Output files

The PRM-file

The different extensions of the PRM-file and their respective contents.
EXTNAME	HDU Type	Purpose
PRIMARY	Primary	Header contains the configuration of PampelMuse.
SOURCES	Binary Table	The source catalogue, contains basic information about every source used in the extraction.
SPECTRA	Image	Contains the extracted spectra and an estimate of the uncertainties.
POSPARS	Binary Table	Contains the coordinate transformation from reference to IFS coordinates.
POSITIONS	Binary Table	Contains the parameters of the polynomial fits to the IFS coordinates.
PSFPARS	Binary Table	Contains the parameters of the fitted PSF.

The PSF-file

For each PSF star in the analysis (i.e. each star that has status 3 in the PRM-file), the FITS file will contain four HDUs with the following content.

The values of the fitted PSF parameters in each layer that was analysed. The information is stored as a FITS-table, containing one column per fitted parameter and the wavelength information in the different rows. The names of these extensions are PM_<source ID>, where <source ID> is the ID of the star in extension SOURCES of the PRM-file.
The radial profiles of the PSF stars in the IFS data as a function of wavelength. This information is stored as a two-dimensional array, containing the profile for one layer per column. The (approximate) wavelengths of the layers can be reconstructed from the CRVAL1 and CDELT1 keys in the header. The names of these extensions are PR_<source ID>, where again <source ID> is the ID of the star in extension SOURCES of the PRM-file. Note that the common radii of the individual points of all profiles (in spaxels) are provided as the data of the primary extension of the FITS-file.
The two-dimensional profile of each PSF star extracted from the IFS data as a function of wavelength is stored as a mini data cube. Again, (approximate) dispersion information is encoded in the CRVAL1 and CDELT1 keys in the header. The names of these extensions are DAT_<source ID>.
The two-dimensional residual maps of the PSF fits to every star as a function of wavelength are also stored as mini data cubes. The format is just the same as for the two dimensional profiles and the extensions are named RES_<source ID>.

The extracted spectra

When using GETSPECTRA to write the set of extracted spectra to disk, the code will create one FITS file per spectrum, using the following naming convention:

"{prefix:s}id{source_id:09d}jd{jd_int:d}p{jd_frac:04d}f{flag:03d}.fits".format(
    prefix="ngc1234",  # The value of the `getspectra|prefix` configuration key
    source_id=2345,  # The ID of the source in the reference catalogue
    jd_int=int(2459110.1234),  # The integer part of the Julian Date of the observation
    jd_frac=int(1e4*np.mod(2459110.1234, 1)),  # The fractional part of the Julian Date of the observation
    flag=0  # The quality flag of the spectrum
    )

Hence each filename is composed of a common prefix that can be specified in the user configuration file, the ID of the source in the reference catalogue, the Julian Date of the observation, and a quality flag. The quality flag is generated via the following bitmask:

Spectrum properties considered in quality flags.
Value	Meaning
1	More than one source contribute to the spectrum.
2	The average S/N of the spectrum is \(<10\).
4	The mean flux of the spectrum is negative.
8	The centroid of the source is outside the field of view of the data cube.

Note

In case the configuration key getspectra|skipflag is set to True, the part "f{flag:03d}" is omitted from the filenames.

Note

Spectra of sky components are stored as well. Their naming convention is the same as for the stellar spectra, only that the part "id{source_id:09d}" is replaced with "sky{sky_id:09d}", where sky_id is the (internally assigned) index of the sky component.

FITS header keywords

Each spectrum written to disk will contain a number of keywords in the primary FITS header, providing some information about its properties and quality. An overview is given below.

OBJECT str: The object name provided in the FITS header of the data cube.
TELESCOP str: The telescope name provided in the FITS header of the data cube.
INSTRUME str: The instrument name provided in the FITS header of the data cube.
DATE-OBS str: The date and time of the observation.
JUL-DATE float: The Julian Date of the observation.
MJD-OBS float: The Modified Julian Date of the observation.
EXPTIME float: The exposure time in seconds.
RA float: The right ascension of the source.
DEC float: The declination of the source.
OBJNAME str: An internally generated object name of the source.
HIERARCH PAMPELMUSE SEEING float: The seeing estimated from the PSF parameters, in spaxels.
HIERARCH STAR ID int: The source ID in reference catalogue.
HIERARCH STAR RA float: The right ascension of the source.
HIERARCH STAR DEC float: The declination of the source.
HIERARCH STAR MAG float: The input magnitude of the source as provided in the reference catalogue.
HIERARCH SPECTRUM MULTISTAR bool: A flag indicating if multiple sources contribute to the spectrum.
HIERARCH SPECTRUM XCUBE float: The source position along the x-axis of the cube in spaxels.
HIERARCH SPECTRUM YCUBE float: The source position along the y-axis of the cube in spaxels.
HIERARCH SPECTRUM INFIELD bool: A flag indicating if the source centroid is inside the cube field of view.
HIERARCH SPECTRUM EDGEDIST float: The distance of the source centroid to the edge of cube field of view in spaxels. Negative values imply that the source centroid is outside the field of view.
HIERARCH SPECTRUM SNRATIO float: The average signal-to-noise of the spectrum, measured per pixel via the DER_SNR algorithm presented in ST-ECF Newsletter 42.
HIERARCH SPECTRUM MAG <PASSBAND> float: The AB magnitude recovered from the spectrum in the passband used for the source selection, as specified by the catalog|passband parameter in the user configuration file. Note that the magnitude is determined under the assumption that the flux unit of the cube is \(\rm{erg}\,\rm{s}^{-1}\,\rm{cm}^{-2}\,{\rm Å}^{-1}\).
HIERARCH SPECTRUM MAG DELTA float: The difference \(\delta\) between input and recovered magnitude of the source.
HIERARCH SPECTRUM MAG ACCURACY float: The relative accuracy of the recovered magnitude. This value is computed by comparing the difference \(\delta\) between input and recovered magnitude to the standard deviation \(\sigma\) of the differences obtained for sources of similar brightness, using the formula

\[a = \frac{1}{1 + \left(\frac{\delta}{2\cdot\sigma}\right)^2}\]
HIERARCH SPECTRUM TYPE str: The type of source.
HIERARCH SPECTRUM QLTFLAG int: The quality flag of the spectrum.