Local Interstellar Matter: The Apex Cloud
- 20 August 2003
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 593 (2), 868-873
- https://doi.org/10.1086/376684
Abstract
Several nearby individual low column density interstellar cloudlets have been identified previously on the basis of kinematical features evident in high-resolution Ca+ observations near the Sun. One of these cloudlets, the "Apex Cloud" (AC), is within 5 pc of the Sun in the solar apex direction. The question of which interstellar cloud will constitute the next Galactic environment of the Sun can, in principle, be determined from cloudlet velocities. The interstellar absorption lines toward α Cen (the nearest star) are consistent within measurement uncertainties with the projected "G" cloud (GC) and AC velocities, and also with the velocity of the cloud inside of the solar system (the local interstellar cloud [LIC]), provided a small velocity gradient is present in the LIC. The high GC column density toward α Oph compared to α Aql suggests that α Aql may be embedded in the GC so that the AC would be closer to the Sun than the GC. This scenario favors the AC as the next cloud to be encountered by the Sun, and the AC would have a supersonic velocity with respect to the LIC. The weak feature at the AC velocity toward 36 Oph suggests that the AC cloud is either patchy or does not extend to this direction. Alternatively, if the GC is the cloud that is foreground to α Cen, the similar values for N(H0) in the GC components toward α Cen and 36 Oph indicate this cloud is entirely contained within the nearest ~1.3 pc, and the Ca+ GC data toward α Oph would then imply a cloud volume density of ~5 cm-3, with dramatic consequences for the heliosphere in the near future.Keywords
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This publication has 24 references indexed in Scilit:
- The Velocity Distribution of the Nearest Interstellar GasThe Astrophysical Journal, 2002
- An ultra-high-resolution study of the interstellar medium in the direction of OphiuchiMonthly Notices of the Royal Astronomical Society, 2001
- Additional ultra-high-resolution observations of Ca+ ions in the local interstellar mediumMonthly Notices of the Royal Astronomical Society, 1998
- Local stellar kinematics from Hipparcos dataMonthly Notices of the Royal Astronomical Society, 1998
- EUVE measurement of the local interstellar wind and geocorona via resonance scattering of solar He I 584‐Å line emissionJournal of Geophysical Research, 1998
- Characteristics of nearby interstellar matterSpace Science Reviews, 1995
- The local interstellar medium. VII - The local interstellar wind and interstellar material in front of the nearby star Alpha OphiuchiThe Astrophysical Journal, 1987
- The local interstellar mediumThe Astrophysical Journal, 1982
- The nearby interstellar mediumNature, 1981
- High-resolution observations of the Lyman alpha sky backgroundThe Astrophysical Journal, 1977