Q: Could you please provide some information regarding the format of APEX 1-D spectra?
A: The format defined in the Phase 3 SDPS for 1-D spectral products applies also in the case of APEX reduced spectra, with few modifications:
1. The following keyword defined as mandatory for spectral products do not apply in the case of APEX spectra: OBID1.
2. While the keyword FEBE1 indicating the Frontend-backend combination becomes mandatory in this case.
Example of the values of some specific keywords:
ORIGIN = 'APEX' / Facility TELSCOP = 'APEX-12m' / Telescope name I NSTRUME= 'APEXHET' / Instrument name FEBE1 = 'HET230-XFFTS2' / Frontend-backend combination OBSTECH = 'SPECTRUM' / Technique of observation PRODCATG= 'SCIENCE.SPECTRUM' / Data product category
EXTNAME = 'SPECTRUM' / FITS Extension name TTYPE1 = 'FREQ ' / Label for field 1 TUTYP1 = 'Spectrum.Data.SpectralAxis.Value' TUNIT1 = 'GHz ' / Physical unit of field 1 TUCD1 = 'em.freq ' / UCD of field 1 TDMIN1 = 229.011 / Start in spectral coord. TDMAX1 = 233.000 / Stop in spectral coord. TTYPE2 = 'FLUX ' / Label for field 2 TUTYP2 = 'Spectrum.Data.FluxAxis.Value' TUNIT2 = 'mJy ' / Physical unit of field 2 TUCD2 = 'phot.flux.density;em.freq' / UCD of field 2 TTYPE3 = 'ERR ' / Label for field 3 TUTYP3 = 'Spectrum.Data.FluxAxis.Accuracy.StatError' TUNIT3 = 'mJy ' / Physical unit of field 3 TUCD3 = 'stat.error;phot.flux.density;em.freq' / UCD of field 3
Please also note that the values of the following keywords need to be provided in nm:
WAVELMIN= 1291867.18750 / [nm] Minimum wavelength
It corresponds to the value of TDMIN1 converted from GHz to nm (conversion factor: 299792458)
WAVELMAX= 1309075.80566 / [nm] Maximum wavelength
It corresponds to the value of TDMAX1 converted from GHz to nm (conversion factor: 299792458)
SPEC_BIN= 111.744273793 / [nm] Wavelength bin size SPEC_VAL= 1300471.49658 / [nm] Mean Wavelength SPEC_BW = 17208.6181641 / [nm] Bandpass Width Wmax – Wmin
The following link may be useful to reconstruct the provenance information, it provides the mapping between the original file name to the archive id, and calculating the exposure time:
Q: What shall I do in the case of GTC data?
A: The origin keywords shall be set as follows:
ORIGIN = 'GRANTECAN' TELESCOP = 'GTC' INSTRUME = 'CANARICAM' or 'OSIRIS'
In addition to the above keywords, the use of GTCPRGID and GTCOBID (to be adopted from the original data) is recommended.
Q: Possible algorithm for ABMAGSAT computation
In the case of the VIMOS imaging pipeline, an adaptation of the method used by the PESSTO survey (A&A, 2015, 579, pg. 25) is the following:
ABMAGSAT = zeropoint -2.5*log10(((pi/4.*ln(2)))*(satlev-mean_sky)*(psf_fwhm/pixel_scale)^2)/EFF_EXPT)
where the parameters are those written to the following keywords:
satlev = HIERARCH ESO QC SATURATION zeropoint = HIERARCH ESO QC MAGZPT mean_sky = HIERARCH ESO QC MEAN_SKY pdf_fwhm = PSF_FWHM pixel_scale = HIERARCH ESO QC WCS_SCALE EFF_EXPT = the effective exposure time (= CASUEXPT)
Q: How to compute the MJD-END of a SOFI spectrum?
The end time of a Phase 3 SOFI 1d spectrum product (MJD-END) must be computed using the following formula:
MJD-END = MJD-OBS of the last raw observation + NDIT * ( DIT + 1.8) / 86400
where the 1.8 seconds accounts for the necessary overheads, and 86400 scales back from seconds to days.
Q: What is the correct EFFRON for median-combined SOFI images?
Example: There are 7 raw images, each resulting from averaging together 5 detector integrations (NDIT = 5). A science product is generated by reducing and median-combining those 7 raw images.
In this case:
EFFRON = 12 * sqrt(PI/2) / sqrt( 7 * 5)
where PI is 3.14159, and 12 is the detector readout noise of SOFI in electrons.
Q: May you please clarify what the OBSTECH keyword values are?
A: We support the OBSTECH keywords listed in the table below, in addition to those defined by the SDP standard document.
|INSTRUME||Mode||Origin of keyword value||TELESCOP||OBSTECH|
|Imaging||Broad band (SDSS filters)||OBSMODE||GTC|
|Narrow band (Tunable filters)|
|Medium band (SHARDS filters)|
|CanariCAM||Imaging||'IMAGE,CHOPNOD' 'IMAGE,NODDING' 'IMAGE,CHOPPING' 'IMAGE,STARE'|
|Spectroscopy||'SPECTRUM,CHOPNOD' 'SPECTRUM,NODDING' 'SPECTRUM,CHOPPING' 'SPECTRUM,STARE'|