Thermal properties of slowly rotating asteroids: results from a targeted survey (original) (raw)

Properties of slowly rotating asteroids from the Convex Inversion Thermophysical Model

Astronomy & Astrophysics

Context. Recent results for asteroid rotation periods from the TESS mission showed how strongly previous studies have underestimated the number of slow rotators, revealing the importance of studying those targets. For most slowly rotating asteroids (those with P > 12 h), no spin and shape model is available because of observation selection effects. This hampers determination of their thermal parameters and accurate sizes. Also, it is still unclear whether signatures of different surface material properties can be seen in thermal inertia determined from mid-infrared thermal flux fitting. Aims. We continue our campaign in minimising selection effects among main belt asteroids. Our targets are slow rotators with low light-curve amplitudes. Our goal is to provide their scaled spin and shape models together with thermal inertia, albedo, and surface roughness to complete the statistics. Methods. Rich multi-apparition datasets of dense light curves are supplemented with data from Kepler...

Thermal properties of large main-belt asteroids observed byHerschelPACS

Astronomy & Astrophysics, 2020

Non-resolved thermal infrared observations enable studies of thermal and physical properties of asteroids via thermo-physical models provided the shape and rotational properties of the target are well determined. We used calibration-programmeHerschelPACS data (70, 100, 160μm) and state-of-the-art shape models derived from adaptive-optics observations and/or optical light curves to constrain for the first time the thermal inertia of twelve large main-belt asteroids. We also modelled previously well-characterised targets such as (1) Ceres or (4) Vesta as they constitute important benchmarks. Using the scale as a free parameter, most targets required a re-scaling ~5% consistent with what would be expected given the absolute calibration error bars. This constitutes a good cross-validation of the scaled shape models, although some targets required larger re-scaling to reproduce the IR data. We obtained low thermal inertias typical of large main belt asteroids studied before, which contin...

Thermophysical Modeling of Asteroid Surfaces Using Ellipsoid Shape Models

The Astronomical Journal

Thermophysical Models (TPMs), which have proven to be a powerful tool in the interpretation of the infrared emission of asteroid surfaces, typically make use of a priori obtained shape models and spin axes for use as input boundary conditions. We test then employ a TPM approach-under an assumption of an ellipsoidal shape-that exploits the combination of thermal multi-wavelength observations obtained at preand post-opposition. Thermal infrared data, when available, at these observing circumstances are inherently advantageous in constraining thermal inertia and sense of spin, among other physical traits. We show that, despite the lack of a priori knowledge mentioned above, the size, albedo, and thermal inertia of an object are well-constrained with precision comparable to that of previous techniques. Useful estimates of the surface roughness, shape, and spin direction can also be made, to varying degrees of success. Applying the method to WISE observations, we present best-fit size, albedo, thermal inertia, surface roughness, shape elongation and sense of spin direction for 21 asteroids. We explore the thermal inertia's correlation with asteroid diameter, after accounting for its dependence on the heliocentric distance.

A refined “standard” thermal model for asteroids based on observations of 1 Ceres and 2 Pallas

Icarus, 1986

We present ground-based thermal infrared observations of asteroids 1 Ceres and 2 Pallas made over a period of 2 years. By analyzing these data in light of the recently determined occultation diameter of Ceres (933-945 km) and Pallas (538 km) and their known small-amplitude lightcurves, we have determined a new value for the infrared beaming parameter used in the "standard" thermal emission model for asteroids. The new value is significantly lower than that previously used, and when applied in the reduction of thermal infrared observations of other asteroids, should yield model diameters that are closer to actual diameters. In our formulation, we also incorporate the recently adopted IAU magnitude convention for asteroids, which uses the zero-phase magnitudes (including the opposition effect) the same as is used for satellites. oid whose surface elements are in instantaneous equilibrium with solar insolation, equivalent to a nonrotating body. In reality these conditions are not true, but given the uncertainties in the infrared calibration, absolute visual magnitudes, etc., these assumptions were acceptable. Although models developed by Morrison and his colleagues (Morrison, 1973; Jones and Morrison, 1974) differed somewhat from those of Matson and Lebofsky (Matson, 1971a,

Thermal evolution models of asteroids

2002

Thermal evolution models for asteroids that experienced metamorphism (ordinary chondrites), aqueous alteration (carbonaceous chondrites), and melting and differentiation (HED achondrites) are compared. These models, based on decay of 26Al, can be used to study a variety of asteroidal processes such as the insulating effect of regolith, the buffering effect of ice and fluid flow, and the complications arising from redistribution of heat sources during differentiation.

Thermal infrared observations of near-Earth asteroid 2002�NY40

Astronomy and Astrophysics, 2004

We obtained N-band observations of the Apollo asteroid 2002 NY40 during its close Earth fly-by in August 2002 with TIMMI2 at the ESO 3.6 m telescope. The photometric measurement allowed us to derive a radiometric diameter of 0.28 ± 0.03 km and an albedo of 0.34 ± 0.06 through the near-Earth asteroid thermal model (NEATM) and a thermophysical model (TPM). The values are in agreement with results from radar data, visual and near-IR observations. In this first comparison between these two model approaches we found that the empirical NEATM beaming parameter η = 1.0 corresponds to a thermal inertia values of about 100 J m −2 s −0.5 K −1 for a typical range of surface roughness, assuming an equator-on viewing angle. Our TPM analysis indicated that the surface of 2002 NY40 consists of rocky material with a thin or no dust regolith. The asteroid very likely has a prograde sense of rotation with a cold terminator at the time of our observations. Although both model approaches can fit the thermal spectra taken at phase angles of 22 • and 59 • , we did not find a consistent model solution that describes all pieces of photometric and spectroscopic data. In addition to the 2002 NY40 analysis, we discuss the possibilities to distinguish between different models with only very few photometric and/or spectroscopic measurements spread over a range of phase angles.

Photometric survey, modelling, and scaling of long-period and low-amplitude asteroids

Astronomy & Astrophysics

Context. The available set of spin and shape modelled asteroids is strongly biased against slowly rotating targets and those with low lightcurve amplitudes. This is due to the observing selection effects. As a consequence, the current picture of asteroid spin axis distribution, rotation rates, radiometric properties, or aspects related to the object’s internal structure might be affected too. Aims. To counteract these selection effects, we are running a photometric campaign of a large sample of main belt asteroids omitted in most previous studies. Using least chi-squared fitting we determined synodic rotation periods and verified previous determinations. When a dataset for a given target was sufficiently large and varied, we performed spin and shape modelling with two different methods to compare their performance. Methods. We used the convex inversion method and the non-convex SAGE algorithm, applied on the same datasets of dense lightcurves. Both methods search for the lowest devi...