The majority of basaltic objects in the main belt are dynamically connected to Vesta, the largest differentiated asteroid known. Others, due to their current orbital parameters, cannot be easily dynamically linked to Vesta. This is particularly true for all the basaltic asteroids located beyond 2.5 au, where lies the 3:1 mean motion resonance with Jupiter.In order to investigate the presence of other V-type asteroids in the middle and outer main belt (MOVs) we started an observational campaign to spectroscopically characterize in the visible range MOV candidates. We observed 18 basaltic candidates from TNG and ESO -NTT between 2015 and 2016. We derived spectral parameters using the same approach adopted in our recent statistical analysis and we compared our data with orbital parameters to look for possible clusters of MOVs in the main belt, symptomatic for a new basaltic family.Our analysis seemed to point out that MOVs show different spectral parameters respect to other basaltic bodies in the main belt, which could account for a diverse mineralogy than Vesta; moreover, some of them belong to the Eos family, suggesting the possibility of another basaltic progenitor.This could have strong repercussions on the temperature gradient present in
The main objective of this work is to compositionally analyse the visible to near-infrared spectra of a total of six V-type candidates identified using the MOVIS (Y-J) versus (J-Ks) colour–colour plot and located outside the Vesta collisional family. We obtained visible and near-infrared spectra of these asteroids using the 2.54m Isaac Newton Telescope, the 2.5m Nordic Optical Telescope, and the 3.58m Telescopio Nazionale Galileo, all located at the El Roque de Los Muchachos Observatory (La Palma, Spain), as well as the 3.0m NASA Infrared Telescope Facility, located at the Mauna Kea Observatory in Hawaii. We computed several diagnostic spectral parameters (slopes, band centres, band depths, band area ratio, or BAR) and compared them to the ones known for HED meteorites and (4) Vesta. The taxonomic classification confirmed five out of the six candidates as V-types, leading to an identification success rate about 83 per cent. In general, the spectral parameters obtained for the five V-types are in good agreement with those of HED meteorites and (4) Vesta. The exception is asteroid (2452) Lyot, a V-type in the outer belt, located very close to (1459) Magnya, but showing distinct [Wo] and [Fs] molar contents both from Magnya and Vesta, pointing toward a diogenitic compostion. We also studied the dependency of the BAR parameter on the way it is computed (removing or not the continuum), the spectral slope, and the last point used to delimit the right wing of the absorption band at 2 μm.
Context. Recent results for asteroid rotation periods from the TESS mission showed how strongly previous studies have underestimated the number of slow rotators, revealing the importance of studying those targets. For most slowly rotating asteroids (those with P > 12 h), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. Also, it is still unclear whether signatures of different surface material properties can be seen in thermal inertia determined from mid-infrared thermal flux fitting. Aims. We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. Our goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Methods. Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler and TESS spacecrafts. In addition to data in the visible range, we also use thermal data from infrared space observatories (mainly IRAS, Akari and WISE) in a combined optimisation process using the Convex Inversion Thermophysical Model. This novel method has so far been applied to only a few targets, and therefore in this work we further validate the method itself. Results. We present the models of 16 slow rotators, including two updated models. All provide good fits to both thermal and visible data.The obtained sizes are on average accurate at the 5% precision level, with diameters found to be in the range from 25 to 145 km. The rotation periods of our targets range from 11 to 59 h, and the thermal inertia covers a wide range of values, from 2 to <400 J m−2 s−1∕2 K−1, not showing any correlation with the period. Conclusions. With this work we increase the sample of slow rotators with reliable spin and shape models and known thermal inertia by 40%. The thermal inertia values of our sample do not display a previously suggested increasing trend with rotation period, which mightbe due to their small skin depth.
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