Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21924418c&link_type=abstract
American Astronomical Society, AAS Meeting #219, #244.18
Astronomy and Astrophysics
Astronomy
Scientific paper
In the past, detailed chemical abundance measurements were limited to stars in the Milky Way and its dwarf satellites since stars in more distant galaxies are too faint for even the most powerful telescopes to obtain the high signal-to-noise spectra needed for such measurements. In this project, we co-added low signal-to-noise spectra of individual red giant stars with similar photometric properties to create high signal-to-noise spectra free of instrumental artifacts. We compared the resulting spectra to a collection of "model" spectra, which are generated from realistic computer models of the interiors of stars. These spectra mimic the behavior of stellar spectra over a wide range of properties, most notably the iron to hydrogen ratio. By adopting the abundance measurements of the best-fit model spectra, we measured iron and alpha element abundances for Andromeda dwarf satellites NGC 147, NGC 185, And I and And II, thereby expanding the data set of detailed abundance measurements beyond the Milky Way for the first time. We found that the abundance of alpha elements decreases as the abundance of iron increases, and that the abundance of iron increases with increasing satellite luminosity, similar to the trends seen in Milky Way dwarf spheroidal satellites. The similarity between Andromeda dwarf spheroidals (And I and And II) and dwarf ellipticals (NGC 147 and NGC 185) in these relations shows that these two galaxy types are closely related. We also calibrated the photometric iron abundance estimates with spectroscopic ones, resulting in more accurate photometric estimates that can be used in future projects.
This research was supported by the Science Internship Program (SIP) at UCSC and the National Science Foundation.
Cheng Lucy
Guhathakurta Puraga
Kirby Emma
SPLASH Collaboration
Yang Lantian
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