Metallicity mapping of the Milky Way

Details Metallicity mapping of the Milky Way Metallicity mapping of the Milky Way

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011sptz.prop80008s&link_type=abstract

Spitzer Proposal ID #80008

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Scientific paper

We have discovered that the mid-infrared [3.6]-[4.5] colors of long-period Cepeids are dominated by a metallicity and temperature sensitive carbon monoxide feature that is squarely situated inside of the 4.5mu bandpass. The [3.6] photometry is unaffected by the CO and its PL relation can deliver distances to Cepheids that are individually good to ±4%. We will use the time-averaged 3.6um photometry of the 120 longest -period Galactic Cepheids to map the spiral structure of the Milky Way out to a radius 6 kpc around the solar neighborhood, and we will then use the [3.6]-[4.5] colors to derive spectroscopic-quality metallicities for each of these Cepheids. This will alow us to measure the radial gradient of metals in the galaxy and to explore its variance at fixed radius. For Cepheids with phased radial-velocity coverage we will for the first time apply the Baade-Wesselink methodology in the mid-infrared for determining the absolute luminosities (and distances) of these Cepheids. These determinations will greatly enhance the precision calibration of the slope, zero point and width of the Cepheid Period-Luminosity relation, well in advance of GAIA (whose nominal mission end is 2017). However, once GAIA has determined direct parallaxes to these same long-period Cepheids we will immediately be in a position to make the necessary intercomparisons and explore the physical consequences.

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