High-resolution observations of the Lyman alpha sky background

The Galactic Environment of the Sun: Interstellar Material Inside and Outside of the Heliosphere

“…The earliest comparisons between ISMa inside of the heliosphere and towards nearby stars showed that the CHISM is warm, low density, and partially ionized (Rogerson et al 1973;McClintock et al 1976;Adams and Frisch 1977). The CHISM properties are regulated by the low average interstellar densities inside of the Local Bubble, and the intensity and spectrum of the interstellar radiation field that follow from our location in a clump of low-opacity ISMa with N (H o ) 10 18.5 cm −2 .…”

“…The first spectrum of interstellar gas inside of the heliosphere was a Copernicus observation of the H • Lyα backscattered emission obtained during 1975, which determined an H • velocity of ∼ −24.7 km s −1 (neglecting heliospheric acceleration and after correcting for the recent Ulysses measurement of the He o upstream direction, Sect. 2.1.1, Adams and Frisch 1977;Frisch 2008a). The nearest star for which optical data were then available, α Oph at 14 pc, showed interstellar Ca + velocities of −24 km s −1 and −26 km s −1 (Marschall and Hobbs 1972;Crawford 2001).…”

“…5.1). Interstellar gas was first discovered inside of the heliosphere through broad-band observations of the fluorescence of solar Lyα and 584 Å emissions from interplanetary H • and He o , respectively (Thomas and Krassa 1971;Bertaux and Blamont 1971;Meier 1974, 1981;Adams and Frisch 1977;Ajello et al 1987), and the importance of these data was quickly recognized (e.g. Holzer 1972;Fahr 1974;Wallis 1975;Thomas 1978).…”

“…Holzer 1972;Fahr 1974;Wallis 1975;Thomas 1978). Copernicus made the first spectrum of the Lyα backscattered radiation and showed that interstellar gas inside of the solar system has a velocity similar to the velocity of interstellar clouds in the solar vicinity (Adams and Frisch 1977). The interplanetary Lyα glow from interstellar H • inside of the heliosphere provided the first glimpse that the CHISM is warm and tenuous, and quite different from the galactic cold dense H • that dominates the H • 21-cm hyperfine emission sky.…”

“…2.1.2). Slavin and Frisch (2008, SF08) have compared the spectra of the H • Lyα interplanetary glow observed by Copernicus during 1975 (Adams and Frisch 1977) with spectra collected by the Hubble Space Telescope (HST) during the 1990s (Clarke et al 1998), and concluded that the velocity of the interstellar cloud feeding H • into the heliosphere has not changed substantially over the intervening two decades, and that the circumheliospheric interstellar cloud extends at least ∼ 115 AU in the interstellar downwind direction. Ulysses observations of interstellar dust inside of the heliosphere during 1992-2002 can be fit with a constant dust density in the CHISM, also providing support for a homogeneous CHISM over scale sizes of ∼ 55 AU (Landgraf 2000).…”