Mineralogical investigation of several Q_p asteroids and their relation to the Vesta family^⋆

¹ Observatório Nacional, COAA, rua Gal. José Cristino 77, 20921-400 Rio de Janeiro, Brazil
e-mail: flavialuzia@on.br; lazzaro@on.br; carvano@on.br
² Universidade Federal do Rio de Janeiro/Observatório do Valongo, Lad. Pedro Antônio 43, 20080-090 Rio de Janeiro, Brazil
thais.mothe@astro.ufrj.br

Received: 4 October 2012
Accepted: 23 January 2013

Abstract

Context. To take advantage of the large dataset provided by the SDSS data, recently a new taxonomic scheme was proposed designed to be compatible with previous taxonomies. One interesting feature in this distribution is the large number of Q_p asteroids scattered all around the main belt with a marked concentration in the Vesta region, where the V_p are found most frequently. Since the mineralogy and thermal evolution traditionally related to the classical Q- and V-type taxonomic classes (and by construction the Q_p and V_p), this finding was quite surprising.

Aims. We aim to observationally determine the mineralogy of a sample of Q_p asteroids of and outside the Vesta family to test whether the Q_p of the Vesta family are indeed basaltic, and whether the difference in band depth implied by the SDSS spectra relates to diffences in mineralogy with respect to the V_p. Moreover, we aim to determine whether the Q_p outside Vesta family have an ordinary chondrite (OC) mineralogy and whether their spectra indeed correspond to Q-class asteroids.

Methods. We observed a sample of asteroids classified as Q_p-type in the literature, mainly located in the Vesta family and neighborhood, to confirm their mineralogy. Spectroscopic observations of 11 asteroids were obtained at the SOAR and IRTF telescopes in the visible and near-infrared region. Thermal observations of three objects were also carried out at the Gemini South telescope in order to determine the albedo of the asteroids.

Results. The analysis indicated that all observed asteroids in the Vesta vicinity have a basalt-rich mineralogy, with no clear difference from other Vesta family members in terms of silicate composition. From our study it is not clear why these particular basaltic asteroids have a relatively suppressed band I so that they are classified as Q_p. Two asteroids with an OC-compatible mineralogy were identified in the external part of the main belt, at around 2.8−2.9 AU. This discovery suggests new dynamical routes for the transport of Q-type asteroids to the near-Earth region and of OC meteorites to the Earth.