Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20917220w&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #172.20; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
Scientific paper
The High-Velocity Clouds (HVC) found in the Galactic halo hold many clues about galactic evolution. Specifically, they can be used to determine, the rate of infall of low-metallicity gas, the potential of the dark matter halo, the rate of circulation between the disk and halo and the number of ionizing photons escaping the Galactic disk. In all of these cases, the usefulness of the HVC depends critically on the determination of distance to the clouds. The most straight-forward method for computing HVC distances is to determine the distances to fore-ground and back-ground blue stars which show the absence/presence of interstellar absorption lines superimposed on their stellar spectra, thus bracketing the distance to the HVC.
We present a new stellar distance calibration for blue stars, based on absolute magnitudes determined from the fit of theoretical isochrones in the Teff-Logg plane. This distance calibration depends critically on the determination of accurate stellar parameters, Teff, Log g and [Fe/H] for the blue horizontal branch, blue straggler and RR Lyrae variable stars. We will present external calibration results for our stellar parameter determination using well studied stars in these luminosity classes and present a balmer-line width/color-index method for determining likely variable stars within the sample. Finally, we will present results for the new distance calibration, through direct comparison to the standard stars and stars in the galactic globular clusters, and use these results to constrain the error in distance measurements to the HVC.
Barentine John
Beers Timothy C.
Wakker Bart P.
Wilhelm Ronald J.
York Don G.
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