Uninterrupted optical light curves of main-belt asteroids from the K2 mission

Abstract

Context. Because the second reaction wheel failed, a new mission was conceived for the otherwise healthy Kepler space telescope. In the course of the K2 mission, the telescope is staring at the plane of the Ecliptic. Thousands of solar system bodies therefore cross the K2 fields and usually cause additional noise in the highly accurate photometric data. Aims. We here follow the principle that some person's noise is another person's signal and investigate the possibility of deriving continuous asteroid light curves. This is the first such endeavor. In general, we are interested in the photometric precision that the K2 mission can deliver on moving solar system bodies. In particular, we investigate space photometric optical light curves of main-belt asteroids. Methods. We studied the K2 superstamps that cover the fields of M35, and Neptune together with Nereid, which were observed in the long-cadence mode (29.4 min sampling). Asteroid light curves were generated by applying elongated apertures. We used the Lomb-Scargle method to determine periodicities that are due to rotation. Results. We derived K2 light curves of 924 main-belt asteroids in the M35 field and 96 in the path of Neptune and Nereid. The light curves are quasi-continuous and several days long. K2 observations are sensitive to longer rotational periods than typical ground-based surveys. Rotational periods are derived for 26 main-belt asteroids for the first time. The asteroid sample is dominated by faint objects (>20 mag). Owing to the faintness of the asteroids and the high density of stars in the M35 field, only 4.0% of the asteroids with at least 12 data points show clear periodicities or trends that signal a long rotational period, as opposed to 15.9% in the less crowded Neptune field. We found that the duty cycle of the observations had to reach ∼60% to successfully recover rotational periods.

The heart of the swarm: K2 photometry and rotational characteristics of 56 Jovian Trojan asteroids

“…In our parallel paper about Main Belt asteroid detections we show that the period determination is usually solid if the coverage exceeds five days and the duty cycle is above 60% (Szabó et al 2016). Since the conditions are well fulfilled for K2 Trojan asteroids, we could derive reliable solutions for most asteroids.…”

“…4. Tabulated data and the light curves of individual Trojans are shown in Appendix A similar study about Main Belt asteroids with K2 will be published in a related paper (Szabó et al 2016). …”

Rotational Properties of Hilda Asteroids Observed by the K2 Mission

“…Since there are few Hildas with identified R and LR taxonomy in our sample, the direct comparison of the distributions are inconclusive. Instead, we compared the R and LR subset of Hildas to the Trojan and Main Belt samples in our previous K2 publications (Szabó et al 2017(Szabó et al , 2016.…”

Thermal properties of slowly rotating asteroids: results from a targeted survey

“…In the last apparition, Hekate was observed for our project by the Kepler Space Telescope, resulting in two continuous, fourday-long lightcurves of great quality. The K2 data have been reduced with the fitsh package, using the same methods that were already applied to targeted observations of Trojan asteroids and chance observations of main-belt asteroids (MBAs) in the mission (Pál 2012;Szabó et al 2016Szabó et al , 2017Molnár et al 2018).…”