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NIFS Performance and Use 
Status and availability: NIFS will be available in 2006B.
Modes of operation: NIFS has two main instrument modes: 
  • 3-dimensional imaging spectroscopy in the  Z through K-bands (0.95- 2.40 microns).
  • ZJHK spectral coronagraphy with 0."2 and 0."5 occulting masks; the 0."1 mask is not currently offered
    for general observations.
Additional details of these modes may be found in the System Verification section.
NIFS Components: See the NIFS components page for details of filters, gratings, detector and other components.
Sensitivity: The 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 NIFS configurations. The current version of the ITC is providing roughly correct S/N ratios for NIFS. ITC estimated limiting magnitudes for S/N~5 (6x600sec on-source exposures) are tabulated here.

The necessary conditions for deriving the sensitivity delivered to the instrument are defined as part of the observing condition constraints.
Observing strategies: See the Observing Strategies page for guidance and special consideration for each observing mode.
Phase II Preparations: See the Phase II instructions. OT examples for NIFS observation can be accessible from the OT Library or fetched from the database (keyword=123456,  Program Reference=GN-NIFS-library).
Observing overheads: Current estimates are that the overheads associated with each new science target (for target acquisition, telescope, WFS and instrument re-configuration etc) depend upon the guide configuration chosen for the observation.

Setup time for various observation types are:
  • NIFS+Altair or NIFS+PWFS : 15 minutes. 
  • NIFS+Altair with an OIWFS star: ~20 minutes.
  • NIFS+Coronagraph :  25 minutes.
We have found that the least efficient setup is for observations with an occulting disk, because properly centering the object behind the disk takes extra time (25 minutes).

For the small 3" x 3" FOV of NIFS, it will be necessary to dither the telescope off the science source to acquire a sky spectrum for nearly all observations (see examples in the OT Library). For dithered observations with sky frames off the detector, a typical on-source efficiency is ~40%.  Very short exposures will have lower efficiency because of the fixed overhead per image (up to 30 seconds for dithers). Longer exposures will have higher efficiency. Note that extra observing overheads are needed for observations in the low noise readout modes. Standard "bright object" readout requires 5 seconds per image, medium read mode is 21 seconds per image, and the "faint object" readmode requires 85 seconds to read out each frame. Details on these readout modes can be found here.

With the current version of the OT (v2.1), some overheads are not correctly calculated (see below). For 2006B proposal preparation, this extra time should be included in the requested time.
  • The current OT assumes a fixed overhead (0.17 min = 10.2 sec) for all telescope & instrument setups.  Actual times for some of these setups are quite off from the fixed overhead of 10.2 sec. Two main discrepancies are offsets (or dithering) and grating changes. For each dither position, overhead is ~30 sec (instead of 10.2 sec) and a grating change takes typically ~65 sec.
  • The "Planned Observing Time" value from the current OT includes only actual exposures plus the initial target setup time. It does not include any telescope and/or instrument overheads after the initial target setup. A true observing time can be obtained by adding up all items which appear in the "Timeline". To see this "Timeline", click sequence -> TimeLine.
Target acquisition: See the generic target acquisition scenarios.
Calibration: A basic calibration set will be obtained for each observation. Flat-fielding and wavelength calibration of NIFS spectra are to be carried out using the facility calibration unit. 

A NIFS grating change can introduce a spectrum shift of 1-2 pixels along the dispersion direction. Therefore, at each grating setting, an arc frame should be taken and it should be treated as a "nighttime partner" observation. For a proper observation setup, follow examples in the OT Library.

Information, catalogues and search engines for spectroscopic standard stars can be found on the NIR Resources page. For NIFS imaging spectroscopy, baseline calibration will include one telluric standard for correction of atmospheric features when each target is observed.

Data processing and software: The Gemini NIFS package of IRAF scripts for reducing data are under development and are not yet available.

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Last updated: 2006 Feb 28; Inseok Song
Previous version: 2005 Nov 21; Inseok Song and Tracy Beck