講演情報
[PPS03-P25]Video Observations of Faint Meteors with Tomo-e PM
*大澤 亮1、酒向 重行1、猿楽 祐樹2、臼井 文彦3、大坪 貴文4、藤原 康徳5、佐藤 幹也6、春日 敏測11、有松 亘7、渡部 潤一7、土居 守1、小林 尚人1、高橋 英則1、本原 顕太郎1、宮田 隆志1、諸隈 智貴1、小西 真広1、青木 勉1、征矢野 隆夫1、樽澤 賢一1、森 由貴1、中田 好一1、満田 和真1、一木 真1、有馬 宣明1、小島 悠人1、戸谷 友則8、松永 典之8、茂山 俊和9、板 由房10、小久保 充10、前原 裕之11、冨永 望12、山下 卓也7、田中 正臣7、猪岡 皓太7、池田 思朗13、森井 幹雄13、吉川 真4、浦川 聖太郎14、奥村 真一郎14 (1.東京大学大学院理学系研究科 天文学教育研究センター、2.京都産業大学 神山天文台、3.神戸大学 理学研究科、4.国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所、5.総合研究大学院大学、6.日本流星研究会、7.国立天文台、8.東京大学大学院理学系研究科 天文学教室、9.東京大学ビッグバン宇宙国際研究センター、10.東北大学 天文学教室、11.京都大学、12.甲南大学、13.統計数理研究所、14.日本スペースガード協会)
キーワード：
流星、動画観測、惑星間空間ダスト
There are vastly different sizes of objects in the solar system, from the Sun, which is obviously the largest object in the solar system, to beta-meteoroids, which are small particles pushed away by radiation into interstellar space. The size distribution of small bodies in the solar system is important to understand the origin and the evolution of the solar system. Particles smaller than about 1 mm are usually referred as to interstellar dust particles (IDPs). The IDPs are rapidly (up to a few thousand years) removed by a radiation pressure or the Poynting-Robertson effect. Present activities of solar system small bodies are reflected in the size distribution of the IDPs. The IDPs in interplanetary space are, however, difficult to investigate directly, since they are too small to be observed and too sparsely distributed for in-situ investigation.
Tons of IDPs fall down to the Earth per day. Interacting with atmosphere, they lose part of their kinetic energy in a form of emission. This phenomenon is called meteor. Thus, we can derive physical parameters of single particles by investigating meteors. The size distribution of the IDPs around the Earth can be examined through the luminosity function of meteors. Fainter meteors should be observed to constrain the size distribution of smaller IDPs.
To efficiently detect faint meteors, a high sensitivity video camera with a large aperture is preferred. We have been developing a new wide-field CMOS mosaic camera, Tomo-e Gozen, for the 1.05-m Kiso Schmidt Telescope. The camera is composed of four individual camera modules, each of which is equipped with 21 CMOS image sensors. Tomo-e Gozen can monitor a sky of about 20 deg2 continuously at up to 2 Hz. The camera will start its operation with a single module in February, 2018. A limiting magnitude of Tomo-e Gozen is expected to be about 18.5 mag. in the V-band for 0.5 s integration, corresponding to a meteor limiting magnitude of about 13 mag. in the V-band. Tomo-e Gozen mounted on the 1.05-m Kiso Schmidt Telescope will be the world-largest video camera, and thus will be an ideal facility to observe faint meteors. As a pathfinder project for Tomo-e Gozen, we have developed a prototype mosaic CMOS camera, Tomo-e PM. Tomo-e PM is equipped with 8 CMOS sensors, which has an ability to continuously obtain images of about 2 deg2 at 2 Hz. A limiting magnitude of the Tomo-e PM is as good as of Tomo-e Gozen. Tomo-e PM is still a powerful facility to observe faint meteors.
We performed meteor observations with the Tomo-e PM mounted on the 1.05-m Kiso Schmidt Telescope. The observations were carried out on 2016-04-11 and 2016-04-14. The lunar ages were 3.6 and 6.6 on 2016-04-11 and 2016-04-14, respectively. Net observing time was about 10.6 hours in total. Tomo-e PM detected 2,220 unique meteor events. The video rate absolute magnitudes of the detected meteors ranged from 4.0 to 10.0 mag. in the V-band. The result clearly demonstrates that the Tomo-e Gozen has an ability to investigate meteors fainter than 10 mag. Since no significant meteor shower activity was reported, most of the detected meteors were expected to be sporadic meteors.
We approximate the luminosity function of meteors by an exponential distribution: log10 N(<M) = log10N0 + Mlog10r, where N(<M) is the number of meteors brighter than M-th magnitude, N0 is the number of meteors brighter than zeroth magnitude, and r is the slope of the luminosity function or the meteor index. The parameters N0 and r were constrained by a fitting based on a statistical model. The present results suggest that r = 3.1±0.4 and log10N0 =-5.5±0.5. The present results are roughly consistent with the luminosity functions obtained for sporadic meteors in literature. We have demonstrated that a wide-field CMOS camera mounted on a large telescope has advantages in observing faint meteors. With Tomo-e Gozen, we are able to efficiently investigate variations in the luminosity function of faint meteors with a sufficiently large number of samples.
Tons of IDPs fall down to the Earth per day. Interacting with atmosphere, they lose part of their kinetic energy in a form of emission. This phenomenon is called meteor. Thus, we can derive physical parameters of single particles by investigating meteors. The size distribution of the IDPs around the Earth can be examined through the luminosity function of meteors. Fainter meteors should be observed to constrain the size distribution of smaller IDPs.
To efficiently detect faint meteors, a high sensitivity video camera with a large aperture is preferred. We have been developing a new wide-field CMOS mosaic camera, Tomo-e Gozen, for the 1.05-m Kiso Schmidt Telescope. The camera is composed of four individual camera modules, each of which is equipped with 21 CMOS image sensors. Tomo-e Gozen can monitor a sky of about 20 deg2 continuously at up to 2 Hz. The camera will start its operation with a single module in February, 2018. A limiting magnitude of Tomo-e Gozen is expected to be about 18.5 mag. in the V-band for 0.5 s integration, corresponding to a meteor limiting magnitude of about 13 mag. in the V-band. Tomo-e Gozen mounted on the 1.05-m Kiso Schmidt Telescope will be the world-largest video camera, and thus will be an ideal facility to observe faint meteors. As a pathfinder project for Tomo-e Gozen, we have developed a prototype mosaic CMOS camera, Tomo-e PM. Tomo-e PM is equipped with 8 CMOS sensors, which has an ability to continuously obtain images of about 2 deg2 at 2 Hz. A limiting magnitude of the Tomo-e PM is as good as of Tomo-e Gozen. Tomo-e PM is still a powerful facility to observe faint meteors.
We performed meteor observations with the Tomo-e PM mounted on the 1.05-m Kiso Schmidt Telescope. The observations were carried out on 2016-04-11 and 2016-04-14. The lunar ages were 3.6 and 6.6 on 2016-04-11 and 2016-04-14, respectively. Net observing time was about 10.6 hours in total. Tomo-e PM detected 2,220 unique meteor events. The video rate absolute magnitudes of the detected meteors ranged from 4.0 to 10.0 mag. in the V-band. The result clearly demonstrates that the Tomo-e Gozen has an ability to investigate meteors fainter than 10 mag. Since no significant meteor shower activity was reported, most of the detected meteors were expected to be sporadic meteors.
We approximate the luminosity function of meteors by an exponential distribution: log10 N(<M) = log10N0 + Mlog10r, where N(<M) is the number of meteors brighter than M-th magnitude, N0 is the number of meteors brighter than zeroth magnitude, and r is the slope of the luminosity function or the meteor index. The parameters N0 and r were constrained by a fitting based on a statistical model. The present results suggest that r = 3.1±0.4 and log10N0 =-5.5±0.5. The present results are roughly consistent with the luminosity functions obtained for sporadic meteors in literature. We have demonstrated that a wide-field CMOS camera mounted on a large telescope has advantages in observing faint meteors. With Tomo-e Gozen, we are able to efficiently investigate variations in the luminosity function of faint meteors with a sufficiently large number of samples.