MIKE Fibers Overview

OVERVIEW OF THE MICHIGAN MIKE FIBER SYSTEM (MMFS) Mario Mateo (mmateo @ umich . edu) November 2006

128 "Red" Fibers that feed the red camera of the MIKE spectrograph.
128 "Blue" Fibers that feed the blue camera.
Provision for interference filters to isolate specific orders on both the red and blue sides. Available filters include Mg (around 5180 Å, one tuned for the red side and one tuned for the blue side), H-alpha, red order 56 (about 6140 Å), and the Ca IR triplet. The current filters isolate single orders, but multi-order operation is possible. Interested users should contact M. Mateo (mmateo @ umich . edu) to inquire about these keeping in mind that new filters require money (a kilo-$ or a few), and a lead time of about 8 weeks. Single order coverage is about delta-lambda/lambda ~ 0.01. Multi-order observations -- at the cost of total number of targets per field -- can cover a range of up to 0.03-0.05.
1.4 arcsec diameter circular apertures for each fiber.
Minimum separation between fibers of 14.5 arcsec.
Fiber access via plugplates to a 20-23 arcmin diameter corrected on the Nasmyth-East focus of the Clay telescope. Since Clay lacks a wide-field corrector, the full 27-arcmin field is likely only available for relatively bright sources.
System throughput is strongly filter/order dependent, but observations so far indicate that the system delivers 1 photon/sec/Angstrom at V=17.2 in the Red fibers, abd 1 photon/sec/Angstrom at V=17.7 with the Blue fibers at about 5180 Å. Throughput is highly seeing-dependent; the values above refer to about 0.8 arcsec seeing. Considerably better seeing gains about a factor of 1.5-2.0 over the realistic range of good seeing at Clay.
All 256 fibers can be used for observations between approximately 4800 and 5250 Angstroms since there is no dichroic in use with the fibers. Only blue fibers can be used below 4800 Å, and only red longward of 5250 Å.
The user is the fiber robot; new users will be thoroughly trained in this process. Experience shows that competent observers can plug 128 fibers in approximately 20 min. Plugging time for all 256 fibers is approximately double or a bit longer. Two people can plug fibers simultaneously, shortening the time significantly (usually!).
Repeatable exposure times are limited to longer than about 2-3 second, with a shutter latency of about 0.2 seconds.
Th-Ar and Th-He comparison lamps are available for calibration. This combination should ensure that every order is devoid of excessively bright comparison lines. Arc exposure times of 60 sec are likely required for most orders.
The effective resolution with the fibers is approximately 70% that of MIKE direct with a 1 arcsec slit, or about 15,000 in the Red and 19,000 in the Blue. The 175 micron diameter fibers project to about 6-8 pixels on the Red and Blue CCDs. We recommend binning the CCDs 2x2 or even 3x3 in normal use. A slit assembly to be located at the fiber ends to increase resolution, but this is not yet available and would only be built if demand warrants.
MMFS has an integral Shack-Hartmann mask that allows normal Shack-Hartmann updates to the primary mirror IF a bright star is positioned at the field center. If no such star is available or desired, the SH system can be used to focus the telescope during fiber observations by offsetting to a bright star periodically. This has been shown to work for 30-60 minutes depending on location of the field relative to the zenith (worse near the zenith).
Guiding is carried out with two coherent fiber bundles that are positioned at the locations of two suitable guide stars. Auto guiding is available, though manual updates are required to tweak rotator errors (if any) during fiber observations. Such guider errors have so far been negligible in observations carried out to date.
Up to 8 stars can be used in each field as "acquisition targets", allowing one to quickly set up on target fields (typical time is ‹ 5 minutes).
Any potential users should ensure that they have relative astrometry good to ± 0.1-0.2 arcsec and that they are certain a suitable order isolation filter is available for their program. Plug plates cost approximately $100 each, plus about $200-300 for machining. Up to three and possibly four fields, each consisting of 256 fiber positions, can be drilled per plate, particularly if the entire FOV is populated more-or-less uniformly with targets. Users must plan to cover the cost of the plates and for machinging the fiber holes (the $200-300 per plate cost). Astrometry should be available at least TWO MONTHS prior to the start of any MMFS observing run.
Software for designing plug plates is available. Please contact MM for details.
If you are interested in using MMFS, please contact Mario Mateo (mmateo @ umich . edu) for further details.

Personal tools

MIKE Fibers Overview

Document Actions