Type Ia supernova spectral line ratios as luminosity indicators

Type Ia supernovae have played a crucial role in the discovery of the dark energy, via the measurement of their light curves and the determination of the peak brightness via fitting templates to the observed light-curve shape. Two spectroscopic indicators are also known to be well correlated with peak luminosity. Since the spectroscopic luminosity indicators are obtained directly from observed spectra, they will have different systematic errors than do measurements using photometry. In addition, these spectroscopic indicators may be useful for studies of effects of evolution or age of the SNe Ia progenitor population. We present several new variants of such spectroscopic indicators that are easy to automate and that minimize the effects of noise. We show that these spectroscopic indicators can be measured by proposed JDEM missions such as SNAP and JEDI.