Telescopes I've Used - JCMT

James Clerk Telescope (JCMT), Mauna Kea, Hawaii

James Clerk Maxwell telescope and cinder cone

The JCMT is a 15-meter millimeter/submillimeter telescope located on Mauna Kea, in an area known as "Millimeter Valley" below the summit cinder cones. It is close to the Caltech Submillimeter Observatory (CSO) and the new Smithsonian millimeter array site. For those of us without the benefits of a British education, we need to be told that the second part of the name is pronounced "Clark" (some interesting family history lies behind that). The JCMT is operated by the Joint Astronomy Centre in Hilo (as is UKIRT) on behalf of the UK, Netherlands, and Canada. Much of the time, it's operated through a windscreen which is reasonably transparent at the relevant wavelengths (which is why I don't have such a great picture of the telescope itself, only its cylindrical enclosure). Most of the recent excitement from the JCMT has arisen through the use of the SCUBA detector array, which is extremely cool in both senses of the word. It is a workable camera at wavelengths 350-850 microns (0.35-0.85 mm), and can do single-point measurements out to 2 mm wavelength. The multiple submillimeter detectors let it map the sky with unprecedented sensitivity, giving the first access to really faint sources (like dust in high-redshift galaxies). It's said that the innards of SCUBA contain the largest known mass so close to absolute zero. We used the JCMT as part of our project on dust in galaxies, measuring (or not detecting as the case may be) the coolest dust component to fill out our inventory of dust emission, aong with far-infrared measurements taken by ISO. This could be compared with the mass derived from optical absorption for spiral galaxies seen in front of elliptical companions, to tell how much dust might be either very cold (and thus hard to find in the far-IR or sub-mm) or in very compact clouds that are hard to see optically. The answer was, "not much". Here's the SCUBA detection of the spiral in AM1316-241 at 850 microns. None too impressive, but there is a dim splotch at just the right place.

SCUBA map of AM1316-241 at 850 microns

Telescope Collection

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