The spectroscopic foundation of radiative forcing of climate by carbon dioxide.

The radiative forcing (RF) of carbon dioxide (CO2) is the leading contribution to climate change from anthropogenic activities. Calculating CO2 RF requires detailed knowledge of spectral line parameters for thousands of infrared absorption lines. A reliable spectroscopic characterization of CO2 forcing is critical to scientific and policy assessments of present climate and climate change. Our results show that CO2 RF in a variety of atmospheres is remarkably insensitive to known uncertainties in the three main CO2 spectroscopic parameters: the line shapes, line strengths, and half widths. We specifically examine uncertainty in RF due to line mixing as this process is critical in determining line shapes in the far wings of CO2 absorption lines. RF computed with a Voigt line shape is also examined. Overall, the spectroscopic uncertainty in present-day CO2 RF is less than 1%, indicating a robust foundation in our understanding of how rising CO2 warms the climate system.

Aberration-corrected echelle spectrometer for measuring ultraviolet branching fractions of iron-group ions.

A high-resolution echelle spectrometer with broad wavelength coverage from the UV to the IR and high sensitivity to weak lines is described. Total instrument astigmatism is suppressed through rotation of the order separation system into an orthogonal plane. A suitable choice of mirror angles avoids increased coma. This spectrometer is used to record UV through IR spectra of Fe-group ions to measure improved branching fractions. These new results reduce transition probability uncertainties and yield more accurate derived stellar abundances. Instrument design and performance, including aberration compensation, are presented.

First results from an all-reflection spatial heterodyne spectrometer with broad spectral coverage.

Operation of an all-reflection, broadband, spatial heterodyne spectrometer (SHS) is reported. This Mark 2 SHS is constructed using a custom diffraction grating and other standard optical components. The custom grating is coarse (18 grooves/mm), with a symmetric blaze that allows its simultaneous use as dispersing element and beam splitter and combiner. The grating is combined with a plane mirror and a roof mirror to form a very stable ring interferometer which has been used successfully in earlier narrowband SHS designs. Fringes from the extra grating orders in the main blaze envelope are unexpectedly found to combine constructively with the desired primary fringes of the interferometer. Elimination of ambiguity between wavelengths above and below blaze in a given order, and order separation are demonstrated using a small tilt of the plane mirror about an axis in the plane of the figure. Coverage of a factor of four in wavelength in a single CCD frame is demonstrated.

Quantitative Atomic Spectroscopy, a Review of Progress in the Optical-UV Region and Future Opportunities†.

The development of tunable dye lasers and a simple atomic and ionic beam source for all elements were critical in establishing a reliable absolute scale for atomic transition probabilities in the optical to near UV regions. The laboratory astrophysics program at the University of Wisconsin - Madison (UW) concentrates on neutral and singly-ionized species transitions that are observable in astronomical spectra of cool stars, emphasizing the rare earth n(eutron)-capture elements and the Fe-group elements that are important inputs to early Galactic nucleosynthesis studies. The UW program is one of several productive efforts on atomic transition probabilities. These programs generally use time-resolved laser-induced-fluorescence (TR-LIF) to accurately measure total decay rates and data from high resolution Fourier transform spectrometers (FTSs) to determine emission branching fractions (BFs). The UW laboratory results almost always are directly linked to astronomical chemical composition efforts. There are good opportunities to extend similar research to other wavelength regions.

Echelle spectrograph optimized for a diffuse interstellar band carrier search using synchrotron radiation.

An echelle spectrograph featuring broad wavelength coverage and resolution optimized for a diffuse interstellar band carrier search using synchrotron radiation is described. Nearly uniform separation of multiple echelle orders is achieved using an external cross-dispersion spectrometer incorporating both a prism and a grating. Performance and benchmark data are presented.

Broadband, high-resolution spatial heterodyne spectrometer.

Design and performance parameters for a broadband, high-resolution spatial heterodyne spectrometer (SHS) are reported. The Mark 1 SHS achieves more than a factor of 5 in continuous wavenumber coverage with a design resolving power in the hundreds of thousands.