What Line Widths Say About the Temperature and Turbulence of the Local Interstellar Cloud

Absorption lines formed in the Local Interstellar Cloud are broadened by both heat and turbulence, and separating the two requires lines from species of very different mass observed along the same sightline. Using representative published Doppler parameters for hydrogen and iron, the two-component decomposition gives a kinetic temperature of 7,018 K and a turbulent broadening of 2.8 kilometres per second, and it predicts the deuterium line width at 8.6 kilometres per second, close to the values reported for deuterium. The temperature agrees with the canonical warm-cloud value near 7,000 K, which means the published line widths and the published temperature are mutually consistent rather than independently assumed. The decomposition is elementary algebra on stated inputs, deposited with the paper, and is computed rather than measured.