Investigating Taxonomic Diversity within Asteroid Families through ATLAS Dual-band Photometry

Abstract

We present here the c-o colors for identified Flora, Vesta, Nysa-Polana, Themis, and Koronis family members within the historic data set (2015-2018) of the Asteroid Terrestrial-impact Last Alert System (ATLAS). The Themis and Koronis families are known to be relatively pure C-and S-type Bus-DeMeo taxonomic families, respectively, and the extracted color data from the ATLAS broadband c-and o-filters of these two families is used to demonstrate that the ATLAS c-o color is a sufficient parameter to distinguish between the C-and S-type taxonomies. The Vesta and Nysa-Polana families are known to display a mixture of taxonomies possibly due to Vesta's differentiated parent body origin and Nysa-Polana actually consisting of two nested families with differing taxonomies. Our data show that the Flora family also displays a large degree of taxonomic mixing and the data reveal a substantial H-magnitude dependence on color. We propose and exclude several interpretations for the observed taxonomic mix. Additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods.

Asteroid models reconstructed from ATLAS photometry

“…There were 95 asteroids for which the periods were the same within the 3σ interval. Of the remaining 39 asteroids, all of the periods reported by Erasmus et al (2020) were either ±2, ±1, ±0.5, or ±0.25-day aliases of the period we report here or the periods extracted were close to 48 h. Aliasing ambiguity in the extracted (by Lomb-Scargle periodogram) rotation period and incorrectly resolving periods close to 12, 24, or 48 h is a common problem with ATLAS data due to the one-day cadence of the ATLAS observations.…”

“…The most time-consuming part of the modeling is the search for the sidereal rotation period. Although ATLAS data are, for many asteroids, dense enough to apply Fourier-based algorithms in order to find periodicity in the signal (Erasmus et al 2020), our aim was different. Instead of determining the synodic rotation period, we wanted to derive the full spin state, including the sidereal rotation period with the relative precision on the order of 10 −5 , which corresponds to knowing the exact number of rotations in the time interval covered by the observations.…”

“…Erasmus et al (2020) used the same ATLAS data set to determine the colors and rotation periods of members of selected asteroid families. There were only 134 asteroids for which we could compare our values with those in Erasmus et al (2020). We only used the periods determined uniquely on the whole 2-1000 h interval, that is to say the values from Tables A.1 and A.3.…”

“…1. The color coding represents the confidence of the period determination according to Erasmus et al (2020). There were 95 asteroids for which the periods were the same within the 3σ interval.…”

Multifilter photometry of Solar System objects from the SkyMapper Southern Survey

“…A large number of 117,356 SSOs in SkyMapper have only one color: g − r. A detailed classification cannot be achieved, but this color can still be used to split asteroids into mafic-silicaterich and opaque-rich objects. Similarly to the work by (Erasmus et al 2020), we thus classified the asteroids into S-like and C-like objects (hereafter labeled S 1 and C 1 ). The g−r colors of asteroids clearly present a bimodal distribution that is well represented by two normal distributions (Figure 14) corresponding to the C 1 (bluer) and S 1 (redder) classes.…”