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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/80372

    Title: 利用冷塵埃的熱輻射追蹤主序後星質量 流失歷史;Tracing Historic Mass Loss from Evolved Stars with Thermal Emission from Cold Dust
    Authors: 戴維莎;Dharmawardena, Thavisha Erandinie
    Contributors: 天文研究所
    Keywords: 進化的恆星;散熱粉塵;質量損失率;亞毫米波;Evolved stars;Thermal dust emission;Mass loss;sub-mm
    Date: 2019-07-17
    Issue Date: 2019-09-03 14:27:02 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 主序後星在宇宙塵埃的生命週期中扮演關鍵角色。由於主序後星數量眾多, 因此能有
    利用塵埃的熱輻射有效地追其質量流失歷程。本論文使用Herschel / PACS遠紅外望遠
    鏡(波長70微米、100微米和160微米)和JCMT / SCUBA-2次毫米波望遠鏡(450微米
    本論文透過觀察研究表面亮度、溫度、塵埃質量- 柱密度和徑向的塵埃輻射率光譜指
    的分離殼層複雜性,並指出進一步研究的需要。兩個著名主序後星IRC + 10216和鯨魚
    座o 星的次毫米波週期的分析顯示,可能可使用主序後星的次毫米波光變曲線來有效研
    究它們包層內部的塵埃形成和分解性質。IRC + 10216顯示可見光和次毫米觀測的偏移
    沒有觀測到的主序後星。由Herschel HERITAGE普查計劃,波長為100微米的調查,可
    重要性。;Evolved stars play a key role in the life cycle of dust in the universe. Through strong
    winds and supernovae they inject the material reprocessed in their cores to the interstellar
    medium, replenishing the interstellar medium with heavy elements. As evolved stars are
    so numerous they are extremely e ective in this role. In this thesis we study this mass loss
    delving deep into their past, exploring dust mass-loss events which occurred throughout
    their lifetime as evolved stars. The typical treatment of evolved stars has been to only
    account for present day mass loss or assume they are quasi-stable undergoing constant
    mass loss throughout their lifetime. Historic mass loss can be e ectively traced using
    thermal emission from the dust which cools down as it moves away from the central star.
    We exploit Herschel/PACS far-infrared (70 m; 100 m and 160 m) and JCMT/SCUBA-
    2 sub-millimetre (450 m and 850 m) observations to study this historic mass loss.
    These two sets of observations are especially powerful, tracing the radial variation in
    the circumstellar envelopes of evolved stars. We establish the presence of variations in
    mass loss for a sample of Milky Way evolved stars by studying features observed in
    surface-brightness, temperature, dust mass-column density and spectral index of dust
    emissivity radial pro les. By comparing these results to predictions for a constant-out
    model we nd signi cant deviations between the total dust masses determined for the
    two scenarios, demonstrating that the e ect of mass-loss variations cannot be ignored.
    We determine the complexities of the detached shell of U Ant with the aid of radiative
    transfer modelling, prompting the need for further study at higher angular resolution.
    The analysis of the sub-mm periodicity of IRC+10216 and o Ceti, two well-known evolved
    stars, shows that it may be possible to use sub-mm light curves of evolved stars to study
    the nature of dust formation/destruction in their inner envelope e ectively. The optical and sub-mm light curves of IRC+10216 shows an o set in phase of 3=4. Using radiative
    transfer modelling as well as ndings in literature we attribute the sub-mm variability and
    phase lag to both the relationship between stellar pulse and dust formation/destruction
    cycle as well as a second unknown mechanism which needs to be narrowed down in the
    future. Moving on from the Milky Way to the Magellanic clouds we combine cutouts of
    evolved stars identi ed in the mid-infrared but not detected in the far-IR. The cutouts are
    generated from the Herschel HERITAGE survey at 100 m allowing a statistical study of
    the existence or absence of a far-IR component as a result of cold dust in these evolved
    stars. We successfully produce detections for three stacks comprised of the highest massloss
    rate sources, showcasing the merits of the stacking method. With this thesis we
    emphasise the variations in structure and hence historic mass loss of evolved stars. By
    doing so we highlight the importance of including these variations in studies which include
    dust production by evolved stars in the future.
    Appears in Collections:[天文研究所] 博碩士論文

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