We present an analysis of a pointed 141 ks Chandra high resolution transmission gratings observation of the Be X-ray emitting star HD110432 , a prominent member of the \gamma Cas analogs .
This observation represents the first high resolution spectrum taken for this source as well as the longest uninterrupted observation of any \gamma Cas analog .
The Chandra lightcurve shows a high variability but its analysis fails to detect any coherent periodicity up to a frequency of 0.05 Hz .
Hardness ratio versus intensity analyses demonstrate that the relative contributions of the [ 1.5-3 ] Å , [ 3-6 ] Å and [ 6-16 ] Å energy bands to the total flux changes rapidly in the short term .
The analysis of the Chandra HETG spectrum shows that , to correctly describe the spectrum , three model components are needed .
Two of those components are optically thin thermal plasmas of different temperatures ( kT \approx 8–9 and 0.2–0.3 keV respectively ) described by the models vmekal or bvapec .
The Fe abundance in each of these two components appears equal within the errors and is sligthly subsolar with Z \approx 0.75 Z _ { \odot } .
The bvapec model describes better the Fe L transitions although it can not fit well the Na xi Ly \alpha line , at 10.02 Å , which appears to be overabundant .
Two different models seem to describe well the third component .
One possibility is a third hot optically thin thermal plasma at kT = 16–21 keV with an Fe abundance Z \approx 0.3 Z _ { \odot } , definitely smaller than for the other two thermal components .
Furthermore , the bvapec model describes well the Fe K shell transitions because it accounts for the turbulence broadening the line Fe xxv and Fe xxvi lines with a v _ { turb } \approx 1200 km/s .
These two lines , contributed mainly by the hot thermal plasma , are significantly wider thant the Fe K \alpha line whose FWHM < 5 mA is not resolved by Chandra .
Alternatively , the third component can be described by a powerlaw with a photon index \Gamma = 1.56 .
In either case , the Chandra HETG spectrum establishes that each one of these components must be modified by distinct absorption columns .
The analysis of a non contemporaneous 25 ks Suzaku observation shows the presence of a hard tail extending up to at least 33 keV .
The Suzaku spectrum is described with the sum of two components : an optically thin thermal plasma at kT \approx 9 keV and Z \approx 0.74 Z _ { \odot } ; and a very hot second plasma with kT \approx 33 keV or , alternatively , a powerlaw with photon index \Gamma = 1.58 .
In either case , each one of the two components must be affected by different absorption columns .
Therefore , the kT = 8–9 keV component is definitely needed while the nature of the harder emission can not be unambiguously established with the present data sets .
The analysis of the Si xiii and S xv He like triplets present in the Chandra spectrum point to a very dense ( n _ { e } \sim 10 ^ { 13 } cm ^ { -3 } ) plasma located either close to the stellar surface ( r < 3 R _ { * } ) of the Be star or , alternatively , very close ( r \sim 1.5 R _ { WD } ) to the surface of a ( hypothetical ) WD companion .
We argue , however , that the available data supports the first scenario .