講演情報
[PPS01-P15]An Improved Upper Limit of Cyanodiacetylene (HC5N) in the Atmosphere of Titan
*飯野 孝浩2,1、佐川 英夫5、谷口 琴美3、窪田 暉5、高橋 茂4、Cordiner MartIn6 (1.東京大学情報基盤センター、2.山梨大学、3.国立天文台、4.兵庫県立大学、5.京都産業大学、6.NASA Goddard Space Flight Center)
キーワード：
タイタン、惑星大気、アストロバイオロジー
In the complex Titan atmospheric chemistry, photochemical reactions involving cyanodiacetylene (HC5N) may be important as reaction pathways that could lead to the production of amines and aromatic molecules. We carried out a new comprehensive search of HC5N in Titan’s atmosphere using Band 6 (215 – 275 GHz or 1.1 – 1.4 mm in wavelength)spectroscopic archival data from the Atacama Large Millimeter/submillimeter Array (ALMA). To search for a faint spectral line feature of HC5N, we used a spectral stacking method that integrates different transition data. Integrating six independent observation datasets with a total integration time of ∼15000 seconds, we found no statistically significant detection of an HC5N spectral feature. Using the Planetary Spectrum Generator (PSG) for radiative transfer modeling and employing the previously predicted vertical distribution proposed by Vuitton et al. (2019), Lellouch et al. (2010a), Loison et al. (2015) and Krasnopolsky (2009), we derived the upper limit column density of HC5N, corresponding to 3–σ noise level, to be 0.3 – 10×1013 molecules/cm2 above ∼60 km altitude (depending on the assumed vertical profile). The corresponding upper limit of [HC5N]/[HC3N] ratio value derived from three of four models seem to be lower than that measured in High-mass Protostellar Objects (HMPOs), possibly due to the lower abundance of C4H2.