gamma Cas has long been famous for its unique hard X-ray characteristics. We
report herein on a 53 ks Chandra HETGS observation of this target. An
inspection of our spectrum shows that it is quite atypical for a massive star,
with abnormally weak Fe XXV, XXVI lines, Ly-alpha lines of H-like species from
Fe XVII, XXIII, XXIV, S XVI, Si XIV, Mg XII, Ne X, O VII, VIII, and N VII.
Also, line ratios of the rif-triplet of for a few He-like ions XVII are
consistent with the dominance of collisional atomic processes. Yet, the
presence of Fe and Si fluorescence K features indicates that photoionization
also occurs in nearby cold gas. The line profiles indicate a mean velocity at
rest and a broadening of 500 km/s. A global fitting analysis of the line and
continuum spectrum finds that there are 3-4 plasma emission components. The
dominant hot (12 keV) component and has a Fe abundance of 0.22 solar. Some
fraction of this component (10-30%) is heavily absorbed. The other 2-3
components, with temperatures 0.1, 0.4, 3 keV, are "warm," have a nearly solar
composition, a lower column absorption, and are responsible for most other
emission lines. The strength of the fluorescence features and the dual-column
absorption model for the hot plasma component suggest the presence near the hot
sites of a cold gas structure with a column density of 10^23 cm^-2. Since this
value is consistent with theoretical estimates of the vertical disk column of
this star, these attributes suggest that the X-rays originate near the star or
disk. It is possible that the Fe anomaly in the hot component is related to the
First Ionization Potential effect found in coronal structures around active
cool stars. This would be yet another indication that the X-rays -rays are
produced in the immediate vicinity of the Be star.Comment: 32 pages, 4 figures (Fig. 3 colorized.) To be published in 01/10/04
Astrophysical Journal, Main Journal; included figures and updated formattin