The Possible White Dwarf-Neutron Star Connection

The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and E. Garcia-Berro (Dordrecht: Kluwer

The gravitational collapse of ONe electron-degenerate cores and white dwarfs: the role of 24^{24}Mg and 12^{12}C revisited

The final stages of the evolution of electron--degenerate ONe cores, resulting from carbon burning in ``heavy weight'' intermediate--mass stars (8 M_{\sun}\la M \la 11 M_{\sun}) and growing in mass, either from carbon burning in a shell or from accretion of matter in a close binary system, are examined in the light of their detailed chemical composition. In particular, we have modelled the evolution taking into account the abundances of the following minor nuclear species, which result from the previous evolutionary history: $^{12}$C, $^{23}$Na, $^{24}$Mg, and $^{25}$Mg. Both $^{23}$Na and $^{25}$Mg give rise to Urca processes, which are found to be unimportant for the final outcome of the evolution. $^{24}$Mg was formerly considered a major component of ONe cores (hence called ONeMg cores), but updated evolutionary calculations in this mass range have severely reduced its abundance. Nevertheless, we have parameterized it and we have found that the minimum amount of $^{24}$Mg required to produce NeO burning at moderate densities is $\sim 23$, a value exceedingly high in the light of recent evolutionary models. Finally, we have determined that models with relatively small abundances of unburnt carbon ($X(^{12}$C)$\sim 0.015$) could be a channel to explosion at low to moderate density ($\sim 1\times 10^9$ g cm$^{-3}$). This is clearly below the current estimate for the explosion/collapse threshold and would have interesting consequences.Comment: 8 pages, 6 figures, to appear in Astronomy and Astrophysic

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

Binary systems and their nuclear explosions

Peer ReviewedPreprin

Analysis of wage differences between native and immigrant workers in Spain

Immigration, Wage differences, Quantile regression, J31, J61, J71,

Imagined races : from environmental determinism to geographical authenticity in twentieth‐century Argentina

This article explores how Argentine intellectuals incorporated the natural environment into their accounts of the racial, cultural and political features of the nation. In the late nineteenth century environmental determinism, based on the assumption of a cause–effect relationship between geographical and racial factors, entered Argentina through three main routes: Lamarckism, Darwinism and Spencerianism. By the mid twentieth century, however, anti‐positivist philosophies had been fully incorporated into a body of work that analysed Argentina's socio‐historical foundations. This article examines the shift that occurred during the first half of the twentieth century in how those seeking to define race incorporated the environment into their arguments. The raza was commonly taken to be synonymous with nation. Selected works by sociologist and legal scholar Carlos Octavio Bunge (1875‐1918) and by writer and ensayista Bernardo Canal Feijóo (1897‐1982) will be analysed as influential yet overlooked examples of how ‘the problem of Argentine culture’ could not be separated from the question of nature understood in terms of both physical and human geography. The goal will be to reveal, firstly, the extent to which the notion of the interior as geographical and anthropological desert deeply informed the political vision of the early national period in relation to race and nation and, secondly, how later interpretations of the nation recast American nature as a foundational element of cultural authenticity based on a sentiment of geographical belonging