F_ERR (Real*4)
- the full beam solid angle and its uncertainty, in armin^{2}
- OMEGA_1, OMEGA_1_DISP (Real*4)
- the beam solid angle out to 1FWHM, and its dispersion, in arcmin^{2}
- OMEGA_2, OMEGA_2_DISP (Real*4)
- the beam solid angle out to 2FWHM, and its dispersion, in arcmin^{2}
- FWHMFull-Width-at-Half-Maximum (Real*4)
- FWHMFull-Width-at-Half-Maximum of a Gaussian beam having the same (total) solid angle, in armin^{2}. This is the best value for source flux determination
- FWHMGAUS (Real*4)
- FWHMFull-Width-at-Half-Maximum derived from best Gaussian fit to beam maps, in armin^{2}. This is the best value for source identification
- NOISE (Real*4)
- This is the typical noise/valid observation sample as derived from the high-l spectra of the half-ring maps, in the units of the corresponding map
For the Omega columns, the 'DISP' (for dispersion) column gives an estimate of the spatial variation as a function of position on the sky. This is the variation induced by combining the scanning beam determined from the planet observations with the scanning strategy, as described in Beams.
LFI(Planck) Low Frequency Instrument
- FREQUENCY (String)
- a 3-digit string giving the reference frequency in GHz, i.e., of the form 030, 044, 070
- FWHMFull-Width-at-Half-Maximum (Real*8)
- FWHMFull-Width-at-Half-Maximum of a Gaussian beam having the same (total) solid angle, in arcmin
- NOISE (Real*8)
- This is the average noise in T s^{1/2}
- CENTRALFREQ (Real*4)
- This is the average central frequency in GHz
- FWHMFull-Width-at-Half-Maximum_EFF, FWHMFull-Width-at-Half-Maximum_EFF_SIGMA (Real*4)
- This is the average FWHMFull-Width-at-Half-Maximum of the effective beam, in arcmin, and its dispersion
- ELLIPTICITY_EFF, ELLIPTICITY_EFF_SIGMA (Real*4)
- This is the average ellipticity and its dispersion
- SOLID_ANGLE_EFF, SOLID_ANGLE_EFF_SIGMA (Real*4)
- This is the average full beam solid angle, in arcmin^{2}, and its dispersion
Effective band transmission profiles
The effective filter bandpasses are given in different BINTABLE extensions. The extension is named BANDPASS_{name}, where name specified the frequency channel. In the case of the maps, the bandpasses are a weighted average of the bandpasses of the detectors that are used to build the map. For details see ^{[1]}. The bandpasses are given as 4-column tables containing:
HFI(Planck) High Frequency Instrument
- WAVENUMBER (Real*4)
- the wavenumber in cm-1, conversion to GHz is accomplished by multiplying by [mks].
- TRANSMISSION (Real*4)
- the transmission (normalized to 1 at the max for HFI(Planck) High Frequency Instrument)
- ERROR (Real*4)
- the statistical uncertainty for the transmission profile.
- FLAG (Integer)
- a flag indicating if the data point is an independent frequency data point (nominally the case), or an FTS instrument line shape (ILSInstrument Line Shape)-interpolated data point. The frequency data has been over-sampled by a factor of ~10 to assist in CO component separation efforts ^{[2]}.
The number of rows will differ among the different extensions, but are the same, by construction, within each extension. Tables with the unit conversion coefficients and color correction factors for the HFI(Planck) High Frequency Instrument detectors (and LFI(Planck) Low Frequency Instrument in some instances), including uncertainty estimates based on the uncertainty of the HFI(Planck) High Frequency Instrument detector spectral response are given in this appendix.
LFI(Planck) Low Frequency Instrument
- WAVENUMBER (Real*8)
- the wavenumber in GHz.
- TRANSMISSION (Real*8)
- the transmission (normalized to have an integral of 1 for LFI(Planck) Low Frequency Instrument)
- UNCERTAINITY (Real*4)
- the statistical LFI(Planck) Low Frequency Instrument) uncertainty for the transmission profile (not provided for
- FLAG (Character)
- a flag, not used by now by the LFI(Planck) Low Frequency Instrument
The number of rows will differ among the different extensions, but are the same, by construction, within each extension.
Beam Window Functions
Beam window functions and associated error descriptions are written into a BINTABLE for each detection unit, where detection unit consists of an auto or a cross product (for HFI(Planck) High Frequency Instrument only) of one (or two) frequency maps or detset maps used in the likelihood. Here they are:
- For the HFI(Planck) High Frequency Instrument
- the 6 HFI(Planck) High Frequency Instrument frequency channels, producing 21 extensions
- 100, 143, 217, 353, 545, 857
- 26 detsets, producing 351 extensions; the detsets used are, by frequency channel:
- 100-DS1, 100-DS2,
- 143-DS1, 143-DS2, 143-5, 143-6, 143-7,
- 217-DS1, 217-DS2, 217-1, 217-2, 217-3, 217-4,
- 353-DS1, 353-DS2, 353-1, 353-2, 353-7, 353-8,
- 545-1, 545-2, 545-4,
- 857-1, 857-2, 857-3, 857-4
- For the LFI(Planck) Low Frequency Instrument
- the 3 LFI(Planck) Low Frequency Instrument frequency channels, producing 3 extensions
- 30, 44, 70
and the extension names are of the form BEAMWF_U1XU2 where U1 and U2 are one (possibly the same) detection unit from one of the main groups above (i.e. there are no cross products between detsets and frequency channels, or between HFI(Planck) High Frequency Instrument and LFI(Planck) Low Frequency Instrument). Each extension contains the columns:
- NOMINAL (Real*4)
- the beam window function proper,
- EIGEN_n (Real*4, n=1-5 for the HFI(Planck) High Frequency Instrument, n=1-4 for the LFI(Planck) Low Frequency Instrument)
- the five/four corresponding error modes.
and the following keywords give further information, only for the HFI(Planck) High Frequency Instrument:
- NMODES (Integer)
- the number of EIGEN_* modes,
- LMIN and LMAX (Integer)
- the starting and ending (both included) multipoles of the vectors NOMINAL and EIGEN_*
- LMIN_EM and LMAX_EM (Integer)
- that give the range of the valid samples of the EIGEN_* vectors. Here LMAX_EM is always less than or equal to LMAX. On the range LMAX_EM+1 to LMAX the values of EIGEN_* are set to NaN, while the values of NOMINAL only are a Gaussian extrapolation of the lower multipole window function, only provided for convenience.
- CORRMAT (string)
- the name of the extension containing the corresponding beam correlation matrix
Beam Correlation Matrix
Two beam correlation matrices are given for the HFI(Planck) High Frequency Instrument, in two IMAGE extensions:
- CORRBEAM_FREQ (Real*8)
- for the frequency channels (21 units), 105x015 pixel matrix,
- CORRBEAM_DSET (Real*8)
- for the detsets (351 units), 1755x1755 pixel matrix
Each is a symmetric matrix with 1-valued diagonal, made of NBEAMS*NBEAMS blocks, each block being NMODES*NMODES in size. The n$^{th}$ row- (and column-) block entry relates to the B(l) model whose name is indicated in ROWn = BEAMWF_U1XU2 keywords, and the corresponding eigenmodes are stored in a HDU of the same name.
Each extension contains also the following keywords:
- NDETS (Integer)
- the number of detector units
- NBEAMS (Integer)
- the number of beams = NSETS * (NSETS+1) / 2
- NMODES (Integer)
- here 5
- L_PLUS (Integer)
- Eigenmode > 0 to break degeneracies
- BLOCKn (string)
- for n=1-NBEAMS, gives the name of the extension containing the beam WF and error eigenmodes for the nth block
and some other ones for internal data checking and traceability
No beam correlation matrices are produced by the LFI(Planck) Low Frequency Instrument by now.
Appendices
References
- ↑ Planck 2013 results: HFI spectral response, Planck Collaboration 2013 IX, A&A, in press, (2014).
- ↑