Objectives
Specific Programs
1- Physical properties of cometary nuclei:
This works consists primarily in the determination of the size of a significant number of cometary nuclei from the Jupiter family comets, in order to study their distribution, as well the determination of the rotational properties of some cometary nuclei, mainly JF comets, and the study of their possible variations (in particular of the rotational period). The size determination of the cometary nuclei is performed by means of CCD photometry of comets at large heliocentric distances, where they are presumed to have no cometary activity. After assuming a value for their albedo, their effective radii are estimated. This photometry is done using small and medium class telescopes (including VLT). It is worth remarking that the group is involved in a wide scope program with SPITZER space telescope, in order to precisely determine the size and the albedo of a hundred comets.
The study of the rotational properties, which is performed by means of CCD photometric series, provides valuable information about the internal structure of the nuclei (inertia moment distribution, density and material quality).
2- Surface properties of TNOs, Centaurs and cometary nuclei:
The study of the surface properties of these objects (mineralogical composition) is of great importance to determine their original composition, as well as the possible differences in the different regions where they originated. Besides, it is important to understand the diverse processes that affect and modify the surface of the icy bodies of the Solar System, and to relate them with the irradiation and density conditions of the objects in the trans-neptunian belt. This study is done basically by means of multi-band photometry or visible and infrared spectroscopy. During the last years the group has been undertaken a spectroscopic program with big results in the near-infrared, using primarily the TNG, and that has been complemented with spectroscopy in the visible range using the TNG, the WHT and the NOT. The infrared spectroscopy is particularly important, as it allows the detection of surface ices, like water and methane ice, that produce deep absorption features in H and K bands. This program makes use of the unique properties of the TNG's infrared camera-spectrograph, NICS, that taking into account its low resolution and high efficiency, provides the user with spectra of faint objects with a S/N similar to that obtained with Keck telescope using comparable exposure times. We have obtained the first infrared spectra of cometary nuclei (28P/Neujmin 1 and 124P/Mrkos), spectra of several TNOs and Centaurs, and even for the case of two Centaurs, we have studied in detail possible spatial variations of their surface properties. It has to be remarked here the recent discovery that the surface of one of the biggest known TNOs, 2005 FY9, is very similar to the surface of Pluto, with an abundant presence of methane ice. This study must continue in order to obtain results for a significant number of objects, that will allow us to work with models of the generation of irradiation mantles and collisional effects as the one of Gil-Hutton. This program was extended in 2008 to study type-D primitive asteroids with a possible trans-neptunian origin. We have also extended the wavelength range to middle and thermal infrared.
3- Surface and rotational properties of NEOs and asteroid-comet transitional objects:
The study of the rotational properties of NEOs and transitional objects started on 2002, and is based on the determination of the light-curve and colours of these objects, using CCD series photometry, that establishes the rotational period of a significant number of objects in order to study the rotational properties of these populations.
The study of the surface properties is done based on spectroscopic observations in the visible and near-infrared, using mainly the NOT, WHT and TNG telescopes, with the aim of doing a more precise determination of the type and mineralogical properties of a significant group of objects in a similar way as it is done for the TNOs. We created a spectroscopic database with observations in the visible and near-infrared of more than 100 objects, primarily NEAs, but including also main belt objects, Mars-crossers (MCs) and asteroids in cometary orbits (ACOs). The mineralogical studies are performed using surface scattering models, and the tools specifically designed for the compositional analysis of the asteroids: the classical method (Gaffey et al. 1993) and the Modified Gaussian Model (Sunshine et al. 1990).
4- Dust and gas properties in cometary comae:
This program is intended to obtain the dust and gas properties of cometary comae by means of CCD images with broadband and narrow filters specifically designed for this work, near-infrared images and infrared CCD spectroscopy of the coma. We study the continuum generated by the sunlight scattering by the dust, as well as the emission bands from the cometary molecules (CN, C2, C3). We also study the abundances and the formation mechanisms of these molecules, and the dust production rates, as well as characteristics like their colour and size. All in all provides important information about the composition of the comets, and the physical-chemical processes that take place in the cometary coma. We are using an extensive database of observations obtained primarily with IAC-80 and TCS telescopes between 1996 and 2000, during the Ph.D. Thesis of J. Licandro, infrared observations done with the TNG, observations done with the interference filters of the JKT en 2002-2003, and observations done at La Silla (imaging and spectroscopy in the visible and near-infrared). Finally, we have to our disposal a database obtained during the Deep-Impact experiment in 2005. We apply dust models (see Moreno et al. 2003) and production and molecular specimens life models like the one from Haser or Festou, in collaboration with L. Lara and F. Moreno from IAA, and G. P. Tozzi from Oss. A.