Visible spectroscopic and photometric survey of Jupiter Trojans: Final results on dynamical families☆

Abstract

We present the results of a visible spectroscopic and photometric survey of Jupiter Trojans belonging to different dynamical families. The survey was carried out at the 3.5m New Technology Telescope (NTT) of the European Southern Observatory (La Silla, Chile) in April 2003, May 2004 and January 2005. We obtained data on 47 objects, 23 belonging to the L5 swarm and 24 to the L4 one. These data together with those already published by Fornasier et al. (2004a) and Dotto et al. (2006), acquired since November 2002, constitute a total sample of visible spectra for 80 objects. The survey allows us to investigate six families (Aneas, Anchises, Misenus, Phereclos, Sarpedon, Panthoos) in the L5 cloud and four L4 families (Eurybates, Menelaus, 1986 WD and 1986 TS6). The sample that we measured is dominated by D-type asteroids, with the exception of the Eurybates family in the L4 swarm, where there is a dominance of C-and P-type asteroids. All the spectra that we obtained are featureless with the exception of some Eurybates members, where a drop-off of the reflectance is detected shortward of 5200Å. Similar features are seen in main belt C-type asteroids and commonly attributed to the intervalence charge transfer transition in oxidized iron. Our sample comprises fainter and smaller Trojans as compared to the literature's data and allows us to investigate the properties of objects with estimated diameter smaller than 40-50 km. The analysis of the spectral slopes and colors versus the estimated diameters shows that the blue and red objects have indistinguishable size distribution, so any relationship between size and spectral slopes has been found. To fully investigate the Trojans population, we include in our analysis 62 spectra of Trojans available in literature, resulting in a total sample of 142 objects. Although the mean spectral behavior of L4 and L5 Trojans is indistinguishable within the uncertainties, we find that the L4 population is more heterogeneous and that it has a higher abundance of bluish objects as compared to the L5 swarm. Finally, we perform a statistical investigation of the Trojans's spectra property distributions as a function of their orbital and physical parameters, and in comparison with other classes of minor bodies in the outer Solar System. Trojans at lower inclination appear significantly bluer than those at higher inclination, but this effect is strongly driven by the Eurybates family. The mean colors of the Trojans are similar to those of short period comets and neutral Centaurs, but their color distributions are different.

Visible spectroscopy of the new ESO large programme on trans-Neptunian objects and Centaurs: final results

“…A comparison between the spectral slope distribution of Jupiter Trojans (Fig. 14 in Fornasier et al 2007) and of Centaurs-TNOs (Fig. 7) shows that the Trojans' distribution is very narrow and distinguishable from that of Centaurs-TNOs.…”

“…Fornasier et al (2007) analysed a sample of 146 Jupiter Trojans (68 L5 and 78 L4) for which visible spectroscopy was available, and calculated an average slope of 9.15 ± 4.19%/10 3 Å for objects populating the L5 swarm and 6.10 ± 4.48%/10 3 Å for the L4 ones. A comparison between the spectral slope distribution of Jupiter Trojans (Fig.…”

On the observational bias of the Trojan swarms

“…Among these objects, there are those that may belong to the same collisional family 3 . However, spectral slopes for these Trojans can differ significantly (Jewitt & Luu 1990;Fornasier et al 2007;Roig et al 2008;Melita et al 2008). There can on the other hand be several causes of these differences that do not affect membership of the same family.…”

Organic materials in planetary and protoplanetary systems: nature or nurture?

“…Several authors (e.g. Cruikshank et al 2001;Emery & Brown 2003;Dotto et al 2006;Fornasier et al 2007;de Luise et al 2010;Emery et al 2011;Yang & Jewitt 2011) have published visible and nearinfrared reflectance spectra of JTs. Despite the expectation that JTs formed with abundant volatiles and organics, as for KBOs, they do not appear to exhibit any of the spectral features of these materials on their surfaces.…”