We describe digital tracking, a method for asteroid searches that greatly increases the sensitivity of a telescope to faint unknown asteroids. It has been previously used to detect faint Kuiper Belt objects using the Hubble Space Telescope and large groundbased instruments, and to find a small, fast-moving asteroid during a close approach to Earth. We complement this earlier work by developing digital tracking methodology for detecting asteroids using large-format CCD imagers. We demonstrate that the technique enables the ground-based detection of large numbers of new faint asteroids. Our methodology resolves or circumvents all major obstacles to the large-scale application of digital tracking for finding main belt and near-Earth asteroids. We find that for both asteroid populations, digital tracking can deliver a factor of ten improvement over conventional searches. Digital tracking has long been standard practice for deep Kuiper Belt surveys, but even there our methodology enables deeper integrations than have yet been attempted. Our search for main belt asteroids using a one-degree imager on the 0.9m WIYN telescope on Kitt Peak validates our methodology, delivers sensitivity to asteroids in a regime previously probed only with 4-meter and larger instruments, and leads to the detection of 156 previously unknown asteroids and 59 known objects in a single field. Digital tracking has the potential to revolutionize searches for faint moving objects ranging from the Kuiper Belt through main belt and near-Earth asteroids, and perhaps even anthropogenic space debris in low Earth orbit.

In an earlier study, we reported nearly 100 previously unknown dusty debris disks around Hipparcos mainsequence stars within 75 pc by selecting stars with excesses in individual WISE colors. Here, we further scrutinize the Hipparcos75 pc sample to (1) gain sensitivity to previously undetected, fainter mid-IR excesses and (2) remove spurious excesses contaminated by previously unidentified blended sources. We improve on our previous method by adopting a more accurate measure of the confidence threshold for excess detection and by adding an optimally weighted color average that incorporates all shorter-wavelength WISE photometry, rather than using only individual WISE colors. The latter is equivalent to spectral energy distribution fitting, but only over WISE bandpasses. In addition, we leverage the higher-resolution WISE images available through the unWISE.me image service to identify contaminated WISE excesses based on photocenter offsets among the W3-and W4-band images. Altogether, we identify 19 previously unreported candidate debris disks. Combined with the results from our earlier study, we have found a total of 107 new debris disks around 75 pc Hipparcos main-sequence stars using precisely calibrated WISE photometry. This expands the 75 pc debris disk sample by 22% around Hipparcos mainsequence stars and by 20% overall (including non-main-sequence and non-Hipparcos stars).

Digital tracking enables telescopes to detect asteroids several times fainter than conventional techniques. We describe our optimized methodology to acquire, process, and interpret digital tracking observations, and we apply it to probe the apparent magnitude distribution of main belt asteroids fainter than any previously detected from the ground. All-night integrations with the Dark Energy Camera (DECam) yield 95% completeness at R magnitude 25.0 and useful sensitivity to R = 25.6 mag when we use an analytical detection model to correct flux overestimation bias. In a single DECam field observed over two nights, we detect a total of 3234 distinct asteroids, of which 3123 are confirmed on both nights. At opposition from the Sun, we find a sky density of 697 ± 15 asteroids per square degree brighter than R = 25.0 mag, and 1031 ± 23 brighter than R = 25.6 mag. We agree with published results for the sky density and apparent magnitude distribution of asteroids brighter than R = 23 mag. For a power law defined by dN/dR ∝ 10 αR , we find marginally acceptable fits with a constant slope α =0.28 ± 0.02 from R = 20 to 25.6 mag. Better fits are obtained for a broken power law with α = 0.218 ± 0.026 for R = 20–23.5 mag, steepening to α = 0.340 ± 0.025 for R = 23.5–25.6 mag. The constant or steepening power law indicates that asteroids fainter than R = 23.5 mag are abundant, contrary to some previous claims but consistent with theory.

Using data from the WISE All-Sky Survey, we have found > 100 new infrared excess sources around main-sequence Hipparcos stars within 75 pc. Our empirical calibration of WISE photospheric colors and removal of non-trivial false-positive sources are responsible for the high confidence (>99.5%) of detections, while our corrections to saturated W1 and W2 photometry have for the first time allowed us to search for new infrared excess sources around bright field stars in WISE. The careful calibration and filtering of the WISE data have allowed us to probe excess fluxes down to roughly 8% of the photospheric emission at 22µm around saturated stars in WISE. We expect that the increased sensitivity of our survey will not only aid in understanding the evolution of debris disks, but will also benefit future studies using WISE.