Results of the PROGRA2 Experiment: An Experimental Study in Microgravity of Scattered Polarized Light by Dust Particles with Large Size Parameter

Worms, Jean-Claude

doi:10.1006/icar.1999.6188

Cited by 54 publications

(22 citation statements)

References 61 publications

(48 reference statements)

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“…All the above mentioned hypotheses may be assessed by laboratory measurements. (Worms et al 1999) studies the red and/or green light scattered by levitating particles in microgravity conditions. It also operates under normal gravity with highly porous particles lifted by an air draught (Hadamcik 1999).…”

Section: Comparison With Other Diagnosticsmentioning

confidence: 99%

Dust evolution of comet C/1995 O1 (Hale-Bopp) by imaging polarimetric observations

Hadamcik

Levasseur-Regourd

2003

A&A

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Abstract. Comet C/1995 O1 (Hale-Bopp) has been observed over a large range of phase angles (7• -47 • ) by the imaging polarimetric method from June 1996 to April 1997. Polarization maps were obtained and long-term evolution (month) of the coma structures followed. Short-term evolution (20 min) during the April 1997 observations has allowed us to measure the period of rotation of the central arc on the polarization maps. The comparison between the polarization maps and the intensity structures confirms a greater polarization in the jets. Phase curves are obtained for different regions of the coma and compared to those obtained for the whole coma. For the region around the nucleus, the phase curve is always underneath the phase curve corresponding to the whole coma, and the polarization at phase angles smaller than 25• is negative (P min = −5%). In the jets, the phase curve is always above the whole coma phase curve, and the polarization is always positive. Whole coma phase curves are obtained with all the available data sets in different wavelengths. A comparison with other diagnostics and laboratory experiments leads us to suggest that small grains build up fluffy aggregates of high porosity; the light scattered by such aggregates is highly polarized, as observed in this active comet.

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Section: Comparison With Other Diagnosticsmentioning

confidence: 99%

Dust evolution of comet C/1995 O1 (Hale-Bopp) by imaging polarimetric observations

Hadamcik

Levasseur-Regourd

2003

A&A

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“…These authors have shown differences in polarimetric properties between levitating dust and dust lying on surfaces. For compact particles of silicon carbide, Worms et al (1999a) found a decrease in P max from packed powder to sifted powder and an increase in P max when the number density of levitating particles in the beam decreases. The polarization is maximum between 90 and 120…”

Section: Introductionmentioning

confidence: 93%

“…The instrument is a polarimeter dedicated to the measurements of the angular dependence of the polarization of light scattered by dust particles under microgravity and ground-based conditions (Worms et al , 1999a. The light sources are helium-neon lasers (632.8 nm and 543.5 nm) with random polarization.…”

Section: Instrument and Proceduresmentioning

confidence: 99%

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Polarization of Light Scattered by Fluffy Particles (PROGRA2 Experiment)

Hadamcik

Renard

Worms³

et al. 2002

Icarus

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“…The DDA technique and assuming the grains to be made up of organic coated silicate monomers ) will be attempted as the next step to match the polarizations in the range from 0.3650 µm to 2.2 µm. The use of computational techniques can be dispensed with and one could directly use (1) the microwave and laser facilities to determine scattering and colour signatures related to the physical properties of dust grains (Weiss-Wrana et al 1985a, 1985b, (2) the database created by Gustafson et al (1999) using microwave analogues of complex grain systems or (3) the data from the scattering experiments (PROGRA) conducted under micro gravity conditions on fluffy grains (Levasseur-Regourd et al 1998;Worms et al 1999) with optical constants similar to Astronomical silicate. In any case, by adapting a superior light scattering theory or using results of laboratory simulations, the present model can be used to fully extract the information available from polarization and intensity maps of cometary shells and coma.…”

Section: Conclusion and Scope For Further Improvementsmentioning

confidence: 99%

A photometric-dynamic model to simulate coma and jets from a comet

Vasundhara

2002

A&A

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Abstract.A model to compute the trajectories of dust grains ejected by comets to simulate intensity and polarization maps on the sky plane is presented. The model is used to constrain the silicate to organic mass ratio, porosity and size distribution of the grains in the shells and coma of comet Hale-Bopp to explain 1) the published polarizations at three continuum wavelengths at 0.6840 µm, 0.4845 µm and 0.3650 µm at different phase angles, 2) higher polarization and bluer colour of the shells compared to the coma, 3) the intensity variation and rapid decline of polarization on the sunward side and 4) higher polarization on the anti-sunward direction. The present results obtained using Mie theory in the model indicate that although it is impossible to determine the nature of the silicate (pyroxenes/olivines or amorphous/crystalline) using the present technique, the porosity, organic fraction and size distribution of the grains can be constrained. The fit to the data set indicates an ensemble of grains in which ≈60% are silicate grains with a range in silicate to organic mass ratio rm between 1 and 2 and of medium porosity <50%. A higher silicate content of rm > 8 on the shells can explain their bluer colour. A narrow size distribution between 0.08 µm−0.6 µm is inferred for 70% of the grains in the coma and shell. These small grains may not be individual grains but part of loosely bound grains in which larger grains may also be present which may control the dynamics. The narrow size distribution may therefore represent statistically the size range of individual subunits of larger highly porous aggregates of fractal dimension close to two. The polarizations in JHK bands also support the aggregate structure. Despite the availability of an extensive and wide range of data set on this comet, the inclusion of a large parameter space, lack of knowledge on the nature of organic material found in comets and use of Mie theory, which does not adequately represent the polarization phase curves of natural grains, set limitations in getting a unique solution in the present work. The results presented here are open to improvements when more realistic light scattering theories are used in the model and our understanding on the nature of the organic content of the grains improves. However, visibility of up to 8-10 shells in well exposed images implies β < 1 for these grains. As a result of this dynamical constraint which is independent of the assumptions on the scattering characteristics of the grains, the results for the dust grains in the shell may be more robust compared to that of the coma.

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Results of the PROGRA2 Experiment: An Experimental Study in Microgravity of Scattered Polarized Light by Dust Particles with Large Size Parameter

Cited by 54 publications

References 61 publications

Dust evolution of comet C/1995 O1 (Hale-Bopp) by imaging polarimetric observations

Dust evolution of comet C/1995 O1 (Hale-Bopp) by imaging polarimetric observations

Polarization of Light Scattered by Fluffy Particles (PROGRA2 Experiment)

A photometric-dynamic model to simulate coma and jets from a comet

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