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Spectroscopic characterization of a primordial S-type family in the inner main belt

Presentation #503.07 in the session Asteroids: Main Belt (Oral Presentation)

Published onOct 23, 2023
Spectroscopic characterization of a primordial S-type family in the inner main belt

A primordial family was discovered recently in the inner main belt. Its age was estimated to be 4.4 ± 1.7 Gyr ago, during the early stages of the Solar System, asteroids started their formation. From a list of 265 asteroids potentially members of the family, we carried out spectroscopic observations, in visible and NIR range, that includes ground-based observations, data from literature and the use of the recent release of Gaia (DR3). In total, we obtained spectra of 263 asteroids out of 265.

We performed taxonomical classification, following the Bus-DeMeo taxonomy, and we computed spectral parameters such as the spectral slope and the center and depth of absorption bands when resent in the spectra. To do so, we used the M4AST online tool, and we gathered information about albedo and size of the objects with the Minor Planet Physical Properties Catalog (MP3C).

From the taxonomical distribution of the potential members, we established a method to identify interlopers, specially among the S- and X-complex, and V-types population. We identified that 68 asteroids are interlopers, reducing the list of PSTF members to 193 objects.

We found that 70% of members belong to the S-complex. Spectral features studies reveal that these S-type members show a variety of silicate composition, ranging from S I to VII in the Gaffey classification scheme. Moreover, the biggest members of that family is the asteroid (30) Urania, with a diameter of around 91 km.

In addition to the S-complex, we found that 15% of these members belong to the L-type and 9% to the V-type. In total, the mean albedo of that family is estimated to be 22.5 ± 2.7%. With the comparison with another S-complex family of the inner main belt, Flora, we found a taxonomical distribution similar to the one of the PSTF.

Through the size distribution of the PSTF, we estimated the size of its parent body to be between 140 and 230 km. This size range is compatible with a progenitor of H or L chondrites.

This family could be the source of some S-complex NEOs, such as asteroid (98943) 2001 CC21, the fly-by target of the extended Hayabusa2 mission.

Acknowledgements: We acknowledge support from the ANR-ORIGINS (ANR-18-CE31-13-0014). This work made use of observations collected at the Copernico telescope (Asiago, Italy) of the Istituto Nazionale di Astrofisica (INAF), at the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma, Spain, and at the Lowell Discovery Telescope at Lowell Observatory. We acknowledge financial support from ASI contract No. 2022-12-HH.0. This work has made use of data from the European Space Agency (ESA) mission Gaia.

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