Laboratory Astrophysics: new atomic and molecular data for astrophysics applications

我们在“实验室天体物理学”方面的研究涉及原子和分子的光谱研究，为天体物理学应用提供新的和准确的原子和分子数据。帝国理工学院实验室光谱学小组一直在研究原子和分子的光谱，这在天体物理物体（如恒星和行星大气）的光谱中也很重要，通过实验使用我们的高分辨率傅立叶变换光谱仪。在大多数情况下，对天体物理对象的研究涉及光谱分析，这需要原子和分子数据库对其进行可靠和有意义的解释。地面和太空望远镜上的新型高分辨率光谱仪使天文学家能够接触到质量空前的天体物理光谱，以及以前未被探索的光谱区域，如近红外和真空紫外。这导致迫切需要足够精确和完整的原子数据来分析这些天文光谱。铁族元素（Ti， V, Cr, Mn, Fe, Co, Ni）丰富的谱线尤其重要，因为它们在恒星等物体的光谱中占主导地位。天文学家利用这些元素的原子数据来分析天体物理光谱。迫切需要原子数据的例子有：低温、低质量恒星、系外行星、太阳和低金属丰度恒星的化学丰度研究，以了解银河系的化学演化；对成千上万颗恒星进行调查，以了解银河系的演化；我们银河系中的热B恒星和麦哲伦星云，用于测试恒星核合成理论；利用类星体光谱对基本常数可能发生的时间变化，以及许多其他研究。虽然近年来原子数据有了很大的改进，但仍然存在一些关键的数据缺失，这些数据不完整或不准确，在中性和单电离物质的红外光谱或双电离物质的紫外光谱中，往往完全缺失。我们将利用帝国理工学院独有的可见光-紫外傅立叶变换光谱仪，以及访问美国国家标准与技术研究院和瑞典隆德大学的红外-可见光傅立叶变换光谱仪，研究这些元素的高分辨率光谱。使用傅立叶变换光谱仪的优点是我们可以在宽光谱范围内以高分辨率测量特定物种的光谱。我们将重点关注波长精度、原子能级、对数（跃迁概率，用于确定天体物理对象中元素的丰度）和超精细结构（需要精确地建模线条，并再次获得可靠的丰度估计）方面的至少数量级改进的测量。除了我们的原子数据测量计划外，我们还计划对双原子硫分子进行第一次高分辨率实验室光谱研究，其中涉及紫外线光谱测量，为各种研究提供迫切需要的数据，包括：了解木星卫星Io的大气和火山羽流；木星的大气层和彗星。我们所产生的所有新的实验室原子和分子数据都被纳入原子和分子数据库和恒星模型大气代码，除了英国的天文学家外，还使全世界的天文学家受益。我们的目标是，我们向天文学界提供的新的实验室原子和分子数据意味着，对昂贵获得的现代天体物理光谱的分析将不再受到他们分析中使用的原子（或分子）数据的质量和数量的限制。

Our research in 'laboratory astrophysics' involves spectroscopic studies of atoms and molecules to provide new and accurate atomic and molecular data needed for astrophysics applications. The Imperial College laboratory spectroscopy group has been studying the spectra of atoms and molecules, that are of importance also in spectra of astrophysical objects such as stars, and planetary atmospheres, through experiments using our high resolution Fourier transform spectrometers. Studies of astrophysical objects, in the majority of cases, involve analyses of spectra which require an atomic and molecular data base for their reliable and meaningful interpretation. New high resolution spectrographs on both ground and space-based telescopes are giving astronomers access to astrophysical spectra of unprecedented quality, and also in previously underexplored spectral regions, such as the near infrared and vacuum ultraviolet. This has resulted in pressing needs for atomic data of sufficient accuracy and completeness to analyse these astronomical spectra. The abundant, line rich spectra of the iron group elements (Ti, V, Cr, Mn, Fe, Co, Ni) are particularly important as they dominant in spectra of objects such as stars. Astronomers use atomic data for these elements in analysing astrophysical spectra. Examples where atomic data are urgently needed are for studies of: cool, low mass stars, exoplanets, chemical abundance studies for the Sun and low metallicity stars for understanding Galactic chemical evolution, surveys looking at many thousands of stars to understand Galactic evolution, hot B stars in our Galaxy and the Magellanic clouds for tests of theories of stellar nucleosynthesis, possible time variation of the fundamental constants using quasar spectra, and many others. Although there has been great improvement in the atomic data in recent years, there remain key missing data, that are incomplete or inaccurate, and in the case of the infrared spectra of neutral and singly ionised species or VUV spectra of doubly ionised species are often missing entirely. Using our unique visible-ultraviolet Fourier Transform (FT) spectrometer at Imperial College and the infrared-visible FT spectrometers by visiting NIST (National Institute Standards & Technology, USA) and Lund University (Sweden) we will study high resolution spectra of these elements. The advantages of using an FT spectrometer are that we can measure the spectrum of a particular species at high resolution over a wide spectral range. We will focus on measurements leading to at least order-of-magnitude improvements in wavelength accuracy, atomic energy levels, loggfs (transition probabilities, needed for determining abundances of elements in astrophysical objects), and hyperfine structure (needed to model lines accurately and, again, obtain reliable abundance estimates). In addition to our programme of atomic data measurements, we plan the first high resolution laboratory spectroscopy study of the diatomic sulphur molecule, which involves spectroscopic measurements in the ultraviolet, to provide data urgently needed for a variety of studies including: understanding the atmosphere and volcanic plumes of Io, a moon of Jupiter; the atmosphere of Jupiter, and cometary comae. All the new laboratory atomic and molecular data we produce is incorporated into atomic and molecular databases and stellar model atmosphere codes, benefiting astronomers worldwide in addition to those in the UK. Our aim is that the new laboratory atomic and molecular data we provide to the astronomical community means that analyses of expensively obtained modern astrophysical spectra will no longer be limited by the quality and quantity of atomic (or molecular) data used in their analyses.