Astreaks

Small Solar System bodies encompass Near-Earth Objects (NEOs), main-belt asteroids and various other smaller groups of asteroids and comets. NEOs are important, not only from a scientific perspective but also because they pose threat to mankind. Their discovery is critical for potentially mitigating the long-term threats from Potentially Hazardous Asteroids (PHAs) by designing planetary defence missions. Several survey telescopes scan the night sky daily and report these potential NEO candidates to Minor Planet Center (MPC). The current survey telescopes have a sensitivity of V = 21 mag, which implies that these NEOs will be discovered at a distance of less than 1 AU. This results in a very high apparent motion of the order of tens of arc-seconds per minute in discovery data, thus degrading the S/N of faint sources and making the discovery even more challenging. The short observation arcs from the discovery data result in very high uncertainties in preliminary orbit estimation, leading to hundreds of arc-seconds of uncertainties in the sky positions of these objects within half a day after discovery. Moreover, as they depart, they become even fainter. Recovery of such objects requires well-timed follow-up with meter class telescopes with relatively wide fields of view.

The Solar System Objects have a significant apparent motion. As the apparent motion of the target increases, the S/N ratio of the target in the sidereally tracked data degrades due to trailing loss. This problem is more prominent in the discovery apparition since the recovery is heavily dependent on accurate astrometry and photometry of the source. Several image processing techniques have been proposed over the years to recover the target and improvise both, astrometry and photometry of the target. Zhai et al. (2018) introduced the technique "Synthetic Tracking", where multiple one-second exposures were combined to recover both, target and reference stars, thereby mitigating the trailing loss, poor sensitivity of centroiding the streaks, and atmospheric and instrumental errors. Veres et al. (2012) presented an analytical function based on a gaussian point spread function (PSF) and constant apparent motion to describe the trails. This function is then fitted to the trails to obtain astrometry and photometry.

The Solar System Objects have a significant apparent motion. As the apparent motion of the target increases, the S/N ratio of the target in the sidereally tracked data degrades due to trailing loss. This problem is more prominent in the discovery apparition since the recovery is heavily dependent on accurate astrometry and photometry of the source. Several image processing techniques have been proposed over the years to recover the target and improvise both, astrometry and photometry of the target. Zhai et al. (2018) introduced the technique "Synthetic Tracking", where multiple one-second exposures were combined to recover both, target and reference stars, thereby mitigating the trailing loss, poor sensitivity of centroiding the streaks, and atmospheric and instrumental errors. Veres et al. (2012) presented an analytical function based on a gaussian point spread function (PSF) and constant apparent motion to describe the trails. This function is then fitted to the trails to obtain astrometry and photometry.

The prime focus of NEO programs is to discover 90% of the NEO population larger than ~140 m. These accelerated NEO discovery rates are expected to be heralded by the next-generation NEO programs like NEO Surveillance Mission and Vera C. Rubin Observatory’s Legacy Survey of Space and Time. In addition to discovery, adequate follow-up observations are needed to decrease the growth in uncertainties for future apparitions. These programs are expected to increase the demand for follow-up near V = 22 mag. The NEO follow-up community, which steers the venture of NEO confirmations, arc extensions and characterization, will be challenged to complement the self-follow-up strategies of these surveys. With this, we look forward to extensive follow-up and robust astrometry techniques to support the improvement in NEO orbital catalogues. The follow-up of V > 19 mag objects usually requires non-sidereal tracking to go deep into the field. Long exposures for tracking such faint and fast-moving NEOs gives reference stars as streaks, thus making conventional astrometry methods based on Gaussian source detection inefficient. Hence, calculating accurate asteroid positions and magnitudes from non-sidereally tracked images is challenging.

Welllllll..... If you're a regular NEO observer, there's a surprise for you in the answer to the next question! Hope you like it :)