GNIRS has a "flip-in" acquisition mirror to allow precise positioning of objects on the slit without moving the grating, prism or camera.  The choice of acquisition filter is independent of the wavelength of the science observations.  PIs must specify the filter in their acquisition observations.  See the OT details for more information on defining GNIRS acquisition observations.

Objects fainter than ~18.5 at H require "blind" acquisition. The PI must provide IR-visible reference star(s), one or two, that can be acquired with the same guide star as the science target, and with the same coordinate system as the science target.  See "blind or offset acquisition" instructions.

Acquisition observations must be defined by the PI in the Phase II definition.  PIs should specify target brightness (and finding charts if needed) in the filter specified for acquisition, if possible. It is also useful to add notes with acquisition instructions if any special conditions apply (e.g., "center on fainter source W of bright nucleus", "acquisition in K filter to match finding chart", etc).

The acquisition sequence

Target acquisition is done in the following manner:

1. The acquisition mirror is inserted with the requested slit and decker in position to take a slit image to measure slit center.
2. The slit and decker are moved to "acquisition" position to image the entire science FOV, nominally in the H (1.65um) filter, but the choice of filter is up to the PI.  Any filter but the broadband L and M filters can be used for acquisition; see the exposure times page for more information.
3. The object is centered at the measured slit center position. Nominally, this requires 2 images (to measure initial position and to confirm offset) for objects visible above the background; 3 images if a sky exposure is needed for background subtraction.
4. Optionally, the slit and decker can be reinserted to image the object through the slit.  However, this is not usually done as the slit position is repeatable to <0.5pixel. (The acquisition mirror is repeatable to 1-2pixels, which is why step 1 is usually repeated with each acquisition.)
5. The acquisition mirror is removed and the instrument is configured for spectroscopy.

More details about IFU acquisitions can be found on the GNIRS IFU page