The O I λ7774 Line as a Luminosity Indicator in M31

Details The O I λ7774 Line as a Luminosity Indicator in M31 The O I λ7774 Line as a Luminosity Indicator in M31

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21715316t&link_type=abstract

American Astronomical Society, AAS Meeting #217, #153.16; Bulletin of the American Astronomical Society, Vol. 43, 2011

Astronomy and Astrophysics

Astronomy

Scientific paper

Yellow supergiants are very useful tools in determining the accuracy of current stellar evolutionary models. These stars represent a short phase in a supergiant’s life; typically they will live only thousands of years. Because of this, their positions on the H-R diagram can reveal errors in current models. Identifying stars as yellow supergiants, however, has proved difficult as foreground Milky Way dwarfs can have similar colors and magnitudes. Still, Drout et al. (2009) and Neugent et al. (2010) identified yellow supergiant members from foreground non-members by using stars’ radial velocities. How does one identify yellow supergiants in galaxies without significant rotational velocity, though? In an effort to answer this, we have turned our attention to the O I λ7774 triplet. This line has been known to be a luminosity indicator in F-type supergiants due to Non-Local Thermal Equilibrium (LTE) and sphericity effects (Osmer 1972). We analyzed the spectra of 900 stars in M31, obtained with the Hectospec multi-fiber spectrometer on the MMT. This sample included 48 rank-1 (nearly certain) M31 members (Drout et al. 2009), looking specifically at the λ7774 line. There was found to be a limit that determines what a ‘significant’ amount of oxygen is, at approximately 1.2 Å. We found that the majority of previously known rank-1’s had a significant amount of oxygen, while 11% of rank-2’s (probable yellow supergiants) and less than 1% of rank-3’s (foreground dwarfs) had a significant amount. These results imply that the O I λ7774 will indeed work as a luminosity indicator.
This work was supported by the National Science Foundation through grants AST-1008020 and AST-1004107.

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