The Local Interstellar Cavity Outlined by K I Absorption

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Session 29 -- General Interstellar Medium
Display presentation, Tuesday, 31, 1994, 9:20-6:30

[29.08] The Local Interstellar Cavity Outlined by K I Absorption

M. L. West (Montclair St. C.), R. E. White (Smith C.)

We have analyzed the kinematics of interstellar K I from the survey of Chaffee \& White (1982) for evidence of the local cavity in the interstellar medium. The survey has a typical detection threshold of log N(K I) = 10.7, corresponding to log N(H) = 20.8 or log E(B-V) = $-0.9$. Consequently, the data define the cavity edge by the occurrence of relatively high concentrations of interstellar material. This northern hemisphere survey includes stars in the longitude range $-13\deg < l < 225\deg$; it provides no constraints on the cavity in the longitude range $225\deg < l < 347\deg$

Stars without detectable K I absorption yield lower limits on the distance to the cavity boundary on 12 independent sight-lines toward 23 stars. Three stars at high galactic latitudes may indicate directions in which the cavity has blown out into the galactic halo. Most of the remaining stars lie along a line roughly parallel to $l = 45\deg - 225\deg$ and inclined to the galactic plane. It extends 150 pc toward Scorpius and about 500 pc toward Orion, with a particularly sharp edge toward Perseus. Another relatively vacant sight-line extends $>$ 700 pc near the galactic plane between $l = 200\deg$ and $l = 225\deg$.

Stars beyond the cavity boundary exhibit the small positive radial velocities (V$_{LSR} <$ 10 km s$^{-1}$) associated with the Gould's Belt "expanding ring." The orientation of the cavity outlined by K I absorption components is consistent with this identification. We identify a few velocity components, notably including the Taurus clouds, that probably represent localized clouds on trajectories from the edges into the interior of the larger cavity.


Chaffee, F. H., \& White, R. E. 1982, ApJS, 50,169.

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