Josh Peek edited section_Methods_Results_The_R__.tex  almost 8 years ago

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and the parameters measured for these lines are distinct between the populations. Unfortunately, we do not have observations of the H$\gamma$ or H$\delta$ line, only the H$\epsilon$ and H$\zeta$ line. To determine whether we can use the (better resolved) H$\epsilon$ line as a similar discriminator, we first assemble a sub-population of BHB, BS, and MS drawn from the catalog presented in \citet{Xue_2008}, selected to be brighter than 16th magnitude in $g$. These targets have already been fit, and classified, but to test our method we refit the H$\gamma$ line in the SDSS DR10 spectra using Equation \ref{sersic}. We find that we can indeed reproduce the bifurcation. We then apply this same fitting procedure to the H$\epsilon$ line. The results for both fits are shown in Figure \ref{hgammahepsilon}. The H$\epsilon$ line fit Sersi\'c parameters b and c do not as clearly delineate between BHB and BS stars, but the differentiation is still quite clearly in place. We then apply this same fit to our VLT/FLAMES spectrum of USNO-A0600-15865535, and overplot the b and c parameters. USNO-A0600-15865535 is clearly a BHB star.  BHB stars have the useful property of being rather accurate standard candles. There is a direct relationship between BHB color and absolute magnitude reported in \citet{Xue_2008} (these values are originally reported in \citet{Sirko_2004} with a typographical error). The observed color in Pan-STARRS1 imaging  is $g-r = -0.21$, and \cite{Schlegel_1998} reports an \citet{Schlegel_1998} report a  reddening of $E\left(B-V\right) = 0.068$ toward this sightline, giving us a corrected color of $g-r = -0.28$ using the parameters from \cite{Schlafly_2011}. This translates to an absolute magnitude of the star to be $M_g = 0.8$. USNO-A0600-15865535's measured $g$ magnitude of 14.2, reddening corrected to 14.0, gives a final distance of 4.4 kpc, with distance errors for BHB stars typically quoted at 10\%.