arXiv subjects

Mikko Kaasalainen

Publications and source records attributed to Mikko Kaasalainen.

23 records · Page 2Linked to original sources

arXiv2011

Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes

Asteroid sizes can be directly measured by observing occultations of stars by asteroids. When there are enough observations across the path of the shadow, the asteroid's projected silhouette can be reconstructed. Asteroid shape models derived from photometry by the lightcurve inversion method enable us to predict the orientation of an asteroid for the time of occultation. By scaling the shape model to fit the occultation chords, we can determine the asteroid size with a relative accuracy of typically ~ 10%. We combine shape and spin state models of 44 asteroids (14 of them are new or updated models) with the available occultation data to derive asteroid effective diameters. In many cases, occultations allow us to reject one of two possible pole solutions that were derived from photometry. We show that by combining results obtained from lightcurve inversion with occultation timings, we can obtain unique physical models of asteroids.

astro-ph.EP↗

arXiv2010

Optimal combination of data modes in inverse problems: maximum compatibility estimate

We present an optimal strategy for the relative weighting of different data modes in inverse problems, and derive the maximum compatibility estimate (MCE) that corresponds to the maximum likelihood or maximum a posteriori estimates in the case of a single data mode. MCE is not explicitly dependent on the noise levels, scale factors or numbers of data points of the complementary data modes, and can be determined without the mode weight parameters. As a case study, we consider the problem of reconstructing the shape of a body in $\R^3$ from the boundary curves (profiles) and volumes (brightness values) of its generalized projections.

math.OC↗

arXiv2010

Maximum compatibility estimates and shape reconstruction with boundary curves and volumes of generalized projections

We show that the boundary curves (profiles) in $\R^2$ of the generalized projections of a body in $\R^3$ uniquely determine a large class of shapes, and that sparse profile data, combined with projection volume (brightness) data, can be used to reconstruct the shape and the spin state of a body. We also present an optimal strategy for the relative weighting of the data modes in the inverse problem, and derive the maximum compatibility estimate (MCE) that corresponds to the maximum likelihood or maximum a posteriori estimates in the case of a single data mode. MCE is not explicitly dependent on the noise levels, scale factors or numbers of data points of the complementary data modes, and can be determined without the mode weight parameters. We present a solution method well suitable for adaptive optics images in particular, and discuss various choices of regularization functions.

math.OC↗

arXiv2009

Physical Properties of (2) Pallas

We acquired and analyzed adaptive-optics imaging observations of asteroid (2) Pallas from Keck II and the Very Large Telescope taken during four Pallas oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km (image scales 13-20 km/pix). We improve our determination of the size, shape, and pole by a novel method that combines our AO data with 51 visual light-curves spanning 34 years of observations as well as occultation data. The shape model of Pallas derived here reproduces well both the projected shape of Pallas on the sky and light-curve behavior at all the epochs considered. We resolved the pole ambiguity and found the spin-vector coordinates to be within 5 deg. of [long, lat] = [30 deg., -16 deg.] in the ECJ2000.0 reference frame, indicating a high obliquity of ~84 deg., leading to high seasonal contrast. The best triaxial-ellipsoid fit returns radii of a=275 km, b= 258 km, and c= 238 km. From the mass of Pallas determined by gravitational perturbation on other minor bodies [(1.2 +/- 0.3) x 10-10 Solar Masses], we derive a density of 3.4 +/- 0.9 g.cm-3 significantly different from the density of C-type (1) Ceres of 2.2 +/- 0.1 g.cm-3. Considering the spectral similarities of Pallas and Ceres at visible and near-infrared wavelengths, this may point to fundamental differences in the interior composition or structure of these two bodies. We define a planetocentric longitude system for Pallas, following IAU guidelines. We also present the first albedo maps of Pallas covering ~80% of the surface in K-band. These maps reveal features with diameters in the 70-180 km range and an albedo contrast of about 6% wrt the mean surface albedo.

astro-ph.EP↗

arXiv2008

Dynamical tomography of gravitationally bound systems

We study the inverse problem of deducing the dynamical characteristics (such as the potential field) of large systems from kinematic observations. We show that, for a class of steady-state systems, the solution is unique even with fragmentary data, dark matter, or selection (bias) functions. Using spherically symmetric models for simulations, we investigate solution convergence and the roles of data noise and regularization in the inverse problem. We also present a method, analogous to tomography, for comparing the observed data with a model probability distribution such that the latter can be determined.

astro-ph↗