Differentiation signatures in the Flora region

¹ Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
e-mail: dagmara.oszkiewicz@gmail.com
² Institute of Physics, Astrophysics Division, Jan Kochanowski University, Swietokrzyska 15, 25-406 Kielce, Poland
³ Polish Astronomical Amateur Society, Powstancow Wlkp. 34, 63-708 Rozdrażew, Poland

Received: 30 March 2015
Accepted: 15 September 2015

Abstract

Context. Most asteroid families are very homogeneous in physical properties. Some show greater diversity, however. The Flora family is the most intriguing of them. The Flora family is spread widely in the inner main belt, has a rich collisional history, and is one of the most taxonomically diverse regions in the main belt. As a result of its proximity to the asteroid (4) Vesta (the only currently known intact differentiated asteroid) and its family, migration between the two regions is possible. This dynamical path is one of the counter arguments to the hypothesis that there may be traces of a differentiated parent body other than Vesta in the inner main belt region. We here investigate the possibility that some of the V- and A-types (commonly interpreted as basaltoids and dunites – parts of the mantle and crust of differentiated parent bodies) in the Flora dynamical region are not dynamically connected to Vesta.

Aims. The goal of this study is to investigate asteroids in the Flora dynamical region that may be witness to the differentiation of a parent body other than (4) Vesta. In particular, we aim at predicting which asteroids may be fragments of a differentiated body or bodies (taxonomical V-types). We also investigate their possible dynamical linkage to the nearby Vesta family.

Methods. To predict the taxonomic types of asteroids we used the naive Bayes classifier. We studied their dynamical past through numerical integration including gravitational and Yarkovsky forces. Each asteroid was cloned, and average orbital elements were computed at each step. When possible, we used observationally constrained physical parameters for the thermal forces.

Results. Most of the asteroids in the Flora region are predicted to originate from the S-complex (around 47.8%). Tens of asteroids with potentially differential origins are identified in the region, including 164 potential V-types. We investigated the dynamical evolution of selected objects to examine possible linkages of selected asteroids with the nearby Vesta family. In addition to the candidate differentiated objects, we also studied the dynamical evolution of those asteroids from the Flora family for which spectroscopic classification exist. In particular, we used all the physical parameters available for asteroid (809) Lundia to show that the asteroid is unlikely to originate in the Vesta region and that it resided on a stable orbit in the Flora dynamical region for at least 80 My. Its observationally constrained prograde rotation shows that asteroid (809) Lundia is unlikely to be a former Vesta family member.

Conclusions. We found that the V-type candidates are plentiful in the Flora dynamical region. Dynamical investigations of selected objects showed that some of these objects were likely not connected to asteroid (4) Vesta and its family for at least 100 My. This adds another piece of evidence to the hypothesis that there are multiple differentiated parent bodies.