Orbits for eighteen visual binaries and two double-line spectroscopic binaries observed with HRCAM on the CTIO SOAR 4m telescope, using a new Bayesian orbit code based on Markov Chain Monte Carlo

We present orbital elements and mass sums for eighteen visual binary stars of spectral types B to K (five of which are new orbits) with periods ranging from 20 to more than 500 yr. For two double-line spectroscopic binaries with no previous orbits, the individual component masses, using combined astrometric and radial velocity data, have a formal uncertainty of ~0.1 MSun. Adopting published photometry, and trigonometric parallaxes, plus our own measurements, we place these objects on an H-R diagram, and discuss their evolutionary status. These objects are part of a survey to characterize the binary population of stars in the Southern Hemisphere, using the SOAR 4m telescope+HRCAM at CTIO. Orbital elements are computed using a newly developed Markov Chain Monte Carlo algorithm that delivers maximum likelihood estimates of the parameters, as well as posterior probability density functions that allow us to evaluate the uncertainty of our derived parameters in a robust way. For spectroscopic binaries, using our approach, it is possible to derive a self-consistent parallax for the system from the combined astrometric plus radial velocity data ("orbital parallax"), which compares well with the trigonometric parallaxes. We also present a mathematical formalism that allows a dimensionality reduction of the feature space from seven to three search parameters (or from ten to seven dimensions - including parallax - in the case of spectroscopic binaries with astrometric data), which makes it possible to explore a smaller number of parameters in each case, improving the computational efficiency of our Markov Chain Monte Carlo code.Comment: 32 pages, 9 figures, 6 tables. Detailed Appendix with methodology. Accepted by The Astronomical Journa

Evidence for precession of the isolated neutron star RX J0720.4-3125

The XMM-Newton spectra of the isolated neutron star RX J0720.4-3125 obtained over 4.5 years can be described by sinusoidal variations in the inferred blackbody temperature, the size of the emitting area and the depth of the absorption line with a period of 7.1 +/- 0.5 years, which we suggest to be the precession period of the neutron star. Precession of a neutron star with two hot spots of different temperature and size, probably not located exactly in antipodal positions, may account for the variations in the X-ray spectra, changes in the pulsed fraction, shape of the light curve and the phase-lag between soft and hard energy bands observed from RX J0720.4-3125. An independent sinusoidal fit to published and new pulse timing residuals from a coherent analysis covering ~12 years yields a consistent period of 7.7 +/- 0.6 years supporting the precession model.Comment: Accepted for publication in A&A Letters, 5 pages, 5 figure

The Promise and Perils of Direct Democracy for the European Union

AbstractDirect democracy exhibits both promise and peril for the EU. The referendum has been deployed by Member States in a way that has shaped and will continue to shape the EU’s geographical boundaries, its constitutional evolution, and salient EU policy matters. The referendum’s promise is to accord a high degree of legitimacy to a political decision, but that promise varies across different types of EU referendum. Their peril for the EU has become increasingly apparent as they have proliferated in number and type and with a growing failure rate. In contrast, the European Citizens’ Initiative is intended to harness the promise of direct democracy for the EU. But current practice raises the question of whether the failure to satisfy the ambitions placed on this novel instrument could, paradoxically, become a source of peril. Contrary to an increasingly pessimistic narrative, it is concluded that practice under the ECI exhibits promise and that the future of this instruments appears bright.</jats:p

The Burst Spectra of EXO 0748-676 during a Long 2003 XMM-Newton Observation

Gravitationally redshifted absorption lines from highly ionized iron have been previously identified in the burst spectra of the neutron star in EXO 0748-676. To repeat this detection we obtained a long, nearly 600 ks observation of the source with XMM-Newton in 2003. The spectral features seen in the burst spectra from the initial data are not reproduced in the burst spectra from this new data. In this paper we present the spectra from the 2003 observations and discuss the sensitivity of the absorption structure to changes in the photospheric conditions.Comment: 18 Pages, 3 Figures. Accepted for publication in Ap