Physical Investigation of the Potentially Hazardous Asteroid (144898) 2004 VD17

In this paper we present the observational campaign carried out at ESO NTT and VLT in April and May 2006 to investigate the nature and the structure of the Near Earth Object (144898) 2004 VD17. In spite of a great quantity of dynamical information, according to which it will have a close approach with the Earth in the next century, the physical properties of this asteroid are largely unknown. We performed visible and near--infrared photometry and spectroscopy, as well as polarimetric observations. Polarimetric and spectroscopic data allowed us to classify 2004 VD17 as an E-type asteroid. A good agreement was also found with the spectrum of the aubrite meteorite Mayo Belwa. On the basis of the polarimetric albedo (p_v=0.45) and of photometric data, we estimated a diameter of about 320 m and a rotational period of about 2 hours. The analysis of the results obtained by our complete survey have shown that (144898) 2004 VD17 is a peculiar NEO, since it is close to the breakup limits for fast rotator asteroids, as defined by Pravec and Harris (2000). These results suggest that a more robust structure must be expected, as a fractured monolith or a rubble pile in a "strength regime" (Holsapple 2002).Comment: 32 pages, 7 figure, paper accepted for publication in Icaru

Low phase angle effects in photometry of trans-neptunian objects: 20000 Varuna and 19308 (1996 TO66)

We present the results of photometric observations of trans-neptunian object 20000 Varuna, which were obtained during 7 nights in November 2004-February 2005. The analysis of new and available photometric observations of Varuna reveals a pronounced opposition surge at phase angles less than 0.1 deg with amplitude of 0.2 mag relatively to the extrapolation of the linear part of magnitude-phase dependence to zero phase angle. The opposition surge of Varuna is markedly different from that of dark asteroids while quite typical for moderate albedo Solar System bodies. We find an indication of variations of the scattering properties over Varuna's surface that could result in an increase of the lightcurve amplitude toward zero phase angle. It is shown that a similar phase effect can be responsible for lightcurve changes found for TNO 19308 (1996 TO66) in 1997-1999.http://www.sciencedirect.com/science/article/B6WGF-4K4PSTX-2/1/447c751a99c7de80e8073e91841b187

Asteroid polarimetric observations using the Torino UBVRI photopolarimeter

Icarus, 179, pp. 304-324 (2005)International audienc

Asteroid observations at low phase angles. I. 50 Virginia, 91 Aegina and 102 Miriam

We present observations of magnitude-phase dependences of three low-albedo asteroids down to phase angles of 0.1 - 0.2 degrees. Data were obtained during 40 nights in 1994-1996 within the joint observational program at ESO and Kharkiv Astronomical Observatories with the aim to reach as low phase angles as possible. All three low-albedo asteroids may display a small nonlinear increase in magnitude-phase dependence at subdegree phase angles. The phase curves of 50 Virginia and 102 Miriam are poorly approximated by the HG function. Rotation periods of the asteroids were also determined: 14.21 +/- 0.010 hours for 50 Virginia, 6.030 +/- 0.001 hours for 91 Aegina and 15.789 +/- hours for 102 Miriam

The strange polarimetric behaviour of Asteroid (234) Barbara

Icarus, 180, pp. 565-567 (2006)International audienc

New Insights on Ices in Centaur and Transneptunian Populations

International audience► All objects classified as BB class objects have icy surfaces. The objects of the IR class, present only among classical and resonant populations, do not contain any body with "sure" water ice determination; ► The possible presence of CHOH have been mainly detected on very red surfaces (objects following the RR class); ► The majority of Centaurs observed multiple times have an heterogeneous composition. This seems to indicate a major characteristics of the Centaur population for which the variation affecting the surface could be due not only to the presence of some "fresh" areas resurfaced by impacts, but also to a temporal/sporadic activity. No Centaur is found with an abundant surface ice content; ► Objects with abundant water ice content tend to have a smaller absolute magnitude which corresponds in general to a larger size; ► The classical objects are abundant both among icy bodies and bodies with no ice content. All dynamically cold objects of the classical population in our sample (3 bodies) have no ice