We present an optical analysis of 55 members of R136, the central cluster in the Tarantula Nebula of the Large Magellanic Cloud. Our sample was observed with STIS aboard the Hubble Space Telescope, is complete down to about 40\,$M_{\odot}$, and includes 7 very massive stars with masses over 100\,$M_{\odot}$. We performed a spectroscopic analysis to derive their physical properties. Using evolutionary models we find that the initial mass function (IMF) of massive stars in R136 is suggestive of being top-heavy with a power-law exponent $\gamma \approx 2 \pm 0.3$, but steeper exponents cannot be excluded. The age of R136 lies between 1 and 2\,Myr with a median age of around 1.6\,Myr. Stars more luminous than $\log L/L_{\odot} = 6.3$ are helium enriched and their evolution is dominated by mass loss, but rotational mixing or some other form of mixing could be still required to explain the helium composition at the surface. Stars more massive than 40\,$M_{\odot}$ have larger spectroscopic than evolutionary masses. The slope of the wind-luminosity relation assuming unclumped stellar winds is $2.41\pm0.13$ which is steeper than usually obtained ($\sim 1.8$). The ionising ($\log Q_0\,[{\rm ph/s}] = 51.4$) and mechanical ($\log L_{\rm SW}\,[{\rm erg/s}] = 39.1$) output of R136 is dominated by the most massive stars ($>100\,M_{\odot}$). R136 contributes around a quarter of the ionising flux and around a fifth of the mechanical feedback to the overall budget of the Tarantula Nebula. For a census of massive stars of the Tarantula Nebula region we combined our results with the VLT-FLAMES Tarantula Survey plus other spectroscopic studies. We observe a lack of evolved Wolf-Rayet stars and luminous blue and red supergiants.

中文翻译：

---

用哈勃太空望远镜/STIS 解剖的 R136 星团。二、R136中质量最大的恒星的物理特性

我们对大麦哲伦星云狼蛛星云的中央星团 R136 的 55 个成员进行了光学分析。我们的样本是在哈勃太空望远镜上用 STIS 观测到的，完整的大约 40\,$M_{\odot}$，包括 7 颗质量超过 100\,$M_{\odot}$ 的非常大的恒星。我们进行了光谱分析以推导出它们的物理特性。使用演化模型，我们发现 R136 中大质量恒星的初始质量函数 (IMF) 暗示其头重脚轻，幂律指数 $\gamma \approx 2 \pm 0.3$，但不能排除更陡峭的指数。R136 的年龄介于 1 和 2\,Myr 之间，年龄中位数约为 1.6\,Myr。比 $\log L/L_{\odot} = 6.3$ 更明亮的恒星富含氦，它们的演化主要是质量损失，但是仍然需要旋转混合或某种其他形式的混合来解释表面的氦成分。质量大于 40\,$M_{\odot}$ 的恒星具有比进化质量更大的光谱。假设未聚集的恒星风，风-光度关系的斜率为 $2.41\pm0.13$，这比通常获得的 ($\sim 1.8$) 陡峭。电离 ($\log Q_0\,[{\rm ph/s}] = 51.4$) 和机械 ($\log L_{\rm SW}\,[{\rm erg/s}] = 39.1$) 输出R136 以最大质量的恒星为主（$>100\,M_{\odot}$）。R136 为狼蛛星云的总体预算贡献了大约四分之一的电离通量和大约五分之一的机械反馈。对于狼蛛星云区域的大质量恒星普查，我们将我们的结果与 VLT-FLAMES 狼蛛调查以及其他光谱研究相结合。