.. include:: ../include/links.rst .. _focas: ************** Subaru FOCAS ************** Overview ======== This file summarizes several instrument specific settings that are related to the Subaru/FOCAS spectrograph. .. warning:: PypeIt currently *cannot* reduce images produced by FOCAS in imaging mode or those taken with certain obsolete readout configurations. All image-handling assumes FOCAS images have been taken in spectroscopic mode with standard CCD readout parameters. PypeIt handles files that do not meet these criteria in two ways: - When running :ref:`pypeit_setup`, any frames not in spectroscopic mode or with non-standard readout will be ignored and should not appear in your :ref:`pypeit_file`. - If you add frames to the :ref:`pypeit_file` that are not in spectroscopic mode or have incompatible readout configurations, the method used to read the FOCAS files will fault. At present,the code has only been testd on DET-ID=2 data, i.e. the second of the two detectors, which is where the primary target lands if one uses the longslit. Deviations ========== The default changes to the PypeIt parameters specific to FOCAS data are listed here: :ref:`instr_par-subaru_focas`. *You do not have to add these changes to your PypeIt reduction file!* This is just a listing of how the parameters used for Subaru/FOCAS differ from the defaults listed in the preceding tables on that page. These are tuned to the standard calibration set taken with FOCAS. .. _focas_detector: DETECTOR ======== FOCAS uses two 2048×4096 MIT/LL CCD detectors. Unlike other multi-detector instruments, FOCAS does not use mosaic construction. The detector is oriented such that the dispersion direction is along the 4096-pixel axis (y-direction) and the spatial direction is along the 2048-pixel axis (x-direction). The detector configuration is automatically handled by PypeIt with: .. code-block:: ini [rdx] spectrograph = subaru_focas This is the default configuration and typically does not need to be modified by the user. Calibrations ============ Edge Tracing ------------ FOCAS long-slit and multi-object spectroscopy requires careful slit edge tracing. The default `edge_thresh` parameter works well for most FOCAS configurations, but may need adjustment for: - Very short exposures - High-resolution modes (VPH gratings) If slit edges are not being detected properly, try: .. code-block:: ini [calibrations] [[slitedges]] edge_thresh = 20 For multi-object spectroscopy (MOS), you may need to adjust additional parameters: .. code-block:: ini [calibrations] [[slitedges]] edge_thresh = 20 trace_thresh = 10 minimum_slit_length = 6 Multi-Object Spectroscopy (MOS) ------------------------------- FOCAS supports multi-object spectroscopy through slit masks. Unlike DEIMOS, FOCAS does not currently support automatic matching to slit-mask design files. Users must rely on the automatic slit detection and may need to manually verify slit assignments. For MOS observations, consider these parameters: .. code-block:: ini [calibrations] [[slitedges]] sync_predict = nearest bound_detector = True minimum_slit_length = 8 Wavelength Calibration ---------------------- FOCAS wavelength calibration depends on the grating and comparison lamp used. Common lamp combinations include: - **HgCd lamps**: Standard for most gratings - **Ne+Ar lamps**: Used for some high-resolution configurations - **ThAr lamps**: Available for high-precision radial velocity work The default lamp selection works for most cases, but can be overridden: .. code-block:: ini [calibrations] [[wavelengths]] lamps = HgI, CdI **Common Grating Configurations:** - **150B, 300B, 600B**: Blue gratings, use HgCd lamps - **150R, 300R, 600R**: Red gratings, use HgCd or Ne+Ar lamps - **VPH gratings**: High-resolution, may require ThAr lamps Flat Fielding ------------- FOCAS flat fielding generally works well with default parameters. However, for certain configurations you may encounter: - **Fringing in red wavelengths** (>7000Å): Common with red gratings - **Illumination gradients**: Particularly in wide-slit modes - **Scattered light**: Can affect faint object spectroscopy To address fringing in red spectra: .. code-block:: ini [calibrations] [[flatfield]] slit_illum_finecorr = False tweak_slits_thresh = 0.9 For severe illumination gradients: .. code-block:: ini [calibrations] [[flatfield]] slit_illum_finecorr = True slit_illum_ref_idx = 0 Flexure ------- FOCAS generally has good mechanical stability, but flexure corrections may be needed for: - **Large telescope movements** between calibrations and science - **High-precision radial velocity work** Enable flexure correction with: .. code-block:: ini [flexure] spec_method = boxcar spec_maxshift = 20 For high-precision work, consider using sky lines for flexure correction: .. code-block:: ini [flexure] spec_method = slitcen spec_maxshift = 10 Flux Calibration ================ FOCAS flux calibration requires standard star observations. Recommended standards include: - **Spectrophotometric standards**: BD+28d4211, HD 19445, etc. - **White dwarf standards**: G191-B2B, GD 153, etc. Standard star configuration: .. code-block:: ini [fluxcalib] extinct_correct = True extinct_file = atm_extinct_subaru_maunakea.dat Troubleshooting =============== **Common Issues:** 1. **Wavelength solution fails** - Check lamp selection matches your grating - Verify arc lamp exposure times are adequate - Consider manual lamp line identification 2. **Poor flat fielding** - Check for saturated flat field exposures - Verify flat lamp matches science configuration 3. **Slit edges not detected** - Lower edge_thresh parameter - Verify adequate flat field signal Additional Reading ================== Here are additional docs related to Subaru/FOCAS: .. toctree:: :maxdepth: 1 ../dev/add_missing_obj ../dev/fluxing