A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry

Observations of Epsilon UMa obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed. This is one of the most precise photometry of an Ap star. The amplitude spectrum is used to set an upper limit of 75 parts per million for the amplitude of stellar pulsations in this star unless it accidentally oscillates with a single mode at the satellite orbit, its harmonics or their one day aliases. This is the tightest limit put on the amplitude of oscillations in an Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it cannot be argued that the observations were made at a wrong rotational phase. Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ

The Mean Drift: Tailoring the Mean Field Theory of Markov Processes for Real-World Applications

The statement of the mean field approximation theorem in the mean field theory of Markov processes particularly targets the behaviour of population processes with an unbounded number of agents. However, in most real-world engineering applications one faces the problem of analysing middle-sized systems in which the number of agents is bounded. In this paper we build on previous work in this area and introduce the mean drift. We present the concept of population processes and the conditions under which the approximation theorems apply, and then show how the mean drift is derived through a systematic application of the propagation of chaos. We then use the mean drift to construct a new set of ordinary differential equations which address the analysis of population processes with an arbitrary size

Circumbinary Molecular Rings Around Young Stars in Orion

We present high angular resolution 1.3 mm continuum, methyl cyanide molecular line, and 7 mm continuum observations made with the Submillimeter Array and the Very Large Array, toward the most highly obscured and southern part of the massive star forming region OMC1S located behind the Orion Nebula. We find two flattened and rotating molecular structures with sizes of a few hundred astronomical units suggestive of circumbinary molecular rings produced by the presence of two stars with very compact circumstellar disks with sizes and separations of about 50 AU, associated with the young stellar objects 139-409 and 134-411. Furthermore, these two circumbinary rotating rings are related to two compact and bright {\it hot molecular cores}. The dynamic mass of the binary systems obtained from our data are $\geq$ 4 M$_\odot$ for 139-409 and $\geq$ 0.5 M$_\odot$ for 134-411. This result supports the idea that intermediate-mass stars will form through {\it circumstellar disks} and jets/outflows, as the low mass stars do. Furthermore, when intermediate-mass stars are in multiple systems they seem to form a circumbinary ring similar to those seen in young, multiple low-mass systems (e.g., GG Tau and UY Aur).Comment: Accepted by Astronomy and Astrophysic

The Paradox Of Repression And Nonviolent Movements

Political repression often paradoxically fuels popular movements rather than undermining resistance. When authorities respond to strategic nonviolent action with intimidation, coercion, and violence, they often undercut their own legitimacy, precipitating significant reforms or even governmental overthrow. Brutal repression of a movement is often a turning point in its history: Bloody Sunday in the March to Selma led to the passage of civil rights legislation by the US Congress, and the Amritsar Massacre in India showed the world the injustice of the British Empire’s use of force in maintaining control over its colonies. Activists in a wide range of movements have engaged in nonviolent strategies of repression management that can raise the likelihood that repression will cost those who use it. The Paradox of Repression and Nonviolent Movements brings scholars and activists together to address multiple dimensions and significant cases of this phenomenon, including the relational nature of nonviolent struggle and the cultural terrain on which it takes place, the psychological costs for agents of repression, and the importance of participation, creativity, and overcoming fear, whether in the streets or online

Triggered massive-star formation on the borders of Galactic HII regions. III. Star formation at the periphery of Sh2-219

Context. Massive-star formation triggered by the expansion of HII regions. Aims. To understand if sequential star formation is taking place at the periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain). Results. In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000\msol lies at the southwestern border of Sh2-219, in the HI gap. Two molecular condensations, elongated along the ionization front, probably result from the interaction between the expanding HII region and the molecular cloud. In this region of interaction there lies a cluster containing many highly reddened stars, as well as a massive star exciting an ultracompact HII region. More surprisingly, the brightest parts of the molecular cloud form a `chimney', perpendicular to the ionization front. This chimney is closed at its south-west extremity by H-alpha walls, thus forming a cavity. The whole structure is 7.5 pc long. A luminous H-alpha emission-line star, lying at one end of the chimney near the ionization front, may be responsible for this structure. Confrontation of the observations with models of HII region evolution shows that Sh2-219 is probably 10^5 yr old. The age and origin of the near-IR cluster observed on the border of Sh2-219 remain unknown.Comment: 11 pages, 10 figures. To be published in A&

Secular increase of the Astronomical Unit and perihelion precessions as tests of the Dvali-Gabadadze-Porrati multi-dimensional braneworld scenario

An unexpected secular increase of the Astronomical Unit, the length scale of the Solar System, has recently been reported by three different research groups (Krasinsky and Brumberg, Pitjeva, Standish). The latest JPL measurements amount to 7+-2 m cy^-1. At present, there are no explanations able to accommodate such an observed phenomenon, neither in the realm of classical physics nor in the usual four-dimensional framework of the Einsteinian General Relativity. The Dvali-Gabadadze-Porrati braneworld scenario, which is a multi-dimensional model of gravity aimed to the explanation of the observed cosmic acceleration without dark energy, predicts, among other things, a perihelion secular shift, due to Lue and Starkman, of 5 10^-4 arcsec cy^-1 for all the planets of the Solar System. It yields a variation of about 6 m cy^-1 for the Earth-Sun distance which is compatible at 1-sigma level with the observed rate of the Astronomical Unit. The recently measured corrections to the secular motions of the perihelia of the inner planets of the Solar System are in agreement, at 1-sigma level, with the predicted value of the Lue-Starkman effect for Mercury and Mars and at 2-sigma level for the Earth.Comment: LaTex2e, 7 pages, no figures, no tables, 13 references. Minor correction

The Emerging Scholarly Brain

It is now a commonplace observation that human society is becoming a coherent super-organism, and that the information infrastructure forms its emerging brain. Perhaps, as the underlying technologies are likely to become billions of times more powerful than those we have today, we could say that we are now building the lizard brain for the future organism.Comment: to appear in Future Professional Communication in Astronomy-II (FPCA-II) editors A. Heck and A. Accomazz