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Taxonomy of asteroid families among the Jupiter Trojans: comparisonbetween spectroscopic data and the Sloan Digital Sky Survey colors

¹ Observatório Nacional, Rua General José Cristino 77, Rio de Janeiro, 20921-400, Brazil e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
² Complejo Astronómico El Leoncito (CASLEO) and Universidad Nacional de San Juan, Av. España 1512 sur, San Juan, J5402DSP, Argentina

Received: 1 December 2007
Accepted: 22 February 2008

Abstract

Aims.We present a comparative analysis of the spectral slope and color distributions ofJupiter Trojans, with particular attention to asteroid families. We use a sample of data fromthe Moving Object Catalog of the Sloan Digital Sky Survey, together with spectraobtained from several surveys.

Methods.We extracted a first sample of 349 observations, corresponding to 250 Trojan asteroids,from the Sloan Digital Sky Survey, and a second sample of 138 spectra, corresponding to 115 Trojans, from the literature. We computed the spectral slopes in the first sample by means of a least-squares fit to a straight line of the fluxes obtained from the Sloan observations, and in the second sample by means of a fit to the rebinned spectra. In both cases the reflectance fluxes/spectra were renormalized to 1 at 6230 Å.

Results.We found that the distribution of spectral slopes among Trojan asteroidsshows a bimodality. About 2/3 of the objects have reddish slopescompatible with D-type asteroids, while the remaining bodies show lessreddish colors compatible with the P-type and C-type classifications. Themembers of asteroid families also show a bimodal distribution with avery slight predominance of D-type asteroids, but the background isclearly dominated by the D-types. The L4 and L5 swarms show differentdistributions of spectral slopes, and bimodality is only observed inL4. These differences can be attributed to the asteroid families since thebackground asteroids show the same slope distributions in both swarms.The analysis of individual families indicates that the families in L5 are taxonomicallyhomogeneous, but in L4 they show a mixture of taxonomic types.We discuss a few scenarios that might help to interpret these results.