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Register a new userFollow-up spectroscopy of comet C/2020 F3 (NEOWISE)
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We present spectroscopy of the coma center of comet C/2020 F3 (NEOWISE), carried out at the end of July 2020 with the Echelle spectrograph FLECHAS at the University Observatory Jena. The comet was observed in 5 nights and many prominent emission features were detected between 4685r{A} and 7376r{A}. Beside the C$_2$ Swan emission bands also several emission features of the amidogen radical, as well as two forbidden lines of oxygen were identified in the FLECHAS spectra of the comet in all observing epochs. In contrast, strong sodium emission was detected only in the spectra of the comet, taken on 21 and 23 July 2020, which significantly faded between these two nights, and was no longer present in the spectra as of 29 July 2020. In this paper we present and characterize the most prominent emission features, detected in the FLECHAS spectra of the comet, discuss their variability throughout our spectroscopic monitoring campaign, and use them to derive the radial velocity of the comet in all observing nights.
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The recent close approach of comet C/2020 F3 (NEOWISE) allowed us to study the morphology of its inner coma. From the measurement of the dust ejection velocityon spiral structures expanding around the nucleus, we estimated a mean deprojectedexpansion velocity Vd= 1.11+/-0.08 km s^-1. Assuming that a new shell formed after every rotation of the comet, a rotation period of 7.8+/-0.2 hours was derived. The spin axis orientation was estimated at RA 210+/-10d, Dec. +3+/-10d. The comamorphology appears related to two strong, diametrically opposite emissions located at mid-latitudes on the nucleus. A qualitative modelling of the coma produced consistent results with a wide range of dust sizes (0.80 to 800 micro-m), with inversely correlated densities (0.003 to 3.0 g cm^-3). Images taken with Vj and r-Sloan filters showed a greater concentration of dust in the first two shells, and an increasing density of radicals emitting in the B and V band-passes from the third shell outwards. Striae-like structures in the tail suggest that dust particles have different sizes.
Comets are the most primordial objects in our solar system which are made of icy bodies. Comets used to release gas and dust when it moves close to the Sun. The C/2020 F3 (NEOWISE) is a large periodic comet that is moving in a near-parabolic orbit. The C/2020 F3 (NEOWISE) is the brightest comet in the northern hemisphere after comet Hale-Bopp in 1997. Here we present the first interferometric high-resolution detection of the comet C/2020 F3 (NEOWISE) using the Giant Metrewave Radio Telescope (GMRT). The observational frequency range is 1050$-$1450 MHz. We detect the radio continuum emission from this comet with flux density level 2.8$-$3.4 mJy between the frequency range 1050--1450 MHz. We also detect atomic HI absorption line at $ u$ = 1420 MHz ($sim$5$sigma$ significance) with column density $N(textrm {HI}) = (1.8 pm 0.09)times 10^{22}$ cm$^{-2}$. The continuum emission from the comet in meter wavelength arises from the large Icy Grains Halo (IGH) region. Significant detection of C/2020 F3 in $sim$21 cm indicates the presence of large size of particles in the coma region of the comet.
We present the results of photometry, linear spectropolarimetry, and imaging circular polarimetry ofcomet C/2009 P1 (Garradd) performed at the 6-m telescope BTA of the Special Astrophysical Observatory(Russia) equipped by the multi-mode focal reducer SCORPIO-2. The comet was observed at two epochspost-perihelion: on February 2-14, 2012 at r=1.6 au and {alpha}=36 {deg}; and on April 14-21, 2012 at r=2.2 au and {alpha}=27 deg. The spatial maps of the relative intensity and circular polarization as well as the spectral distribution of linear polarization are presented. There were two features (dust and gas tails) orientedin the solar and antisolar directions on February 2 and 14 that allowed us to determine rotation periodof the nucleus as 11.1 hours. We detected emissions of C2 , C3 , CN, CH, NH2 molecules as well as CO+ and H2O+ ions, along with a high level of the dust continuum. On February 2, the degree of linear polarization in the continuum, within the wavelength range of 0.67-0.68 {mu}m, was about 5% in the near-nucleus region up to near 6000 km and decreased to about 3% at near 40,000 km. The left-handed (negative) circular polarization at the level approximately from -0.06% to -0.4% was observed at the distances up to 3*10^4 km from the nucleus on February 14 and April 21, respectively.
We analyze the dust environment of the distant comet C/2014 A4 (SONEAR), with a perihelion distance near 4.1~au, using comprehensive observations obtained by different methods. We present an analysis of spectroscopy, photometry, and polarimetry of comet C/2014 A4 (SONEAR), which were performed on November 5~--~7, 2015, when its heliocentric distance was 4.2~au and phase angle was 4.7$^circ$. Long-slit spectra and photometric and linear polarimetric images were obtained using the focal reducer SCORPIO-2 attached to the prime focus of the 6-m telescope BTA (SAO RAS, Russia). We simulated the behavior of color and polarization in the coma presenting the cometary dust as a set of polydisperse polyshapes rough spheroids. No emissions were detected in the 3800~--~7200~$AA$ wavelength range. The continuum showed a reddening effect with the normalized gradient of reflectivity 21.6$pm$0.2% per 1000~$AA$ within the 4650~--~6200~$AA$ wavelength region. The fan-like structure in the sunward hemisphere was detected. The radial profiles of surface brightness differ for r-sdss and g-sdss filters, indicating predominance of submicron and micron-sized particles in cometary coma. The dust color (g--r) varies from 0.75$ pm $0.05$^m$ to 0.45$ pm $0.06$^m$ along the tail. For aperture radius near 20~000~km, the dust productions in various filters were estimated as $Afrho $~=~680$pm$18~cm (r-sdss) and 887$ pm $16~cm (g-sdss). The polarization map showed spatial variations of polarization over the coma from about --3% near the nucleus to --8% at cometocentric distance about 150~000~km. Our simulations show that the dust particles were dominated (or covered) by ice and tholin-like organics. Spatial changes in the color and polarization can be explained by particle fragmentation.
We present an analysis of the photometric and spectroscopic observations of the split comet C/2019 Y4 (ATLAS). Observations were carried out on the 14th and 16th of April 2020 when the heliocentric distances of the comet were 1.212 and 1.174 au, its geocentric distances 0.998 and 0.991 au, and the phase angle 52.9{deg} and 54.5{deg}, respectively. The comet was observed with the 6-m BTA telescope of the Special Astrophysical Observatory (Russia) with the SCORPIO-2 multi-mode focal reducer. The narrow-band BC and RC cometary filters in the continuum were used. We identified numerous emissions of the CN, C2, C3, and NH2 molecules within the range of 3750-7100 {AA}. The C2/CN and C3/CN production rate ratios coincide with those of typical comets. Four fragments belonging to the coma were detected in both observational runs. We compared and analyzed temporal variations of the visual magnitudes, gas productivity, and dust colour. Based on our dynamical investigation of the orbits of comets C/1844 Y1 (Great comet) and C/2019 Y4 (ATLAS), we can claim that, with high probability, two comets do not have a common progenitor.
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