deletions | additions       diff --git a/sectionIntroduction_.tex b/sectionIntroduction_.tex  index ba5a7e3..c7e1882 100644  --- a/sectionIntroduction_.tex  +++ b/sectionIntroduction_.tex 
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important clue lies in the spectral-type distribution of classical Be stars (i.e. the isolated variety) which  is uniform, and those in high mass X-ray binaries (HMXB) which cluster strongly around spectral type  B0 \cite{Negueruela 1998}. The presence of the neutron-star companion in HMXB has been shown to  affect both the size and density of the disk (e.g. \cite{Zamanov 1998}). \cite{Zamanov1998}).  Be star disks are very dynamic on timescales of months to years, sometimes exhibiting quasi-periodic  fluctuations in both the equivalent width and profile of the H{$\alpha$} emission line. Occasionaly the disk dissipates and later re-forms. 
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the quasi-periodic behavior (e.g. \cite{Clark2001}. However the perturbing entity has yet to be identified.  In HMXB the neutron star exerts a tidal influence on the circumstellar disk \cite{Okazaki2001},  leading to strings of X-ray outbursts correlated with the binary period (For extensive examples  see Galache et al 2008). \cite{Galache2008}).  The tidal interaction would also be present in the "isolated" Be stars if faint companions are present, and is plausibly the driver of quasi-periodic disk behavior. This can be tested  by estimating orbital periods from the binary separations and comparing against the disk  quasi-periods.  There is compelling observational evidence for binarity in classical Be-stars: Carrieret al (2002)  conducted spectroscopic (RV monitoring) of 4 Be stars selected for their periodic photometric  variations, finding two spectroscopic binaries. The period of one of these binaries (398d) closely  matched its photometric period. period \cite{Carrier2002}.  No companions were found for the other 2 stars (one of which was found to exhibit non-radial pulsations). Companions to a few Be-stars are known at much larger  separations (for example the famous double-star Albireo). With AO we can search the parameter space  not explored by natural imaging and RV studies.  VLT/AO observations by Kervella et al (2008) \cite{Kervella2008}  have found a companion to the closest Be star "Achernar". The separation is 0.15" (6.7 AU at D=44pc) and the orbital period is about 15 years,  similar to the quasi-periodicity of the circumstellar disk. The spectrum of Achernar-B shows an  A1V-A3V star. The two stars differ in brightness by 3.5 mag.