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We present multiwavelength time-series spectroscopy of SN 2013aa and SN 2017cbv, two Type Ia supernovae (SNe Ia) on the outskirts of the same host galaxy, NGC 5643. This work utilizes new nebular-phase near-infrared (NIR) spectra obtained by the Carnegie Supernova Project-II, in addition to previously published optical and NIR spectra. Using nebular-phase [Feii] lines in the optical and NIR, we examine the explosion kinematics and test the efficacy of several common emission-line-fitting techniques. The NIR [Feii] 1.644μm line provides the most robust velocity measurements against variations due to the choice of the fit method and line blending. The resulting effects on velocity measurements due to choosing different fit methods, initial fit parameters, continuum and line profile functions, and fit region boundaries were also investigated. The NIR [Feii] velocities yield the same radial shift direction as velocities measured using the optical [Feii]λ7155 line, but the sizes of the shifts are consistently and substantially lower, pointing to a potential issue in optical studies. The NIR [Feii] 1.644μm emission profile shows a lack of significant asymmetry in both SNe, and the observed low velocities elevate the importance for correcting for any velocity contribution from the host galaxy’s rotation. The low [Feii] velocities measured in the NIR at nebular phases disfavor progenitor scenarios in close double-degenerate systems for both SN 2013aa and SN 2017cbv. The time evolution of the NIR [Feii] 1.644μm line also indicates moderately high progenitor white dwarf central density and potentially high magnetic fields.

 

The observed diversity in Type Ia supernovae (SNe Ia) – the thermonuclear explosions of carbon–oxygen white dwarf stars used as cosmological standard candles – is currently met with a variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase (>200 d past peak) for each of these events, all of which had time series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g. double-detonation, off-centre detonation, stellar collisions), progenitor star (e.g. ejecta mass, metallicity), and binary companion (e.g. another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the subgroup of SNe Ia which appear to be transitional between the subluminous ‘91bg-like’ events and normal SNe Ia, and for which nebular-phase spectra are rare.

 

Abstract We present deep Chandra X-ray observations of two nearby Type Ia supernovae, SN 2017cbv and SN 2020nlb, which reveal no X-ray emission down to a luminosity L X ≲ 5.3 × 10 37 and ≲ 5.4 × 10 37 erg s −1 (0.3–10 keV), respectively, at ∼16–18 days after the explosion. With these limits, we constrain the pre-explosion mass-loss rate of the progenitor system to be M ̇ < 7.2 × 10 −9 and < 9.7 × 10 −9 M ⊙ yr −1 for each (at a wind velocity v w = 100 km s −1 and a radius of R ≈ 10 16 cm), assuming any X-ray emission would originate from inverse Compton emission from optical photons upscattered by the supernova shock. If the supernova environment was a constant-density medium, we would find a number density limit of n CSM < 36 and < 65 cm −3 , respectively. These X-ray limits rule out all plausible symbiotic progenitor systems, as well as large swathes of parameter space associated with the single degenerate scenario, such as mass loss at the outer Lagrange point and accretion winds. We also present late-time optical spectroscopy of SN 2020nlb, and set strong limits on any swept up hydrogen ( L H α < 2.7 × 10 37 erg s −1 ) and helium ( L He, λ 6678 < 2.7 × 10 37 erg s −1 ) from a nondegenerate companion, corresponding to M H ≲ 0.7–2 × 10 −3 M ⊙ and M He ≲ 4 × 10 −3 M ⊙ . Radio observations of SN 2020nlb at 14.6 days after explosion also yield a non-detection, ruling out most plausible symbiotic progenitor systems. While we have doubled the sample of normal Type Ia supernovae with deep X-ray limits, more observations are needed to sample the full range of luminosities and subtypes of these explosions, and set statistical constraints on their circumbinary environments. 

Apolipoprotein E (APOE) interacts with Alzheimer's disease pathology to promote disease progression. We investigated the moderating effect of APOE on independent associations of amyloid and tau positron emission tomography (PET) with cognition.

For 297 nondemented older adults from the Alzheimer's Disease Neuroimaging Initiative, regression equations modeled associations between cognition and (1) cortical amyloid beta (Aβ) PET levels adjusting for tau and (2) medial temporal lobe (MTL) tau PET levels adjusting for Aβ, including interactions with APOE ε4‐carrier status.

Adjusting for tau PET, Aβ was not associated with cognition and did not interact with APOE. In contrast, adjusting for Aβ PET, MTL tau was associated with all cognitive domains. Further, there was a stronger moderating effect of APOE on MTL tau and memory associations in ε4‐carriers, even among Aβ‐negative individuals.

Findings suggest that APOE may interact with tau independently of Aβ and that elevated MTL tau confers negative cognitive consequences in Aβ‐negative ε4 carriers.

 

In this work, BVRI light curves of 55 Type II supernovae (SNe II) from the Lick Observatory Supernova Search programme obtained with the Katzman Automatic Imaging Telescope and the 1 m Nickel telescope from 2006 to 2018 are presented. Additionally, more than 150 spectra gathered with the 3 m Shane telescope are published. We conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. Typically, our light curves are sampled with a median cadence of 5.5 d for a total of 5093 photometric points. In average, V-band plateau declines with a rate of 1.29 mag (100 d)−1, which is consistent with previously published samples. For each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: SNe II with steeper decline have shorter plateau duration and are brighter. A time-evolution analysis of spectral lines in term of velocities and pseudo-equivalent widths is also presented in this paper. Our spectroscopic sample ranges between 1 and 200 d post-explosion and has a median ejecta expansion velocity at 50 d post-explosion of 6500 km s−1 (H α line) and a standard dispersion of 2000 km s−1. Nebular spectra are in good agreement with theoretical models using a progenitor star having a mass <16M⊙. All the data are available to the community and will help to understand SN II diversity better, and therefore to improve their utility as cosmological distance indicators.