Aperture polarimetry and photometry of comet Hale-Bopp (original) (raw)
Related papers
Icarus, 2001
Efforts to apply a single-scattering polarized radiative transfer code to interpret photopolarimetric measurements of coma dust optical properties in Comet Hale-Bopp corroborate previous photometrically derived conclusions concerning the predominance of small sized particles in Hale-Bopp's coma. Calculations of the degree of linear polarization (DP) as a function of observation phase angle (α) produced by prolate spheroidal crystalline olivine particles with effective radii (a = 0.216 µm) are compatible with the comet's measured polarization in standard filters at λ = 0.4845 and 0.684 µm. Our rudimentary "trade-off" studies highlight the extreme sensitivity of DP to dust particle size and shape. A combination of viewing geometry effects in association with enhanced multiple scattering might provide a quantitative explanation of the negative polarization for 0 • ≤ α ≤ 20 • seen in Hale-Bopp and other comets.
Near-infrared photometric and polarimetric observations of comet Hale-Bopp
Earth, Moon, and …, 1997
Near-infrared photometric and polarimetric observations of comet Hale-Bopp (1995 O1) using KONIC (Kiso Observatory Near-Infrared Camera) are reported. Observations were carried out on March 18 UT and April 26 UT 1997, when the heliocentric distances of the comet were 0.94 and 1.02 AU, and the phase angles were 48.5 deg and 32.9 deg, respectively. In the J , H , and K bands, we obtained linear polarization of the near-nucleus region of 16.4 ± 1.2, 18.8 ± 1.3, and 15.1 ± 0.9 percent on March 18UT and 7.1 ± 1.1, 8.9 ± 1.0, and 6.9 ± 0.6 percent on April 26, respectively. These values were higher than those observed for 1P/Halley. The maximum polarization was found at H band on both dates. Polarization maps showed higher polarization regions toward the anti-solar direction in the J and H bands. No distinct correlation was found between high polarization regions and bright regions. The projected expansion velocity of the arc structure of the dust jet was 375 ± 35.7 m/s on 17-19 March. The periodicity was found to be 11.1 ± 2.8 hours.
Imaging polarimetry of cometary dust: different comets and phase angles
Journal of Quantitative Spectroscopy and Radiative Transfer, 2003
Polarimetric observations of the light scattered by dust in cometary comae have been carried out at Pic-du-Midi Observatory and at Haute-Provence Observatory (France) between 1990 and 2001. The whole coma polarization can easily be inferred from integration of the uxes on the aperture. Maps are obtained for seven comets by CCD imaging polarimetry, which allow to observe three main regions in a cometary coma: the background coma, a circumnuclear halo and bright structures (jets or arcs) which correspond to di erent values of the polarization. The polarization maps of short period comets are compared to the maps obtained for comet Hale-Bopp, for phase angles smaller than 50 • (smaller than 15 • with negative polarization, near the inversion angle of approximately 20 • , between 30 • and 50 • on the linear part of the phase curve). At ∼ = 60 • the polarization map of comet C/2000 WM1 is presented. Between 109 • and 121 • the evolution of brightness images and polarization maps of comet C/1999 S4 is followed during the complete disruption of its nucleus. The polarimetric phase curve for the circumnuclear halo presents highly negative values for ¡ 20 •. On the opposite for the same phase angles range, the polarization in jets is positive for the four studied comets. The di erences between the regions are discussed in terms of physical properties of the particles (size distribution, packing density, mixtures of materials) by comparison to other observational techniques and laboratory measurements.
Imaging Polarimetry and Color of the Inner Coma of Comet Hale-Bopp(C/1995 O1)
Publications of the Astronomical Society of Japan, 1999
Optical-imaging polarimetry of comet Hale-Bopp (C/1995 Ol) was performed on 1997 March 17, using the Okayama Optical Polarimetry and Spectroscopy system (OOPS), which was mounted on the 91-cm reflector at Okayama Astrophysical Observatory. Using two different narrow-band filters for the continuum, color maps and polarization maps of dust particles of comet Hale-Bopp were obtained. A dust "jet" structure (also called 'arc structure') was seen in the intensity, polarization, and color maps. The polarization degree of the arc structure was higher than in other parts of the coma, and the color of the arc structure was bluer compared to other coma regions.
Polarimetric observations of comets C/1995 O1 Hale-Bopp and C/1996 B2 Hyakutake
Icarus, 2000
We present polarimetric observations of Comet C/1995 O1 Hale-Bopp. Polarimetric data was obtained with a Pockels cell polarimeter at the Observatoire du Mont Mégantic, between July 1996 and May 1997. An intermediate bandpass red filter and five cometary filters, in the continuum and in emission bands, have been used. The comet was measured in linear and circular polarimetry, in the nuclear region and in the coma and tail, and through apertures of different sizes. The polarization was always parallel or perpendicular to the scattering plane within 4 • or 5 • . The curve of polarization as a function of the phase angle β has a steeper slope than usually seen in comets: a trigonometric fit gives 0.303 ± 0.014% per degree. The crossover value of the phase angle, β co , is evaluated to be around 20 • , which is typical for comets. Polarization and the angle of polarization show some variations when using different apertures and also as calculated in concentric rings centered on the nuclear region. Polarization was found to be significantly lower in the blue in the CO + and C 3 emission filters (426 and 406 nm) than in an adjacent 484-nm continuum filter and significantly higher in the red in the H 2 O + emission filter (700 nm) than in the adjacent 684-nm continuum filter. Polarization has been measured in the coma and tail up to a distance of about 200 , corresponding to 2.2 × 10 5 km, in two continuum filters; the polarization increases and then decreases when going away from the nuclear region. Circular polarization at a maximum value of 0.2% was detected and was found to be variable. We present also a few observations of Comet C/1996 B2 Hyakutake that show that P max ≈ 28.6% occurs at β ≈ 91 • .
Astronomy & Astrophysics, 2005
We present results of imaging and aperture polarimetry of the dust of comet 2P/Encke at phase angles 91-105 • , obtained during the 2003 apparition. We investigate how strongly molecular emissions transmitted by the filters used in the observations can affect the resulting polarization of cometary dust. This problem is of particular importance for so-called gasrich comets like comet 2P/Encke which has particularly strong molecular emission as compared to its dust continuum. Aperture polarimetry in the wide-band UBVR filters was performed at the 2.6-m Shain telescope and 1.25-m telescope of the Crimean Astrophysical Observatory on November 17-24. From these measurements a dust polarization of ≈8% is derived, which puts the comet in the class of comets with low polarization. The imaging observations of comet 2P/Encke were carried out at the 2-m telescope of the Bulgarian National Astronomical Observatory on November 20-22, 2003. Narrow-band filters centered on the 0-7-0 transition of the à 2 A 1-X 2 B 1 electronic band system of NH 2 (662 nm) and on an adjacent red continuum at 642 nm were employed. The polarization of NH 2 averaged over the 0-7-0 vibronic transition amounts to ≈7% at phase angles close 90 • , similar to the polarization of the two-atomic molecules CN and C 2. The dust polarization however, when corrected for the effect of molecular emissions, is larger than 30%. We conclude that the division of comets into two polarimetric classes with one class having in the visual wavelength range a maximum polarization less than 20% is caused by ignoring the contribution of molecular emission and therefore is an artifact. Whether the comet displays a strong silicate feature (i.e. its dust grains are small) or not, the dust polarization is high.
Imaging polarimetry of comet Hale-Bopp (C/1995 O1) around perihelion
1997
The polarization distribution of the inner coma of comet Hale-Bopp was measured by CCD imaging around perihelion. The dust shell positions correlate well with relative maxima of polarization. The images taken in the I-band identify different shell systems, each showing individual polarization properties. This could be related to differences in the dust properties of the associated jets.
Optical and Near-infrared Polarimetry of Non-periodic Comet C/2013 US10 (Catalina)
The Astronomical Journal, 2017
We present an optical and near-infrared (hereafter NIR) polarimetric study of a comet C/2013 US10 (Catalina) observed on UT 2015 December 17-18 at phase angles of α=52°.1-53°. 1. Additionally, we obtained an optical spectrum and multi-band images to examine the influence of gas emission. We find that the observed optical signals are significantly influenced by gas emission; that is, the gas-to-total intensity ratio varies from 5 to 30% in the R C and 3%-18% in the I C bands, depending on the position in the coma. We derive the "gas-free dust polarization degrees" of 13.8%±1.0% in the R C and 12.5%±1.1% in the I C bands and a gray polarimetric color, i.e., −8.7%±9.9% μm −1 in optical and 1.6%±0.9% μm −1 in NIR. The increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. In this process, the cometocentric distance dependence of polarization has disappeared. We also find that the R C-band polarization degree of the southeast dust tail, which consists of large dust particles (100 μm-1 mm), is similar to that in the outer coma where small and large ones are mixed. Our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. This conclusion can provide a strong support for similarity in origin of comets.
Unusual polarimetric properties for interstellar comet 2I/Borisov
Nature Communications, 2021
So far, only two interstellar objects have been observed within our Solar System. While the first one, 1I/‘Oumuamua, had asteroidal characteristics, the second one, 2I/Borisov, showed clear evidence of cometary activity. We performed polarimetric observations of comet 2I/Borisov using the European Southern Observatory Very Large Telescope to derive the physical characteristics of its coma dust particles. Here we show that the polarization of 2I/Borisov is higher than what is typically measured for Solar System comets. This feature distinguishes 2I/Borisov from dynamically evolved objects such as Jupiter-family and all short- and long-period comets in our Solar System. The only object with similar polarimetric properties as 2I/Borisov is comet C/1995 O1 (Hale-Bopp), an object that is believed to have approached the Sun only once before its apparition in 1997. Unlike Hale-Bopp and many other comets, though, comet 2I/Borisov shows a polarimetrically homogeneous coma, suggesting that it...
Spatial variations of brightness, colour and polarization of dust in comet 67P/Churyumov–Gerasimenko
Monthly Notices of the Royal Astronomical Society, 2017
We present post-perihelion photometric and polarimetric observations of comet 67P/Churyumov-Gerasimenko performed at the 6-m telescope of the SAO RAS in the gsdss (465/65 nm), r-sdss (620/60 nm) and R filters. Observations in November and December 2015 and April 2016 covered the range of heliocentric distance 1.62-2.72 au and phase angle 33.2 •-10.4 •. The comet was very active. Two persistent jets and long dust tail were observed during the whole observing period; one more jet was detected only in December. The radial profiles of surface brightness, colour and polarization significantly differed for the coma, jets and tail, and changed with increasing heliocentric distance. The dust production Afρ decreased from 162 cm at r = 1.62 au to 51 cm at r = 2.72 au. The dust colour (g-r) gradually changed from 0.8 mag in the innermost coma to about 0.4 mag in the outer coma. The spectral slope was 8.2 ± 1.7 per cent/100 nm in the 465 to 620 nm wavelength domain. In November and December, the polarization in the near-nucleus area was about 8 per cent, dropped sharply to 2 per cent at the distance above 5000 km and then gradually increased with distance from the nucleus, reaching ∼8 per cent at 40 000 km. In April, at a phase angle 10.4 • , the polarization varied between-0.6 per cent in the near-nucleus area and-4 per cent in the outer coma. Circular polarization was not detected in the comet. The spatial variations of brightness, colour and polarization in different structural features suggest some evolution of particle properties, most likely decreasing the size of dust particles.