The formation of high-field magnetic white dwarfs from common envelopes

The origin of highly-magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, such as a planet, brown dwarf, or low-mass star is engulfed by a post-main-sequence giant, the hydrodynamic drag in the envelope of the giant leads to a reduction of the companion's orbit. Sufficiently low-mass companions in-spiral until they are shredded by the strong gravitational tides near the white dwarf core. Subsequent formation of a super-Eddington accretion disk from the disrupted companion inside a common envelope can dramatically amplify magnetic fields via a dynamo. Here, we show that these disk-generated fields are sufficiently strong to explain the observed range of magnetic field strengths for isolated, high-field magnetic white dwarfs. A higher-mass binary analogue may also contribute to the origin of magnetar fields.Comment: Accepted to Proceedings of the National Academy of Sciences. Under PNAS embargo until time of publicatio

Anaktuvuk Pass goes to town

Voilà longtemps que d’une manière ou d’une autre, les Nunamiut d’Anaktuvuk Pass, Alaska, vont en ville et ce, avant même qu’ils n’aient abandonné, en 1949-1950, leur vie de nomades pour se sédentariser dans un village à 100 milles de la route la plus proche et à 250 milles de Fairbanks. Des années avant qu’ils ne mettent pied en ville, quelques-uns avait déjà des comptes créditeurs à la Northern Commercial Company. Au milieu des années cinquante, quelques hommes du village furent recrutés pour participer à des expériences d’adaptation au froid menées par le Ladd AFB dans les environs de Fairbanks. Ce fut leur premier vol en avion et leur première expérience de la vie citadine. Les urgences médicales —une épidémie de grippe, la tuberculose et d’autres maladies demandant soins médicaux— constituaient, dans les années cinquante, l’autre ticket pour la ville, et dans ce cas, il fallait habituellement attendre l’arrivée du vol mensuel pour pouvoir être transporté. Mais dès les années soixante, les services médicaux pour autochtones firent en sorte que les femmes d’Anaktuvuk venaient en ville pour accoucher à l’hôpital. Aujourd’hui, Fairbanks n’est pas seulement un cabinet médical, c’est aussi un centre commercial et un supermarché pour les villages isolés comme Anaktuvuk Pass. C’est encore beaucoup d’autres choses pour les Nunamiut —le site des jeux olympiques annuels eskimos-indiens, le festival des arts autochtones de l’Université d’Alaska à Fairbanks et la foire estivale de la vallée de la Tanana (Tanana Valley Fair). C’est la deuxième avenue avec sa succession de bars défraîchis. Cet article examine plus de 50 ans de voyages en ville, l’importance de la «ville» dans la vie des villageois et les associations variées que Fairbanks représente pour les Nunamiut.The Nunamiut of Anaktuvuk Pass, Alaska have been going to town, one way or another, even before they relinquished their nomadic life in 1949-1950 to become settled in a village 100 miles from the nearest road and 250 miles from Fairbanks. Some years before they ever set foot in town, a few had credit accounts at the city’s Northern Commercial Company. In the mid-1950s a few village men were recruited as human subjects for cold adaptation experiments carried out at Ladd AFB outside of Fairbanks. This was their first plane ride and their first taste of city life. Medical emergencies—a flu epidemic, TB, and other illnesses that demanded medical treatment were the other ticket to Fairbanks in the 1950s, and then one typically had to wait to be flown out until the monthly mail plane came in. But by the 1960s the Native health care system saw to it that Anaktuvuk women came to town to deliver their babies in the hospital. Today Fairbanks is not only the doctor’s office but also the shopping mall and supermarket for outlying villages like Anaktuvuk Pass. It is many other things as well to the Nunamiut—site of the annual World Eskimo-Indian Olympics, the University of Alaska’s annual Festival of Native Arts, and the summer Tanana Valley Fair. It is Second Avenue with its string of dingy bars. This paper looks at more than 50 years of going to town, the significance of “town” in villagers’ lives, and the varied associations Fairbanks holds for the Nunamiut

99721: The Place of Many Caribou Droppings

Article

Distinguishing Solar Flare Types by Differences in Reconnection Regions

Observations show that magnetic reconnection and its slow shocks occur in solar flares. The basic magnetic structures are similar for long duration event (LDE) flares and faster compact impulsive (CI) flares, but the former require less non-thermal electrons than the latter. Slow shocks can produce the required non-thermal electron spectrum for CI flares by Fermi acceleration if electrons are injected with large enough energies to resonate with scattering waves. The dissipation region may provide the injection electrons, so the overall number of non-thermal electrons reaching the footpoints would depend on the size of the dissipation region and its distance from the chromosphere. In this picture, the LDE flares have converging inflows toward a dissipation region that spans a smaller overall length fraction than for CI flares. Bright loop-top X-ray spots in some CI flares can be attributed to particle trapping at fast shocks in the downstream flow, the presence of which is determined by the angle of the inflow field and velocity to the slow shocks.Comment: 15 pages TeX and 2 .eps figures, accepted to Ap.J.Let