New ‘digital tracking’ technique detects more than 150 new asteroids, measures distance

A new international collaborative study describes how an image stacking technique known as ‘digital tracking’ can be used to discover large numbers of new asteroids that are too difficult to detect using traditional methods.

More computationally intensive than conventional analysis techniques, digital tracking can detect moving objects 10 times fainter than is typically possible, effectively increasing the aperture of the telescope used for the study.

The international research team from Western University and Stony Brook University validated the approach using data from the WIYN 0.9m telescope on Kitt Peak at National Optical Astronomical Observatory in Tucson, Arizona.

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The collaborators detected approximately 200 asteroids in a one-degree square field at a brightness level that was previously accessible only to 4-metre and larger telescopes. More than 75 per cent of the asteroids are new discoveries. The researchers have also investigated the distance measurement to the newly discovered asteroids and the efficiency of the measurement tools.

“When determining distances of the asteroids observed in full nights, we can take advantage of the Earth’s spin around its own axis. Between the beginning and the end of the observation, the asteroid appears at slightly different locations on the sky, which is a combined effect of the asteroid’s and the Earth’s orbital motions, the Earth’s spin, and the distance between the Earth and the asteroid. The challenge is to distinguish among these factors,” explains Stanimir Metchev, an associate professor in Western’s Department of Physics & Astronomy and the Canada Research Chair in Extrasolar Planets.

The orbital motions of the asteroid and of the Earth make the asteroid trace a big, smooth curve on the sky. However, the rotation of the Earth changes that slightly as it causes the asteroid’s sky motion to speed up and slow down in a regular cycle once a day.

“We have developed a way to measure this cyclical change in the asteroid’s sky motion and use the measurement to calculate how far the asteroid is from the Earth,” says Aren Heinze, a postdoctoral researcher at Stony Brook University and the lead author of the study. “As you would probably guess, the more the asteroid’s sky motion is changed by the Earth’s rotation, the closer to us it must be.”

The technique, which the team calls Rotational Reflex Velocity (RRV) distance measurement, can yield accurate distances to asteroids over unprecedentedly short observing sequences on a small telescope. It can be done in only one or two nights, compared to the traditional approach that requires at least a week on much bigger telescopes.

“Knowing the distance to an asteroid and measuring its brightness is important in determining how big an asteroid is,” explains Metchev. “Our technique allows us to do that very quickly – after one or two nights of observations – and for asteroids that are substantially further than has been done to date. Both the information about the asteroid size, and its earlier discovery, can be vital should an asteroid actually be headed towards Earth in short order.”

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