Photometry, spectroscopy, and polarimetry of distant comet C/2014 A4 (SONEAR) (original) (raw)
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Observations of distant comet C/2011 KP36 (Spacewatch): photometry, spectroscopy, and polarimetry
Astronomy & Astrophysics
Aims. The main objective of our study is to obtain new observational results for the active long-period comet C/2011 KP36 (Spacewatch). This comet has unusual orbital properties and moves at distances larger than 5 au from the Sun. Methods. We carried out extensive observations of comet C/2011 KP36 (Spacewatch) at the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the focal reducer SCORPIO-2. We obtained quasi-simultaneous long-slit spectra in the visible, as well as photometric and linear polarimetric images with the g-sdss and r-sdss filters on November 25, 2016 when the heliocentric and geocentric distances of the comet were 5.06 au and 4.47 au, respectively. We modeled the behavior of the color and polarization in the coma, considering the dust as an ensemble of polydisperse nonspherical particles. Results. Two strong jet-like structures in solar and antisolar directions and two short and narrow jet features in the perpendicula...
Planetary and Space Science, 2015
We present first measurements of the degree of linear polarization of distant comets C/2010 S1 (LINEAR) and C/2010 R1 (LINEAR) at heliocentric distances r = 5.9-7.0 AU. Observations were carried out with the SCORPIO-2 focal reducer at the 6-m telescope of the Special Astrophysical Observatory (Russia). Both comets showed considerable level of activity (significant dust comae and tails) beyond a zone where water ice sublimation is negligible (up to 5 AU). Significant spatial variations both in the intensity and polarization are found in both comets. The slope of radial profiles of intensity changes gradually with the distance from the photocenter: from 0.7 near the nucleus up to about 1.3 for larger distances (up to 100000 km). The variation in polarization profiles indicates the non uniformity in the polarization distribution over the coma. The polarization degree over the coma gradually increases (in absolute value) with increasing the photocentric distance from of about 1.9% up to 3% for comet C/2010 S1 (LINEAR), and from of about 2.5% up to 3.5% for comet C/2010 R1 (LINEAR). These polarization values are significantly higher than typical value of the whole coma polarization ( −1.5%) for comets at heliocentric distances less than 5 AU. The obtained photometric and polarimetric data are compared with those derived early for other comets at smaller heliocentric distances. Numerical modeling of light scattering characteristics was performed for media composed of particles with different refractive index, shape, and size. The computations were made by using the superposition T-matrix method. We obtained that for comet C/2010 S1 (LINEAR), the dust in the form of aggregates of overall radius R ~ 1.3 μm composed of N = 1000 spherical monomers with radius a = 0.1 μm, refractive index m = 1.65 + i 0.05, allows to obtain a satisfactory agreement between the results of polarimetric observations of comet C/2010 S1 and computations.
Polarimetry, photometry, and spectroscopy of comet C/2009 P1 (Garradd)
Icarus, 2017
We present the results of photometry, linear spectropolarimetry, and imaging circular polarimetry of comet C/2009 P1 (Garradd) performed at the 6m telescope BTA of the Special Astrophysical Observatory (Russia) equipped by the multi-mode focal reducer SCORPIO-2. The comet was observed at two epochs post-perihelion: on February 2-14, 2012 at r h ∼1.6 au and α∼36° ; and on April 14-21, 2012 at r h ∼2.2 au and α∼27° The spatial maps of the relative intensity and circular polarization as well as the spectral distribution of linear polarization are presented. There were two features (dust and gas tails) oriented in the solar and antisolar directions on February 2 and 14 that allowed us to determine rotation period of the nucleus as 11.1 ± 0.8 hours. We detected emissions of C 2 , C 3 , CN, CH, NH 2 molecules as well as CO + and H 2 O + ions, along with a high level of the dust continuum. On February 2, the degree of linear polarization in the continuum, within the wavelength range of 0.67-0.68 μm, was about 5 ± 0.2% in the near-nucleus region up to ∼60 0 0 km and decreased to about 3 ± 0.2% at ∼40,0 0 0 km. After correction for the continuum contamination, the inherent degree of polarization in the emission band C 2 (ν= 0) is about 3.3%. We detected a small increase of linear polarization with the wavelength with the spectral gradient P/ λ=+ 4 ± 0.8%/μm and P/ λ=+ 6.2 ± 1.3%/μm, respectively, on February 2 and April 14. Linear polarization indicates that this dust-rich comet can be attributed to the high-P max comets. The left-handed (negative) circular polarization at the level approximately from −0.06 ± 0.02% to −0.4 ± 0.02%was observed at the distances up to 3 ×10 4 km from the nucleus on February 14 and April 21, respectively.
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.
Spectrophotometric monitoring of distant Comet C/2002 VQ94 (LINEAR) was performed with the 6-m telescope of SAO RAS (Special Astrophysical Observatory of Russian Academy of Sciences) and with the 2.5-m Nordic Optical Telescope (Observatory del Roque de los Muchachos, Canarias, Spain) between 2008 and 2013. During this period the comet was on the outbound segment of its orbit, between helio-centric distances of 8.36 au and 16.84 au. Analysis of the spectra revealed the presence of the CO + and N þ 2 emissions in the cometary coma at a distance of 8.36 au from the Sun. This distance is larger than ionic emissions have been detected in any previous objects. Only continuum, with no traces of emissions, was detected in the spectrum obtained in 2009 when the comet was at a distance of 9.86 au. From the spectra obtained in 2008, average column densities of 2.04 Â 10 9 mol cm À2 for N þ 2 and 3.26 Â 10 10 mol cm À2 for CO + were measured in the cometary coma. The derived values correspond to N þ 2 =CO þ ¼ 0:06 within the projected slit. Images obtained through a red continuum filter in 2008 showed a bright, dust coma, indicating a high level of physical activity. A considerably lower level of activity was observed in 2009 and 2011 at distances of 9.86 au and 13.40 au respectively. No noticeable activity was detected in 2013 at a heliocentric distance of 16.84 au. The Afq parameter, which is used as an indicator of cometary activity, was measured as 2000 cm in 2008, and 800 cm in 2009 and 2011. The Afq values correspond to dust production rates between 10–20 kg s À1 , 4–6 kg s À1 and 3–5 kg s À1 at 8.36, 9.86, and 13.40 au respectively. There is an obvious correlation between the decrease of the dust production rate of the nucleus and the disappearance of the emissions in the spectrum of C/2002 VQ94 (LINEAR) at heliocentric distances greater than 9 au. The colors and size of the nucleus of C/2002 VQ94 (LINEAR) were estimated from the images obtained during the late stage at a heliocentric distance of 16.84 au, when the activity had probable ceased. The B–V and V–R colors were estimated to be 1.07 ± 0.05 and 0.54 ± 0.03 respectively. The effective nucleus radius of 48 ± 2 km is in agreement with the previously published results, obtained from the observations of the comet during its early inactive stage (Jewitt, D. [2005]. Astron.
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 C/2012 L2 (LINEAR)
2015
We present the polarimetric results and analysis of comet C/2012 L2 (LINEAR) observed at 31∘.1 phase angle before perihelion passage. The observations of the comet were carried out using ARIES Imaging Polarimeter (AIMPOL) mounted on the 1.04-m Sampurnanand telescope of ARIES, Nainital, India on 11 and 12 March, 2013 using R photometric band (λ = 630 nm, Δλ =120nm). The extended coma of the comet (∼65000 km) shows a significant variation in the intensity as well as polarization profile in all considered directions which suggest that the dust particles originate from the active areas of the nucleus. The elongation of the coma is prominent along the Sun-comet position angle. The polarization of Comet C/2012 L2 (LINEAR) does not show steep radial dependence on the aperture size during both the nights of observation. A jet extended in the antisolar direction is well observed in both intensity and polarization map.
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.
Optical spectroscopy of comets using Hanle Echelle Spectrograph (HESP)
MNRAS, 2024
Observing the vibrational/rotational lines in a comet’s optical spectrum requires high-resolution spectroscopy, as they are otherwise seen as a blended feature. To achieve this, we have obtained medium and high-resolution (R ( λ/ dλ) = 30 000 and 60 000) spectra of several comets, including C/2015 V2 (Johnson), 46P/Wirtanen, 41P/Tuttle–Giacobini–Kres ´ak, and 38P/Stephan–Oterma, using the Hanle Echelle Spectrograph (HESP) mounted on the 2-m Himalayan Chandra Telescope (HCT) in India. The spectra effectively cover the wavelength range 3700–10 000 Å, allowing us to probe the various vibrational bands and band sequences to identify the rotational lines in the cometary molecular emission. We were also able to separate the cometary Oxygen lines from the telluric lines and analyse the green-to-red (G/R) forbidden oxygen [O I ] ratios in a few comets. For comets C/2015 V2, 46P, and 41P, the computed G/R ratios, 0.04 ±0.01, 0.04 ±0.01, and 0.08 ±0.02, respectively, point to H 2 O being a major source of Oxygen emissions. Notably, in the second fibre pointing at a location 1000 km away from the photocentre of comet 46P, the G/R ratio reduced by more than half the value observed in the first fibre, indicating the effects of quenching within the inner coma. We also measured the NH 2 ortho-to-para ratio of comet 46P to be about 3.41 ±0.05 and derived an ammonia ratio of 1.21 ±0.03 corresponding to a spin temperature of ∼26 K. With these, we present the results of the study of four comets from different cometary reservoirs using medium and high-resolution optical spectroscopy, emphasizing the capabilities of the instrument for future cometary studies.
Optical spectroscopy of comet C/2014 Q2 (Lovejoy) from the Mount Abu Infrared Observatory
Monthly Notices of the Royal Astronomical Society, 2016
Spectra of comet C/2014 Q2 (Lovejoy) were taken with a low-resolution spectrograph mounted on the 0.5-m telescope at the Mount Abu Infrared Observatory (MIRO), India during 2015 January to May, covering the perihelion and post-perihelion periods. The spectra showed strong molecular emission bands (C 2 , C 3 and CN) in January, close to perihelion. We obtained the scale-lengths for these molecules by fitting the Haser model to the observed column densities. The variations of gas production rates and production rate ratios with heliocentric distance were studied. The extent of dust continuum and its variation with heliocentric distance was also investigated using the Afρ parameter. The comet is seen to become more active in the post-perihelion phase, thus showing an asymmetric behaviour about the perihelion.