利用泛星計劃在反銀河系中心方向尋找疏散星團並分析其特性

Searching for and Characterization of Galactic Open Clusters toward the Galactic Anti-Center with Pan-STARRS

林建爭(Chien-Cheng Lin)

指導教授 ： 陳文屏

國立中央大學/理學院/天文研究所/博士(2014年)

摘要

依照觀測到的星團數量估計結果指出，在本銀河系裡的星團數量應該存在有十多萬個，然而目前被研究列表出來的星團數量僅幾千個，且絕大部分都分佈在太陽系遭周大約兩千秒差距。我們的研究工作的主要目的是利用泛星計劃的大天區及高解析力的特性，從其資料庫去尋找更多尚未發現的星團以及分析他們的特性。本篇論文利用數星的方法先從反銀河系方向的區域進行試驗性的搜尋及分析。我們的搜尋方法對於半徑小於十角分的已知星團可以達到百分之八十三的偵測效率。在反銀河系四百平方角度的區域裡，我們偵測到四百九十一個星數密度高的區域，其中有五十個是已知星團。我們另外建立了分析星團特性的程式，此程式利用星星的自行運動以及二維米巡天計劃和泛星計劃的光度資料挑出星團裡可能的成員星，接著利用這些成員星去估計出候選星團的半徑大小、紅化程度、距離、年齡、以及可以偵測到的最低質量星體。這份新的星團樣本，讓我們將在反銀河方向星團數量的完整性推估至將近五千秒差距。除此之外，我們也利用這份新的星團樣本加上已知的樣本來推估出射手座懸臂跟雙魚座懸臂的間距約三千兩百個秒差距，以及推估出射手、獵戶、雙魚座在太陽附近三個懸臂的寬度分別約一千四、一千六、三千三個秒差距。

在利用泛星資料分析之前，我們把數星的方法應用在二維米巡天的資料上，其中G144.0+0.4星團被我們偵測並分析其特性。在此星團裡，我們發現有幾個成員星的光譜有強烈的氫發射譜線，因此驗證了此星團的年齡約一兩百萬年，另外利用顏色星等圖估計其距離大約一千秒差距。此星團的自行運動以及距離跟鹿豹座裡的OB星協相當接近，因此我們認為他們在形成或演化上互有關聯性。除此之外，我們利用光度及自行運動的資料庫，更進一步發現九十一個新的OB星候選源，在此之前的已知OB星數量只有四十三個。在此區域裡的OB星協成員有著不同年齡的分佈，而這個年輕的星團的位置以及種種特性暗示著這區域還持續有著新的恆星形成的過程。

關鍵字

年輕星球 ； 疏散星團及星協 ； 銀河系結構

並列摘要

Hundreds of thousands star clusters were suggested to exist in the Galactic disk, but so far only a few thousands had been catalogued, all in the solar neighborhood (less than 2 kpc).
We therefore aim to use Pan-STARRS 3π data with its wide-field sky and sensitive camera to search for and to characterize star clusters.
This thesis conducted a pilot study using a star-counting algorithm to identify stellar density enhancements toward the Galactic anti-center.
The detection rate of known star clusters in this region with radii less than 10' from the algorithm used was approximately 83%.
In the field of 20 × 20 degrees, we identified 491 stellar cluster candidates, 50 of which were matched with known star cluster catalog.
The remaining 441 candidates were characterized with radius, reddening, distance, age, and lowest mass members, along with PPMXL proper motions and 2MASS and Pan-STARRS multi-band photometry.
The revised star cluster sample was estimated to be complete up to a heliocentric distance of 5 kpc toward the Galactic anti-center.
Moreover, this sample allowed us to estimate the separation between Sagittarius and Perseus arms was about 3.2 kpc with 0.2 kpc uncertainty and the widths of the nearby spiral arms---Sagittarius, Orion, and Perseus---with the full-width-half-maximum to be 1.4±0.1, 1.6±0.1, and 3.3±0.2 kpc, respectively.

In the early study, one star cluster G144.9+0.4 identified from the 2MASS point sources catalog was characterized.
We showed that the cluster at a distance of about 1 kpc is physically associated with the Cam OB1 association with an age of 1-2 Myr.
Pre-main sequence stars were identified, on the basis of photometric and proper motion data.
A total of 91 additional OB star candidates were photometrically and kinematically found in subgroups 1A and 1B, a significant increase from the currently known 43 OB stars.
The OB members showed an age spread that indicated a sustained star formation for at least the last 10-15 Myr.
The young cluster G144.9+0.4 represented the latest episode of sequential star formation in this cloud complex.

並列關鍵字

infrared stars ； open clusters and associations ； galaxy structure

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