Yoshiharu Shinnaka

14NH2/15NH2 RATIO IN COMET C/2012 S1 (ISON) OBSERVED DURING ITS OUTBURST IN 2013 NOVEMBER*

We performed high-dispersion optical spectroscopic observations of comet C/2012 S1 (ISON) using the High Dispersion Spectrograph (R = 72,000) at the Subaru Telescope on UT 2013 November 15.6, during an outburst that started on UT 2013 November 14. Due to the high gas-production rate of NH2 during the outburst, we successfully detected weak emission lines of 15NH2 and many strong emission lines of 14NH2 in the optical wavelength region from 5500 to 8200 ?. The ratio of 14NH2/15NH2 is derived to be 139 ? 38 in comet C/2012 S1 (ISON). This ratio is close to that recently revealed based on the averaged spectrum of 12 comets, ~130. This is also comparable to the typical cometary isotopic ratio of CN (12C14N/12C15N, observed in optical) and HCN (H12C14N/H12C15N, observed in radio), ~150. However, these ratios are much smaller than the protosolar value, 14N/15N = 441 ? 5. Because NH2 is considered to be a photodissociation product of NH3 in cometary coma, our result implies the occurrence of 15N fractionation of NH3 in the solar nebula or in the presolar molecular cloud.

ORTHO-TO-PARA ABUNDANCE RATIO OF WATER ION IN COMET C/2001 Q4 (NEAT): IMPLICATION FOR ORTHO-TO-PARA ABUNDANCE RATIO OF WATER*

The ortho-to-para abundance ratio (OPR) of cometary molecules is considered to be one of the primordial characteristics of cometary ices, and contains information concerning their formation. Water is the most abundant species in cometary ices, and OPRs of water in comets have been determined from infrared spectroscopic observations of H2O rovibrational transitions so far. In this paper, we present a new method to derive OPR of water in comets from the high-dispersion spectrum of the rovibronic emission of H2O+ in the optical wavelength region. The rovibronic emission lines of H2O+ are sometimes contaminated by other molecular emission lines but they are not affected seriously by telluric absorption compared with near-infrared observations. Since H2O+ ions are mainly produced from H2O by photoionization in the coma, the OPR of H2O+ is considered to be equal to that of water based on the nuclear spin conservation through the reaction. We have developed a fluorescence excitation model of H2O+ and applied it to the spectrum of comet C/2001 Q4 (NEAT). The derived OPR of water is 2.54+0.32 – 0.25, which corresponds to a nuclear spin temperature (T spin) of 30+10 – 4 K. This is consistent with the previous value determined in the near-infrared for the same comet (OPR = 2.6 ± 0.3, T spin = 31+11 – 5 K).

Inversion Angle of Phase-polarization Curve of Near-Earth Asteroid (3200) Phaethon

The linear polarization degree (referred to the scattering plane, P_r) as a function of the solar phase angle, {\alpha}, of solar system objects is a good diagnostic to understand the scattering properties of their surface materials. We report Pr of Phaethon over a wide range of {\alpha} from 19.1 deg to 114.3 deg in order to better understanding properties of its surface materials. The derived phase-polarization curve shows that the maximum of P_r, P_max, is >42.4% at {\alpha} >114.3 deg, a value significantly larger than those of the moderate albedo asteroids (P_max ~9%). The phase-polarization curve classifies Phaethon as B-type in the polarimetric taxonomy, being compatible with the spectral property. We compute the geometric albedo, p_v, of 0.14 +/- 0.04 independently by using an empirical slope-albedo relation, and the derived p_v is consistent with previous results determined from mid-infrared spectra and thermophysical modeling. We could not find a fit to the period in our polarimetric data in the range from 0 up to 7.208 hr (e.g., less than twice the rotational period) and found significant differences between our P_r during the 2017 approach to the Earth and that of the 2016. These results imply that Phaethon has a region with different properties for light scattering near its orbital pole.

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

MID-INFRARED SPECTROSCOPIC OBSERVATIONS OF THE DUST-FORMING CLASSICAL NOVA V2676 OPH*

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ORIGINS OF ABSORPTION SYSTEMS OF CLASSICAL NOVA V2659 CYG (NOVA CYG 2014)

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Ortho-to-para Abundance Ratio (OPR) of Ammonia in 15 Comets: OPRs of Ammonia Versus 14N/15N Ratios in CN

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Optical low-dispersion spectroscopic observations of Comet 103P/Hartley 2 at Koyama Astronomical Observatory during the EPOXI flyby

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Revisit to the Nuclear Spin Temperature of NH

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