(Euclid, WFIRST) will contribute to distinguishing the nature of dark energy ( Albrecht et al. Present-day limits are weak, but future work with large, carefullyĬalibrated samples from the ground (Pan-STARRS, Dark Energy Survey, LSST) and from space Redshift come from from high-redshift observations with the Hubble Space Telescope ( Riess et al. The first results show that forĪ flat universe with constant w, the dark energy is compatible with aĬosmological constant (for which w = −1) within about 10% ( Astier et al. 2006) can be combined to constrain theĮquation-of-state for dark energy, noted w. The present state-of-the-art givesĭistances to well-observed individual objects with uncertainties of order 10%, so that It is important to construct the best possible distance indicators to extract the maximumĬosmological information from supernova surveys. Harvard-Smithsonian Center for Astrophysics (CfA Matheson Statistical tests to a subset of the ~250 SN Ia for which we have good light curvesĪnd spectra based on the ongoing program of supernova observations at the (2009) that spectra can contribute to improved distance measurements. Paper we explore the suggestion of Bailey et al. Intrinsically dim ( Phillips 1993 Riess et al. Of supernova light curves and their colors to tell which supernovae are bright and which are Precise distances to Type Ia supernovae (SN Ia) formed the cornerstone of the discovery ofĬosmic acceleration ( Riess et al. Precise distances to SN Ia and the implications for future surveys which seek to determineĪppendices are only available in electronic form at We discuss the use of spectra in measuring more Width etc.), but none appear to lead to a significant improvement over the standard Indicators related to line-profile morphology (absorption velocity, pseudo-equivalent (WRMS = 0.143 ± 0.020 mag) with respect to the standard combination of light-curve widthĪnd color, at ~2 σ significance. T = −2.5 d from maximum light, which leads to ~30% lower scatter Theīest flux ratio overall is the color-corrected ℛ c(4610/4260) at The iron-group-dominated absorption features around ~4300 Å and ~4800 Å. We consider flux ratios at other ages, as well as the use of pairs ofįlux ratios, revealing the presence of small-scale intrinsic spectroscopic variations in Comparison with synthetic spectra from 2D delayed-detonationĮxplosion models shows that the correlation of ℛ(6630/4400) with SN Ia absolute magnitudesĬan be largely attributed to intrinsic color variations and not to reddening by dust in Importance of an accurate relative flux calibration and the failure of this method for (<2 σ) given the size of our sample (26 SN Ia). (WRMS = 0.175 ± 0.025 mag), although the improvement has low statistical significance ℛ c(6420/5290) at maximum light leads to an even lower scatter In combination with the SALT2 color parameter, the color-corrected flux ratio We confirm the ability of spectral flux ratios aloneĪt maximum light to reduce the scatter of Hubble residuals by ~10% [weighted rms, or Using light-curve width and color parameters (determined using the SALT2 light-curveįitter) and a spectroscopic indicator, and evaluate the resulting Hubble diagram scatter We consider linear models for predicting distances to SN Ia We investigate the use of a wide variety of spectroscopic measurements to determineĭistances to low-redshift Type Ia supernovae (SN Ia) in the Hubble flow observed through Kirshner 2Ĭentre de Physique des Particules de Marseille (CPPM),
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