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Models for Old, Metal-Poor Stars with Enhanced α-Element Abundances. II. Their Implications for the Ages of the Galaxy's Globular Clusters and Field Halo Stars
VandenBerg, Don A.
The ages of globular clusters (GCs) and post-turnoff field stars in the Galactic halo are derived using new stellar evolutionary models that explicitly take into account the observed abundances of the α-elements. Whereas the distances of the field subgiants considered in this study are based on Hipparcos parallax measurements, theoretical zero-age…
The Local Interstellar Medium in Puppis-Vela
Blaauw, A.; Moos, H. Warren; Sahu, M. S. +1 more
The first study of the local interstellar medium (LISM) toward Puppis-Vela (l=245deg to 275°, b=-15deg to +5°, d<200 pc) is presented in this paper. A study of the locations, sizes, and physical characteristics of local interstellar gas, i.e.``astronephography,'' is included, and relies upon the improved distance measureme…
Using Balmer Line Shapes to Diagnose Physical Conditions in Collisionless Shock Waves
Hartigan, Patrick; Raymond, John C.; Ghavamian, Parviz
When a collisionless shock propagates through a partially ionized, tenuous medium (n<=1 cm-3), the neutral atoms overrun by the shock produce Balmer line emission as they are excited by collisions in the hot postshock gas. The collisional excitation of neutral atoms and their charge exchange with hot postshock protons produces both n…