Massive stars at low metallicity: an empirical investigation

低金属丰度的大质量恒星：实证研究

• 批准号: 398753382
• 负责人: Professor Dr. Wolf-Rainer Hamann
• 金额: --
• 依托单位: Institut für Physik und Astronomie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/398753382?language=en
• 关键词: Massive; stars; low; metallicity; empirical

With the first detection of a gravitational wave on September 14, 2015, the focus of scientific interest moved to stars with a high mass. The two Black Holes which merged when emitting this gravitational wave had about 30 solar masses each, and must have formed by the collapse of stars which were initially even much more massive. It has been suggested that these stars must have been formed in a low-metallicity environment, because a low metal content leads to weaker winds; hence, at the end of the stellar evolution, a larger mass is left that collapses into the Black Hole.Massive stars are still not well understood. Most of the existing investigations of massive stars concern objects in our own Galaxy. The agreement with theoretical simulations of their evolution is not satisfactory. Major reasons for the discrepancies are presumably our poor knowledge of two important effects, the mass loss by stellar winds, and the interior mixing processes induced by stellar rotation.Our Milky Way has a relatively high metal content. Galaxies with low metallicity, as invoked as the birth place of the gravitational wave progenitors, are also found in our immediate cosmic neighborhood, namely the Small Magellanic Cloud. It is close enough that the relatively bright massive stars can be studied individually. About half of all massive stars of this dwarf galaxy belong to the relatively young cluster NGC346. This cluster thus provides an ideal laboratory to study a complete massive star population in a starburst at low metallicity.To this purpose, we have secured the spectra of the massive stars in NGC346. In the visual light, we employed the integral-field spectrograph MUSE at the Very Large Telescope (VLT) of the European Southern Observatory (ESO). This instrument takes spectra simultaneously for each of the 90000 pixels in the field-of-view. First inspection of the data show 200-300 stellar sources. Since the full spectral analysis also requires the ultraviolet spectral range, we have additionally applied for observations with the Hubble Space Telescope, which have been approved as well. With the long-slit spectrograph STIS, major parts of the cluster will be covered in form of a mosaic.Within the project proposed here, these new and superb data shall be analyzed in due time. The scientific exploitation will address various questions of high interest in current astrophysics. We will establish in which respects this population differs from those at higher metallicity. How small is the mass loss at this low metallicity? How does the smallness of their mass loss affect the evolution of the stars? How are the stellar masses statistically distributed?Our unique new observations will also allow to investigate this young, metal-poor stellar cluster as a whole. We will model the feedback of the combined stellar radiation and winds on the diffuse matter, i.e. on the giant region that is ionized by the embedded stars.

随着2015年9月14日首次探测到引力波，科学兴趣的焦点转移到了高质量的恒星上。这两个黑洞在发射引力波时合并在一起，每个黑洞都有大约30个太阳质量，肯定是由最初质量更大的恒星坍塌形成的。有人提出，这些恒星一定是在低金属丰度的环境中形成的，因为低金属含量会导致较弱的风；因此，在恒星演化结束时，会留下更大的质量，塌陷到黑洞中。巨大的恒星仍然没有被很好地理解。现有的大部分对大质量恒星的研究都与我们银河系中的天体有关。它们的演化与理论模拟的一致性并不令人满意。造成这种差异的主要原因大概是我们对两种重要效应的认识不足，一种是恒星风造成的质量损失，另一种是恒星自转引起的内部混合过程。我们银河系的金属含量相对较高。具有低金属丰度的星系，被称为引力波前体的诞生地，也在我们的宇宙近邻，即小麦哲伦星云中被发现。距离足够近，相对明亮的大质量恒星可以单独研究。这个矮小星系中大约一半的大质量恒星属于相对年轻的星系团NGC346。因此，这个星团提供了一个理想的实验室来研究低金属星暴中完整的大质量恒星群。为此，我们获得了NGC346中大质量恒星的光谱。在可见光下，我们在欧洲南方天文台的甚大望远镜(VLT)上使用了积分场光谱仪缪斯。该仪器同时为视野中的90000个像素中的每一个拍摄光谱。第一次检查的数据显示有200-300个恒星源。由于全光谱分析还需要紫外光谱范围，我们还申请了哈勃太空望远镜的观测，这也得到了批准。随着长缝光谱仪STIS的使用，星系团的主要部分将以马赛克的形式被覆盖。在这里提出的项目中，这些新的和优秀的数据将在适当的时候进行分析。科学利用将解决当前天体物理学中高度感兴趣的各种问题。我们将确定这一群体在哪些方面不同于那些金属丰度较高的群体。在这种低金属丰度下，质量损失有多小？它们的微小质量损失如何影响恒星的演化？恒星质量是如何在统计上分布的？我们独特的新观测也将使我们能够作为一个整体来研究这个年轻的、缺乏金属的星团。我们将模拟恒星辐射和风对弥散物质的反馈，即对被嵌入的恒星电离的巨大区域的反馈。