[7.10] Thermal Infrared (8-13 micron) Spectra of the NEA 2100 Ra-Shalom

37th DPS Meeting, 4-9 September 2005
Session 7 Asteroids II
Oral, Monday, September 5, 2005, 2:00-3:50pm, Law LG19

[7.10] Thermal Infrared (8-13 micron) Spectra of the NEA 2100 Ra-Shalom

L. F. Lim (NASA/GSFC), J. P. Emery (SETI Institute), T. H. McConnochie (Cornell University)

Thermal infrared spectra of the near-Earth asteroid 2100 Ra-Shalom were measured on August 22 and 23 (UT) 2003 at Palomar Observatory using Spectrocam-10 on the 200'' Hale telescope. Total integration time was 186 minutes. These observations were part of the multi-wavelength observing campaign organized by Shepard et al. (2004).

The thermal spectra of most main-belt asteroids can be well modelled by the Standard Thermal Model (STM) with a ``beaming parameter'' \eta=0.756 ± 0.014, which implies rough ``dusty'' surfaces of negligible thermal inertia. A STM fit of our Ra-Shalom data, however, yields \eta=1.2, corroborating the conclusion of Harris et al. (1998) and Lebofsky et al. (1979) that Ra-Shalom has a substantial thermal inertia. Harris et al., however, derived a higher value \eta=1.6--1.8 from their 1997 spectrophotometric data.

We have used the pole solution of Kaasalainen et al. (2004) to apply a more sophisticated thermophysical model (Emery et al., 1998) to the circumstances of both our observations and those of Harris et al. Our preliminary result is that both data sets are consistent with asteroid radius R=1.15 km and thermal inertia \ge 580 J/m²/s^0.5/K. This is a lower limit because at the phase angles of these observations, surface roughness increases color temperature by infrared ``beaming''. Further modelling will be conducted with varying surface roughnesses.

Despite its unusually high thermal inertia, Ra-Shalom appears to be similar to its main-belt counterparts in lacking spectral emissivity variation at the 5% level.

(1) Shepard et al. (2004), LPSC XXXV, #1120. (2) Harris et al. (1998), Icarus 135, 441-450. (3) Lebofsky et al. (1979), Astron. J. 84, 885-888. (4) Kaasalainen et al. (2004), Icarus 167, 178-196. (5) Emery et al. (1998), Icarus 136, 104-123.

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