{"created":"2023-06-20T13:22:51.860692+00:00","id":3573,"links":{},"metadata":{"_buckets":{"deposit":"95049ead-46bb-4273-bd64-c8d058a3c2f7"},"_deposit":{"created_by":21,"id":"3573","owners":[21],"pid":{"revision_id":0,"type":"depid","value":"3573"},"status":"published"},"_oai":{"id":"oai:ir.soken.ac.jp:00003573","sets":["2:427:11"]},"author_link":["1417","1415","1416"],"item_1_creator_2":{"attribute_name":"著者名","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"〓, 正〓"}],"nameIdentifiers":[{}]}]},"item_1_creator_3":{"attribute_name":"フリガナ","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ザオ, ジェンシイ"}],"nameIdentifiers":[{}]}]},"item_1_date_granted_11":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2012-09-28"}]},"item_1_degree_grantor_5":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"総合研究大学院大学"}]}]},"item_1_degree_name_6":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（理学）"}]},"item_1_description_12":{"attribute_name":"要旨","attribute_value_mlt":[{"subitem_description":"Blue straggler stars (BSSs) lie above the current main sequence turn off\r\non the color-magnitude diagram of star cluster. Their positions on the\r\ncolor-magnitude diagram imply that they are more massive than current\r\nmain sequence turn-off stars in the same cluster. Thus, their presence of\r\nsuch an upper main sequence was a challenge for standard stellar evolution\r\ntheory, as normal stars with the same mass have already evolved into white\r\ndwarfs. To explain their extraordinary long lifespan on the main sequence,\r\nvarious mechanisms have been suggested, all involving in additional hydrogen\r\nmaterial input to normal stars. Two of the most popular mechanisms\r\nare merger by direct collisions in single stars and coalescence or mass transfer\r\nin close binary systems. As products of dynamical processes in the host\r\ncluster and stellar evolution itself, studying BSSs can shed a light on the\r\nprocess of merger and/or mass transfer, and be a tracer of the dynamical\r\nevolution of the host cluster.\r\nThe first discovery of BSSs in a globular cluster M3 dates back to six\r\ndecades ago. Since then, many observational \fndings suggest that BSSs\r\nare present in globular clusters, open clusters, as well as dwarf spheroidal\r\ngalaxies (dSphs), and even in the \felds and the bulge of the Milky Way\r\nand imply that di\u000berent formation mechanisms may operate in different\r\ndynamical environments. Though we are still facing with problems in understanding\r\nthese objects clearly and completely. The aim of this thesis is\r\nto derive a comprehensive interpretation for origins of BSS by investigating\r\nthe BSS properties in di\u000berent star systems, such as open clusters, globular\r\nclusters and dSphs based on observational data of the highest quality up to\r\nthe present day.\r\nWe have collected homogeneous deep photometric data for 9 dSphs\r\ntaken from Subaru/ Suprime-Cam. The sample includes 3 classical dSphs,\r\nDraco, Ursa Minor (UMi) and Sextans and 6 ultra faint dwarf galaxies. For\r\nthese classical dSphs, we have analyzed the BSSs' radial distributions and\r\nluminosity functions. BSSs radial distribution shows a lack of strong central\r\npeak and luminosity function is independent of radius. These results imply\r\nthat in these dSphs, the blue plume stars are most likely to be real BSSs\r\nformed mainly by mass transfer in primordial binaries. The frequency of\r\nBSSs in the 9 galaxies does not correlate with galaxy parameters, such as\r\nhalf light radius rh, metallicity [Fe/H], central surface brightness μV;C, concentration\r\nparameter c, central density pc, velocity dispersion δV , half mass\r\nrelaxation time log trh and collisional rate Γ , as well as integrated absolute\r\nmagnitude, MV. This result suggests that the evolution of primordial binaries,\r\nwhich would form BSSs, was not affected significantly by dynamical\r\ninteractions in such sparse environments. Thus, the observed BSS frequency\r\nis almost the same in these galaxies under the simple hypothesis that the\r\nprimordial binary fraction was the same in all galaxy.\r\nWe have also collected homogeneous deep photometric data for 51 GC\r\nobtained by ACS/HST. 8 GCs in our sample show bimodal BSSs frequency\r\nradial distributions. Among them, the bimodal distribution is reported for\r\nthe first time in NGC 5286, NGC 5986, NGC 6362, NGC 6535, NGC6541\r\nand NGC7099, in total 6 GCs. It has raised the number of this kind of\r\nGCs by twice the number known before. Moreover, the significant anticorrelation\r\nbetween BSS frequency and MV is confimed with our sample.\r\nBSS frequency is also significantly anti-correlated to central density, central\r\nvelocity dispersion and collision rate. Furthermore, luminosity functions of\r\nBSSs in bright (MV < -8.8) and faint (MV > -8.8) clusters do not show\r\nsignificant differences. One possible interpretation for all these properties is\r\nthat BSSs formation from binaries is the dominant mechanism in globular\r\nclusters. However, The effect of collision on BSS formation is still considerable\r\nbecause collisions destroy primordial binaries and/or accelerate\r\nevolution of binary systems.\r\nFinally, we have observed 30 BSSs and 9 main sequence turn-off candidates\r\nin three old Galactic open clusters, NGC 2682, NGC 2112 and NGC\r\n6819. Among them, radial velocities (Vr) of all target stars in NGC 2682\r\nand NGC 6819, and 5 BSSs and all TOs in NGC 2112 are consistent with\r\nmean Vr of member stars in the clusters. Rotational velocity (vsini ) of\r\nBSSs spans a wide range from few kms-1 to hundreds km_s-1, while those\r\nof turn-off stars vary in small range from few kms-1 to 25 kms-1. The\r\nhigh rotation velocity of current BSS is consistent with predictions both\r\nfrom mass transfer and collision formation mechanism. Some turn-off stars\r\nand a few of BSSs show normal Li abundances. For the other BSSs, only\r\nthe upper limit of Li abundance is estimated. Interestingly, BS1371 in NGC\r\n2112 and BS 10010 in NGC 6819, show very high Li abundance, A(Li) 3.94\r\ndex and A(Li) 3.52 dex. Two BSSs show depletion in oxygen abundance,\r\nwhile the most of BSSs show similar oxygen abundance to turn-off stars.\r\nSome BSSs show depletion in carbon abundance, while other BSSs show\r\nthe normal carbon abundance comparing to turn-off stars. These abundance\r\nanomalies in light elements found in some BSSs suggest that mass\r\ntransfer from such highly evolved stars is the origin of these BSSs. On the\r\nother hand, the progenitor of other BSSs with normal carbon and oxygen\r\nabundances and low lithium abundances might be normal red giant stars.","subitem_description_type":"Other"}]},"item_1_description_7":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_description":"総研大甲第1543号 ","subitem_description_type":"Other"}]},"item_1_select_14":{"attribute_name":"所蔵","attribute_value_mlt":[{"subitem_select_item":"有"}]},"item_1_select_8":{"attribute_name":"研究科","attribute_value_mlt":[{"subitem_select_item":"物理科学研究科"}]},"item_1_select_9":{"attribute_name":"専攻","attribute_value_mlt":[{"subitem_select_item":"09 天文科学専攻"}]},"item_1_text_10":{"attribute_name":"学位授与年度","attribute_value_mlt":[{"subitem_text_value":"2012"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"ZHAO, Zhengshi","creatorNameLang":"en"}],"nameIdentifiers":[{}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2016-02-17"}],"displaytype":"simple","filename":"甲1543_要旨.pdf","filesize":[{"value":"282.5 kB"}],"format":"application/pdf","licensetype":"license_11","mimetype":"application/pdf","url":{"label":"要旨・審査要旨","url":"https://ir.soken.ac.jp/record/3573/files/甲1543_要旨.pdf"},"version_id":"44ca4ccb-6b22-4901-bb37-b16f864772c9"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Origins of Blue Straggler Stars in Open Clusters, Globular Clusters and Dwarf Spheroidal Galaxies","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Origins of Blue Straggler Stars in Open Clusters, Globular Clusters and Dwarf Spheroidal Galaxies"},{"subitem_title":"Origins of Blue Straggler Stars in Open Clusters, Globular Clusters and Dwarf Spheroidal Galaxies","subitem_title_language":"en"}]},"item_type_id":"1","owner":"21","path":["11"],"pubdate":{"attribute_name":"公開日","attribute_value":"2013-05-24"},"publish_date":"2013-05-24","publish_status":"0","recid":"3573","relation_version_is_last":true,"title":["Origins of Blue Straggler Stars in Open Clusters, Globular Clusters and Dwarf Spheroidal Galaxies"],"weko_creator_id":"21","weko_shared_id":-1},"updated":"2023-06-20T15:29:02.042930+00:00"}