Johanna Torppa

Shapes and rotational properties of thirty asteroids from photometric data

We have analyzed photometric lightcurves of 30 asteroids, and present here the obtained shapes, rotational periods and pole directions. We also present new photometric observations of five asteroids. The shape models indicate the existence of many features of varying degrees of irregularity. Even large main-belt asteroids display such features, so the resulting poles and periods are more consistent than those obtained by simple ellipsoid-like models. In some cases the new rotational parameters are rather different from those obtained previously, and in a few cases there were no proper previous estimates at all.

Binary structures among large asteroids

The imaging of well-observed large asteroids by lightcurve inversion has revealed objects, such as 44 Nysa and 41 Daphne, that are distinctly asymmetric and globally very different from equilibrium-like figures, indicating contact-binary structures. The shape of the Trojan asteroid 624 Hektor is very probably globally bifurcated. Together with the known large binary asteroids 216 Kleopatra, 90 Antiope, and 617 Patroclus, these findings indicate that a nonvanishing portion of large asteroids have binary structures.

Three-dimensional Stochastic Shape Modelling for Potato Tubers

Tuber shape is a genetically determined, important varietal characteristic that is also influenced by environmental factors. In this study, the overall dimensions of tubers of two potato cultivars (Van Gogh and Yukon Gold) were determined using a triaxial ellipsoid model that was found to encompass the main varietal differences. The more detailed surface features were captured using a spherical-harmonics series representation for the residual undulation. The method was then applied to four additional cultivars (Bellona, Lady Rosetta, Pito, and Sabina). Modelling the undulation of tuber surface in addition to the overall dimensions indicated that cultivars differed in the global shape and, in specific cases, also in the surface undulation of tubers. The new, improved method for modelling tuber shapes can thus capture and distinguish the overall three-dimensional shape and irregularities caused by growth conditions and other factors. It is envisaged to be useful for quantitative genetics approaches aiming to resolve the relative impact of different genes on tuber shape, as well as for various machine vision and other applications.

Reflectance of various snow types: measurements, modeling, and potential for snow melt monitoring

Seasonal snow covers large parts of the northern hemisphere annually. It can change the albedo of the surfaces from dark to bright overnight (and back), causing significant climate feedback (Manninnen and Stenberg, 2008; Flanner and Zender, 2006; Pirazzini, 2008; Nolin and Frei, 2001; Roesch et al., 2001). It forms large energy reservoirs which can be exploited by hydro energy power plants, and is the source of big floods when melting. It can significantly impact traffic and construction safety. It changes living and environmental conditions radically, and has major recreational value.

Spins, shapes, and orbits for near-Earth objects by Nordic NEON

The Nordic Near-Earth-Object Network (NEON) observing program accrues knowledge about the physical and dynamical properties of near-Earth objects (NEOs) using state-ofthe-art inverse methods. Photometric and astrometric observations are being carried out at the Nordic Optical Telescope. Here, the NEON observations from June 2004 - September 2006 are reviewed. Statistical orbital inversion is illustrated by the application of the so-called Volume-of-Variation method to NEON observations. Spins and shapes are characterized using shape models that allow analytical computation of disk-integrated brightnesses in arbitrary illumination and observation geometries for Lommel-Seeliger and Lambert scattering laws. The analytical treatment allows error analyses for the spins and shapes using large numbers of discrete sample solutions to the statistical inverse problem. Currently, statistical spin and shape solutions have been derived for 2002 FF12, 2003 MS2, 2003 RX7, 2004 HW as well as for (1685) Toro and (1981) Midas. For (1862) Apollo, an unambiguous spin and shape solution has been obtained using the convex inversion method.