MICHIGAN/MIKE Fiber System


Overview: Fiber feed for the MIKE spectrograph.

Fibers: 256 total; 128 Red and 128 Blue.  All of the fibers can be
used simultaneously, or any subset may be used as desired.

Fiber size at the focal plane:   The MMFS fiber ends are not placed
at the telescope focal plane (see below); rather, an entrance aperture of
1.4 arcsec diameter is placed at the focal plane, defining the patch of
sky a single fiber observes.   The outer fiber diameter is 14 arcsec at
the focal plane; this is the closest distance between adjacent fibers.

Field of View: In principle, MMFS has the full Magellan FOV of 30
arcmin in diameter.  In practice, the useable FOV is limited by the
presence or absence of a wide-field corrector.  On Clay, which
currently has no such corrector, MMFS can be used over a 23 arcmin
diameter field with minimal losses due to poor image quality.
Adaptors are available for operations on Clay with no wide-field
corrector, and on Baade with or without such a corrector.

Format: Fibers arrayed in `cassettes' of 16 with 8 cassettes each on
the red and blue sides.   The spaces between cassettes in the raw data
correspond to the locations of mounting screws for the cassettes in the
fiber `shoes'.

Detectors: Same as in MIKE: Two 2048 x 4096 SITe CCD detectors with xx
micron pixels.  Full detector properties can be found on the MIKE web
site.

Fiber Positioning: MMFS is a manual plugplate system.  Typical
plugging times range from 15 minutes for 128 fibers to 30-45 minutes
for all 256 fibers.  The system is designed so that two people can
simultaneously plug fibers.  In practice, a typical user can become
expert in fiber plugging in one to two nights.  Support for new users
is available.

Plugplates: Plugplates are made from aluminum and are shaped to
roughly the form of the focal surface.  Raw plugplates cost $86 each.
The holes in the plugplates are generated at the Carnegie Machine Shop
using user-supplied coordinates.  Full support for converting
astronomical coordinates to machine-shop coordinates is available.
Typical machining and shipping costs for plates is about $100-150
each.  A given plate can hold from 1-4 different field setups (even
more if fewer than the maximum number of fibers are used), meaning that
the per-field cost is ranges from $250 to $80.

Fiber Properties: All fibers are Polymicro 175-micron core diameter
silica fibers.  The red fibers are `low-OH' fibers to improve
transmission redward of 6500 A.  The fibers range in size from 7.5 ft
(red) to 8.0 ft (blue); fiber transmission losses are negligible.
Fiber ends are all AR coated to minimize losses there.  

Other optics: MMFS includes other optical elements.  The first is the
telecentrator that moves the image of the pupil located at the
flat-field screen location to infinity.  This results in parallel
chief rays across the entire MMFS field so that the fibers (and
plugplate holes) are parallel.  Each fiber contains an small lens to
image the pupil (not the image) on the fiber ends.  At the other end,
the light from all fibers passes through a lens to simulate the CCD
field lenses, an interference filter to isolate a given order, and a
mirror to inject the light into the MIKE camera optics.  All lens
surfaces are AR coated.

The telecentrator also serves as the mechanical stop for the fibers,
ensuring that they are placed along the proper surface at the
telescope focus.

Calibration: Wavelength calibration is provided by downward-looking
Th-Ar and Th-He lamps placed on the flat-field screen.  Continuum
calibration can be provided by standard quartz lamps on the Magellan
Telescopes that shine on the flatfield screen.  Both wavelength and 
continuum calibration can also be obtained from twilight exposures.

Shutters:  Shutter opening and closing times are about 0.25 seconds.

Interference Filters: Medium band interference filters are required to
isolate individual MIKE orders.  Any number of orders can be isolated,
but at the cost of fewer targets if more than one order is observed.
Single order filters cost about $2500 for three.  MMFS currently has
order filters for the Mg triplet at 5150 A, H-alpha, and the two IR Ca
II triplet lines near 8500 A.  If you require a different wavelength
range, contact Mario Mateo (mmateo@umich.edu); it may be possible to
get these for MMFS using instrument funds.  If not, he can provide
technical details for filter orders.