Staffing with clergy teams in the United Methodist Church

https://place.asburyseminary.edu/ecommonsatsdissertations/1428/thumbnail.jp

SN1991bg-like supernovae are a compelling source of most Galactic antimatter

The Milky Way Galaxy glows with the soft gamma ray emission resulting from the annihilation of $\sim 5 \times 10^{43}$ electron-positron pairs every second. The origin of this vast quantity of antimatter and the peculiar morphology of the 511keV gamma ray line resulting from this annihilation have been the subject of debate for almost half a century. Most obvious positron sources are associated with star forming regions and cannot explain the rate of positron annihilation in the Galactic bulge, which last saw star formation some $10\,\mathrm{Gyr}$ ago, or else violate stringent constraints on the positron injection energy. Radioactive decay of elements formed in core collapse supernovae (CCSNe) and normal Type Ia supernovae (SNe Ia) could supply positrons matching the injection energy constraints but the distribution of such potential sources does not replicate the required morphology. We show that a single class of peculiar thermonuclear supernova - SN1991bg-like supernovae (SNe 91bg) - can supply the number and distribution of positrons we see annihilating in the Galaxy through the decay of $^{44}$Ti synthesised in these events. Such $^{44}$Ti production simultaneously addresses the observed abundance of $^{44}$Ca, the $^{44}$Ti decay product, in solar system material.Comment: Accepted for publication in Proceedings of IAU Symposium 322: The Multimessenger Astrophysics of the Galactic Center 4 page

Evaluating the use of lecture capture using a revealed preference approach

This article discusses the introduction of lecture capture technology on a large undergraduate module with diverse student cohorts. Literature has so far relied on surveying students to discover their use of the technology or attempted to quantify the impact of watching lecture recordings on assessment performance. Alternatively, the principal contribution of this article is an evaluation of the use of the recorded lectures using a revealed preference approach. Specifically we identify to what extent students watched lecture recordings, rather than simply claimed to watch them when asked to provide comments on the technology. Data indicates the number of distinct students who watched recordings, the frequency with which they watched recordings, the average length of viewings as well as the time of day when lectures were viewed. We monitored viewings over two academic years, identifying ‘spikes’ in the number of viewings in the days before tests, as well as regularities in the viewing patterns across the two years. We analyse the data to assess the extent to which students used the recordings, how and when they watched the recordings. We conclude that the students value lecture recordings, making more extensive use of the recordings than has been identified in the literature to date. Ultimately, lecture recordings are suggested to offer valuable support for students’ independent study

SN1991bg-like supernovae are associated with old stellar populations

SN1991bg-like supernovae are a distinct subclass of thermonuclear supernovae (SNe Ia). Their spectral and photometric peculiarities indicate their progenitors and explosion mechanism differ from `normal' SNe Ia. One method of determining information about supernova progenitors we cannot directly observe is to observe the stellar population adjacent to the apparent supernova explosion site to infer the distribution of stellar population ages and metallicities. We obtain integral field observations and analyse the spectra extracted from regions of projected radius $\sim\,\mathrm{kpc}$ about the apparent SN explosion site for 11 91bg-like SNe in both early- and late-type galaxies. We utilize full-spectrum spectral fitting to determine the ages and metallicities of the stellar population within the aperture. We find that the majority of the stellar populations that hosted 91bg-like supernovae have little recent star formation. The ages of the stellar populations suggest that that 91bg-like SN progenitors explode after delay times of $>6\,\mathrm{Gyr}$, much longer than the typical delay time of normal SNe Ia, which peaks at $\sim 1\,\mathrm{Gyr}$.Comment: 12 pages, 3 figures, 3 tables, submitted to Publications of the Astronomical Society of Australi

Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations

Our Galaxy hosts the annihilation of a few $\times 10^{43}$ low-energy positrons every second. Radioactive isotopes capable of supplying such positrons are synthesised in stars, stellar remnants, and supernovae. For decades, however, there has been no positive identification of a main stellar positron source leading to suggestions that many positrons originate from exotic sources like the Galaxy's central super-massive black hole or dark matter annihilation. %, but such sources would not explain the recently-detected positron signal from the extended Galactic disk. Here we show that a single type of transient source, deriving from stellar populations of age 3-6 Gyr and yielding ~0.03 $M_\odot$ of the positron emitter $^{44}$Ti, can simultaneously explain the strength and morphology of the Galactic positron annihilation signal and the solar system abundance of the $^{44}$Ti decay product $^{44}$Ca. This transient is likely the merger of two low-mass white dwarfs, observed in external galaxies as the sub-luminous, thermonuclear supernova known as SN1991bg-like.Comment: 28 pages main text with 4 figures in preprint style; 26 pages of Supplementary Informatio

Prospects of direct detection of 48^{48}V gamma-rays from thermonuclear supernovae

Detection of gamma-rays emitted by radioactive isotopes synthesized in stellar explosions can give important insights into the processes that power transients such as supernovae, as well as providing a detailed census of the abundance of different isotope species relevant to the chemical evolution of the Universe. Observations of nearby supernovae have yielded observational proof that $^{57}$Co powered the late-time evolution of SN1987A's lightcurve, and conclusive evidence that $^{56}$Ni and its daughter nuclei power the light curves of Type Ia supernovae. In this paper we describe the prospects for detecting nuclear decay lines associated with the decay of $^{48}$V, the daughter nucleus of $^{48}$Cr, which is expected to be synthesised in large quantities - $M_{\mathrm{Cr}}\sim1.9\times10^{-2}\,\mathrm{M_\odot}$ - in transients initiated by explosive helium burning ($\alpha$-capture) of a thick helium shell. We calculate emergent gamma-ray line fluxes for a simulated explosion model of a thermonuclear explosion of carbon-oxygen white dwarf core of mass $0.45\,M_{\odot}$ surrounded by a thick helium layer of mass $0.21\,M_{\odot}$. We present observational limits on the presence of $^{48}$V in nearby SNe Ia 2014J using the \textit{INTEGRAL} space telescope, excluding a $^{48}$Cr production on the surface of more than $0.1\,\mathrm{M_{\odot}}$. We find that the future gamma-ray mission AMEGO will have an approximately 5 per cent chance of observing $^{48}$V gamma-rays from such events during the currently-planned operational lifetime, based on our birthrate predictions of faint thermonuclear transients. We describe the conditions for a $3\sigma$ detection by the gamma-ray telescopes \textit{INTEGRAL}/SPI, COSI and AMEGO.Comment: 9 pages, 3 figures, submitted to MNRAS, minor revisions Sept 202

The ANU WiFeS SuperNovA Program (AWSNAP)

This paper presents the first major data release and survey description for the ANU WiFeS SuperNovA Program (AWSNAP). AWSNAP is an ongoing supernova spectroscopy campaign utilising the Wide Field Spectrograph (WiFeS) on the Australian National University (ANU) 2.3m telescope. The first and primary data release of this program (AWSNAP-DR1) releases 357 spectra of 175 unique objects collected over 82 equivalent full nights of observing from July 2012 to August 2015. These spectra have been made publicly available via the WISeREP supernova spectroscopy repository. We analyse the AWSNAP sample of Type Ia supernova spectra, including measurements of narrow sodium absorption features afforded by the high spectral resolution of the WiFeS instrument. In some cases we were able to use the integral-field nature of the WiFeS instrument to measure the rotation velocity of the SN host galaxy near the SN location in order to obtain precision sodium absorption velocities. We also present an extensive time series of SN 2012dn, including a near-nebular spectrum which both confirms its "super-Chandrasekhar" status and enables measurement of the sub-solar host metallicity at the SN site.Comment: Submitted to Publications of the Astronomical Society of Australia (PASA). Spectra publicly released via WISeREP at http://wiserep.weizmann.ac.il