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Determination of Asteroid Rotation Periods from WISE Data

Presentation #504.07 in the session Seek and Find (Asteroids).

Published onOct 20, 2022
Determination of Asteroid Rotation Periods from WISE Data

WISE observations of ~100,000 asteroids at four infrared bands (W1–4) centered at 3.4, 4.6, 12, and 22 μm have been used primarily to estimate asteroid diameters and albedos [e.g., 1]. The accuracy of the solutions was improved when applying a regularized approach to a curated set of 4420 asteroids [2]. Here, we used this dataset to determine the rotation periods of asteroids with a method specifically designed for sparse photometry [3]. We focused on the lightcurves of 2487 asteroids that have discernible (>0.3 mag) flux variations and at least 12 data points in W4, typically spread over a ~36-hour window. This observational cadence is adequate for most asteroids but prevents the determination of spin periods for fast (<3.2 h) and slow (>18 h) rotators. The spin period solutions for 1622 asteroids satisfied our convergence and quality criteria. Among those, 1051 asteroids do not have a high-quality-code (U≥3-) estimate in the Lightcurve Database (LCDB). The remaining 571 asteroids with reliably known LCDB periods were used to evaluate the accuracy of our solutions. We found that 52% of our period solutions are within 5% of the high-quality-code LCDB estimates. We then used a random forest classifier with 1000 cross-validation trials to identify the most reliable solutions and improve the accuracy rate to ~65%. These results indicate that infrared surveys can provide spin period estimates for a substantial number of previously uncharacterized asteroids.

[1] Mainzer, A., Usui, F., & Trilling, D. E. 2015, in Asteroids IV, ed. P. Michel, F. E. DeMeo, & W. F. Bottke (Univ. of Arizona Press), 89–106.

[2] Myhrvold, N., Pinchuk, P., & Margot, J.-L. 2022, Analysis of Four-band WISE Observations of Asteroids. Planetary Science Journal, 3, 30.

[3] Waszczak, A., Chang, C.-K., Ofek, E. O., et al. 2015, Asteroid Light Curves from the Palomar Transient Factory Survey: Rotation Periods and Phase Functions from Sparse Photometry. Astronomical Journal, 150, 75.

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