Towards a better understanding of Haumea’s family tree

The dwarf planet Haumea is the only object in the trans-Neptunian population known to be the parent body of a collisional family (Brown et al. 2007). The accepted family of objects share extremely low escape velocity (Δv) values relative to Haumea, and very strong water ice absorption bands together with a neutral slope in the visible, like Haumea itself (Brown et al., 2007; Schaller & Brown, 2008; Pinilla-Alonso et al. 2007,2008, 2009). Proudfoot and Ragozzine 2022 recently proposed that a proto-Haumea binary merged in a graze-and-merge style impact (Leinhardt et al. 2010) with additional changes in the orbital distribution of objects caused by the tail end of Neptune migration. Models for Haumea’s formation are based on only around 15 known confirmed family members and recent deep surveys in the trans-Neptunian region have detected new objects that could be part of the family. A dynamical study by Proudfoot and Ragozzine 2019 has identified new objects with comparably low Δv values to the accepted family members.

Here we report observations of ten objects that have been classified as candidates of Haumea’s family with HST/WC3. We have obtained the F139M–F153M and F606W–F139M colors in order to characterize the 1.5 μm absorption band of H₂O. We compare the colors of our sample with those found in previous large WFC3 studies of TNOs (e.g., Fraser et al. 2012) in order to test if those absorption are stronger than the expected absorption for the TNO population and we will put these results into the context of the Haumea’s family members. Preliminary results on the relationship between band strength and ejection velocity (Δv), albedo, and visible colors, will be reported in this talk. Some heterogeneity among Haumea family members with confirmed strong water-ice features is already demonstrated. The strengths of their H₂O bands varies by a factor of about 2 (Brown et al. 2007), and their visible albedos vary by a similar factor (Müller et al, 2020). By expanding the sample of Haumea family candidates, we will be able to better study how the members are affected by resonances, improve the accuracy of the size distribution for comparison with different formation models, and better constrain the formation of the Haumea family.