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

Competing on Speed

Two forces have reshaped global securities markets in the last decade: Exchanges operate at much faster speeds and the trading landscape has become more fragmented. In order to analyze the positive and normative implications of these evolutions, we study a framework that captures (i) exchanges' incentives to invest in faster trading technologies and (ii) investors' trading and participation decisions. Our model predicts that regulation that protect prices will lead to fragmentation and faster trading speed. Asset prices decrease when there is intermediation competition and are further depressed by price protection. Endogenizing speed can also change the slope of asset demand curves. On normative side, we find that for a given number of exchanges, faster trading is in general socially desirable. Similarly, for a given trading speed, competition among exchange increases participation and welfare. However, when speed is endogenous, competition between exchanges is not necessarily desirable. In particular, speed can be inefficiently high. Our model sheds light on important features of the experience of European and U.S. markets since the implementation of Reg. NMS, and provides some guidance for optimal regulations.

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

Biographical Paths of the Italians in the Ecuador since the End of the 19th Century to the First Half of the 20th Century

En este artículo pretendo reconstruir las trayectorias biográficas y las redes migratorias del grupo italiano presente en Ecuador a finales del siglo XIX y primera mitad del siglo XX. Me interesa aquí poner de relieve los puntos en común entre los diferentes protagonistas de la migración, para esbozar una biografía colectiva —cuantitativamente significativa— de los inmigrantes italianos en ese país, basada en las fichas consulares recopiladas por las representaciones diplomáticas en Quito y en Guayaquil entre 1897 y 1941.This article aims to explore the biographical paths and the migratory networks of the Italians settled in Ecuador between the end of 19th century and the first half of the 20th century. To make that, it will focus on the common elements among the various protagonist of the migration. Through the analysis of the registrations of the Italian Consulate in the Diplomatic Representations in Quito and in Guayaquil between 1897 and 1941, It will be realising a collective biography quantitatively significant

Asset Pricing Frictions in Fragmented Markets

We study the consequences of trading fragmentation and speed on liquidity and asset prices. Exchanges invest in speed-enhancing technologies and price trading services to attract investors. Investors trade due to idiosyncratic preference shocks. We show how the resulting market organization affects asset liquidity and the composition of participating investors. In a consolidated market, speed investments raise liquidity and prices. When markets fragment, liquidity and asset prices can move in opposite directions. We also show how mechanisms that protect execution prices, such as the SEC’s trade-through rule, can decrease price levels and trading volume relative to unregulated markets. Our results suggest that recent regulatory reforms in secondary markets may have unintended negative consequences for public corporations

Cicerone nell’opera e nel pensiero politico di Machiavelli: alcune considerazioni introduttive

Cicero was well known in Florence during Humanism and Renaissance. He is particularly relevant in two masterpieces of N. Machiavelli: Il Principe and the Discorsi sopra la prima deca di Tito Livio; but their connections are still more important. Cicero’s and Machiavelli’s biographies show some interesting correspondences: they both began their political career starting from a condition of homines novi since their families didn’t belong to the rich urban aristocracies in Rome and in Florence. They both were persecuted because of their political commitment: Cicero was exiled and assassinated, Machiavelli was progressively marginalized from public and political life. They composed their greater political works when their political relevance was clearly reduced. Cicero’s and Machiavelli’s political thought is characterized by two opposite anthropological conceptions, nevertheless they both agree on the importance that statesman has a good knowledge of history

A New Review of Old Novae

Novae are certainly very exciting at the time of their eruptions, and there is much work left to be done in understanding all of the details of that part of their existence, but there is also much to be learned by looking at the systems decades, centuries, and even millennia after their peak. I give a brief overview of some of the history and motivation behind studying old novae and long-term nova evolution, and then focus on the state of the field today. Exciting new results are finally starting to shed some light on the secular behavior of post-nova systems, although as is often the case in astronomy, the observations are at times conflicting. As is always the case, we need more observations and better theoretical frameworks to truly understand the situation