Gaia spectroscopy and application to asteroid families

Context. The third data release by the Gaia mission of the European Space Agency (DR3) contains 60 518 asteroid reflectance spectra over the range 374 nm−1034 nm, representing a huge improvement in spectroscopic data compared to previous surveys available in the literature. Gaia spectra are however affected by systematic deviations in the near infrared when compared to ground-based and template spectra. Aims. I explored possible correlations of the deviations with several parameters of the observed objects, such as the magnitude and the spectral type, in order to assess the internal consistency of Gaia spectra. In addition, I explored different approaches able to mitigate the deviations and classify Gaia spectra into a consistent taxonomy scheme. Finally, I determined whether if asteroid families could be identified using Gaia spectra alone. Methods. In order to determine if the deviations were correlating with the magnitude, I quantified them for groups of asteroids of the same spectral type and different luminosity. To explore the correlation with the taxonomy class, I quantified the deviations for groups of objects of different spectral types. I then developed a procedure able to mitigate the deviations, which I tested with the classy Python tool. Finally, I tested a colorbased taxonomy, which by converting Gaia reflectance spectra in SDSS colors retrieves the spectral type of a specific asteroid given its position on a color-color diagram. With this taxonomy system I classified Gaia observations in specific regions of the Main Belt in order to identify the Tirela and Watsonia families. By converting the observations in diameters, I then fitted the slopes of the v-shapes in order to constrain the ages of the families. Results. I found that the systematic deviations in the near infrared correlate with the spectral type, being maximum for S- complex asteroids, intermediate for the C- complex and almost null for M- and P- types. Classifying Gaia observations with the color-based taxonomy, I identified the Tirela and the Watsonia families, whose memberships resulted to be in very good agreement with the literature. I then constrained the age of the Tirela family, which resulted to be 670 ± 570 Myr for the inner side and 688 ± 377 Myr for the outer side. The same analysis for the Watsonia family turned out to be less precise due to the limited number of objects observed by Gaia and resulted in an age of the order of 1 Gyr. Conclusions. Gaia spectra have been found to be internally coherent, such that asteroids of the same spectral type present similar spectra. In addition, I proved that asteroid families can be recognized using Gaia spectra alone. In particular, the Tirela and the Watsonia families were correctly identified. I then constrained their ages, showing one of the many possibilities in which Gaia spectra can be exploited.