deletions | additions       diff --git a/section_Introduction_Massive_stars_strongly__.tex b/section_Introduction_Massive_stars_strongly__.tex  index 23b10f4..55b772e 100644  --- a/section_Introduction_Massive_stars_strongly__.tex  +++ b/section_Introduction_Massive_stars_strongly__.tex 
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Watson et al. (2010) used 2MASS and GLIMPSE photometery to analyze the YSO population around 46 bubbles and found about a quarter showed an overabundance of YSOs near the boundary between the ionized interior and molecular exterior. These YSOs are interesting because they are candidates for being triggered by the expanding ionization and shock fronts created by the hot star. Star-formation triggered by previous generations of stars is known to occur (citation?) but the specific physical mechanism is still undetermined. The collect-and-collapse model (Elmegreen \& Lada, 1977) describes the ambient material swept up by the shock fronts as eventually becoming gravitationally unstable, resulting in collapse. Other mechanisms, however, have been proposed. Radiatively-driven implosion (Lefloch \& Lazareff, 1994), for example, described ambient material as an already existent clump, but whose contraction is aided by the external radiation of the hot star.   The selection of bubbles with an overabundance of YSOs along the bubble-ISM boundary are a potentially excellent set of sources to study the mechanisms of triggered star-formation. The method of identifying YSOs through photometry, however, is limited. Robitaille \& Whitney (20XX) (2006)  showed that YSO age is degenerate with the observer's inclination angle. Briefly, an early-stage YSO and  a late-stage YSO seen edge on, so the accretion or debris  disk is observed as thick and blocking the inner regions, will can  appear similar, even in the IR, so an early stage YSO. IR.  Thus, we require other diagnostics of the YSOs along the bubble edge to determine the youngest, and most likely to have been triggered, YSOs. The current project aimed to identify the youngest YSOs by observing the CS (1-0) transition near 49 GHz with the Green Bank Telescope (GBT). CS is a probe of young star-formation. It has been detected in outflows from protostars, infall and in hot cores (citations?). The chemistry is, naturally, complex, and it appears that CS can play several roles. Our aim here is to use CS as a broad identifier of young star-formation and use any non-gaussian line-shapes to infer molecular gas behavior.   After describing the CS  survey and CS  mapping observations (sec 2) and numerical results (sec 3), we analyze the Herschel-HiGAL emission toward all our sources to determine, along with our CS detections, the CS abundances (sec 4.1). We also analyze three sources for evidence of rapid infall (sec 4.2) and the three  mapped regions. We end with a summary of the conclusions.