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Narrowing Down the Physical Characteristics of Optical Fast Rotating NEOs from Spectrophotometry

Presentation #306.09 in the session “Asteroids, the Moon, and Meteorites”. Cross-listed as presentation #401.03.

Published onOct 03, 2021
Narrowing Down the Physical Characteristics of Optical Fast Rotating NEOs from Spectrophotometry

Rapidly rotating Near-Earth Objects (NEO) tend to be small, and therefore faint (above V magnitude 19). Using spectroscopy to study their physical characteristics becomes a challenge particularly while using a 2-m class telescope where most spectrometers have a limiting magnitude of 16. Thus, the best method continues to be filter-spectrophotometry (e.g., B, V: Chapman et al. (1975); Johnson-Cousins B, V, R: Bowell et al. (1978); ECAS: Tholen (1984)).

We observed 20 NEOs from 2018 to 2020 using broadband filters (Johnson-Cousins) whose bandwidths allow us to collect sufficient signal in a reasonable time (under 120s per image) to physically characterize NEOs. The first step in our effort to determine asteroid taxonomy is to plot their colors (B-V versus V-R, and V-I versus V-R) which gives a quick distinction between the 4 main types: C, S, X, and D (Zellner et al. (1985); Yoshida et al. (2004); Dandy et al. (2007); Kikwaya et al. (2018, 2019)). To narrow down the search to even more specific asteroid subtypes (C, Cg, Cgh, S, Sq, …), a second step is needed which consists of computing their relative reflectance. This can be compared with the observed asteroid spectral curves (Bus and Binzel (2002a); Bus and Binzel (2002b); Binzel et al. (2018)) using either a standard deviation or chi-squared test (Popescu, Birlan, and Nedelcu (2012)). The third step investigates any match between the asteroid relative reflectance with laboratory meteorite spectra from the Brown RELAB data. As we only concentrate on the optical part of the spectrum, some asteroids fit both carbonaceous chondrite and ordinary chondrite meteorites. The fourth step of our study determines the escape mechanics of each NEO (Granvik et al. (2016)). This provides us with the information needed to distinguish between C-type and S-type asteroids, and from ordinary chondrite meteorites by assuming that LL arrive from the nu6 resonance, while H preferably originate from 3:1 main belt resonance, and L from main belt outer region (Binzel et al. (2018)).

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