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Interstellar H-Alpha Line Profiles toward HD 93521 and the Lockman Window
We have used the Wisconsin H-Alpha Mapper (WHAM) facility to measure the
interstellar H-Alpha emission toward the high Galactic latitude O star HD 93521
(l = 183.1, b = +62.2). Three emission components were detected having radial
velocities of -10 km s^{-1}, -51 km s^{-1}, and -90 km s^{-1} with respect to
the local standard of rest (LSR) and H-Alpha intensities of 0.20 R, 0.15 R, and
0.023 R, respectively, corresponding to emission measures of 0.55 cm^{-6} pc,
0.42 cm^{-6} pc, and 0.06 cm^{-6} pc. We have also detected an H-Alpha emission
component at -1 km s^{-1} (LSR) with an intensity of 0.20 R (0.55 cm^{-6} pc)
toward the direction l = 148.5, b = +53.0, which lies in the region of
exceptionally low H I column density known as the Lockman Window. In addition,
we studied the direction l = 163.5, b = +53.5. Upper limits on the possible
intensity of Galactic emission toward this direction are 0.11 R at the LSR and
0.06 R at -50 km s^{-1}. We also detected and characterized twelve faint
(~0.03-0.15 R), unidentified atmospheric lines present in WHAM H-Alpha spectra.
Lastly, we have used WHAM to obtain [O I] 6300 spectra along the line of sight
toward HD 93521. We place an upper limit of 0.060 R on the [O I] intensity of
the -51 km s^{-1} component. If the temperature of the gas is 10,000 K within
the H-Alpha emitting region, the hydrogen ionization fraction n(H+)/n(H_total)
> 0.6.Comment: 23 pages, 4 figures. Acccepted for publication in the 1 Feb issue of
The Astronomical Journa
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