The Initial Mass Function and Massive Star Evolution in the OB Associations of the Northern Milky Way
The Initial Mass Function and Massive Star Evolution in the OB Associations of the Northern Milky Way
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DOI：
10.1086/176474
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发表时间：
1995-11
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影响因子：
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通讯作者：
P. Massey;Kelsey E. Johnson;K. DeGioia-Eastwood
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作者：
P. Massey;Kelsey E. Johnson;K. DeGioia-Eastwood
我们研究了银河系星团和 OB 星团中的大质量恒星含量，以回答三个问题：（1）恒星形成的同时期如何？ (2) 初始质量函数 (IMF) 的常数是多少？ (3) 沃尔夫-拉叶星的前身质量是多少？我们的样品包括 NGC 6823/Vul OB1、NGC 6871/Cyg OB3、Berkeley 86/Cyg OB1、NGC 6983/Cyg OB1、NGC 7235、NGC 7380/Cep OB1、Cep OB5、IC 1805/Gas OB6、NGC 1893/Aug OB2 和NGC 2244/周一 OB2。大视场 CCD 成像和多目标光纤光谱学已经实现了针对超过 14000 颗恒星的 UBV 光度测量和针对大约 200 颗恒星的新光谱类型。这些数据用于重新确定这些区域的距离和红化，并帮助在构建 H-R 图时排除可能的非成员。我们重新分析了之前在 Cyg OB2、Tr 14/16 和 NGC 6611 上发布的可比数据，并使用所有这些数据来描绘恒星形成的图景并测量 IMF。我们发现以下内容：（1）大多数大质量恒星诞生于 Delta tau 7 M 时期。与麦哲伦星云中类似研究的 OB 关联的比较表明 IMF 斜率没有差异，因此我们得出结论，星团中大质量恒星的恒星形成与金属丰度无关，至少在 z = 0.02 和 z = 0.002 之间。银河系、LMC 和 SMC 星团中质量最高恒星的质量大致相等，这与该值在该金属丰度范围内变化 3 倍的预期相反。我们得出的结论是，颗粒上的辐射压力一定不会限制可以形成的最高质量恒星的质量，这与沃尔菲尔和卡西内利的建议一致，即大质量恒星的存在本身就表明冲击或其他机制已经在恒星形成事件中破坏了颗粒。 (3) 我们样本中的四颗沃尔夫-拉叶星来自质量超过 40 M 的恒星；一颗 WC 星和一颗晚型 WN 星似乎都来自非常巨大（大约 100 M.）的祖星。
We investigate the massive star content of Milky Way clusters and OB associations in order to answer three questions: (1) How coeval is star formation? (2) How constant is the initial mass function (IMF)? (3) What is the progenitor mass of Wolf-Rayet stars? Our sample includes NGC 6823/Vul OB1, NGC 6871/Cyg OB3, Berkeley 86/Cyg OB1, NGC 6983/Cyg OB1, NGC 7235, NGC 7380/Cep OB1, Cep OB5, IC 1805/Gas OB6, NGC 1893/Aug OB2, and NGC 2244/Mon OB2. Large-field CCD imaging and multiobject, fiber spectroscopy has resulted in UBV photometry for >14000 stars and new spectral types for approximate to 200 stars. These data are used to redetermine distances and reddenings for these regions and to help exclude probable nonmembers in constructing the H-R diagrams. We reanalyze comparable data previously published on Cyg OB2, Tr 14/16, and NGC 6611 and use all of these to paint a picture of star formation and to measure the IMFs. We find the following: (1) Most of the massive stars are born during a period Delta tau 7 M. A comparison with similarly studied OB associations in the Magellanic Clouds reveals no difference in IMF slope, and hence we conclude that starformation of massive stars in clusters proceeds independently of metallicity, at least between z = 0.02 and z = 0.002. The masses of the highest mass stars are approximately equal in the Milky Way, LMC, and SMC associations, contrary to the expectation that this value should vary by a factor of 3 over this metallicity range. We conclude that radiation pressure on grains must not limit the mass of the highest mass star that can form, in accord with the suggestion of Wolfire & Cassinelli that the mere existence of massive stars suggests that shocks or other mechanisms have disrupted grains in star-forming events. (3) The four Wolf-Rayet stars in our sample have come from stars more massive than 40 M.; one WC star and one late-type WN star each appear to have come from very massive (approximate to 100 M.) progenitors.