Measuring the Millimeter-Wavelength Flux of Asteroids With the South Pole Telescope

Millimeter-wavelength (mm-wave) measurements of asteroids are useful for constraining their shapes and thermophysical properties. The South Pole Telescope (SPT) is a 10-meter mm-wave telescope located at the geographic South Pole and designed to measure the cosmic microwave background (CMB). Using observations from the SPTpol camera in two observing bands centered at 95 and 150 GHz during austral summer 2016, we examine known asteroids passing through the two 270 square-degree observation fields close to the ecliptic plane. By stacking maps of individual ~2-hour observations on a particular asteroid’s predicted location, we detect and measure the average mm-wave flux of the following three large asteroids at moderate to high-significance (5-11 sigma): (13) Egeria, (22) Kalliope, and (324) Bamberga, where the values in parentheses are the asteroids’ designation numbers.