Epsilon Aurigae in an evolutionary context

Basic observational data of Epsilon Aurigae are summarized and used as the basis of a discussion of possible evolutionary states of the system. Constraints posed by the presence of a cold disk surrounding the secondary star are also outlined. Possible evolutionary models of the F0 Ia supergiant range from pre-main sequence contraction through shell hydrogen burning, core helium burning, to shell helium burning, depending on the absolute luminosity of the system, for models in which no mass transfer has taken place. Models invoking binary interaction include core and shell helium burning stars, and pre-white dwarfs, again depending on the absolute luminosity of the system. A massive shell helium burning star or a pre-white dwarf mass transfer remnant would appear the most likely of these models at present. Observational tests of these models are briefly outlined

Formation of low-mass x-ray binaries; 1, constraints on hydrogen-rich donors at the onset of the x-ray phase

We identify and quantify the set of constraints that neutron star-normal star binaries must satisfy in order to become observable LMXBs. These constraints are related to (i) the thermal and hydrostatic equilibrium of the donors, (ii) the degree to which the mass transfer process is conservative, and (iii) the age of the systems. They divide the parameter space of potential LMXBs in several distinct parts, of which those that actually become LMXBs at the onset of mass transfer occupy only a small part. Of the remainder, many become unstable to dynamical time scale mass transfer either at the onset or later in the course of mass transfer, and enter common envelope evolution. Others experience super-Eddington mass transfer but may eventually survive to become LMXBs. These survivors arguably include binary millisecond pulsars with orbital periods in excess of 100\,d ultrashort-period LMXBs with hydrogen-deficient donors, and long-period LMXBs with giant donors

LISA Measurement of Gravitational Wave Background Anisotropy: Hexadecapole Moment via a Correlation Analysis

We discuss spatial fluctuations in the gravitational wave background arising from unresolved Galactic binary sources, such as close white dwarf binaries, due to the fact the galactic binary source distribution is anisotropic. We introduce a correlation analysis of the two data streams of the Laser Interferometer Space Antenna (LISA) to extract spherical harmonic coefficients, in an independent manner, of the hexadecapole moment ($l=4$) related to the projected two-dimensional density distribution of the binary source population. The proposed technique complements and improves over previous suggestions in the literature to measure the gravitational wave background anisotropy based on the time modulation of data as LISA orbits around the Sun. Such techniques, however, are restricted only to certain combinations of spherical harmonic coefficients of the galaxy with no ability to separate them individually. With LISA, $m=2,3$ and 4 coefficients of the hexadecapole ($l=4$) can be measured with signal-to-noise ratios at the level of 10 and above in a certain coordinate system. In addition to the hexadecapole coefficients, when combined with the time modulation analysis, the correlation study can also be used, in principle, to measure quadrupole coefficients of the binary distribution.Comment: 8 pages, 2 figure

Cataclysmic Variables and a New Class of Faint UV Stars in the Globular Cluster NGC 6397

We present evidence that the globular cluster NGC 6397 contains two distinct classes of centrally-concentrated UV-bright stars. Color-magnitude diagrams constructed from U, B, V, and I data obtained with the HST/WFPC2 reveal seven UV-bright stars fainter than the main-sequence turnoff, three of which had previously been identified as cataclysmic variables (CVs). Lightcurves of these stars show the characteristic ``flicker'' of CVs, as well as longer-term variability. A fourth star is identified as a CV candidate on the basis of its variability and UV excess. Three additional UV-bright stars show no photometric variability and have broad-band colors characteristic of B stars. These non-flickering UV stars are too faint to be extended horizontal branch stars. We suggest that they could be low-mass helium white dwarfs, formed when the evolution of a red giant is interrupted, due either to Roche-lobe overflow onto a binary companion, or to envelope ejection following a common-envelope phase in a tidal-capture binary. Alternatively, they could be very-low-mass core-He-burning stars. Both the CVs and the new class of faint UV stars are strongly concentrated toward the cluster center, to the extent that mass segregation from 2-body relaxation alone may be unable to explain their distribution.Comment: 11 pages plus 3 eps figures; LaTeX using aaspp4.sty; to appear in The Astrophysical Journal Letter

Consequences of gravitational radiation recoil

Coalescing binary black holes experience an impulsive kick due to anisotropic emission of gravitational waves. We discuss the dynamical consequences of the recoil accompanying massive black hole mergers. Recoil velocities are sufficient to eject most coalescing black holes from dwarf galaxies and globular clusters, which may explain the apparent absence of massive black holes in these systems. Ejection from giant elliptical galaxies would be rare, but coalescing black holes are displaced from the center and fall back on a time scale of order the half-mass crossing time. Displacement of the black holes transfers energy to the stars in the nucleus and can convert a steep density cusp into a core. Radiation recoil calls into question models that grow supermassive black holes from hierarchical mergers of stellar-mass precursors.Comment: 5 pages, 4 figures, emulateapj style; minor changes made; accepted to ApJ Letter

The last mile in analysing well-being and poverty: Indices of Social Development

Development practitioners worldwide increasingly recognize the importance of informal institutions -- such as norms of cooperation, non-discrimination, or the role of community oversight in the management of investment activities -- in affecting well-being, poverty, and even economic growth. While there have been many country- or region-specific studies that explore relationships between such social development indicators and other development outcomes, there has been less empirical analysis that tests these relationships at the international level. This is largely due to data limitations: few reliable, globally- representative data sources exist that can provide a basis for cross-country comparison of social norms and practice, social trust and community engagement. The International Institute of Social Studies (ISS) now hosts a large database of social development indicators compiled from a wide range of sources in a first attempt to overcome such data constraints, at a low cost (www.IndSocDev.org). It will continuously expand the power of the database by including new data and variables and by developing new techniques to integrate, enrich and analyze the data to make the best possible use of this rich dataset. The Indices of Social Development (ISD) are based on over 200 measures from 25 reputable data sources for the years 1990 to 2010. These measures are aggregated into five composite indices: civic activism, interpersonal safety and trust, inter-group cohesion, clubs and associations, and gender equity/equality and non-discrimination against women. Not all data sources provide observations for indicators in each country, but together these data sources allow for comprehensive estimates of social behavior and norms of interaction across a broad range of societies, and increasingly with possibilities to track changes over time. The indices allow the estimation of the effects of social development for a large range of countries, broadening the scope for cross-country statistical and analytical work on social development and the relationship with economic development. This paper presents this database, highlight the differences, similarities and complementarities with other measures of well-being, including around income poverty, multi-dimensional poverty, and human development

Force Dependence of RF MEMS Switch Contact Heating

Contact-type RF MEMS switches have demonstrated low on-state resistance, high off-state impedance, and very large bandwidth; however, their power handling capability is low due to failure caused by contact heating. This paper examines contact heating by measuring V-I curves for contacts in gold switches. Multiphysics modeling allows extraction of contact temperature. Contacts are found to soften and self-anneal at a temperature of about 100¡C, corresponding to a contact voltage of about 80 mV. Larger contact force induces a larger decrease in contact resistance during softening, suppressing contact heating. The data provide a better understanding of micro-scale contact physics, leading to design for switches for improved power-handling capability.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87263/4/Saitou88.pd

RS Ophiuchi: Thermonuclear Explosion or Disc Instability?

Sokoloski et al (2008) have recently reported evidence that the recurrent nova RS Ophiuchi produced a pair of highly collimated radio jets within days of its 2006 outburst. This suggests that an accretion disc must be present during the outburst. However in the standard picture of recurrent novae as thermonuclear events, any such disc must be expelled from the white dwarf vicinity, as the nuclear energy yield greatly exceeds its binding energy. We suggest instead that the outbursts of RS Oph are thermal--viscous instabilities in a disc irradiated by the central accreting white dwarf. The distinctive feature of RS Oph is the very large size of its accretion disc. Given this, it fits naturally into a consistent picture of systems with unstable accretion discs. This picture explains the presence and speed of the jets, the brightness and duration of the outburst, and its rise time and linear decay, as well as the faintness of the quiescence. By contrast, the hitherto standard picture of recurrent thermonuclear explosions has a number of severe difficulties. These include the presence of jets, the faintness of quiescence, and the fact the the accretion disc must be unstable unless it is far smaller than any reasonable estimate.Comment: MNRAS, in pres