Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?

The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds. We investigate whether the tidal interaction of a Wolf-Rayet star with a compact object in a binary system can spin up the Wolf-Rayet star enough to produce a collapsar. We compute the evolution of close Wolf-Rayet binaries, including tidal angular momentum exchange, differential rotation of the Wolf-Rayet star, internal magnetic fields, stellar wind mass loss, and mass transfer. The Wolf-Rayet companion is approximated as a point mass. We then employ a population synthesis code to infer the occurrence rates of the various relevant binary evolution channels. We find that the simple scenario -- i.e., the Wolf-Rayet star being tidally spun up and producing a collapsar -- does not occur at solar metallicity and may only occur with low probability at low metallicity. It is limited by the widening of the binary orbit induced by the strong Wolf-Rayet wind or by the radius evolution of the Wolf-Rayet star that most often leads to a binary merger. The tidal effects enhance the merger rate of Wolf-Rayet stars with black holes such that it becomes comparable to the occurrence rate of long gamma-ray bursts.Comment: 9 pages, 11 figures, accepted for publication in A&

Rebecca White, soprano and Christina Wright-Ivanova, piano, May 3, 2015

This is the concert program of the Rebecca White, soprano and Christina Wright-Ivanova, piano performance on Sunday, May 3, 2015 at 6:30 p.m., at the Concert Hall, 855 Commonwealth Avenue. Works performed were Basta vincesti.. Ah, non lasciarmi, no by Wolfgang Amadeus Mozart, Elfenlied by Hugo Wolf, Nixe Binsefuss by H. Wolf, Das verlassene Mägdlein by H. Wolf, Nimmersatte Liebe by H. Wolf, Auch Kleine Dinge by H. Wolf, Er ist's by H. Wolf, La courte paille by Francis Poulenc, The Silver Swan by Ned Rorem, Stopping by Woods on a Snowy Evening by N. Rorem, A Birthday by N. Rorem, and I Hate Music! by Leonard Bernstein. Digitization for Boston University Concert Programs was supported by the Boston University Humanities Library Endowed Fund

The impact of rotation on the line profiles of Wolf-Rayet stars

Massive Wolf-Rayet stars are recognized today to be in a very common, but short, evolutionary phase of massive stars. While our understanding of Wolf-Rayet stars has increased dramatically over the past decades, it remains unclear whether rapid rotators are among them. There are various indications that rapidly rotating Wolf-Rayet stars should exist. Unfortunately, due to their expanding atmospheres, rotational velocities of Wolf-Rayet stars are very difficult to measure. However, recently observed spectra of several Wolf-Rayet stars reveal peculiarly broad and round emission lines. Could these spectra imply rapid rotation? In this work, we model the effects of rotation on the atmospheres of Wolf-Rayet stars. We further investigate whether the peculiar spectra of five Wolf-Rayet stars may be explained with the help of stellar rotation, infer appropriate rotation parameters, and discuss the implications of our results. We make use of the Potsdam Wolf-Rayet (PoWR) non-LTE model atmosphere code. Since the observed spectra of Wolf-Rayet stars are mainly formed in their expanding atmospheres, rotation must be accounted for with a 3D integration scheme of the formal integral. For this purpose, we assume a rotational velocity field consisting of an inner co-rotating domain and an outer domain, where the angular momentum is conserved. We find that rotation can reproduce the unique spectra analyzed here. However, the inferred rotational velocities at the stellar surface are large (~200 km/s), and the inferred co-rotation radii (~10 stellar radii) suggest the existence of very strong photospheric magnetic fields (~20 kG)

Clifford-Wolf Translations of Finsler spaces

In this paper, we study Clifford-Wolf translations of Finsler spaces. We first give a characterization of Clifford-Wolf translations of Finsler spaces in terms of Killing vector fields. In particular, we show that there is a natural correspondence between Clifford-Wolf translations and the Killing vector fields of constant length. In the special case of homogeneous Randers spaces, we give some explicit sufficient and necessary conditions for an isometry to be a Clifford-Wolf translation. Finally, we construct some explicit examples to explain some of the results of this paper.Comment: 13 page

Monitoring wolf populations using howling points combined with sign survey transects

Wolves respond to simulated howling, especially during the mating and breeding seasons. Simulated howling points are, therefore, commonly used by many wolf researchers around the world to estimate pack numbers in a given area. A large amount of information is available on various pack breeding areas in Asturias, the only region in north-western Spain where the Iberian wolf (Canis lupus signatus, Cabrera 1907) is not classed as a game species. Wolf research began there in the early 1980s. We present the results of the latest study on population status, conducted between July and November, 2001. Using sampling transects to detect wolf scat and scratch marks and designated howling and observation points, twenty one (21) wolf packs were definitely located, with two others considered “likely”. Nineteen (19) packs were detected using howling points (n=314). The results of this study show that simulated howling points and sampling transects are reliable and inexpensive way of detecting wolf packs

Whole-genome sequence analysis shows that two endemic species of North American wolf are admixtures of the coyote and gray wolf.

Protection of populations comprising admixed genomes is a challenge under the Endangered Species Act (ESA), which is regarded as the most powerful species protection legislation ever passed in the United States but lacks specific provisions for hybrids. The eastern wolf is a newly recognized wolf-like species that is highly admixed and inhabits the Great Lakes and eastern United States, a region previously thought to be included in the geographic range of only the gray wolf. The U.S. Fish and Wildlife Service has argued that the presence of the eastern wolf, rather than the gray wolf, in this area is grounds for removing ESA protection (delisting) from the gray wolf across its geographic range. In contrast, the red wolf from the southeastern United States was one of the first species protected under the ESA and was protected despite admixture with coyotes. We use whole-genome sequence data to demonstrate a lack of unique ancestry in eastern and red wolves that would not be expected if they represented long divergent North American lineages. These results suggest that arguments for delisting the gray wolf are not valid. Our findings demonstrate how a strict designation of a species under the ESA that does not consider admixture can threaten the protection of endangered entities. We argue for a more balanced approach that focuses on the ecological context of admixture and allows for evolutionary processes to potentially restore historical patterns of genetic variation

BL-WoLF: A Framework For Loss-Bounded Learnability In Zero-Sum Games

We present BL-WoLF, a framework for learnability in repeated zero-sum games where the cost of learning is measured by the losses the learning agent accrues (rather than the number of rounds). The game is adversarially chosen from some family that the learner knows. The opponent knows the game and the learner's learning strategy. The learner tries to either not accrue losses, or to quickly learn about the game so as to avoid future losses (this is consistent with the Win or Learn Fast (WoLF) principle; BL stands for ``bounded loss''). Our framework allows for both probabilistic and approximate learning. The resultant notion of {\em BL-WoLF}-learnability can be applied to any class of games, and allows us to measure the inherent disadvantage to a player that does not know which game in the class it is in. We present {\em guaranteed BL-WoLF-learnability} results for families of games with deterministic payoffs and families of games with stochastic payoffs. We demonstrate that these families are {\em guaranteed approximately BL-WoLF-learnable} with lower cost. We then demonstrate families of games (both stochastic and deterministic) that are not guaranteed BL-WoLF-learnable. We show that those families, nevertheless, are {\em BL-WoLF-learnable}. To prove these results, we use a key lemma which we derive