Meagan Phillips

© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We use observedUVthrough near-IR spectra to examine whether SN 2011fe can be understood in the framework of Branch-normal Type Ia supernovae and to examine its individual peculiarities. As a benchmark, we use a delayed-detonationmodel with a progenitormetallicity of Z⊙/20. We study the sensitivity of features to variations in progenitor metallicity, the outer density profile, and the distribution of radioactive nickel. The effect of metallicity variations in the progenitor have a relatively small effect on the synthetic spectra. We also find that the abundance stratification of SN 2011fe resembles closely that of a delayed-detonation model with a transition density that has been fit to other Branch-normal SNe Ia. At early times, the model photosphere is formed in material with velocities that are too high, indicating that the photosphere recedes too slowly or that SN 2011fe has a lower specific energy in the outer ≈0.1 M⊙ than does the model. We discuss several explanations for the discrepancies. Finally, we examine variations in both the spectral energy distribution and in the colours due to variations in the progenitor metallicity, which suggests that colours are only weak indicators for the progenitor metallicity, in the particular explosion model that we have studied. We do find that the flux in the U band is significantly higher at maximum light in the solar metallicity model than in the lower metallicity model and the lower metallicity model much better matches the observed spectrum.

I am concerned with epistemic possibility expressions (EPEs) such as “It might be raining.” Much of the discussion of EPEs has concerned the fact that a given EPE can seem true in one context and false in another. Motivated by this data, contextualists have argued that modal expressions are sensitive to information at a context of use. Contextualist analyses encounter problems when it comes to disagreements centered on EPEs. Relativists such as John MacFarlane argue that epistemic modals are sensitive to information available to an assessor at a circumstance of evaluation. I side with a relativistic account of epistemic possibility, on which the truth conditions of EPEs depend not only on a context of use but also as on a context of assessment. The stipulation of contexts of assessments explains why third parties can judge an interlocutor’s utterance false, and why the interlocutor will retract her previous utterance. However, judgements of falsity and retraction seem to be absent in future-oriented EPEs such as “It might rain tomorrow.” I propose an mendment to John MacFarlane’s semantics that better models this quirk of epistemic possibility expressions.