Photometer calibration problem for extended astronomical sources: comments

Weinberg, J. L.; Schuerman, D. W.; Beeson, D. E.

doi:10.1364/ao.15.2620_1

Cited by 4 publications

(4 citation statements)

References 3 publications

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“…Therefore, polarimetry rules out a significant contribution of very small grains, in agreement with the lack of Rayleigh scattering found in several comets. Polarimetric observations along the tail of comet Ikeya-Seki by Weinberg and Beeson (1976) revealed a change in P from about 20 to -40%. Krishna Swamy (1978) found it likely that such a polarisation reversal was the result of segregation of dielectric grains according to their size.…”

Section: Optical and Infrared Photometry And Polarimetrymentioning

confidence: 99%

Nature and origin of comets

Fernández¹,

Jockers²

1983

Rep. Prog. Phys.

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After an introduction to the basic history and morphology of comets we turn in 0 2 to a description of their motion which is disturbed by the planets, non-gravitational forces due to out-gassing of the cometary nucleus and, for the near-parabolic comets, by the gravitation of nearby passing stars. An overview of the dynamical evolution of long-and short-period comets is presented, paying special attention to the resulting distribution of orbital elements. Section 3 is mainly concerned with the physical properties of the neutral gaseous matter. After a discussion of the excitation mechanisms for radiation of coma molecules we describe the sublimation (vaporisation) of gases and their outflow from the cometary nucleus. The chemistry of the coma gases is then addressed and the individual molecules, radicals and atoms are studied in the framework of their presumed parent species. Section 4 is devoted to the as yet unobserved comet nucleus. We present what is known about nuclear sizes and masses. The nucleus is likely to be a homogeneous mixture of ices (e.g. H 2 0 , CO2, CO, NH3) and dust particles but which may temporarily be covered by an insulating dust crust. Splittings and outbursts of cometary nuclei give information on their reduced internal strength. Certain periodic features observed in the cometary comae allow one to

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Section: Optical and Infrared Photometry And Polarimetrymentioning

confidence: 99%

Nature and origin of comets

Fernández¹,

Jockers²

1983

Rep. Prog. Phys.

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“…A variety of telescopes, filters, and analysis techniques has been used. From the data set, only comet Ikeya-Seki has been excluded, since its observations comprised the tail rather than the coma (Weinberg & Beeson 1976 ;Bappu et al 1967 ). Averaged comet photocentre polarization of comet C/2010 E6 (STEREO) from this work has been added for contrast (larger filled brown circles).…”

Section: Phase Angle Cur V Esmentioning

confidence: 99%

Polarimetric analysis of STEREO observations of sungrazing Kreutz comet C/2010 E6 (STEREO)

Nežič

Bagnulo

Jones

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Twin STEREO spacecraft pre-perihelion photometric and polarimetric observations of the sungrazing Kreutz comet C/2010 E6 (STEREO) in March 2010 at heliocentric distances 3 − 28 R⊙ were investigated using a newly-created set of analysis routines. The comet fully disintegrated during its perihelion passage. Prior to that, a broadening and an increase of the intensity peak with decreasing heliocentric distance was accompanied by a drop to zero polarisation at high phase angles (∼105–135○, STEREO-B) and the emergence of negative polarisation at low phase angles (∼25–35○, STEREO-A). Outside the near-comet region, the tail exhibited a steep slope of increasing polarisation with increasing cometocentric distance, with the slope becoming less prominent as the comet approached the Sun. The steep slope may be attributed to sublimation of refractory organic matrix and the processing of dust grains, or to presence of amorphous carbon. The change in slope with proximity to the Sun is likely caused by the gradual sublimation of all refractory material. The polarisation signatures observed at both sets of phase angles closer to the comet photocentre as the comet approached the Sun are best explained by fragmentation of the nucleus, exposing fresh Mg-rich silicate particles, followed by their gradual sublimation. The need for further studies of such comets, both observational and theoretical, is highlighted, as well as the benefit of the analysis routines created for this work.

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“…A variety of telescopes, filters, and analysis techniques has been used. From the dataset, only comet Ikeya-Seki has been excluded, since its observations comprised the tail rather than the coma (Weinberg & Beeson 1976;Bappu et al 1967). Averaged comet head polarisation of comet C/2010 E6 (STEREO) from this work has been added for contrast (larger filled brown circles).…”

Section: Effects Of the Near-sun Environmentmentioning

confidence: 99%

Polarimetric analysis of STEREO observations of sungrazing Kreutz comet C/2010 E6 (STEREO)

Nežič,

Bagnulo,

Jones

et al. 2020

Preprint

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Twin STEREO spacecraft pre-perihelion photometric and polarimetric observations of the sungrazing Kreutz comet C/2010 E6 (STEREO) in March 2010 at heliocentric distances 3 − 28 𝑅 were investigated using a newly-created set of analysis routines. The comet fully disintegrated during its perihelion passage. Prior to that, a broadening and an increase of the intensity peak with decreasing heliocentric distance was accompanied by a drop to zero polarisation at high phase angles (∼105 − 135 • , STEREO-B) and the emergence of negative polarisation at low phase angles (∼25 − 35 • , STEREO-A). Outside the near-comet region, the tail exhibited a steep slope of increasing polarisation with increasing cometocentric distance, with the slope showing a marked decrease with decreasing heliocentric distance. The steep slope is attributed to sublimation of refractory organic matrix and the accompanied processing of the fluffy aggregate dust grains, exposing silicates. The decrease in slope is likely caused by the gradual sublimation of all refractory material closer to the Sun, with resulting gases suppressing polarisation signal of the dust. Near-zero polarisation closer to the comet head may be explained by the same mechanism, stronger there due to the large amounts of material being ejected and sublimated from the presumably disintegrating core, which correlates with intensity data. Negative polarisation at small phase angles may be explained by the presence of freshly ejected large silicate-rich aggregates. Despite both zero and negative polarisation being observed simultaneously, the two hypotheses on their causes are not easily reconciled. The need for further studies of such comets, both observational and theoretical, is highlighted.

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Photometer calibration problem for extended astronomical sources: comments

Cited by 4 publications

References 3 publications

Nature and origin of comets

Nature and origin of comets

Polarimetric analysis of STEREO observations of sungrazing Kreutz comet C/2010 E6 (STEREO)

Polarimetric analysis of STEREO observations of sungrazing Kreutz comet C/2010 E6 (STEREO)

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