Investigation of the Progenitors of the Type Ia Supernovae Associated With the LMC Supernova Remnants 0505-67.9 and 0509-68.7

Although Type Ia supernovae have been heavily scrutinized due to their use in making cosmological distance estimates, we are still unable to definitively identify the progenitors for the entire population. While answers have been presented for certain specific systems, a complete solution remains elusive. We present observations of two supernova remnants (SNRs) in the Large Magellanic Cloud, SNR 0505-67.9 and SNR 0509-68.7, for which we have identified the center of the remnant and the 99.73% containment central region in which any companion star left over after the supernova must be located. Both remnants have a number of potential ex-companion stars near their centers; all possible single and double degenerate progenitor models remain viable for these two supernovae. Future observations may be able to identify the true ex-companions for both remnants.Comment: 8 pages, 4 figures, 4 tables, ApJ In Press; Table 2 truncated, full version available in published paper or directly from author

Identifying and Quantifying Recurrent Novae Masquerading as Classical Novae

Recurrent novae (RNe) are cataclysmic variables with two or more nova eruptions within a century. Classical novae (CNe) are similar systems with only one such eruption. Many of the so-called 'CNe' are actually RNe for which only one eruption has been discovered. Since RNe are candidate Type Ia supernova progenitors, it is important to know whether there are enough in our galaxy to provide the supernova rate, and therefore to know how many RNe are masquerading as CNe. To quantify this, we collected all available information on the light curves and spectra of a Galactic, time-limited sample of 237 CNe and the 10 known RNe, as well as exhaustive discovery efficiency records. We recognize RNe as having (a) outburst amplitude smaller than 14.5 - 4.5 * log(t_3), (b) orbital period >0.6 days, (c) infrared colors of J-H > 0.7 mag and H-K > 0.1 mag, (d) FWHM of H-alpha > 2000 km/s, (e) high excitation lines, such as Fe X or He II near peak, (f) eruption light curves with a plateau, and (g) white dwarf mass greater than 1.2 M_solar. Using these criteria, we identify V1721 Aql, DE Cir, CP Cru, KT Eri, V838 Her, V2672 Oph, V4160 Sgr, V4643 Sgr, V4739 Sgr, and V477 Sct as strong RN candidates. We evaluate the RN fraction amongst the known CNe using three methods to get 24% +/- 4%, 12% +/- 3%, and 35% +/- 3%. With roughly a quarter of the 394 known Galactic novae actually being RNe, there should be approximately a hundred such systems masquerading as CNe.Comment: 3 figures, 7 tables, accepted for publication in Ap

The Diffuse Source at the Center of LMC SNR 0509-67.5 is a Background Galaxy at z = 0.031

Type Ia supernovae (SNe Ia) are well-known for their use in the measurement of cosmological distances, but our continuing lack of concrete knowledge about their progenitor stars is both a matter of debate and a source of systematic error. In our attempts to answer this question, we presented unambiguous evidence that LMC SNR 0509-67.5, the remnant of an SN Ia that exploded in the Large Magellanic Cloud 400 +/- 50 years ago, did not have any point sources (stars) near the site of the original supernova explosion, from which we concluded that this particular supernova must have had a progenitor system consisting of two white dwarfs (Schaefer & Pagnotta 2012). There is, however, evidence of nebulosity near the center of the remnant, which could have been left over detritus from the less massive WD, or could have been a background galaxy unrelated to the supernova explosion. We obtained long-slit spectra of the central nebulous region using GMOS on Gemini South to determine which of these two possibilities is correct. The spectra show H-alpha emission at a redshift of z = 0.031, which implies that the nebulosity in the center of LMC SNR 0509-67.5 is a background galaxy, unrelated to the supernova.Comment: 2 figures, accepted for publication in Ap

On the progenitor of SNR 0509-67.5

We have used three independent methods to determine an accurate and precise geometric center of SNR 0509-67.5, at RA = 05:09:31.208, DEC = -67:31:17.48 (J2000). This supernova, which occurred approximately 400 years ago in the Large Magellanic Cloud, was confirmed to be a Type Ia by Rest et al. (2005), Rest et al. (2008) based on spectra of a light echo from the eruption. If this supernova had a single-degenerate progenitor system, we would see the leftover companion star within a certain distance of the remnant\u27s center. Accounting for an offset due to enhanced ISM in the west-southwest quadrant of the remnant, we find the eruption position to be at RA = 05:09:30.976, DEC = -67:31:17.90; the error circle which should contain any possible ex-companion star has a radius of 1.60″ for 99.73% (3-sigma) containment. This accounts for the proper motion of the stars, the possibility of kicks from the supernova, and asymmetries in the explosion and remnant expansion. We find no possible ex-companion stars within this ellipse, to a limiting magnitude of V = 26.9: there are no red giants, which precludes symbiotic progenitors, no subgiants, which when combined with the lack of red giants precludes recurrent nova progenitors, and no main sequence stars with mass greater than 1.16 solar masses (V brighter than 22.7 mag), which precludes persistent supersoft X-ray source progenitors. Indeed, all published SD models are eliminated, so we conclude that this particular Type Ia supernova had a double-degenerate progenitor. Copyright © International Astronomical Union 2013

The Disability-Employability Divide: Bottlenecks to Equal Opprotunity

Equal opportunity might appear to comprise a relatively simple question: Do similarly situated persons have an equal chance to attain a particular goal, or do obstacles irrelevant to their qualifications or to the desired goal preclude achievement? But equal opportunity is complicated.1 There are descriptive and prescriptive dimensions to this question. Nuances exist when determining who is similarly situated, whether those individuals have the same opportunity, what goals we care about equalizing, and whether the ultimate aspiration is equality of opportunity or equality of outcome. Moreover, what means should we employ to remove obstacles, are these means likely to be successful, and do the cultural means justify the societal ends? And some readily apparent factors leading to inequalities of opportunity seem inexorable, including our individual genetic makeup, the environments in which we are raised, and our overall social circumstances. These considerations have prompted some scholars to argue that equality of opportunity is possible only if both law and government are committed to achieving it.2 To discuss equal opportunity in a coherent way often requires focusing on specific domains.3 One field in which equal opportunity has special resonance is employment. Societal support exists both for the descriptive idea that racial discrimination poses an obstacle to equal opportunity and for the prescriptive idea that such an obstacle ought to be overcome. Accordingly, a law like Title VII of the Civil Rights Act of 1964 conveys something specific about what opportunities are important (work), what obstacles are inappropriate (discrimination), and what type of equality of opportunity is desired (race, color, sex, religion, and national origin). Such antidiscrimination laws generally enjoy strong support in the United States.4 Joseph Fishkin’s new book, Bottlenecks: A New Theory of Equal Opportunity, 5 reinvigorates the concept of equal opportunity by simultaneously engaging with its complications and attempting to simplify its ambitions. Fishkin describes bottlenecks as narrow spaces in the opportunity structure through which people must pass if they hope to reach a range of opportunities on the other side (p. 13). A significant component of the American opportunity structure that Bottlenecks leaves largely unexplored, however, relates to people with disabilities.6 This Review applies Fishkin’s theory to explore how disability law creates and perpetuates bottlenecks that keep people with disabilities from achieving a greater degree of human flourishing. In particular, disability policy’s opportunity structure features a conceptual disability– employability divide that ultimately prevents people with disabilities from reaching a wider array of opportunities. Fishkin’s book, in concert with this Review, introduces new and inventive ways of reimagining and implementing structural solutions to these bottlenecks. Part I provides an overview of Fishkin’s arguments, including his theory of opportunity pluralism, which he advances as a theoretical framework for broadening the opportunity structure. Part II then applies Fishkin’s theory to administrative disability policy to address and evaluate the disability– employability divide as a bottleneck. In particular, this Part explores how people with disabilities are frequently unable to pass through certain bottleneck policies to reach productive employment on the other side. Part III then proffers several policy solutions that could enable people with disabilities to move through or around the bottlenecks that keep them from accessing productive work opportunities

The Disability-Employability Divide: Bottlenecks to Equal Opprotunity

Equal opportunity might appear to comprise a relatively simple question: Do similarly situated persons have an equal chance to attain a particular goal, or do obstacles irrelevant to their qualifications or to the desired goal preclude achievement? But equal opportunity is complicated.1 There are descriptive and prescriptive dimensions to this question. Nuances exist when determining who is similarly situated, whether those individuals have the same opportunity, what goals we care about equalizing, and whether the ultimate aspiration is equality of opportunity or equality of outcome. Moreover, what means should we employ to remove obstacles, are these means likely to be successful, and do the cultural means justify the societal ends? And some readily apparent factors leading to inequalities of opportunity seem inexorable, including our individual genetic makeup, the environments in which we are raised, and our overall social circumstances. These considerations have prompted some scholars to argue that equality of opportunity is possible only if both law and government are committed to achieving it.2 To discuss equal opportunity in a coherent way often requires focusing on specific domains.3 One field in which equal opportunity has special resonance is employment. Societal support exists both for the descriptive idea that racial discrimination poses an obstacle to equal opportunity and for the prescriptive idea that such an obstacle ought to be overcome. Accordingly, a law like Title VII of the Civil Rights Act of 1964 conveys something specific about what opportunities are important (work), what obstacles are inappropriate (discrimination), and what type of equality of opportunity is desired (race, color, sex, religion, and national origin). Such antidiscrimination laws generally enjoy strong support in the United States.4 Joseph Fishkin’s new book, Bottlenecks: A New Theory of Equal Opportunity, 5 reinvigorates the concept of equal opportunity by simultaneously engaging with its complications and attempting to simplify its ambitions. Fishkin describes bottlenecks as narrow spaces in the opportunity structure through which people must pass if they hope to reach a range of opportunities on the other side (p. 13). A significant component of the American opportunity structure that Bottlenecks leaves largely unexplored, however, relates to people with disabilities.6 This Review applies Fishkin’s theory to explore how disability law creates and perpetuates bottlenecks that keep people with disabilities from achieving a greater degree of human flourishing. In particular, disability policy’s opportunity structure features a conceptual disability– employability divide that ultimately prevents people with disabilities from reaching a wider array of opportunities. Fishkin’s book, in concert with this Review, introduces new and inventive ways of reimagining and implementing structural solutions to these bottlenecks. Part I provides an overview of Fishkin’s arguments, including his theory of opportunity pluralism, which he advances as a theoretical framework for broadening the opportunity structure. Part II then applies Fishkin’s theory to administrative disability policy to address and evaluate the disability– employability divide as a bottleneck. In particular, this Part explores how people with disabilities are frequently unable to pass through certain bottleneck policies to reach productive employment on the other side. Part III then proffers several policy solutions that could enable people with disabilities to move through or around the bottlenecks that keep them from accessing productive work opportunities