TEL17 Hungarian automated telescope HAT1

The Hungarian Automated Telescope, with the domes of the Spacewatch 0.9-meter telescope, Steward Observatory 90-inch telescope and Mayall 4-meter telescope in the background. Photo courtesy of Gaspar Bakos.

A brilliant Princeton astronomer - Bohdan Paczynski - recently pointed out that less than 10 percent of variable stars appear to have been discovered, even amongst relatively bright stars. Other phenomena such as gamma-ray bursts (see above), novae and supernovae, and perhaps even "killer asteroids," can lead to temporary brightenings in the sky. But monitoring a large part of the sky for these transient signals is a tremendous technical challenge.

To help you imagine the scale of the problem, let's look at a few numbers. The full Moon has a diameter of approximately half a degree, and the entire sky contains 40000 square degrees, although only half of that is ever visible above the horizon at one time. Of all the large research telescopes at Kitt Peak, the one with the largest field of view is the WIYN 0.9-meter, which can look at 1 square degree at a time. In order for that telescope to map the entire visible sky, it would need to look at 20000 different positions. If each image took only 2 seconds (which would not really be useful) it would still take about 12 hours to complete, not including the time needed to move the telescope, or to read out the CCD chip. In practical terms, only about 200 useful exposures could be taken in a full night, leaving the rest of the sky unexplored. Of those 200, a certain number would have to be for "calibration," and would not actually have scientifically useful information in them.

A small telescope from a group consisting of one professional astronomer (Gaspar Bakos of the Konkoly Observatory in Budapest, Hungary, and the Harvard-Smithsonian Center for Astrophysics) and three amateur astronomers from the Hungarian Astronomical Association in Budapest, is trying to meet the challenge of monitoring variability across the night sky, using a robotically operated telescope. Located on the Steward Observatory grounds, near Super-LOTIS, is a white box about 3 feet across on every side. Inside the box is a Nikon 180-millimeter telephoto lens with a diameter of 6.4 centimeters (about 2.5 inches), on a mount that looks like a 1/50 scale model of the horseshoe mount of the 4-meter telescope. Attached to the lens is a CCD camera with over 4 million pixels; the combination gives a field of view on the sky of about 9X9 degrees, which brings the scale of the problem under control, because it is looking at an area of the sky 80 times larger than the WIYN 0.9 can view at once.

Through a sophisticated observing strategy the HAT-1 monitors some regions of the sky up to 30 times a night, with other regions being observed twice a night. Priorities for the observations are changed on a weekly and monthly basis, so that every part of the night sky gets some coverage for very short-term variability. In addition, the software can also break the pattern to observe a GRB, if one is reported through the global alert network. A remote astronomer can monitor or even take control of the telescope through a cell phone.

Altogether, the facility cost about $25 000, of which about half went for the CCD camera. It was built by Gaspar Bakos, who was then an undergraduate student in Hungary, using the plans of a prototype developed by Dr. Grzegorz Pojmanski (who has a similar but more complicated facility running in Chile). It went from design concept to working telescope on Kitt Peak in less than two years, and is now collecting about 1.6 GB of data each winter night (about 1 GB on a shorter summer night). Analyzing this flood of data remains a significant challenge.

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