Astrometric VLBI observations of H2_2O masers in an extreme OH/IR star candidate NSV17351

Results of astrometric very long baseline interferometry (VLBI) observations towards an extreme OH/IR star candidate NSV17351 are presented. We used the VERA (VLBI Exploration of Radio Astrometry) VLBI array to observe 22\,GHz H$_2$O masers of NSV17351. We derived an annual parallax of 0.247$\pm$0.035 mas which corresponds to a distance of 4.05$\pm$0.59 kpc. By averaging the proper motions of 15 maser spots, we obtained the systemic proper motion of NSV17351 to be ($\mu_{\alpha}\cos{\delta}, \mu_{\delta}$)$^{\mathrm{avg}}$ $=$ ($-$1.19 $\pm$ 0.11, 1.30 $\pm$ 0.19) mas\,yr$^{-1}$. The maser spots spread out over a region of 20 mas $\times$ 30 mas, which can be converted to a spatial distribution of $\sim$80 au $\times$ $\sim$120 au at the source distance. Internal motions of the maser spots suggest an outward moving maser region with respect to the estimated position of the central star. From single dish monitoring of the H$_2$O maser emission, we estimate the pulsation period of NSV17351 to be 1122$\pm$24 days. This is the first report of the periodic activity of NSV17351, indicating that NSV17351 could have a mass of $\sim$4\,M$_{\odot}$. We confirmed that the time variation of H$_2$O masers can be used as a period estimator of variable OH/IR stars. Furthermore, by inspecting dozens of double-peaked H$_2$O maser spectra from the last 40 years, we detected a long-term acceleration in the radial velocity of the circumstellar matter to be $0.17\pm0.03$ km\,s$^{-1}$\,yr$^{-1}$ Finally, we determined the position and kinematics of NSV17351 in the Milky Way Galaxy and found that NSV17351 is located in an interarm region between the Outer and Perseus arms. We note that astrometric VLBI observations towards extreme OH/IR stars are useful samples for studies of the Galactic dynamics.Comment: Published in the Publications of the Astronomical Society of Japa

フカンゼン キン FUSIDIUM SP BX-1 ニヨル ユシルイ ノ リヨウセイ

不完全菌Fusidium sp. BX-1の油脂類の利用性とリパーゼ生産性に関して検討した。BX-1株は広い範囲の油脂類を利用することができ,本菌のオリーブ油の利用性について酵母類や糸状性菌類と比較したところ,本菌の利用性は,酵母より糸状菌に近いことが明らかになった。BX-1株は,オレイン酸を炭素源として培養した場合には直ちに旺盛な生育を示したが,オリーブ油を炭素源として培養した場合には,生育の立ち上がらない誘導期があったのち,オレイン酸培地におけるより早い速度で増殖を始めた。このオリーブ油培地において,BX-1株はリパーゼを細胞外に生産したが,その生産量(約3U/ml)は,既知のリパーゼ生産菌と比較してかなり低いものであった。本研究を遂行するにあたり,実験に協力下さった千葉大学藤井一太氏にお礼申し上げます。また,実験協力やご助言を下さった千葉大学藤井貴明教授,篠山浩文助教授に深謝いたします