24 hours on Pompeja: time-resolved spectrophotometry of an unusual Main Belt asteroid

Main belt asteroid 203 Pompeja shows evidence of spectral variability in the visible and near-infrared (VNIR). During most epochs, Pompeja’s spectrum resembles a typical X-type asteroid [1, 2]. However, during its 2021 apparition, steeply red sloped spectra were observed in the VNIR, invoking comparisons to the ultra-red VR and RR TNOs and leading to the suggestion that Pompeja may have migrated from the TNO region to the Main Belt [3]. An uneven distribution of ultra-red material across its surface may contribute to Pompeja’s observed spectral variability.

 

In order to assess the extent of ultra-red material across Pompeja’s surface, in October 2024, we observed this asteroid using the Las Cumbres Observatory global telescope network [4], obtaining grizy photometry over nearly its entire 24 hour rotational period. The observing geometry relative to the earth and Sun during this epoch was close to equatorial, providing nearly-complete longitudinal coverage of Pompeja at low and mid-latitudes. We present the results of this observing campaign and discuss their implications for the abundance and distribution of ultra-red material on Pompeja in light of current models of its shape and rotational pole orientation [5]. We derive upper limits on the abundance of ultra-red material at equatorial and mid-latitudes, discuss the implications of our observations on the origin of Pompeja, and evaluate future observational prospects.

 

 

[1] Hasegawa, S., DeMeo, F. E., Marsset, M., et al. 2022 ApJL, 939, L9, doi: 10.3847/2041-8213/ac92e4

[2] Humes, O. A., Thomas, C. A., & McGraw, L. E. 2024, PSJ, 5, 80, doi: 10.3847/PSJ/ad2e99

[3] Hasegawa, S., Marsset, M., DeMeo, F. E., et al. 2021 ApJL, 916, L6, doi: 10.3847/2041-8213/ac0f05

[4] Brown, T. M., Baliber, N. et al. 2013 PASP, 125, 931, 1031-1055, doi: 10.1086/673168

[5] Humes, O. A., Hanuš, J. 2024 PSJ, 5, 271, doi: 10.3847/PSJ/ad8f3a