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SPECTROSCOPIC AND POLARIMETRIC SURVEY OF L-TYPE ASTEROIDS
Devogele, Maxime; Tanga, P; Cellino, A et al.
2017Asteroids, Comets, Meteors, 2017
 

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Keywords :
Asteroids; Spectroscopy; Polarization
Abstract :
[en] Introduction: Spectroscopic and polarimetric observations are of fundamental importance in order to derive information about the surface properties of asteroids. In 2006, the asteroid (234) Barbara was found to possess a pecular polarimetric response characterized by an abnormaly large value of the inversion angle. Later on, several other similar asteroids were discovered. They were called Barbarian asteroids in reference to (234) Barbara. Spectroscopically, all the Barbarian asteroids belong to the L, Ld and in a few cases K types in the Bus and Binzel visible taxonomy. When a classification extended to near-infrared is considered, all those known to date group into the L class. The most commonly accepted explanation for the polarimetric anomaly is the high abundance of Spinel-bearing, fluffy (type A) CAIs (Calcium-Aluminium rich Inclusion) whose optical properties could reproduce the observed polarimetry. If this hypothesis is confirmed, Barbarian asteroids could contain an anomalous amount of the first minerals condensed after the formation of the Solar system. Based on these motivations, we organized a systematic campaign of spectroscopy and polarimetry of Barbarians/L-type asteroids. Observations: 35 asteroids were observed using spectroscopy or polarimetry, or both. These asteroids include members of Watsonia, Henan and Klumpkea families which are known to be made of Barbarian and/or L type asteroids. The polarimetric data were obtained with the ToPol instrument at the Calern station of the Observatoire de la Côte d’Azur. The spectroscopic data were obtained at the IRTF NASA facility. Data analysis: The phase-polarization curve of the polarimetric data was analysed to derive the inversion angle of the asteroids. The spectroscopic data were analysed using a Hapke spectral mixing model. This method combines end-member spectra in order to fit the asteroid spectrum and derive its composition. The end-members used are the Allende matrix from which CAIs were removed, MgO rich olivine, and fluffy type A CAI. A Hapke space-weathering model was used in order to simulate the space-weathering effect on the spectra of asteroids. Results: The polarimetric data allowed us to discover 3 new Barbarian asteroids and to remove 4 asteroids from the Barbarian candidate list. We found that the inversion angle of Barbarian asteroids ranges from 26° to 30°. High CAI abundances ranging from 5 to 50% were found in L type asteroid spectra. We find for the first time a link between the abundance of CAIs and the polarimetric response. Spaceweathering also appears to play a role in polarimetry, showing an aging effect on the granularity of the surface regolith.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Devogele, Maxime ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Tanga, P
Cellino, A
Rivet, JP
Surdej, Jean  ;  Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Bagnulo, S
Bus, S
Borisov, G
Campins, H
Carry, B
Licandro, J
Mc Lein, W
Pinilla-Alonso, N
Sunshine, J
Vernet, D
More authors (5 more) Less
Language :
English
Title :
SPECTROSCOPIC AND POLARIMETRIC SURVEY OF L-TYPE ASTEROIDS
Alternative titles :
[en] Survey spectroscopique et polarimetrique d'astéroïdes de type L
Publication date :
14 April 2017
Event name :
Asteroids, Comets, Meteors, 2017
Event date :
10 au 14 avril 2017
Available on ORBi :
since 29 May 2017

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