Data products

Raw detector frames

Raw FITS files from the ICS are the authoritative acquisition products. All original headers should be retained, and raw files should not be overwritten during reduction.

ICS header conventions

The ICS retains camera-provided cards where useful and organizes its additions into provenance, instrument, sensor, target/pointing, observation, timing, and file-metadata sections. Important conventions are:

  • INSTRUME is CLASSI; ORIGIN, LOCATION, TELESCOP, and OBSERVER identify the facility and observer.

  • CAMERAFL, COLLIMFL, NGROOVES, GRATING, FILTER, and DISPERS record the configured optical setup. These values come from the deployment’s config.ini.

  • DETECTOR identifies the sensor. BINNING records the requested setting, while camera-provided PIXSIZE1, PIXSIZE2, XBINNING, YBINNING, XPIXSZ, and YPIXSZ cards preserve the reported detector state when present. GAIN and GAINMODE describe the readout state; SET-TEMP, CCD-TEMP, and TECPOWER record the sensor setpoint, measured temperature, and cooler power.

  • RA and DEC are sexagesimal target coordinates. RA_OBJ and DEC_OBJ contain the same target position in decimal degrees, while RA_TEL and DEC_TEL record the actual telescope pointing. AIRMASS and GUIDED describe the state at the end of the exposure.

  • IMAGETYP is one of light, flat, dark, bias, or arc. USERCMNT stores an optional observer comment; STAGEX, STAGEY, STAGEZ, TELFOCUS, CAMFOCUS, and CAMAPER record mechanism positions where available.

  • REQEXPT is the requested duration, whereas EXPTIME is the duration reported by the camera. TIMESYS is UTC; DATE-OBS, MJD-OBS, DATE-END, and SIDEREAL describe exposure timing. FILENAME and DATE identify the written product and its last modification time.

The requested exposure should not be inferred from EXPTIME when REQEXPT is present, and target coordinates should not be substituted for the separately recorded telescope pointing.

Calibrated detector frames

Pipeline calibration products should preserve data, unit, mask, and uncertainty information together. The exact serialization can evolve, but the scientific meaning of those components should remain explicit.

Extracted spectra

The pipeline should retain one product per extracted fiber through the low-level processing stages. A final science product can then associate fiber spectra with roles or spatial positions according to the observation metadata.

The L1 FITS product contains a primary HDU followed by one binary-table HDU per trace. Each trace table contains PIXEL, COUNTS, SIGMA, and MASK columns. PIXEL is the zero-based detector dispersion coordinate; for rebinned products it is the mean native coordinate of each contributing group. COUNTS is summed when rebinned and SIGMA is propagated in quadrature.

The primary and trace headers record REBIN, the number of native dispersion pixels per output bin. Each trace header also records NTRIM, the number of trailing native pixels omitted because they did not form a complete bin, and EXTRACT=BOXCAR. A rebinned sample is masked if any contributing native sample was masked.

Wavelength-calibration references

The baseline wavelength calibration is a versioned ASDF reference product, not a science spectrum. One file contains every fiber trace under the classi_wavesol tree. Its top-level metadata records format=CLASSI-WAVESOL, format version 1, creation time, trace count, zero-based pixel origin, dispersion axis 1, wavelength unit and air/vacuum medium, source arc filename, and lamp names.

Each trace stores its ID, a GWCS-backed WavelengthSolution1D and native pixel bounding box, fit RMS values, and the matched arc-line pixels, wavelengths, residuals, used/rejected flags, and identifiers. All traces in one file must use the same wavelength unit and medium. read_wavesol() validates these conventions when restoring the trace-ID mapping.

The pipeline Level-2 reference is the authoritative format description. No Level-2 science FITS product is defined; the ASDF file is the reusable calibration object that such a product will reference or consume.

Simulation products

Synthetic detector frames should record enough simulator configuration to be reproduced: physical spectrograph parameters, native detector model and binning, atmosphere and sky selections, throughput data versions, exposure time, random seed, and input-spectrum provenance.