The Structure of the Local Interstellar Medium. V. Electron Densities
By S. Redfield, R. E. Falcon. 2007
270 citations recorded by the source corpus.
We present a comprehensive survey of C II* absorption detections toward stars within 100 pc in order to measure the distribution of electron densities present in the local interstellar medium (LISM). Using high spectral resolution observations obtained by GHRS and STIS on board HST, we searched for all detections of LISM C II* absorption. We identify 13 sight lines with 23 individual C II* absorption components, which provide electron density measurements. We employ several strategies to determine more accurate C II column densities from the saturated C II resonance line, including constraints of the line width from the optically thin C II* line, constraints from independent temperature measurements of the LISM gas based on line widths of other ions, and third, using measured S II column densities as a proxy for C II column densities. The distribution of electron densities based on using S II as a proxy for C II is similar to the distribution based on carbon alone, while significantly tighter, and proves to be a promising technique to avoid grossly overestimating the C II column density based on the saturated line profile. The sample of electron densities appears consistent with a lognormal distribution and an unweighted mean value of ne(C IIS II) = 0.11+0.10−0.05 cm−3. Seven individual sight lines probe the Local Interstellar Cloud (LIC), and all present a similar value for the electron density, with a weighted mean of ne(LIC) = 0.12 ± 0.04 cm−3. Given some simple assumptions, the range of observed electron densities translates into a range of thermal pressures, P/k = 3300+ 5500−1900 K cm −3. This work greatly expands the number of electron density measurements and provides important constraints on the ionization, abundance, and evolutionary models of the LISM.
Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Spectroscopy
View Paper: https://www.semanticscholar.org/paper/a511ee9bf8bc1d2d7d09f22096f14365bc853bd3
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Citations in the corpus
- OBSERVATIONS OF MASS LOSS FROM THE TRANSITING EXOPLANET HD 209458b (2010, background): “The deep minimum observed in the C II 1334.5323 Å line at –6.60 km s−1 (heliocentric) is interstellar absorption due to the Eri cloud located within 3.5 pc of the Sun (Redfield & Linsky 2008).”
- NEUTRAL INTERSTELLAR HELIUM PARAMETERS BASED ON IBEX-Lo OBSERVATIONS AND TEST PARTICLE CALCULATIONS (2012, methodology): “By contrast, the LIC flow vector that Redfield & Linsky (2008) obtained from a careful analysis of all available lines of sight toward nearby stars agrees with our solution.”
- INTERSTELLAR GAS FLOW PARAMETERS DERIVED FROM INTERSTELLAR BOUNDARY EXPLORER-Lo OBSERVATIONS IN 2009 AND 2010: ANALYTICAL ANALYSIS (2012, methodology): “Shown are the velocities of the LIC and the G-Cloud, with their respective error bars, obtained by Redfield & Linsky (2008) with rather small uncertainties.”
- The Interstellar Medium Surrounding the Sun (2011, unknown): “A variety of methods have been used to approximate the CII column density (see Slavin & Frisch 2006, Redfield & Falcon 2008), the most viable being to use S as a proxy for C, because S is typically undepleted in low density, tenuous clouds.”
- A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays - II. Results for the diffusion model combining B/C and radioactive nuclei (2010, unknown): “The Sun is located inside a local interstellar cloud (LIC) of typical extension∼50 pc whose density NHI ∼ 0.1 cm−3 (Gloeckler et al. 2004; Redfield & Falcon 2008).”