Asteroids as calibration standards in the thermal infrared for space observatories

Müller, Thomas; Lagerros, J. S. V.

doi:10.1051/0004-6361:20011491

Cited by 83 publications

(80 citation statements)

References 17 publications

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“…thermal inertias, albedoes, and sizes) and also on the development of the TPM method itself. Some of them may prove to be good candidates for secondary calibrators for infrared observatories like ALMA, APEX, or IRAM (Müller & Lagerros 2002) as their infrared flux is only weakly and slowly variable (although in a predictable way), which are desirable features of calibrator asteroids.…”

Section: Summary and Future Workmentioning

confidence: 99%

“…Apart from studying asteroid parameters for themselves, such research has other very practical applications. Large asteroids are very good calibration standards for infrared observatories like Herschel, APEX, and ALMA, perfectly filling the gap in the flux levels of stellar and planetary calibration sources (Müller & Lagerros 2002;Müller et al 2014a). However, their flux changes have to be clearly predictable, and should not vary much over short timescales.…”

Section: Introductionmentioning

confidence: 97%

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

Marciniak

Bartczak

Müller

et al. 2018

A&A

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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 deviations between observed and modelled lightcurves, though using different approaches. Unlike convex inversion, the SAGE method allows for the existence of valleys and indentations on the shapes based only on lightcurves. Results. We obtain detailed spin and shape models for the first five targets of our sample: (159) Aemilia, (227) Philosophia, (329) Svea, (478) Tergeste, and (487) Venetia. When compared to stellar occultation chords, our models obtained an absolute size scale and major topographic features of the shape models were also confirmed. When applied to thermophysical modelling, they provided a very good fit to the infrared data and allowed their size, albedo, and thermal inertia to be determined. Conclusions. Convex and non-convex shape models provide comparable fits to lightcurves. However, some non-convex models fit notably better to stellar occultation chords and to infrared data in sophisticated thermophysical modelling (TPM). In some cases TPM showed strong preference for one of the spin and shape solutions. Also, we confirmed that slowly rotating asteroids tend to have higher-than-average values of thermal inertia, which might be caused by properties of the surface layers underlying the skin depth.

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Section: Summary and Future Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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

Marciniak

Bartczak

Müller

et al. 2018

A&A

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“…However, a care was taken not to doublecount the flux component in the extended shell part that is accounted for as part of the core emission via aperture correction. For each flux value obtained for the core and shell, we independently applied color correction and obtained the final flux values, which are listed in Table 1. For PSF calibration purposes, we also observed an M5 III giant β Gru (Engelke et al 2006) with AKARI on 2006 November 16 and an asteroid Ceres (Müller & Lagerros 2002) with Spitzer on 2008 February 17. The same instrumental/mapping set-up was used for both PSF observations, except for Spitzer observations, for which the photometry/movingcluster-offset mode was used because Ceres is a moving target.…”

Section: Photometry and Deconvolutionmentioning

confidence: 99%

The interface between the stellar wind and interstellar medium around R Cassiopeiae revealed by far-infrared imaging

Ueta¹,

Stencel²,

Yamamura

et al. 2010

A&A

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Aims. The circumstellar dust shells of intermediate initial-mass (∼1 to 8 M ) evolved stars are generated by copious mass loss during the asymptotic giant branch phase. The density structure of their circumstellar shell is the direct evidence of mass loss processes, from which we can investigate the nature of mass loss. Methods. We used the AKARI infrared astronomy satellite and the Spitzer space telescope to obtain the surface brightness maps of an evolved star R Cas at far-infrared wavelengths, since the temperature of dust decreases as the distance from the star increases and one needs to probe dust at lower temperatures, i.e., at longer wavelengths. The observed shell structure and the star's known proper motion suggest that the structure represents the interface regions between the dusty wind and the interstellar medium. The deconvolved structures are fitted with the analytic bow shock structure to determine the inclination angle of the bow shock cone. Results. Our data show that (1) the bow shock cone of 1−5 × 10 −5 M dust mass is inclined at 68 • with respect to the plane of the sky; and (2) the dust temperature in the bow shock cone is raised to more than 20 K by collisional shock interaction in addition to the ambient interstellar radiation field. By comparison between the apex vector of the bow shock and space motion vector of the star we infer that there is a flow of interstellar medium local to R Cas whose flow velocity is at least 55.6 km s −1 , consistent with an environment conducive to dust heating by shock interactions.

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“…Almost all LWS observations of Vesta were taken on one day (revolution 805) under very similar aspect angles. This might also influence the outcome of the TPM technique which works best when combining data from different wavelengths, phase angles, rotational phases and aspect angles (Müller & Lagerros 2002). Shevchenko & Tedesco (2006) derived an albedo of p H = 0.370 from occultation measurements, while we obtained a radiometric value of p V = 0.32 ± 0.02; again this discrepancy might be explained by emissivity effects or the limited aspect angle range.…”

Section: Diameter and Albedo Calculationsmentioning

confidence: 87%

“…The TPM with the "default thermal properties" has been tested and validated extensively in the context of ISO for large, regolith-covered main-belt-asteroids (Müller & Lagerros 2002). The surface roughness and heat conduction properties are less important for our far-IR analysis since they mainly influence the mid-IR radiation at the Wien-part of the spectral energy distribution (e.g.…”

Section: Diameter and Albedo Calculationsmentioning

confidence: 99%

Catalogue of ISO LWS observations of asteroids

Hormuth

Müller

2009

A&A

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Context. The long wavelength spectrometer (LWS) onboard the infrared space observatory (ISO) observed the four large main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (10) Hygiea multiple times. The photometric and spectroscopic data cover the wavelength range between 43 and 197 μm, and are a unique dataset for future investigations and detailed characterisations of these bodies. Aims. The standard ISO archive products, produced through the last post-mission LWS pipeline, were still affected by instrument artefacts. Our goal was to provide the best possible data products to exploit the full scientific potential of these observations. Methods. For all asteroid observations we analysed in detail the dark current, the calibration reference flashes, the space environment effects (glitches), memory effects, tracking influences, and various other sources of uncertainty. We performed a refined reduction of all measurements, corrected for the various effects, and re-calibrated the data. We outline the data reduction process and give an overview of the available data and the quality of the observations. We apply a thermophysical model to the flux measurements to derive far-IR based diameter and albedo values of the asteroids. The measured thermal rotational lightcurve of (4) Vesta is compared to model predictions. Results. The catalogue of LWS (long wavelength spectrometer) observations of asteroids contains 57 manually reduced datasets, including seven non-standard observations, which as such did not have final pipeline products available before. In total, the archive now contains 11 spectral scans and 46 fixed grating measurements with a simultaneous observation at 10 key wavelengths distributed over the full LWS range. The new data products are now accessible via the ISO data archive as highly processed data products (HPDP).Conclusions. The quality of the data products was checked against state-of-the-art thermophysical model predictions and an excellent agreement was found. The absolute photometric accuracy is better than 10%. The calibrated spectra will serve as a source for future mineralogical studies of dwarf planets and dwarf planet candidates.

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Asteroids as calibration standards in the thermal infrared for space observatories

Cited by 83 publications

References 17 publications

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

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

The interface between the stellar wind and interstellar medium around R Cassiopeiae revealed by far-infrared imaging

Catalogue of ISO LWS observations of asteroids

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