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:

Primary header

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

Extension header

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:
http://archive.eso.org/wdb/wdb/eso/apex_origfile/form

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.