FEB 15 Tue 10:00～11:30 太陽系小天体セミナー / Solar System Minor Body Seminar zoom
FEB 16 Wed 15:30～17:00 NAOJ Science Colloquium zoom
FEB 18 Fri 16:00～17:00 NAOJ Seminar zoom
詳細は以下をご覧下さい
2月15日（火）
キャンパス：三鷹
セミナー名：太陽系小天体セミナー
定例・臨時の別：定例
日時：2月15日（火曜日）10時00分～11時30分
場所：zoom
講演者：田中壱
世話人の連絡先
名前：渡部潤一
備考：テレビ会議またはスカイプによる参加も可
2月16日（水）
Campus：Mitaka
Seminar：NAOJ Science Colloquium
Regularly Scheduled/Sporadic：Every Wednesday
Date and time：2022 Feb. 16, 15:30-17:00
Place：zoom
Speaker：Nishigaki Moka
Affiliation：NAOJ (M1 student)
Title：TBD
Abstract：TBD
Speaker：Seo Chanoul
Affiliation：NAOJ (D1 student)
Title：Atmospheres of sub-Neptune-sized exoplanets in contact with magma ocean
Abstract：Previous observational studies revealed the bimodal distribution of the radius for the planets with R<4R_⊕. The larger size group, sub-Neptune, is likely to have a substantial atmosphere under which the rocky interior may be molten (i.e., “magma”) depending on the temperature. As the rocky core still dominates the mass, direct contact between the magma and the atmosphere implies that magma affects the atmospheric composition significantly. Intending to understand the relation between the final atmospheric composition and the origin of volatile, we study the effect of magma on the volatile distribution in the sub-Neptune-sized planets. Our model is based on the model of a former study, but we introduce a more realistic behavior of the fluids, new solubility laws, and carbon-bearing species simultaneously. Our calculation shows a much more reduced atmosphere than the former study with the same amount of accreted H2 at higher pressure (>2GPa), mainly due to the newly introduced pressure dependence of H2 solubility. The C-bearing species are mainly present as methane in the atmosphere because the role of the magma on the distribution of C-bearing species is limited. We show how H2O and CH4 mixing ratios in the atmospheric composition as well as mass and radius can help us constrain the atmospheric origin and the initial magma composition. Within the current framework, the small H2O/H2 ratio (<1) and carbon depleted atmosphere cannot be attained simultaneously, implying that the sub-Neptunes like K2-18b which show small water fractions require a carbon-enriched atmosphere or additional carbon-erasing mechanism.
Facilitator
-Name：Akimasa Kataoka
Comment：English,
2月18日（金）
Campus：Mitaka
Seminar：NAOJ Seminar
Regularly Scheduled/Sporadic： Every Friday
Date and time：2022 Feb. 18, 18:00-17:00
Place：zoom
Speaker：田村 良明 / Tamura, Yoshiaki
Affiliation：国立天文台水沢VLBI観測所 / Mizusawa VLBI Observatory,NAOJ
Title：水沢VLBI観測所で超伝導重力計と絶対重力計で観測された 2011年東北地方太平洋沖地震後の重力変化
Post-seismic gravity change of the 2011 Tohoku Earthquake observed by the Superconducting Gravimeters and the Absolute Gravimeters at Mizusawa VLBI Observatory
Abstract：
なぜ重力変化の観測を水沢で行っているのか。 VLBIやGPSの連続観測では、座標値の変化が詳細に求められている。しかし座標の変化の観測だけでは、地下で何が起こっているのか知るすべが無い。水沢では超伝導重力計により重力の連続観測を2008年から、また、東京大学地震研究所と共同で絶対重力測定を2015年から毎年実施している。これらの観測を組み合わせて、2014年以降の東北地方太平洋沖地震のpostseismicな重力変化を議論する。観測点の隆起にともなう重力変化「free air 補正」を行うと、exp(-t) 型の重力増加が水沢で観測されている。この変化の様相は、より広域な重力変化を観測しているGRACE衛星の結果とは異なる様相を示している。衛星重力の結果は、長波長の現象（2、300km、上部マントル）の変動を、地上重力の観測はより小さなスケール（～50km）の現象を捉えているものと考えられる。
Why we measure gravity at the VLBI site? The VLBI observation and the GPS observation at Mizusawa show co-seismic and post seismic ground motion of the 2011 Tohoku Earthquake. To understand the physical process of the motion, we carried out continuous gravity change observation with the superconducting gravimeters and yearly absolute gravity measurements from 2015. The observed gravity data were corrected the instrumental drift, Earth tide, atmospheric pressure change, ground water change and uplift of the ground motion. The results shows exponential decay of the gravity increase. It’s decay time constant is estimated about 1.5 years. It is shorter compared with the time constant witch is obtained by the GRACE satellite data. The cause of the difference may be considered that the satellite observation is not sensitive to small scale (<100km) phenomena. The ground observation is sensitive to the shallow area (< a few tens km, crust) material change, while the satellite observation is sensitive to the deep area (a few hundred km, upper mantle) one.
Facilitator
-Name： 青木 和光 / Aoki, Wako