Another One Bites the Dust -- Chandra Observations of MBM12 and Models of the Local Bubble
Randall Smith
Chandra observations toward the nearby molecular cloud MBM12 show
unexpectedly strong and nearly equal foreground O VIII and
O VII emission. As the observed portion of MBM12 is optically
thick at these energies, the emission lines must be formed nearby,
coming either from the Local Bubble (LB) or charge exchange with ions
from the Sun. Equilibrium models for the LB predict stronger
O VII than O VIII, so these results suggest that the LB is either
far from equilibrium or a substantial portion of O VIII is from
another source. However, despite the likelihood of contamination by
charge exchange within the Solar system, we can combine these results
with other EUV and X-ray observations to reject LB models which posit
a cool recombining plasma as the source of LB X-rays.