Spectral Irradiance Calibration in the Infrared. VIII. 5–14 Micron Spectroscopy of the Asteroids Ceres, Vesta, and Pallas

Cohen, Martin; Witteborn, F. C.; Roush, T. L.; Bregman, J. D.; Wooden, D. H.

doi:10.1086/300271

Cited by 49 publications

(35 citation statements)

References 33 publications

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“…If IDPs are dominated by silicate-type particles of the size distribution with an enhancement of submicron particles, such as the lunar microcrater distribution (Grün et al, 1985), they may show band features in the 10 μm region (Reach et al, 1996b). A recent study of asteroids also suggests the presence of band features in the 10 μm region of the spectrum of Ceres (Cohen et al, 1998). Therefore, the presence of features in the 10 μm region of the zodiacal emission is not unexpected and the near-infrared zodiacal light and the mid-infrared zodiacal emission may be interpreted consistently in terms of the silicate-type IDPs.…”

Section: Discussionmentioning

confidence: 73%

IRTS observation of the mid-infrared spectrum of the zodiacal emission

et al. 2014

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We present the mid-infrared spectrum (3-12 μm) of the zodiacal emission obtained by the Infrared Telescope in Space (IRTS), the first Japanese cryogenically cooled orbital infrared telescope. The Near-Infrared Spectrometer (NIRS) on board IRTS provided the spectrum of 3-4 μm, while that of 4.5-11.7 μm has been observed by the Mid-Infrared Spectrometer (MIRS). In this paper we present the data reduction and results of the observations by MIRS. Spectra of the background emission at high galactic latitudes (|b| > 30• ) have been extracted from the MIRS observations by excluding point sources. The observed sky brightness has a clear dependence on the ecliptic latitude, indicating that the zodiacal emission dominates in the mid-infrared sky brightness. On the other hand, the spectral shape does not show any appreciable dependence on the ecliptic latitude for β = 0• -75• . The spectrum combining the NIRS and MIRS observations can be fitted by a grey body radiation at 250 K, but excess emission is seen in the 3-6 μm range. Alternatively, the spectrum of the zodiacal emission can be reproduced fairly well by a grey body at 280 K with an excess around 10 μm. In this case the excess may be attributed to a silicate emission band. Other than these excesses, no spectral features above the 10% level are seen in the MIRS spectrum.

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Section: Discussionmentioning

confidence: 73%

IRTS observation of the mid-infrared spectrum of the zodiacal emission

et al. 2014

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“…At shorter wavelength, between 8 and 11 µm, broadband silicate features have been seen (Cohen et al 1998;Dotto et al 2000). Heras et al (2000) report mid-IR emission signatures on Vesta, tentatively identified with olivine and pyroxene silicate groups.…”

Section: Asteroid Ir Observational Aspectsmentioning

confidence: 96%

Asteroids as calibration standards in the thermal infrared for space observatories

Müller

Lagerros

2002

A&A

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Abstract.Asteroids have been used extensively as calibration sources for the Infrared Space Observatory (ISO) and are planned to be used by future groundbased, airborne and space-based projects in the thermal infrared (IR) and in the sub-millimetre. We summarize the general IR observational parameters with a focus on space observatories and discuss brightness variations, apparent velocities and background influences. During the ISO mission ten wellstudied asteroids were used for the photometric calibration of ISOPHOT, but additionally the bright asteroids turned out to be of great interest for many technical tests and calibration aspects. We evaluated the different applications, like testing the photometry of the spectrometers, validation of relative spectral response functions, determination of beam profiles or colour correction tests. The description of the asteroids' thermal emission has been obtained by a recent thermophysical model (TPM). The important model aspects are size, albedo, shape together with the spin vector, a beaming model, thermal inertia and a wavelength-dependent emissivity. With a large sample of observational data provided by three different ISO instruments we had for the first time the possibility to study the thermal emission of several asteroids in detail. The intercomparison between results from different instruments allowed us to distinguish between observational errors and model shortcomings. It turned out that the accuracy of TPM predictions is in many cases strongly related to the limited knowledge of the asteroid shapes. The concepts of beaming, thermal inertia and wavelength dependent emissivities were nicely confirmed for a wide range of observing and illumination geometries under many aspect angles for different asteroids. The TPM predictions for Ceres, Pallas and Vesta are accurate within 5% over the full wavelength range from 5 to 200 µm, for Hygiea and a few other asteroids the predictions and observations agree within 10 to 15%. We found similar emissivity behaviour for the four large asteroids over the full ISO wavelength range. Up to now, no clear spectral features have been seen in the asteroid far-IR spectra.

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“…The mid-infrared spectral region is also proving to be diagnostic of the surface composition of primitive asteroids, and in ways complementary to the shorter wavelengths (e.g., Cohen et al 1998;Müller & Blommaert 2004;Lim et al 2005;Emery et al 2006;Campins et al 2007). The three published midinfrared spectra, from 5 to 38 μm of Trojan asteroids (Emery et al 2006) exhibit clear emissivity features from which the compositional and physical properties can be inferred.…”

Section: Introductionmentioning

confidence: 99%

(65) Cybele: detection of small silicate grains, water-ice, and organics

Licandro

Campins

Kelley

et al. 2010

A&A

109

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Context. (65) Cybele is the most representative member of a population of primitive asteroids in the outer edge of the main belt, the Cybele asteroids. Recent dynamical models suggest that a significant fraction of them originated in the primordial transneptunian disk, so the study of the physical properties of these asteroids is potentially a useful test of these models. Aims. Our aim is to obtain information on the surface composition of this asteroid. In particular we want to obtain information on the composition and properties of the regolith and the possible presence of ices and organic materials. Methods. We present 2-4 μm and 5-14 μm spectroscopy of (65) Cybele obtained with the NASA IRTF telescope and Spitzer Space Telescope respectively. We compare the results with spectra of Trojan asteroids and asteroid (24) Themis. We analyze the 2-4 μm spectrum using scattering models and we apply thermal models to the 5-14 μm data. Results. The 2-4 μm spectrum of (65) Cybele presents an absorption band centered at ∼3.1 μm and more weaker bands in the 3.2-3.6 μm region, very similar to those observed in (24) Themis. No hydrated silicates are detected. From the spectrum in the 5-14 μm region an effective diameter D = 290 ± 5 km, a beaming paramete η = 0.967 ± 0.014, and a geometric visible albedo p V = 0.05 ± 0.01 are derived using the NEATM thermal model. The emisivity spectrum in the 5-14 μm range exhibits an emission plateau at about 9 to 12 μm with an spectral contrast of ∼5%. This emission is similar to that of Trojan asteroids and active comets and may be due to small silicate grains being imbedded in a relatively transparent matrix, or to a very under-dense (fairy-castle) surface structure. The lower amplitude of the silicate emission in Cybele's spectrum with respect to that of Trojan asteroids could be attributed to larger dust particles and/or a slightly denser structure. Conclusions. The surface of (65) Cybele is covered by a fine anhydrous silicate grains mantle, with a small amount of water ice and complex organic solids. This is similar to comet surface where non-equilibrium phases coexist. The presence of water-ice and anhydrous silicates is indicative that hydration did not happened or is incomplete, suggesting that the temperatures were always sufficiently low.

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Spectral Irradiance Calibration in the Infrared. VIII. 5–14 Micron Spectroscopy of the Asteroids Ceres, Vesta, and Pallas

Cited by 49 publications

References 33 publications

IRTS observation of the mid-infrared spectrum of the zodiacal emission

IRTS observation of the mid-infrared spectrum of the zodiacal emission

Asteroids as calibration standards in the thermal infrared for space observatories

(65) Cybele: detection of small silicate grains, water-ice, and organics

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