Isotopic ratios in outbursting comet C/2015 ER61

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp increase in brightness offered a rare opportunity to measure the isotopic ratios of the light elements in the coma of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017 April 13 and 17. At the time of our observations, the comet was fading gradually following the outburst. We measured the nitrogen and carbon isotopic ratios from the CN violet (0,0) band and found that $^{12}$C/$^{13}$C=100 $\pm$ 15, $^{14}$N/$^{15}$N=130 $\pm$ 15. In addition, we determined the $^{14}$N/$^{15}$N ratio from four pairs of NH$_2$ isotopolog lines and measured $^{14}$N/$^{15}$N=140 $\pm$ 28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets.Comment: 4 pages, 4 figures, accepted to be published by A&

High-Dispersion Spectroscopic Observations of Comet C/2012 S1 (ISON) with the Subaru Telescope

Comet C/2012 S1 (ISON) was one of the Oort cloud comets and dynamically new. This comet was broken at its perihelion passage on UT 2013 November 28.1 (at Rh ~ 17 solar radius). We observed the comet C/2012 S1 (ISON) on UT 2013 November 15 with the High Dispersion Spectrograph (HDS) mounted on the Subaru Telescope atop Mauna Kea, Hawaii. Its heliocentric and geocentric distances were 0.601 and 0.898 AU, respectively. We selected the slit size of 0”.5 x 9”.0 on the sky to achieve the spectral resolution of R = 72,000 from 550 to 830 nm. The total exposure time of comet C/2012 S1 (ISON) was 1200 seconds. We detected many emission lines caused from radicals (e.g., CN, C2, NH2), ions (H2O+), atoms ([OI] and Na I) and also many unidentified lines in the spectra. We report the (1) the ortho-to-para abundance ratios (OPRs) of water and ammonia estimated from the high-dispersion spectra of H2O+ and NH2, (2) the green-to-red line ratio of forbidden oxygen emissions, (3) the isotopic ratios of C2 (the carbon isotopic ratio from Swan band) and CN (the carbon and nitrogen isotopic ratios from red band), (4) the sodium-to-continuum ratio of comet C/2012 S1 (ISON). </HTML

Possibility of Concentration of Non-volatile Species near the Surface of Comet 67P/Churyumov-Gerasimenko

The cometary materials are thought to be the reservoir of primitive materials in the Solar System. The recent detection of glycine and CH$_3$NH$_2$ by the ROSINA mass spectrometer in the coma of 67P/Churyumov-Gerasimenko suggests that amino acids and their precursors may have been formed in an early evolutionary phase of the Solar System. We investigate the evolution of cometary interior considering the evaporation process of water followed by the concentration of non-volatile species. We develop a Simplified Cometary Concentration Model (SCCM) to simulate the evaporation and concentration processes on the cometary surface.We use 67P/Churyumov-Gerasimenko as the benchmark of SCCM. We investigate the depth of the layer where non-volatile species concentrate after the numerous passages of perihelion after the formation of the Solar System. As a result, the SCCM explains the observed production rates of water and CH$_3$NH$_2$ at 100 comet years. SCCM results suggest that the non-volatile species would concentrate at depths between 0 and 100cm of comet surface within 10 comet years. Our results also suggest that the non-volatile species would concentrate several meters beneath the surface before it hit the early Earth. This specific mass of non-volatile species may provide unique chemical condition to the volcanic hot spring pools.Comment: accepted to A&