The Chess Sounding Rocket: Interstellar H2 Towards Beta Scorpii and Gamma Arae

Kruczek, Nicholas

Graduate Thesis Or Dissertation

The Chess Sounding Rocket: Interstellar H2 Towards Beta Scorpii and Gamma Arae Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/7w62f825p

Abstract

We describe the scientific motivation, technical development, and flight performance of the Colorado High-resolution Echelle Stellar Spectrograph (CHESS). CHESS is a far ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within translucent cloud regions in the interstellar medium. CHESS is an objective echelle spectrograph, which uses a mechanically-ruled echelle, a powered (f/12.4) cross-dispersing grating, and a cross-strip anode microchannel plate detector, and is designed to achieve a resolving power R > 100,000 over the bandpass λ λ 1000--1600 Å. The final two flights of the instrument (CHESS-3 and CHESS-4) observed β¹; Scorpii β Sco and γ Arae (γ Ara). For CHESS-4, we describe our novel method for increasing the resolution of the instrument by physically stressing the echelle grating, introducing a curvature to the surface of the optic. We present flight results of interstellar molecular hydrogen absorption, including measurements of the column densities and temperatures, on the sightlines. For β Sco, we find that the derived column density of the J'' = 1 rotational level differs by a factor of 2--3 when compared to the previous observations of Savage et al. (1977). We discuss the discrepancies between the two measurements and show that the source of the difference is likely due to the opacity of higher rotational levels contributing to the J'' = 1 absorption wing, increasing the inferred column density in the previous work. We extend this analysis to 9 Copernicus and 13 FUSE spectra to explore the interdependence of the column densities of different J'' levels and how the H₂ kinetic temperature is influenced by these relationships. Based off of our results, we find a revised average gas kinetic temperature of the diffuse ISM of T₀₁ = 68 ± 13 K, 12% lower than the value found in the previous work.

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