| dc.description.abstract | 此論文包含了兩個部份，一個是利用光度變化研究在星團星場裡的變星，一個是利用星體位置的變化尋找自行運動大的白矮星，透過對這些星體的研究，我們想要了解變星與星團間的關係及銀河的結構。
我們在疏散星團 NGC 7039 的星場中，找到了 42 個變星及 6 個疑似變星的星體，根據它們的週期，光度變化的振幅，在可見光顏色星等圖及進紅外的顏色圖的位置，我們將找到的變星分類，其中包含了 14 個蝕雙星，1 個 RR Lyrae，2 個 Cepheid，1 個 beta-Cephei，3 個 delta-Scuti，8 個光度變化疑似脈動變星，5 個變星的周長長於我們的總觀測時間 41 天，以及 8 個不規則變星。根據對著這星變星估算的距離，及變星在星等顏色圖的分布，有兩組密接雙星疑似是 NGC 7039 的成員星。其中一組密接雙星在近紅外的顏色偏紅，但是在可見光的星等顏色圖在雙星分支的區域，我們推測，這組密接雙星有可能有星際物質圍繞著。
在此論文的第二部份，我們發表了用 Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) 的資料,，找到的在兩段時間內自行運動很快的白矮星。CFHTLS 的觀測提供了四度和五個波段 ( u*, g’, r’, i’, z’) 的觀測資料。其中有兩度 ( D1 & D4 ) 的資料，相隔了五年; 另外兩度 ( D2 & D3 ) 的資料，相隔了四年。研究目的是尋找自行速度快的白矮星，因為運行軌度的不同，他們通常來自銀暈的第二代恆星 (population II)，他們有著溫度低和年齡大的性質。根據星體的光譜能量分布分析和自行運動量與顏色的關係，我們找到了 20 個星等亮於 g’= 24 的溫度低且自行運動快的白矮星候選星，其中有四個星的溫度低於 4000 K，根據它們的速度推算，這四個星可能在銀河盤面上。白矮星候選星當中，有一個星溫度為 4500 K，有著很高的自行運動大約 140 mas/yr，這個星有可能是銀暈裡的星。
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| dc.description.abstract | The work contains two parts about using stellar photometric variation and astrometric variation to probe the stellar evolution and the Galactic structure. One is to search for variable stars in the Galactic Open Cluster NGC 7039 by the photometric variation. The time-series observations provide information of the transient photometry for population I in the Galactic disk. The other part in this work is to use the astrometric variation to find high proper motion white dwarfs. High proper motion objects can be used to investigate the stellar populations in, and the formation of, the Galaxy. The different moving orbits of the halo and the disk give us a way to find the population II stars such as ultracool and old white dwarfs in the halo.
We report variable stars identified in the field of the Galactic open cluster, NGC 7039. In the fall/winter of 2009, imaging photometry has been acquired, mainly in the R band, for 8 open clusters using the 81-cm Tenagra telescope in Arizona. We present the results for our first target, NGC 7039. We have found 42 new variable stars and 6 suspected variables stars. Among the variable stars, there are 14 eclipsing binaries including 1 RS Canum Venaticorum type system, 1 RR Lyrae, 2 Cepheid, 1 beta-Cephei, 3 delta-Scuti, 8 pulsating-like stars, 5 variable stars with periods longer than the observation window, 41 days, and 8 irregular variable stars. Two contact binary systems could be members of NGC 7039 because of their loci in the color-magnitude diagram and their distance moduli close to that of the open cluster. One of the contact binary systems shows infrared excess in the (J-H) and (H-K) diagram. It could has circumstellar dust. None of the pulsating stars belong to the open cluster.
For high proper motion white dwarfs, we present the results of a search
in the deep survey of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The CFHTLS Deep Survey covers 4 square degrees in 5 filters (u*,g’’,r’’,i’’,and z’’). For the first and the fourth fields, D1 and D4, we use data for a five-year baseline from 2004 to 2009. For the second and the third fields, D2 and D3, we have a four-year baseline from 2004 to 2008. Proper motion selection is used to distinguish cool high velocity white dwarfs from distant objects with similar blue colors such as compact faint galaxies and quasars.
We discovered twenty white dwarf candidates brighter than g’’=24 on the basis of their spectral energy distribution and reduced proper motions. We found four white dwarf candidates with effective temperatures less than to 4000 K. From their estimated velocities and distances they all appear to be located in the thin or thick disk of the Galaxy. One object with the effective temperatures 4500K has a high proper morion of 140 mas/yr. The object could be a halo object because of its high tangential velocity.
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