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Using High-Resolution Optical Spectra to Measure Intrinsic Properties of Low-Mass Stars: New Properties for KOI-314 and GJ 3470

We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby dwarfs spanning K7 to M4, taken with Keck/HIRES as part of the California Planet Search. We identify several spectral regions in the visible (370 - 800 nm) that are sensitive to the stellar luminosity and metallicity. We use these regions to develop a spectral calibration method to measure the mass, metallicity, and distance of low-mass stars, without the requirement of geometric parallaxes. Testing our method on a sample of nearby M dwarfs we show that we can reproduce stellar masses to about 8 - 10%, metallicity to ~0.15 dex and distance to 11%. We were able to make use of HIRES spectra obtained as part of the radial velocity monitoring of the star KOI-314 to derive a new mass estimate of 0.57 +/- 0.05 Msun, a radius of 0.54 +/- 0.05 Rsun, a metallicity, [Fe/H], of -0.28 +/- 0.10 and a distance of 66.5 +/- 7.3 pc. Using HARPS archival data and combining our spectral method with constraints from transit observations, we are also able to derive the stellar properties of GJ3470, a transiting planet hosting M dwarf. We estimate a mass of 0.53 +/- 0.05 Msun, a radius of 0.50 +/- 0.05 Rsun, a metallicity, [Fe/H] = 0.12 +/- 0.12 and a distance of 29.9_{-3.4}^{+3.7} pc.