Observatorio Nacional COAA

Rio de Janeiro, Brazil

Observatorio Nacional COAA

Rio de Janeiro, Brazil
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Carvano J.M.,Observatorio Nacional COAA | Lazzaro D.,Observatorio Nacional COAA
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

Here we present visible and mid-infrared observations of the asteroid (298) Baptistina, obtained with the Gemini South telescope, the 2.2-m European Southern Observatory (ESO) telescope in La Silla and the 1.5-m telescope at the Observatório do Pico dos Dias (OPD). From photometry at the R band and observations with a solar phase angle separation of 11° we have determined HR = 10.92+0.13-0.11 and GR = 0.25+0.13-0.11. From VRI photometry we determined V -R = 0.38 ± 0.03 and R - I = 0.39 ± 0.02. Finally, from thermal photometry in the N band, and using the derived values of H and G, we obtained pv = 0.347+0.1090.076 -, η = 0.969+0.221-0.210 and D = 12.4 km, for the geometric albedo, beaming parameter and diameter, respectively. If one assumes that Baptistina is indeed a member of the family it names, these results rule out the recently suggested link between the dynamical family associated with this asteroid and the cretaceous/tertiary (K/T) event since (1) this albedo is incompatible with the mineralogy of the impactor and (2) the age of the family derived through Yarkovisky spreading would be too young to be related to that event. © 2010 The Authors. Journal compilation © 2010 RAS.

Reddy V.,University of North Dakota | Carvano J.M.,Observatorio Nacional COAA | Lazzaro D.,Observatorio Nacional COAA | Michtchenko T.A.,University of Sao Paulo | And 7 more authors.
Icarus | Year: 2011

Bottke et al. [Bottke, W.F., Vokrouhlicky, D., Nesvorný, D., 2007. Nature 449, 48-53] linked the catastrophic formation of Baptistina Asteroid Family (BAF) to the K/T impact event. This linkage was based on dynamical and compositional evidence, which suggested the impactor had a composition similar to CM2 carbonaceous chondrites. However, our recent study [Reddy, V., Emery, J.P., Gaffey, M.J., Bottke, W.F., Cramer, A., Kelley, M.S., 2009. Meteorit. Planet. Sci. 44, 1917-1927] suggests that the composition of (298) Baptistina is similar to LL-type ordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any possibility of it being related to the source of the K/T impactor, if the impactor was of CM-type composition. Mineralogical study of asteroids in the vicinity of BAF has revealed a plethora of compositional types suggesting a complex formation and evolution environment. A detailed compositional analysis of 16 asteroids suggests several distinct surface assemblages including ordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII subtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a carbonaceous chondrite. Based on our mineralogical analysis we conclude that (298) Baptistina is similar to ordinary chondrites (LL-type) based on olivine and pyroxene mineralogy and moderate albedo. S-type and V-type in and around the vicinity of BAF we characterized show mineralogical affinity to (8) Flora and (4) Vesta and could be part of their families. Smaller BAF asteroids with lower SNR spectra showing only a 'single' band are compositionally similar to (298) Baptistina and L/LL chondrites. It is unclear at this point why the silicate absorption bands in spectra of asteroids with formal family definition seem suppressed relative to background population, despite having similar mineralogy. © 2011 Elsevier Inc.

Carvano J.M.,Observatorio Nacional COAA | Hasselmann P.H.,Observatorio Nacional COAA | Hasselmann P.H.,Federal University of Rio de Janeiro | Lazzaro D.,Observatorio Nacional COAA | Mothe-Diniz T.,Federal University of Rio de Janeiro
Astronomy and Astrophysics | Year: 2010

Aims: The present paper aims to derive a new classification scheme for SDSS MOC asteroid colors that is compatible with previous taxonomies based on spectroscopic data. The distribution of these can give important clues to the formation and evolution of this region of the Solar System, as well as to locate candidates with mineralogically interesting spectra for detailed observations. Methods: Themethodology is based on the large database SDSSMOC4. Templates of the main taxonomic classes are derived and then used to classify the asteroid observations in the SDSS MOC4. The derived taxonomic scheme is compatible with the Bus taxonomy and is suitable to the peculiarities of the SDSS observations, in particular, the low spectral resolution. Results: Density maps of the seven classes defined by the method reproduce classical results for the background which is mainly dominated by the S p class in the inner belt and by the Xp and the Cp classes beyond 2.8 AU. It also shows new structures, such as the fact that the Xp and Cp seem evenly distributed in the inner belt while in the outer belt the S p class increase in density only at the location of asteroid families. Although their overall distribution is similar, the Xp class seems less frequently associated with large families than do the Cp class asteroids. Although only clustering around the Vesta family, the Vp class asteroidsnappear scattered all around the main belt. Besides the lack satisfactory explanations of most of the highlighted features, they may provide strong constraints on the models of the formation and evolution of the Solar System. © 2010 ESO.

Hasselmann P.H.,Observatorio Nacional COAA | Hasselmann P.H.,University Paris Diderot | Barucci M.A.,University Paris Diderot | Fornasier S.,University Paris Diderot | And 4 more authors.
Icarus | Year: 2016

(21) Lutetia has been visited by Rosetta mission on July 2010 and observed with a phase angle ranging from 0.15° to 156.8°. The Baetica region, located at the north pole has been extensively observed by OSIRIS cameras system. Baetica encompass a region called North Pole Crater Cluster (NPCC), shows a cluster of superposed craters which presents signs of variegation at the small phase angle images. For studying the location, we used 187 images distributed throughout 14 filter recorded by the NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) of the OSIRIS system on-board Rosetta taken during the fly-by. Then, we photometrically modeled the region using Minnaert disk-function and Akimov phase function to obtain a resolved spectral slope map at phase angles of 5° and 20°. We observed a dichotomy between Gallicum and Danuvius-Sarnus Labes in the NPCC, but no significant phase reddening (-0.04±0.045%μm-1deg-1). In the next step, we applied the Hapke (Hapke, B. [2008]. Icarus 195, 918-926; Hapke, B. [2012]. Theory of Reflectance and Emittance Spectroscopy, second ed. Cambridge University Press) model for the NAC F82+F22 (649.2nm), WAC F13 (375nm) and WAC F17 (631.6nm) and we obtained normal albedo maps and Hapke parameter maps for NAC F82+F22. On Baetica, at 649.2nm, the geometric albedo is 0.205±0.005, the average single-scattering albedo is 0.181±0.005, the average asymmetric factor is -0.342±0.003, the average shadow-hiding opposition effect amplitude and width are 0.824±0.002 and 0.040±0.0007, the average roughness slope is 11.45°±3° and the average porosity is 0.85±0.002. We are unable to confirm the presence of coherent-backscattering mechanism. In the NPCC, the normal albedo variegation among the craters walls reach 8% brighter for Gallicum Labes and 2% fainter for Danuvius Labes. The Hapke parameter maps also show a dichotomy at the opposition effect coefficients, single-scattering albedo and asymmetric factor, that may be attributed to the maturation degree of the regolith or to compositonal variation. In addition, we compared the Hapke (Hapke, B. [2008]. Icarus 195, 918-926; Hapke, B. [2012]. Theory of Reflectance and Emittance Spectroscopy, second ed. Cambridge University Press) and Hapke (Hapke, B. [1993]. Theory of Reflectance and Emittance Spectroscopy) parameters with laboratory samples and other small Solar System bodies visited by space missions. © 2015 Elsevier Inc.

Hasselmann P.H.,Observatorio Nacional COAA | Hasselmann P.H.,University Paris Diderot | Fulchignoni M.,University Paris Diderot | Carvano J.M.,Observatorio Nacional COAA | And 2 more authors.
Astronomy and Astrophysics | Year: 2015

Context. The 4th release of the SDSS Moving Object Catalog (SDSSMOC) is presently the largest photometric dataset of asteroids. Up to this point, the release of large asteroid datasets has always been followed by a redefinition of asteroid taxonomy. In the years that followed the release of the first SDSSMOC, several classification schemes using its data were proposed, all using the taxonomic classes from previous taxonomies. However, no successful attempt has been made to derive a new taxonomic system directly from the SDSS dataset. Aims. The scope of the work is to propose a different interpretation scheme for gauging u′g′r′i′z′ asteroid observations based on the continuity of spectral features. The scheme is integrated into previous taxonomic labeling, but is not dependent on them. Methods. We analyzed the behavior of asteroid sampling through principal components analysis to understand the role of uncertainties in the SDSSMOC. We identified that asteroids in this space follow two separate linear trends using reflectances in the visible, which is characteristic of their spectrophotometric features. Results. Introducing taxonomic classes, we are able to interpret both trends as representative of featured and featureless spectra. The evolution within the trend is connected mainly to the band depth for featured asteroids and to the spectral slope for featureless ones. We defined a different taxonomic system that allowed us to only classify asteroids by two labels. Conclusions. We have classified 69% of all SDSSMOC sample, which is a robustness higher than reached by previous SDSS classifications. Furthermore, as an example, we present the behavior of asteroid (5129) Groom, whose taxonomic labeling changes according to one of the trends owing to phase reddening. Now, such behavior can be characterized by the variation of one single parameter, its position in the trend. © 2015 ESO.

Brucato J.R.,National institute for astrophysics | Migliorini A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Barucci M.A.,University of Paris Descartes | Carvano J.M.,Observatorio Nacional COAA | And 2 more authors.
Astronomy and Astrophysics | Year: 2010

Context. Laboratory experiments provide a great support to astronomical studies in that they are the most suited technique to reproduce, model and interpret the observational data. Aims. We investigate the spectroscopic properties of particulate and flat slab of tholin samples in a wide MIR and FIR spectral range at cryogenic temperature to contribute to the interpretation of the observation of Saturn satellite Phoebe obtained with the Cassini CIRS instrument. Methods. Reflectance spectra of Titan tholin were obtained in the 7000-10 cm-1 spectral region by a Fourier transform spectrometer operating in vacuum. Several optical setups were used to cover this wide spectral range. Specular and diffuse reflectance spectra were obtained. A cryostat was interfaced to the spectrometer for reflectance measurements at low temperatures. It was cooled by a continuum flux of cryogenic fluid from about 300 to 72 K. Results. It is shown that powder and slab tholin have a different reflectance that depends on geometrical factors and wavelength ranges. The emissivity of Phoebe is reproduced by flat slab tholin covered by a thin layer of water ice. Conclusions. A considerable amount of compact smooth millimeter-size carbonaceous compounds are present on the Phoebe satellite covered with water ice and tholin regolith. This confirms a surface highly processed by small object impacts and a peculiar nature of Phoebe with respect to other Saturn satellites. It could be a primitive Kuiper belt object captured by Saturn that contains an high amount of HCN-like polymers active in prebiotic chemistry. © 2010 ESO.

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