The spectroscopic diversity of Type Ia supernovae

S. Blondin, T. Matheson, R. P. Kirshner, K. S. Mandel, P. Berlind, M. Calkins, P. Challis, P. M. Garnavich, S. W. Jha, M. Modjaz, A. G. Riess, B. P. Schmidt

    Research output: Contribution to journalArticlepeer-review


    We present 2603 spectra of 462 nearby Type Ia supernovae (SNeIa), including 2065 previously unpublished spectra, obtained during 1993-2008 through the Center for Astrophysics Supernova Program. There are on average eight spectra for each of the 313 SNeIa with at least two spectra. Most of the spectra were obtained with the FAST spectrograph at the Fred Lawrence Whipple Observatory 1.5m telescope and reduced in a consistent manner, making this data set well suited for studies of SNIa spectroscopic diversity. Using additional data from the literature, we study the spectroscopic and photometric properties of SNeIa as a function of spectroscopic class using the classification schemes of Branch et al. and Wang et al. The width-luminosity relation appears to be steeper for SNeIa with broader lines, although the result is not statistically significant with the present sample. Based on the evolution of the characteristic Si IIλ6355 line, we propose improved methods for measuring velocity gradients, revealing a larger range than previously suspected, from ∼0 to ∼400 km s -1 day -1 considering the instantaneous velocity decline rate at maximum light. We find a weaker and less significant correlation between Si II velocity and intrinsic B - V color at maximum light than reported by Foley et al., owing to a more comprehensive treatment of uncertainties and host galaxy dust. We study the extent of nuclear burning and the presence of unburnt carbon in the outermost layers of the ejecta and report new detections of C IIλ6580 in 23 early-time SNIa spectra. The frequency of C II detections is not higher in SNeIa with bluer colors or narrower light curves, in conflict with the recent results of Thomas et al. Based on nebular spectra of 27 SNeIa, we find no relation between the FWHM of the iron emission feature at ∼4700 Å and Δm 15(B) after removing the two low-luminosity SN1986G and SN1991bg, suggesting that the peak luminosity is not strongly dependent on the kinetic energy of the explosion for most SNeIa. Finally, we confirm the correlation of velocity shifts in some nebular lines with the intrinsic B - V color of SNeIa at maximum light, although several outliers suggest a possible non-monotonic behavior for the largest blueshifts.

    Original languageEnglish (US)
    Article number126
    JournalAstronomical Journal
    Issue number5
    StatePublished - May 2012


    • supernovae: general
    • surveys

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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