THE 4-METER INSTRUMENT ROTATOR AND GUIDER
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.
- Wide field RCA ISIT camera on the Rotator North Port
- A Phillips ICCD camera attached to the Front Slit Viewer for long slit work or
- A Phillips ICCD attached to the Rear Slit Viewer for multi-slit work
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:
- For large rotations (>2deg.), the telescope must be within 30 degrees of the zenith.
- 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 'firstname.lastname@example.org'.
Specifications - 4-Meter Automatic Guider Probes
- 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.
- Guide Star Magnitude Range: 9 < B < 14
- Offsetting precision (~+-0.1")
- Range of the probes:
- X (east/west) +-140mm from center
- Y (north/south) 0-210mm from center
- Guide stars must be >45mm off-axis or the probe will vignette the slit
- Telescope Scale: 6.624 arc-seconds/mm (150 microns/arc-sec)
- Guide Probe Filters (north probe IDT only)
- A = Blue - BG37 (1mm)
- B = Red - OG590 (2mm)
- C = Neutral Density (NG3,1mm), ~2.5 mags.
- 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.
Friday, August 4, 1995