^1,2S. Fornasier, ^1,3I.N. Belskaya, ¹D. Perna
¹LESIA, Observatoire de Paris, CNRS, UPMC Univ Paris 06, Univ. Paris Diderot, 5 Place J. Janssen, 92195 Meudon Pricipal Cedex, France
²Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris Cedex 13
³Astronomical Observatory of Kharkiv National University, 35 Sumska str., 61022 Kharkiv, Ukraine Submitted to Icarus: September 2014

In this paper we present the results on the polarimetric and spectroscopic observations of the Potentially Hazardous Asteroid (214869) 2007 PA8 obtained during its favorable apparition in October-November 2012, when it approached the Earth at the minimal distance of 0.043 AU. Polarimetry was carried out at the NOT in the B, V, R, and I bands covering both low (12-23°) and large phase angles (88-99°). Spectroscopy in the visible and near infrared range was obtained at the TNG telescope.

The spectrum of 2007 PA8 shows silicates absorption features and a behavior consistent with a Q-type classification. The olivine and pyroxene BI band is centered at 0.9578±0.0042 μm, with a band depth of 16.5%, the BII band is centered at 1.95±0.01 μm, and it has a band depth of about 3.9%. The 2007 PA8 spectral parameters are consistent with those of L chondrites. Also the spectral comparison with meteorites gives the L-type chondrites, and L6 in particular, as best match.

The NEA (214869) 2007 PA8 is the forth moderate albedo asteroid and the first Q-type asteroid for which the value of the polarization maximum is determined. The inversion angle of the polarization curve in the V filter is 19.0±1.1°, the corresponding slope parameter (h ) is of 0.078±0.010%/°, the maximum value of polarization is 5.99±0.16%, and the extreme value of negative polarization is estimated to be lower than -0.52%. Using the polarimetric slope we derive a geometric albedo of 0.29±0.08 in the V band, that gives an estimated diameter of 1.4±0.2 km, assuming an absolute HvHv magnitude of 16.2 mag. We find a strong dependence of the polarization in the B, V, R, and I bands with wavelength, and the polarimetric albedo in the four bands is strongly correlated with the asteroid’s spectrum. The 2007 PA8 polarimetric properties resemble those of other 2 NEAs, 1566 Icarus and 25143 Itokawa, which are both S(IV)/Q type.

Our spectral and polarimetric analysis indicate that 2007 PA8 has a young and fresh surface almost unweathered, similar to L-type chondrites. These results, together with dynamical simulations made by Nedelcu et al., 2014 and Nesvorny et al., 2009, indicate that 2007 PA8 may be a member of the Gefion family recently ejected from the 5:2 resonance and a potential source of L chondrites.

Reference
Fornasier S, Belskaya IN, Perna D (2014) The potentially hazardous asteroid (214869) 2007 PA8: an unweathered L chondrite analogue surface. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.12.015]

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