(Proposal ID) S10B-065

(PI) Zhao, Zhengshi

(Proposal Title)
Abundance analysis of blue stragglers in a galactic globular cluster M30

(Abstract)
We propose to take high resolution spectra of blue straggler stars (BSSs) in a 
galactic globular cluster M30. Two different origins, mass transfer in a 
binary system and merger via collisions between single stars, are proposed to 
explain the properties of BSSs. Numbers of photometric studies and dynamical 
simulations suggest that even in the same galactic globular cluster the 
dominant BSSs' formation scenario would differ in regions with different 
density and radius. Previous spectroscopic studies of BSSs imply that 
abundance analysis is the most important and effective way to clarify 
differences between BSSs formed by different mechanisms. Currently, two 
different BSS sequences on color-magnitude diagram of M30 are reported as 
the verification of occurrence of two mechanisms in M30. That is the first 
observational evidence for that the BSSs formed by different mechanisms 
separated clearly into two sequences. We wish to obtain high resolution 
spectra for 6 bright (V>17.5 mag) BSSs (3 stars for each sequence) in M30 
to confirm the reality of separation in BSS sequences in this GC and 
distinctions in chemical compositions between BSSs formed via different 
mechanisms.