MX Spectrometer Information

The MX Spectrometer uses 32 robotic arms to position optical fibers at the positions of galaxies in the telescope focal plane. The optical fibers allow us to collect spectra of many galaxies simultaneously. This efficiency gain comes with the penalty of making the observing process fairly complicated since the observer has to keep track of the telescope, the robot arms, the spectrograph and the CCD detector. "The MX Spectrometer Design" was J. M. Hill's dissertation topic at the University of Arizona in 1984. The instrument itself has been operating regularly since 1985 on Steward Observatory's 2.3 meter "Bok" telescope on Kitt Peak.

New Fibers

Thanks to many months of work by Elizabeth Rizza of NMSU polishing a new set of fibers and a few days of work by J. Hill, the MX Spectrometer received a new set of 62 2-arcsec fibers in the form of a 6-meter long cable in October 1997. The new fibers are Polymicro type FVP200220240 "wet" silica fibers. They have good UV transmission so there are only minor losses at the blue end of the spectrum. They also have the characteristic silica "OH" absorption bands in the near infrared. There are 32 object fibers and 30 sky fibers. This is a few more than we had previously. The slit has been split into two rows since all the teflon tubing wouldn't fit in a single row. Now the image of the slit looks like this:

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4-arcsecond fibers are no longer available in MX. (The next fiber cable replacement is planned for 2005 when I've finished LBT and Elizabeth has her own grad student to do the polishing.) MX also has a new set of probe tips and a new slit plate. The holes in the inner and outer probe tips are drilled at an angle so that the fibers are on average telecentric and point at the telescope exit pupil (near the secondary). This will also increase the throughput slightly and result in better flat field stability. The fibers are fitted with #26 gauge hypodermic tubing on their tips before polishing. We also jacketed them with thin-wall teflon tubing to prevent damage or stress inside the fiber cable. The fibers themselves are 6.6 meters long while the cable is 5.3 meters long. The fibers run inside 1.25 inch flexible stainless conduit between MX and the B&C. The new 6-meter long fiber cable allows the B&C Spectrograph to sit on the floor rather than flying around the sky with MX. The top cover of the B&C has been modified to accept the snout of this cable with the MX slit plate and CCD shutter.

Related Topics


 "Steward Observatory's Bok 2.3m telescope (right foreground) where the MX Spectrometer is used. (photo by J.J. Valenzuela)"


 "Suspicious crew of night guys ready to use MX.(photo by M. Ledlow)"

Thanks to Pat Hall ( pathall@as.arizona.edu ) for his assistance in creating this page.

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Last modified: Wed Mar 28 17:57:04 2001