2.7 m Telescope

Cassegrain f/8.8


Fiber Multi-Object Spectrometer (FMOS) - PI Instrument
Scientist: Dr. Arlin Crotts, Columbia University, NY, (212) 854-7899, arlin@astro.columbia.edu

A 120-fiber spectrometer available at the f/8.8 Ritchey-Chretien focus, the spectrometer has 10 Å resolution over the standard setup with coverage 3900-7600 Å, with an alternative 5 Å resolution setup for 3900-5700 Å (which is currently untested, but for which the grism exists). The spectrometer can be expected to deliver up to about 90 spectra of celestial targets, accounting for some poorly-transmitting and sky fibers (10-20). Fibers are inserted by hand into a drilled plate prepared from accurate celestial coordinates prior to the run. (Better than 0.2 arcsec r.m.s. accuracy is recommended.) The field accessible to the fibers is 66 arcmin in diameter and the closest positioning between two fibers is 15 arcmin. Closer positions could be accommodated with the construction of special fibers, as might a "Dense Pack" array. The spectrometer has a dedicated, AR-coated TK 1024 x 1024 CCD with high optical QE and low noise. It also works with TK4, instead. Once thinned Loral 2048 x 2048 CCDs become available for this instrument, the number of fibers can be increased by about 40%. The instrument was originally designed to work with the Quantex acquisition camera and was then adapted to the SpectraSource 1024 x 1024. Since that camera has now failed, a new adapter needs to be made for the PXL guider. Use of this spectrograph was difficult with the old 2.7 m telescope control system, and suffered under earlier versions of the new control system.

Range of Safe Motion Allowed by Fiber Cable
Light is fed from the telescope to the spectrograph station on the south pier by a 10 m fiber cable. Instrument controls are in the South Control Room. The telescope motion allowed by the fibers is generous but not unlimited. It is possible to cause great damage to the fibers by improperly moving the telescope, even though they are well-protected against many other hazards. The primary concern is to insure that the black, 2 in. diameter fiber conduit passes easily through the rollers on the Polar Axis and is not snagged along its travel. (The conduit must pass through the rollers or else it may be pinched by the varying gap between the Polar Axis and South Pier platform.) Some preparation must be made before using the instrument: be sure that no railings are inserted into the platform above the South Pier, remove ladders, carts, cables and other items which might snag the conduit. Whenever slewing, have someone check that the conduit is not snagged anywhere along its length. Also check hourly as the telescope tracks West. At certain positions in tracking, one must be particularly careful of interfering with the South Pier platform, as out lined in the table below.

 
Given these precautions, it is possible to track from East to West in the declination range -30 < Dec < +90 degrees over the following ranges in hour angle. (These are ranges safe for the conduit; always obey Observatory regulations on the motion of the telescope itself.)

 Dec (degrees)

HA Range of Operation

Cautionary HA

-30 -3 h < HA < +3.5h  
-20 -4h < HA < +3.75h (a)  
-10 -4.5h < HA < +4.5h (a)  
0 -4.5h < HA < +4.5h (a)  
10 -4.5h < HA < +5.25h (a) 4.5h (b)
20 -4.5h < HA < 6h (a) 4.25h (b)
30 -4h < HA < 4.25h (a) 3.5h (b)
40 -3h < HA < 4.25h (a) 3.25h (b)
50 -2.5h < HA < 4h (a) 3h (b)
60 -2h < HA < 4h (a) 3h (b)
70 -1.75h < HA < 4h (a) 3.5h (b)
80 -1.5h < HA < 6h (a) 5.5h (c)
90 -0.5h < HA < 6h (a) 4.5h (c)

Notes:
(a) At this (west) hour angle, conduit starts to bind in Polar Axis roller.
 
(b) At this hour angle, conduit touches South Pier and/or IR Pump. Its possible interference with object on the South Pier platform should be monitored.
 
(c) At this hour angle, the conduit shifts weight from the East to the West side of the Polar Axis. This should be monitored, and assisted if possible.
 
East Service position is NOT accessible with the fibers installed. South Service position is easily accessible with the fibers installed; approach South Service position by moving directly South for at least the last 30 degrees of motion.


       
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7 January 2000
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