THE 4-METER INSTRUMENT ROTATOR AND GUIDER

Introduction

The Rotator/Guider provides the interface between the telescope and the R.C. Spectrograph. These auxiliary devices are multi-functional providing rotation for the spectrograph, guide probes for locating guide stars, calibration light sources and auxiliary optics for TV acquisition systems. A set of Risley prisms is available for atmospheric dispersion correction. (These are currently being performance checked by KPNO staff before they go into operational status).

TV Acquisition Systems

The acquisition systems currently in use are: The ISIT camera on the North Port is normally always in place for target acquisition and provides a 5 arc-minute field. It is anticipated that the ISIT will be replaced by an ICCD in the near future. This camera cannot be used during integrations since a auxiliary on-axis mirror must be in the beam.

The slit viewing ICCD camera provides a 2.5' field and can be used during integrations to monitor the field. Auto-guiding is possible using the Leaky Memory Video Integrator.

In the rear slit viewing mode for multi-slit work, the ICCD cannot be used during integrations since a auxiliary on-axis mirror must be in the beam. The entire 5' field can be viewed in this mode of operation. Using this camera and a manually inserted lens, the telescope can be focused using the knife-edge test.

An integrating video memory, the "Leaky Memory" is available for acquisition of faint objects. Stellar objects of V~19.5 can be seen under good seeing conditions with ~8 seconds of integration (or "leak") using the wide-field system. The slit viewing systems have a limiting range of about V~19 under good conditions using the "Leaky Memory".

Spectrograph Position Angle Rotation

The range of rotation is +-90 degrees from the default east/west position. This corresponds to a range 0 <= PA <= 180 degrees. The spectrograph and auto-guider are remotely rotatable from the console room. Due to the asymmetrical weight distribution of the spectrograph, there are some restrictions with zenith distance. The guidelines are:
  1. For large rotations (>2deg.), the telescope must be within 30 degrees of the zenith.
  2. For small rotations or "tweaking" (<=2 deg.), the telescope must be within 50 degrees of the zenith.

Additionally, for safety reasons, no one is permitted in the Cass cage during rotation if the telescope is more than 3 degrees from zenith. See the memo posted in the console room.

The position angle can be readout either in the cage or in the console room. One can read to the nearest half degree on the cage readout and to the nearest tenth of a degree using the status monitor (VDU) in the console room. The Telescope Operators are responsible for the safety of the equipment and personnel when rotating remotely.

Guide Star and Target Acquisition

The acquisition of guide stars can be done quickly by the Telescope Operator using a special program "gstar" on the SUN to search the Space Telescope Guide Star Catalogue. The observer generally need not be concerned about selecting and pre-measuring guide stars, unless one is working well away from the galactic plane or in dark-cloud regions. Full capabilities exist to electronically transfer target coordinates to the telescope control computer from outside the Observatory. See NOAO Newsletter, #30, June 1992, page 14 for details. Send your coordinates to 'coords@noao.edu'.

Specifications - 4-Meter Automatic Guider Probes

  1. Guide Probes - two exist, one for the north half of the field and one for the south half. The north probe is an image dissector tube (IDT) while the south is an ILS TV camera.
  2. Guide Star Magnitude Range: 9 < B < 14
  3. Offsetting precision (~+-0.1")
  4. Range of the probes:
  5. Telescope Scale: 6.624 arc-seconds/mm (150 microns/arc-sec)
  6. Guide Probe Filters (north probe IDT only)
    1. A = Blue - BG37 (1mm)
    2. B = Red - OG590 (2mm)
    3. C = Neutral Density (NG3,1mm), ~2.5 mags.
    4. D = Clear (quartz plate, 1mm)

Calibration Light Sources

The calibration sources are located on the northeast side of the Instrument Rotator and are controlled via the a GUI from the Telescope Control System (TCS). The main mirror in the Instrument Rotator must be in position 4 to allow the light to pass into the spectrograph.

The lamp housing consists of three individual sources coupled to an integrating sphere. The ports are labeled A, B, and C. Each port has an optional stepping motor controlled circular neutral density wheel and also a filter carrier for a 2x2 inch filter. Normally the motorized ND housings are removed for increased lamp brightness. Port A, the quartz lamp, however, has a permanently attached ND filter wheel. Port A is dedicated to the quartz lamp, ports B and C can have either the Helium-Neon-Argon source or a thorium-argon hollow-cathode lamp or a bright quartz lamp attached. The He-Ne-A is used for low-to-moderate resolution work and the Th-A hollow-cathode is useful for higher resolution work. A bright quartz lamp is intended for use at high dispersion.


deveny@noao.edu
Friday, August 4, 1995