The Universe Tonight
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Three Decades of Infrared Astronomy at UKIRT
By Andy Adamson
United Kingdom Infrared Telescope
Infrared light, although first discovered more than 200 years ago, has become a necessary tool for astronomy only in the last thirty years. There are many reasons for this but chief among them is that technology to detect infrared light with any degree of sensitivity has grown up only over the last three decades. This period has seen an enormous expansion in our ability to observe the sky at these wavelengths, and to dissect the infrared light from astronomical sources in ever more precise ways.
In previous discussions in this series, I have highlighted the fact that infrared observations have become a "must have" in modern astronomy. There are many reasons for this. Firstly, many of the most important astronomical objects (for example, planets circling nearby stars) have temperatures much cooler than the Sun; these are expected to be much brighter in infrared light than they are in the visible. Secondly, the Universal expansion first tentatively observed in the 1930s is now proven beyond any doubt, and it causes galaxies seen at great distances to be much redder than those seen in the neighborhood of our own Milky Way galaxy. Such galaxies can be detected much further away when observed in infrared light. Thirdly, interstellar dust obscures a great deal of our local Universe from sight. For example, although we live right in the mid-plane of the Milky Way galaxy, in visible light we can see only a small fraction of this huge stellar system, typically only out to a few thousand light years from the Sun. Yet the Milky Way is more than 60,000 light years across. Interstellar dust clouds are much more transparent at infrared wavelengths, and so we see clear through to the Galactic Center and beyond. Finally, the formation of new stars occurs within very dense regions of interstellar molecular clouds. These regions are very dusty, and entirely hidden from observers of visible light. To answer the major questions of how star formation takes place, therefore, we need to observe at the longer wavelengths – in other words, infrared and submillimeter.
Mauna Kea is one of the finest observing sites in the world, and particularly excels for infrared observations due to its high altitude and dry upper atmosphere. UKIRT is nearing the thirtieth anniversary of its opening, and it is time to look back at some of the science that has come from this extraordinary combination of telescope and site. There are many science highlights – too many for a short talk – but I will attempt to convey both the science and the way in which it has developed over time as the technology of infrared detectors has advanced. To give one example, the earliest users of UKIRT came to the telescope to use a "single-element detector". To put this in more modern terms, we had a camera with just one pixel! It was almost a decade before UKIRT received the first-ever facility infrared array camera, incorporating a chip with a total of just over 3500 pixels. Even this relatively modest device revolutionized infrared astronomy in its day, and so it is not hard to imagine the impact that the current UKIRT camera, with more than 16 million pixels, is having.
In this discussion, then, I will review three decades of infrared astronomy at UKIRT. We will go all the way back to the single-element detectors, to the first infrared cameras and spectrometers, and then sweep through the 1990s and the present decade to describe how the observatory has continued its commitment to doing the very best infrared astronomy from the very best site in the world.
Andy Adamson is currently Associate Director of the United Kingdom Infrared Telescope. Before arriving on the Big Island he was for ten years a lecturer and computer systems manager at the University of Central Lancashire in the northwest of England, alternately teaching Physics and Astronomy to undergraduate students and running a network of computers for the reduction of astronomical data obtained from observatories around the world, including Mauna Kea. His research has for many years concentrated on the properties of interstellar dust: microscopic particles of silicate and carbonaceous dust which populate the spaces between the stars.