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A survey of interstellar H I from L-alpha absorption measurements. II
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The study compared Copernicus L‑α data for 47 stars with OAO‑2 results, computed gas‑to‑E(B‑V) ratios for intercloud, cloud, and combined samples, and examined the anomalous Rho Oph ratio to assess the Galactic distribution of neutral hydrogen. The mean neutral‑hydrogen to color‑excess ratio is 5.8 × 10²¹ atoms cm⁻² mag⁻¹, and within 500 pc of the Sun the mean total hydrogen density is 1.15 atoms cm⁻³, H₂ 0.143 molecules cm⁻³, and H I 0.86 atoms cm⁻³. Published in The Astrophysical Journal (1978), DOI 10.1086/156357.
view Abstract Citations (3019) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A survey of interstellar H I from L-alpha region with the U2 detector of the Copernicus satellite. The data for 47 stars are compared with OAO 2 results, and ratios of gas to E(B-V) color excess are computed for 30 'intercloud' stars, 45 'cloud' stars, and the combined sample of 75 stars. A definitive value of 5.8 x 10 to the 21st power atoms/sq cm per mag is obtained for the mean ratio of total neutral hydrogen to color excess, indicating that this ratio seems to be a constant, independent of location in the sky, except possibly toward stars with anomalous extinction. The anomalous ratio determined for Rho Oph is examined, and the galactic distribution of neutral hydrogen is evaluated. The following values are estimated for matter in the galactic plane within 500 pc of the sun: a total mean hydrogen space density of 1.15 atoms/cu cm, a mean H2 space density of 0.143 molecule/cu cm (possibly a lower limit), and a mean H I space density of 0.86 atom/cu cm (a possible overestimate). Publication: The Astrophysical Journal Pub Date: August 1978 DOI: 10.1086/156357 Bibcode: 1978ApJ...224..132B Keywords: Hydrogen Clouds; Interstellar Gas; Lyman Alpha Radiation; Molecular Absorption; Ultraviolet Spectra; Abundance; Hydrogen Atoms; Interstellar Extinction; Neutral Particles; Oao 2; Satellite Observation; Astrophysics; Interstellar Matter:Molecules; Interstellar Matter:Neutral Hydrogen full text sources ADS | data products SIMBAD (101)