A New World Class Infrared Spectrometer for Fundamental Atomic Data for Astrophysics

Modern astronomical spectra are being recorded at unprecedented resolutions in the infrared (IR), visible and ultraviolet (UV) regions by both ground- and space-based telescopes including JWST, ELT, VLT, HST, Keck II, Subaru, UKIRT. The analysis of the spectra recorded by these multi-billion-pound instruments requires laboratory atomic data of at least matching accuracy and completeness. However, for many elements and ionisation states, the existing atomic data date back over 50 years, based on grating and even prism spectrometers. Spectroscopy techniques have improved enormously since then, but the large-scale effort needed to produce new high-resolution, high-accuracy atomic data has meant that the atomic database has lagged behind the needs of the astrophysics and astronomy communities. In many cases, order-of-magnitude improvements in accuracy of atomic data are required for unambiguous identification of all features of interest in an astrophysical spectrum and meaningful interpretation of the astronomical spectra. It is not possible to theoretically calculate atomic data with sufficient precision for analyses of high-resolution astrophysical spectra, and so experimental spectroscopy is the only method to generate atomic data of the necessary accuracy.

The Imperial College Spectroscopy Group has a strong track record in significantly improving atomic data with Fourier Transform (FT) spectroscopy. Previously, our work was focussed on the visible and UV spectral regions, with spectra measured using our record-holding vacuum UV (VUV) FT spectrometer. The capital funding of this grant will enable us to increase our capabilities into the infrared (IR) through the addition of a world-class, high-resolution FT spectrometer tailored to the IR spectral region. This vital addition to our facility, in combination with our existing unique visible-ultraviolet FT spectrometer, means that we will be able to study high-resolution spectra of astrophysically important elements across the entire IR-visible-UV region. The timing of this increase in spectral coverage has come just as the IR is growing tremendously in importance for astronomers, with new telescopes, such as the JWST, launched with unprecedented capabilities in the IR region.

We will focus on measurements leading to at least order-of-magnitude improvements in wavelength accuracy, atomic energy levels, log(gf)s (transition probabilities, needed for determining chemical abundances of elements in astrophysical objects), and isotope and hyperfine structure (needed to model lines accurately and, again, obtain reliable abundance estimates). The much greater resolution of FT spectroscopy, compared to the best grating spectrometers used in the past, provides wavelengths and energy levels accurate to at least parts in 108, log(gf)s accurate to a few percent, and resolved line broadening effects such as isotope and hyperfine structure. Our atomic data are relevant to many STFC Challenge questions such as: "How do stars and galaxies evolve?", "How does the Sun and other stars work and what drives their variability?" and "What effects do the Sun and other stars have on their local environment?".

All the new laboratory atomic data produced by the ICL Spectroscopy Group is incorporated into atomic databases and stellar model atmosphere codes, benefiting astronomers worldwide in addition to those in the UK. The new IR spectrometer will allow our Group to continue our world leading research into the new era of IR astronomical discoveries. Our aim is that the new laboratory atomic 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 data used in their analyses.