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NIRI Performance and Use

Information on near-IR calibrations (baseline calibrations, standard stars, etc.) can now be found on the general NIR resources page.

Status and availability: NIRI is available standalone for f/6, f/14, and f/32 imaging and f/6 spectroscopic observations. With adaptive optics observations using ALTAIR NIRI is available at f/32 (imaging or spectroscopy) and f/14 (imaging only). Recent updates on NIRI can be found at Hot News. For its availability in the next semester please see the most recent Call for Proposals.
Modes of operation: NIRI has five available instrument modes:
  • Wide-field imaging (f/6 camera, J through K bands; peripheral wavefront sensors only)
  • Grism long-slit spectroscopy (f/6: 1.0-5.5um;  f/32: 1.0-2.5 microns))
  • High-background imaging (f/14 or f/32 L and f/32 M)
  • Adaptive Optics imaging (f/32 JHKL' - all but L' are low background; L' not available on extended sources
  • Adaptive Optics spectroscopy (f/32 1.0-2.4um)
Additional details of these modes may be found in the System Verification section. Coronagraphy and polarimetry modes are not yet available. 
NIRI Components: See the NIRI components page for details of filters, cameras, grisms, slits, and other components, as well as information on array performance and exposure times.
Sensitivity NIRI standalone: The NIRI Integration Time Calculator can be used to determine limiting magnitudes, exposure times, S/N ratios, background levels, etc. for a wide range of source properties, observing conditions, filters, and NIRI configurations. The ITC has been used to generate tables of sensitivity estimates for both imaging and spectroscopy modes (without AO). The ITC predictions agree with throughputs measured on the telescope to 20%. Because some conditions vary unpredictably (e.g., the OH sky emission can vary by a factor of two from hour to hour), one should consider the ITC S/N prediction to be accurate only to within a few tens of percent.

The estimated image quality delivered to the instrument is given as part of the observing condition constraints.
Sensitivity NIRI+ALTAIR: Use the Altair ITC to determine performance parameters for NIRI+AO imaging. An ITC is not yet available for NIRI+AO spectroscopy; for now one can get a rough and conservative estimate for AO spectroscopy by using the NIRI ITC with the f/6 camera, the narrowest (2 pixel wide) slits, best image quality, and much shorter individual exposures than planned for the actual f/32 observations). Note that the f/6 ITC result can be misleading if the same individual exposure times are used at f/32. The background per pixel is ~25 times less at f/32 than at f/6, and thus individual exposure times need to be ~25 times longer at f/32 than at f/6 to produce the same background (i.e., the same noise) and to achieve the same S/N in the same total exposure time. E.g., to estimate the S/N in one hour consisting of twelve 300-second exposures for f/32 spectroscopy, specify 300 12-second exposures in the f/6 ITC.
Observing strategies: See the Observing Strategies page for guidance and special considerations for each observing mode. When you're done, don't forget to check the Checklist.
Phase II Preparations: See the Phase II Special Instructions. Example OT files for NIRI can be retrieved from the OT Library webpage. For help getting started, please see the OT Tutorial page. Note that all calibrations (except darks) must be included in Phase II files, for both NIRI and NIRI+ALTAIR.
Observing overheads: See NIRI Overheads for information on estimating acquisition and observing overheads. Note that only overheads actually used will be charged to the program.
Target acquisition: See the generic target acquisition scenarios.
Calibration: The PI must specify a basic calibration set of flats, arcs (or spectra of telluric lines), and standards, as listed on the NIR baseline calibration webpage. Note that two photometric standards or spectroscopic calibration stars must be specified, one that would match the airmass of the target if observed before it and one that would match it if observed after it.

Flat and arc calibrations will be carried out using the facility calibration unit, except that for L and M spectroscopy no arcs are taken; wavelength calibrations are derived from spectra of standard stars.

Lists of faint photometric standards and imaging sequences for them are available in the in the OT library or can be "fetched" from the database (in the "Other" programs using the Observing Tool. Additional lists of photometric standards are also available on the NIR photometric standards webpage.

Information about spectroscopic calibration stars (and a search engine) are provided on the NIR telluric standards webpage.

Typical values of measured zero points, background flux levels, and extinction values are provided for reference to help with data reduction and analysis.
Data processing and software: The NIRI package of IRAF scripts for reducing imaging and spectroscopic data has been released.


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Last update 2006 September 1; Andrew Stephens, Tom Geballe & Joe Jensen