Third World ageing crisis

A typical case, culled from the author's own experience in the Third World, points towards a major crisis in ageing in the near future for many developing countries. Whilst the increase in numbers of elderly, both gross and proportionate, is well-known, it is not so widely realised that the increase in developing countries will far outstrip that in industrialized nations. Although the elderly were historically cared for within the traditional extended family structure, that system is now breaking down before the advance of migration and easy divorce. Many elderly persons are left alone in depopulated communities. Others fail to adapt in the rural-to-urban transition. Most developing countries have no firmly established services for the elderly. However, as awareness of the impending crisis increases, community groups assist the elderly in developing their own initiatives to avoid the local effects of the crisis

Angular Momentum Loss by Magnetic Braking and Gravitational Radiation in Relativistic Binary Stars

Angular momentum loss (AML) mechanisms and dynamical evolution owing to magnetic braking and gravitational radiation in relativistic binary stars (RBS) are studied with use of physical parameters collected from the literature. We have calculated and compared AML time scales for the RBS with non-degenerate components and double degenerate (DD) systems.Comment: 6 pages, 3 figure

Zeeman tomography of magnetic white dwarfs. II, The quadrupole-dominated magnetic field of HE 1045-0908

We report time-resolved optical flux and circular polarization spectroscopy of the magnetic DA white dwarf HE 1045−0908 obtained with FORS1 at the ESO VLT. Considering published results, we estimate a likely rotational period of P rot 2.7 h, but cannot exclude values as high as about 9 h. Our detailed Zeeman tomographic analysis reveals a field structure which is dominated by a quadrupole and contains additional dipole and octupole contributions, and which does not depend strongly on the assumed value of the period. A good fit to the Zeeman flux and polarization spectra is obtained if all field components are centred and inclinations of their magnetic axes with respect to each other are allowed for. The fit can be slightly improved if an offset from the centre of the star is included. The prevailing surface field strength is 16 MG, but values between 10 and ∼ 75 MG do occur. We derive an effective photospheric temperature of HE 1045−0908 of T eff = 10 000 ± 1000 K. The tomographic code makes use of an extensive database of pre-computed Zeeman spectra (Paper I)

The Additional Line Component within the Iron K\alpha Profile in MCG-6-30-15: Evidence for Blob Ejection?

The EPIC data of MCG -6-30-15 observed by XMM-Newton were analyzed for the complexities of the iron K-alpha line. Here we report that the additional line component (ALC) at 6.9 keV undoubtedly appears within the broad iron Kalpha; line profile at the high state, whereas it disappears at the low state. These state-dependent behaviors exclude several possible origins and suggest an origin of the ALC in matter being ejected from the vicinity of the black hole. At the low state, the newborn blob ejected from the accretion disk is so Thomson-thick that hard X-rays are blocked from ionizing the old blobs, leading to the disappearance of the ALC. When the blob becomes Thomson-thin as a result of expansion, the hard X-ray will penetrate it and ionize the old ones, emitting the ALC at the high state. The blob ejection is the key to switching the ALC on or off.Comment: 6 pages, 4 Figure

Are the jets accelerated from the disk coronas in some active galactic nuclei?

We use a sample of radio-loud active galactic nuclei (AGNs) with estimated central black hole masses to explore their jet formation mechanisms. The jet power of AGNs is estimated from their extended radio luminosity. It is found that the jets in several AGNs of this sample are too powerful to be extracted from the standard thin accretion disks or rapidly spinning black holes surrounded by standard thin disks. If the advection dominated accretion flows (ADAFs) are present in these AGNs, their bright optical continuum luminosity cannot be produced by pure-ADAFs due to their low accretion rates and low radiation efficiency, unless the ADAFs transit to standard thin disks at some radii $R_{\rm tr}$. If this is the case, we find that the dimensionless accretion rates as high as 0.05 and transition from ADAFs to standard thin disks at rather small radii around 20GM/c^2 are required to explain their bright optical continuum emission. We propose that the disk-corona structure is present at least in some AGNs in this sample. The plasmas in the corona are very hot, and the pressure scale-height of the corona H\sim R. Powerful jets with Q_jet \sim L_bol (bolometric luminosity) can form by the large-scale magnetic fields created by dynamo processes in the disk corona of some AGNs. The maximal jet power extractable from the corona Q_jet^max\le 0.6L_c (L_c is the corona luminosity) is expected by this jet formation scenario. The statistic results on the sample of AGNs are consistent with the predictions of this scenario. Finally, the possibility that the jet is driven from a super-Keplerian rotating hot layer located between the corona and the cold disk is discussed. We find that, in principle, this layer can also produce a powerful jet with Q_jet\sim L_bol.Comment: 9 pages, accepted for publication in Ap

Envelope Ejection: an Alternative Process for some Early Case B Binaries

We discuss the evolution of binaries with moderately high masses (about 10 - 30 solar masses), and with periods of about 3 - 300d, corresponding mostly to early Case B. These are usually thought to evolve either by reasonably conservative Roche-lobe overflow, if the initial mass ratio is fairly mild, or else by highly non-conservative common-envelope evolution, with spiral-in to short periods (hours, typically), if the initial mass ratio is rather extreme. We discuss here a handful of binaries from part of this period range (about 50 - 250d), which appear to have followed a different path: we argue that they must have lost a large proportion of initial mass (about 70 - 80%), but without shortening their periods at all. We suggest that their behaviour may be due to the fact that stars of such masses, when evolved also to rather large radii, are not far from the Humphreys-Davidson limit where single stars lose their envelopes spontaneously in P Cygni winds, and so have envelopes which are only lightly bound to the core. These envelopes therefore may be relatively easily dissipated by the perturbing effect of a companion. In addition, some or all of the stars considered here may have been close to the Cepheid instability strip when they filled their Roche lobes. One or other, or both, of high luminosity and Cepheid instability, in combination with an appropriately close binary companion, may be implicated

A New Evolutionary Path to Type Ia Supernovae: Helium-Rich Super-Soft X-Ray Source Channel

We have found a new evolutionary path to Type Ia supernovae (SNe Ia) which has been overlooked in previous work. In this scenario, a carbon-oxygen white dwarf (C+O WD) is originated, not from an asymptotic giant branch star with a C+O core, but from a red-giant star with a helium core of $\sim 0.8-2.0 M_\odot$. The helium star, which is formed after the first common envelope evolution, evolves to form a C+O WD of $\sim 0.8-1.1 M_\odot$ with transferring a part of the helium envelope onto the secondary main-sequence star. This new evolutionary path, together with the optically thick wind from mass-accreting white dwarf, provides a much wider channel to SNe Ia than previous scenarios. A part of the progenitor systems are identified as the luminous supersoft X-ray sources or the recurrent novae like U Sco, which are characterized by the accretion of helium-rich matter. The white dwarf accretes hydrogen-rich, helium-enhanced matter from a lobe-filling, slightly evolved companion at a critical rate and blows excess matter in the wind. The white dwarf grows in mass to the Chandrasekhar mass limit and explodes as an SN Ia. A theoretical estimate indicates that this channel contributes a considerable part of the inferred rate of SNe Ia in our Galaxy, i.e., the rate is about ten times larger than the previous theoretical estimates for white dwarfs with slightly evolved companions.Comment: 19 pages including 12 figures, to be published in ApJ, 519, No.

The Binarity of Eta Carinae and its Similarity to Related Astrophysical Objects

I examine some aspects of the interaction between the massive star Eta Carinae and its companion, in particular during the eclipse-like event, known as the spectroscopic event or the shell event. The spectroscopic event is thought to occur when near periastron passages the stellar companion induces much higher mass loss rate from the primary star, and/or enters into a much denser environment around the primary star. I find that enhanced mass loss rate during periastron passages, if it occurs, might explain the high eccentricity of the system. However, there is not yet a good model to explain the presumed enhanced mass loss rate during periastron passages. In the region where the winds from the two stars collide, a dense slow flow is formed, such that large dust grains may be formed. Unlike the case during the 19th century Great Eruption, the companion does not accrete mass during most of its orbital motion. However, near periastron passages short accretion episodes may occur, which may lead to pulsed ejection of two jets by the companion. The companion may ionize a non-negligible region in its surrounding, resembling the situation in symbiotic systems. I discuss the relation of some of these processes to other astrophysical objects, by that incorporating Eta Car to a large class of astrophysical bipolar nebulae.Comment: Updated version. ApJ, in pres