A Be-type star with a black-hole companion

Stellar-mass black holes have all been discovered through X-ray emission, which arises from the accretion of gas from their binary companions (this gas is either stripped from low-mass stars or supplied as winds from massive ones). Binary evolution models also predict the existence of black holes accreting from the equatorial envelope of rapidly spinning Be-type stars1, 2, 3 (stars of the Be type are hot blue irregular variables showing characteristic spectral emission lines of hydrogen). Of the approximately 80 Be X-ray binaries known in the Galaxy, however, only pulsating neutron stars have been found as companions2, 3, 4. A black hole was formally allowed as a solution for the companion to the Be star MWC 656 (ref. 5; also known as HD 215227), although that conclusion was based on a single radial velocity curve of the Be star, a mistaken spectral classification6 and rough estimates of the inclination angle. Here we report observations of an accretion disk line mirroring the orbit of MWC 656. This, together with an improved radial velocity curve of the Be star through fitting sharp Fe ii profiles from the equatorial disk, and a refined Be classification (to that of a B1.5–B2 III star), indicates that a black hole of 3.8 to 6.9 solar masses orbits MWC 656, the candidate counterpart of the γ-ray source AGL J2241+4454 (refs 5, 6). The black hole is X-ray quiescent and fed by a radiatively inefficient accretion flow giving a luminosity less than 1.6 × 10−7 times the Eddington luminosity. This implies that Be binaries with black-hole companions are difficult to detect in conventional X-ray surveys.

Raluca L. Radulescu and Cory James Rushton, eds. 2009: A Companion to Medieval Popular Romance. Studies in Medieval Romance 10. Cambridge: D. S. Brewer. XIV + 209 pp. ISBN 9781843841920

This review is part of a research project funded by the Spanish Ministry of Science and Innovation (ref. FFI 2008-02165).

A VLT/FLAMES survey for massive binaries in Westerlund 1. IV. Wd1-5 – binary product and a pre-supernova companion for the magnetar CXOU J1647-45?

Context. The first soft gamma-ray repeater was discovered over three decades ago, and was subsequently identified as a magnetar, a class of highly magnetised neutron star. It has been hypothesised that these stars power some of the brightest supernovae known, and that they may form the central engines of some long duration gamma-ray bursts. However there is currently no consenus on the formation channel(s) of these objects. Aims. The presence of a magnetar in the starburst cluster Westerlund 1 implies a progenitor with a mass ≥40 M⊙, which favours its formation in a binary that was disrupted at supernova. To test this hypothesis we conducted a search for the putative pre-SN companion. Methods. This was accomplished via a radial velocity survey to identify high-velocity runaways, with subsequent non-LTE model atmosphere analysis of the resultant candidate, Wd1-5. Results. Wd1-5 closely resembles the primaries in the short-period binaries, Wd1-13 and 44, suggesting a similar evolutionary history, although it currently appears single. It is overluminous for its spectroscopic mass and we find evidence of He- and N-enrichement, O-depletion, and critically C-enrichment, a combination of properties that is difficult to explain under single star evolutionary paradigms. We infer a pre-SN history for Wd1-5 which supposes an initial close binary comprising two stars of comparable (~ 41 M⊙ + 35 M⊙) masses. Efficient mass transfer from the initially more massive component leads to the mass-gainer evolving more rapidly, initiating luminous blue variable/common envelope evolution. Reverse, wind-driven mass transfer during its subsequent WC Wolf-Rayet phase leads to the carbon pollution of Wd1-5, before a type Ibc supernova disrupts the binary system. Under the assumption of a physical association between Wd1-5 and J1647-45, the secondary is identified as the magnetar progenitor; its common envelope evolutionary phase prevents spin-down of its core prior to SN and the seed magnetic field for the magnetar forms either in this phase or during the earlier episode of mass transfer in which it was spun-up. Conclusions. Our results suggest that binarity is a key ingredient in the formation of at least a subset of magnetars by preventing spin-down via core-coupling and potentially generating a seed magnetic field. The apparent formation of a magnetar in a Type Ibc supernova is consistent with recent suggestions that superluminous Type Ibc supernovae are powered by the rapid spin-down of these objects.

L'ús d'animals a la medicina de la tradició llatina: estudi del Tresor de la Beutat, un tractat medieval dedicat als cosmètics femenins

L’ús de productes derivats d’animals (Zooteràpia) ha format part de l’arsenal terapèutic dermatològic en les diverses cultures a través del temps. El Tresor de Beutat és un tractat medieval dedicat als cosmètics femenins i la salut, escrit en català medieval que es conserva a la Biblioteca de la Universitat de Barcelona. Descriu més de 200 remeis i tractaments per a les dones del segle XIV . Molts d’aquests tractaments eren productes d’origen animal. Estudiem el Tresor de Beutat per determinar quins animals i quines de les seves parts eren emprades, així com la forma d’utilització i indicacions terapèutiques. El document original va ser transcrit al català formal i el text analitzat per tal d’identificar totes les substàncies d’origen animal destinades a la teràpia. Aquestes substàncies van ser ordenades segons l’espècie, i es van estudiar les diferents parts emprades dels animals, la manera de preparació i les seves indicacions. Es van identificar un total de 223 substàncies o elements (animals, plantes i minerals) utilitzats com a remeis. D’ells, 47 (21%) eren d’origen animal, pertanyents a 30 animals, 15 mamífers, 7 aus, 4 animals marins, 2 de rèptils i amfibis i 2 insectes. Les diferents parts dels animals utilitzats inclouen la pell, el greix, els ronyons, el cervell, les banyes, les ungles, les secrecions anals, glàndules mamàries o salivals, la femta, o fins i tot l’animal sencer, en el cas dels mamífers. De les aus, s’usaven les plomes, ous, greixos, els nius, el cap, el suc propi de l’animal, i els excrements. Dels animals marins es va emprar l’animal a trossos, els ossos i els ous, i dels insectes els ous de formiga; la mel i la cera d’abelles; dels rèptils i amfibis els ous i la sang. Els tractaments s’utilitzen principalment per a la cara, com a cosmètics per al cabell i el cos, la higiene, la salut general i per la pell. També per l’esfera otorinolaringològica, ocular, els trastorns dentals, i ginecològics, així com per a l’alleugeriment del dolor. El Tresor de Beutat proporciona informació sobre el coneixement dels tractaments tòpics, amb una base científica (i no màgica) amb una àmplia gamma de recursos d’origen animal, amb les formulacions acuradament elaborades per a fins cosmètics i terapèutics dissenyats per assolir l’ideal de la bellesa i la salut en les dones medievals, sent evident en les bases d’alguns tractaments tòpics utilitzats en el segle XXI.