A COMPREHENSIVE STUDY OF FE L-SHELL ABSORPTION IN THE INTERSTELLAR MEDIUM

DETERMINING THE COMPOSITION AND LOCATION OF INTERSTELLAR DUST IS KEY TO OUR UNDERSTANDING OF STELLAR NUCLEOSYNTHESIS AND THE ELEMENTAL ABUNDANCES IN OUR GALAXY AS WELL AS BROADER ISSUES SUCH AS THE LIFE CYCLES OF STARS. KNOWLEDGE ABOUT THE COMPOSITION OF THE DUST GRAINS CAN ALSO BE USED TO FOLLOW THEIR PATHWAY TO LARGER ASTRONOMICAL BODIES ENABLING US TO TRACE OUT THE FORMATION HISTORY OF PLANETARY SYSTEMS. UNFORTUNATELY TRADITIONAL TECHNIQUES FOR DERIVING ELEMENTAL DEPLETIONS ONTO GRAINS USING OPTICAL AND ULTRAVIOLET (UV) ABSORPTION SPECTRA OF INDIVIDUAL METAL IONS SUFFER FROM UNCERTAINTIES INTRODUCED BY THE IONIZATION CORRECTIONS (I.E. ACCOUNTING FOR THE UNSEEN IONIZATION STATES). ADDITIONALLY A LARGE BUT POORLY CONSTRAINED FRACTION OF THE INTERSTELLAR FE IS LOCKED UP IN THE SOLID-PHASE NAMELY IN DUST GRAINS WHICH ARE NOT DETECTABLE IN THE UV. HIGH RESOLUTION X-RAY PHOTOABSORPTION SPECTRA OF THE INTERSTELLAR MEDIUM (ISM) IS THE SOLE TECHNIQUE THAT CAN SIMULTANEOUSLY DETECT METALS IN ALL CHARGE STATES AND PHASES OF THE ISM. THIS MAKES X-RAY OBSERVATIONS UNIQUE AND COMPLEMENTARY TO ISM STUDIES IN THE RADIO INFRARED AND UV. WE PROPOSE TO ANALYZE ALL SUITABLE HIGH RESOLUTION X-RAY PHOTOABSORTION SPECTRA OF THE ISM CURRENTLY AVAILABLE FROM THE REFLECTION GRATING SPECTROMETER (RGS) ON BOARD X-RAY MULTI-MIRROR MISSION NEWTON (XMM-NEWTON) ENCOMPASSING APPROXIMATELY TWO DOZEN DIFFERENT SIGHT LINES THROUGH THE ISM. WE WILL SUPPLEMENT THE ARCHIVAL RGS WITH ARCHIVAL DATA FROM HIGH ENERGY TRANSMISSION GRATING SPECTROMETER (HETGS) ON BOARD THE CHANDRA X-RAY OBSERVATORY.