Central Bureau for Astronomical Telegrams

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An American amateur astronomer has discovered a new addition to the rare class of near-earth objects known as Atens.

Arizona astronomer Roy Tucker was observing fields in the Milky Way for his HELIOS (High Ecliptic Latitude Interplanetary Object Search) program on June 28 (local time, June 29 U.T.) when he detected a fast-moving object. He followed it up the next night, then reported accurate measurements from both nights to the Minor Planet Center (MPC). With a daily motion of about 1.1 degrees (for comparison, the diameter of the moon is 0.5 degrees and main-belt minor planets will have daily motions smaller than this) the object was clearly interesting, so it was added to the Center's NEO Confirmation Page in the expectation that other observers would confirm the object and obtain sufficient observations to allow orbit computations.

Early attempts by other observers to confirm the object were not successful, possibly because the object was fainter than expected on the basis of Tucker's initial report. Tucker reported his third night of observation at 13:45 UT on July 1. The first follow-up observations by observers other than the discoverer came from two Japanese observers around 16:00 UT that day. The prediction on the Confirmation Page was updated, but it was felt that there were not yet enough observations to announce the discovery on a Minor Planet Electronic Circular (MPEC).

Over the next ten hours additional observations came from observers in the Czech Republic, Australia, Italy and the U.S. By the morning of July 2 the orbit computations was considered secure. The object was designated 1997 MW1 and an MPEC announcing the discovery was issued at 12:29 UT.

Aten-type minor planets have mean distances from the sun less than 1 astronomical unit (roughly the distance of the earth from the sun, 150 million km), but move out beyond the orbit of the earth when farthest from the sun. Because Atens spend a lot of time close to the sun as seen from the earth they are rather difficult to discover. 1997 MW1 is the 25th Aten discovered and is the first to be discovered by an amateur astronomer.

The orbit of 1997 MW1 is inclined at about 13° to the plane of the earth's orbit. The distance from the sun varies from 91 million km (at perihelion) to 189 million km (at aphelion) over the course of a 331.5-day orbit, but 1997 MW1 does not currently come within 15 million km of the earth. 1997 MW1 will pass its aphelion point on July 9 and the object should be observable for a few months, but it will fade quite rapidly. Although the diameter of 1997 MW1 is unknown, a possible range is 260 to 590 metres, depending on how much light the surface reflects (if the surface is dark, the object's size will be near the upper limit). 1997 MW1 is the second Aten discovered so far in 1997 and potentially the largest such object since October 1994. (A 26th Aten has recently been reported that may be about 1 km in diameter.)

With his discovery of 1997 MW1 Tucker has become the first recipient of the recently-announced "Benson Prize for the Amateur Discovery of Near-Earth Asteroids". It is worth emphasizing that Tucker's ability to produce accurate astrometric positions for his discovery was vital in allowing the object to be confirmed. Without accurate coordinates reported immediately, the object could well have become lost.

Roy Tucker was born in Jackson, Mississipi, in 1951, grew up in Memphis, Tennessee and currently lives in Tucson, Arizona. He gained a BS in Physics in 1978 from Memphis State University and a MS in Scientific Instrumentation in 1981 from the University of California, Santa Barbara. He is currently chief electronics engineer for an optical metrology company in Tucson and sole proprietor of Southwest Cryostatics, a company offering construction of homebuilt charge-coupled device (CCD) detectors. His private observatory, the Goodricke-Pigott Observatory, houses a 0.36-m Schmidt-Cassegrain equipped with a CCD detector. The telescope's field-of-view is 0.2 degrees and the faintest stars detectable (mag. 20.5) are 1/640000 as bright as the faintest stars detectable by the unaided eye. 1997 MW1 is the first major result of his HELIOS program, begun in May 1997, and was found after a total of 28 hours of imaging and the examination of 83 pairs of images.

1997 July 2, updated July 3 and July 7.

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