古老疏散星團柏克萊17成員星的選取;Determining Membership Candidates for Aged Open Cluster Berkeley 17

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題名:	古老疏散星團柏克萊17成員星的選取;Determining Membership Candidates for Aged Open Cluster Berkeley 17
作者:	雷拉;Gallardo, Mikhaela Leia A.
貢獻者:	天文研究所
關鍵詞:	散星
日期:	2021-10-27
上傳時間:	2021-12-07 11:18:45 (UTC+8)
出版者:	國立中央大學
摘要:	柏克萊17 是位於距離太陽大約2700秒差距的疏散星團，其是銀河系中最古老的開放星團之一。其年齡約為一百億年、[Fe/H]金屬豐度值為0.33 dex、有?數量龐大的藍離散星、顯著的水平分支，使其相似於球狀星團。這星團外型因為其被潮汐力的影響而整體形成拉長的形狀。在以前對於核心-尾部的形態分析當中發現大質量恆星的數量超越小質量恆星的數量。這則可以說明了質量層化在此星團的影響，而其中大質量成員“下沉”到核心，低質量成員佔據更大的外圍空間，造成這個現象的主要成因目前還不清楚。然而其中一個可能成因是來自於星團其獨特位置: 接近英仙旋臂進而產生的潮汐力影響。這論文使用了來自於PS1、2MASS、ALLWISE和GAIA EDR3的多波段資料來作測光分析，並提供了可以找出最有可能是這在瓦解中的星團內的成員星，及其光譜型態和其當下的演化階段的資訊。利用視差及自行的資料我們可以去除掉一半的已知候選成員星，而藍離散星的數量從21個減少至12個。利用LAMOST的光譜資料我們得到[Fe/H]金屬豐度的值為-0.75 dex。根據這星團相對於銀河系運動的狀態可以看出柏克萊 17受到英仙旋臂的顯著影響，因為它的運動方向與銀河自轉方向相反並朝向銀河中心。;\noindent Berkeley 17, located at a heliocentric distance of 2700 pc, is among the oldest Galactic open clusters. The cluster is noted to resemble globular clusters for its ~10 Gyr age, [Fe/H] of -0.33 subsolar metallicity, excessive number of blue stragglers, and a prominent horizontal branch. The cluster displays an elongated shape due to a tail and anti-tail. In previous analysis of its core-tail morphology, massive stars outnumber less massive ones. This indicated the effect of dynamical mass segregation, where massive members ′sink′ to the core, while the low-mass members occupy larger volumes. The cause of this phenomenon is unclear, however, one possible tidal source is the Perseus arm, where distinct field population of Berkeley 17 is attributed to. Multi-wavelength photometry and astrometry from PS1, 2MASS, AllWISE, and GAIA EDR3 were processed to gain the disintegrating cluster’s highest-probable members and their spectral types, as well as current stage in dynamical evolution. Almost half of the previously known members are removed due to parallax and proper motion, also reducing the blue straggler population from 21 to 12. LAMOST spectrosocpy returned a near solar metallicity at [Fe/H] = -0.175 dex. Galactic motion also suggests that Berkeley 17 is heavily affected by the Perseus arm due to its motion against the Galactic rotation and towards the Galactic center.
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