Physical properties of B-type asteroids from WISE data

Abstract

Aims. Our aim is to obtain more information about the physical nature of B-type asteroids and extend previous work by studying their physical properties as derived from fitting an asteroid thermal model to their NASA's Wide-field Infrared Survey Explorer (WISE) data. We also examine the Pallas collisional family, a B-type family with a moderately high albedo in contrast to the large majority of B-types. Methods. We applied a combination of the near-Earth asteroid thermal model and a model of the reflected sunlight to WISE asteroid data in order to derive up to four parameters: effective diameter (D), the so-called infrared beaming parameter (η), ratio of infrared to visible albedo (R p = p IR /p V ), and visible geometric albedo (p V ). Results. We obtained the effective diameter, geometric visible albedo, infrared-to-visible albedo ratio, and beaming parameter for > ∼ 100 B-types asteroids and plotted the value distributions of p V , R p , and η (p V = 0.07 ± 0.03,R p = 1.0 ± 0.2, andη = 1.0 ± 0.1). By combining the IR and visible albedos with 2.5 μm reflectances from the literature we obtained the ratio of reflectances at 3.4 and 2.5 μm, from which we found statistically significant indications that the presence of a 3-μm absorption band related to water may be commonplace among the B-types. Finally, the Pallas collisional family members studied (∼50 objects) present moderately high values of p V ,p V = 0.14 ± 0.05, which is significantly higher than the average albedo of B-types. In addition, this family presents the lowest and most homogeneously distributed R p -values of our whole sample, which shows that this group is clearly different from the other B-types, probably because its members are fragments likely originating from the same region of (2) Pallas, a particularly high-albedo B-type asteroid.

Spectral variability on primitive asteroids of the Themis and Beagle families: Space weathering effects or parent body heterogeneity?

“…1-3, and 7), including asteroids with blue/neutral and moderately red spectra (relative to the Sun). Our findings are consistent with, and complement previous spectroscopic studies that hinted at spectral diversity within the Themis family in the visible (Florczak et al 1999;Kaluna et al, 2016), the near-infrared (Ziffer et al 2011;de León et al 2012;Alí-Lagoa et al 2013), and the mid-infrared ). On the other hand, the robust and younger Beagle family members look different, with a smaller spectral slope variability.…”

“…Alí- Lagoa et al (2013), in the analysis of B-type asteroids and p IR albedo, found that an absorption in the 3 µm region may be common on these bodies. Figure 11 confirms the huge spectral variability of Themis members, which have small to moderate albedo values (3-16%) and a P IR /p v ratio varying from ∼ 0.5 to 2.2.…”

“…According to Licandro et al (2011Licandro et al ( , 2013 works, the visible spectra of the main belt comets 133P, 176P, and 288P…”

Thermophysical properties of near-Earth asteroid (341843) 2008 EV5from WISE data

“…Finally, because even though its visible-to-near-infrared spectrum suggests that EV 5 belongs to the C-complex (Reddy et al 2012) and is thus rich in carbonaceous materials, its geometric albedo of 0.12 ± 0.04 -derived from a diameter of 400 ± 50 m measured from radar observations by Busch et al (2011) -is slightly outside the limit of what has traditionally been considered primitive. This is also the case for (2) Pallas and the Pallas collisional family (see, for example, Alí-Lagoa et al 2013).…”

Space-Based Thermal Infrared Studies of Asteroids

“…Consequently, if p IR can be determined, it can be used as a proxy for distinguishing between taxonomic types that otherwise have nearly identical visible albedos (Grav et al 2012a,b;Alí-Lagoa et al 2013;Masiero et al 2014). While the STM, FRM, and NEATM are useful tools for rapidly determining effective spherical diameter, p V , and p IR for large numbers of asteroids, they are of limited use for determining additional parameters such as emissivity and thermal inertia.…”