Perspective acceleration and gravitational redshift. Measuring masses of individual white dwarfs using Gaia + SIM astrometry

According to current plans, the SIM/NASA mission will be launched just after the end of operations for the Gaia/ESA mission. This is a new situation which enables long term astrometric projects that could not be achieved by either mission alone. Using the well-known perspective acceleration effect on astrometric measurements, the true heliocentric radial velocity of a nearby star can be measured with great precision if the time baseline of the astrometric measurements is long enough. Since white dwarfs are compact objects, the gravitational redshift can be quite large (40-80 km/s), and is the predominant source of any shift in wavelength. The mismatch of the true radial velocity with the spectroscopic shift thus leads to a direct measure of the Mass--Radius relation for such objects. Using available catalog information about the known nearby white dwarfs, we estimate how many masses/gravitational redshift measurements can be obtained with an accuracy better than 2%. Nearby white dwarfs are relatively faint objects (10 < V < 15), which can be easily observed by both missions. We also briefly discuss how the presence of a long period planet can mask the astrometric signal of perspective acceleration.Comment: 3 pages, 2 Figures. Proceedings of the IAU Symposium 261 : Relativity in Fundamental Astronomy. 27 April - 1 May 2009, Virginia Beach, VA, USA. refereed and accepted versio

Reflections on Cultural Superiority and the Just War: A Neomodern Imperative

If all cultures are morally equivalent, then all individuals are not endowed with the same human rights, because some cultures award some men more rights than are allotted to other men and women. If, on the other hand, all men and women are endowed with the same human rights, then all cultures are not morally equivalent, because cultures that acknowledge that "all men are created equal" are ethically superior to those that do not. These two statements are mutually contradictory and cannot both be true. Moreover, there is a natural conflict between them, leading to inevitable intra and inter-civilizational clashes. Relativism will confront evolutionism and hierarchical theocracy will confront secularized republicanism. This essay takes sides and argues that cultural superiority can be asserted on two different levels: moral and epistemological. A culture that acknowledges a set of universal human rights is superior to one that does not, even if it often deviates from these very norms. A culture capable of delving into nature increasing life expectancy through scientific discovery is superior to one that cannot. Furthermore, waging war to defend a superior culture is a moral imperative.

The anthropomorphic fallacy in international relations theory and practice

A headline of the Venezuelean daily El Nacionalista, published June 16, 2008, read: “Venezuela se negó a seguir de rodillas ante las pretensiones del gobierno norteamericano”. A few weeks before, on May 8, president Hugo Chávez himself had said that Venezuela “would not watch crossed-armed” (“Venezuela no se quedará de brazos cruzados”) while Bolivia was driven into territorial desintegration by imperialist forces. The image of Venezuela with her arms crossed is one of slovenliness and negligence, whilst the image of it on its knees is humiliating. They both generate outrage and the need to set things “right”. This is only an example of the often unnoticed practical and theoretical consequences of the anthropomorphic language we all use when referring to states in terms of (for example) "weak" and "strong" actors who "suffer", are "honored", are "humiliated", have "pride" and aspire to "glory". This language obscures the fact that, oftentimes, when a weak state challenges a strong one at a great cost to itself, we are not witnessing an epic of courage (as might be the case when a weak individual challenges a strong one), but rather the sacrifice of the interests, welfare and sometimes even the lives of multitudes of poor people, to the vanity of their elite. The very fact that this is being obscured biases the value structure of international relations theory, which is not only not value-free, but often has totalitarian values unintendedly built into it.

State Personhood, Reality or Fiction? The Divergent Views of C. Escudé (1994) and A. Wendt (2004)

This paper counterpoises Carlos Escudé's 1994, 1995 and 1997 treatment of anthropomorphic metaphors of the state, with Alexander Wendt's 2004 treatment of the same subject. It stresses the need for a historical memory in IR scholarship, suggesting that the lack of an epistemological equivalent to the concept of ‘discovery’ in the harder sciences may open the way for less-than-scholarly attitudes towards precedents, making the accumulation of knowledge less likely. It discusses whether or not state personhood is actually a fiction. Finally, it explores the consequences, for IR theory in general and peripheral realist theory in particular, of state personhood being indeed a harmful fiction. The author argues that if anthropomorphisms of the state lead to fallacy, then Hedley Bull’s domestic analogy is likewise fallacious. And if this is the case, the hierarchy of the structure of the interstate system is exposed, together with Waltz’s error in postulating an anarchy.

A star disrupted by a stellar black hole as the origin of the cloud falling toward the Galactic center

We propose that the cloud moving on a highly eccentric orbit near the central black hole in our Galaxy, reported by Gillessen et al., is formed by a photoevaporation wind originating in a disk around a star that is tidally perturbed and shocked at every peribothron passage. The disk is proposed to have formed when a stellar black hole flew by the star, tidally disrupted its envelope, and placed the star on its present orbit with some of the tidal debris forming a disk. A disrupting encounter at the location of the observed cloud is most likely to be caused by a stellar black hole because of the expected dynamical mass segregation; the rate of these disk-forming encounters may be as high as $\sim 10^{-6}$ per year. The star should also be spun up by the encounter, so the disk may subsequently expand by absorbing angular momentum from the star. Once the disk expands up to the tidal truncation radius, the tidal perturbation of the outer disk edge at every peribothron may place gas streams on larger orbits which can give rise to a photoevaporation wind that forms the cloud at every orbit. This model predicts that, after the cloud is disrupted at the next peribothron passage in 2013, a smaller unresolved cloud will gradually grow around the star on the same present orbit. An increased infrared luminosity from the disk may also be detectable when the peribothron is reached. We also note that this model revives the encounter theory for planet formation.Comment: To be published in Ap

Israel, Latin America and the United States: A peripheral-realist perspective

This document is the paper-format version of the keynote address delivered by its author on August 2, 2009, to the opening session of the Latin American section (AMILAT) of the 15th World Congress of Jewish Studies, at the Hebrew University of Jerusalem. It attempts to understand the long-term shift towards the worse of Israeli- Latin American relations, which started with an almost unqualified support for the establishment of the State of Israel on the side of both Latin American right-wing governments and left-wing parties and popular organizations, but have been deteriorating ever since. It suggests that this involution can be largely explained in terms of at least four intervening variables: Israel’s vulnerability, its special relationship with the United States after 1967, Latin American social structure, and the class identity of the leadership of the Latin American Jewry. It argues that overlooking the peripheral character of Israel in the interstate system has led to distortions in the understanding of Israeli-Latin American relations.

Strictly strategy-proof auctions

A strictly strategy-proof mechanism is one that asks agents to use strictly dominant strategies. In the canonical one-dimensional mechanism design setting with private values, we show that strict strategy-proofness is equivalent to strict monotonicity plus the envelope formula, echoing a well-known characterisation of (weak) strategy-proofness. A consequence is that strategy-proofness can be made strict by an arbitrarily small modification, so that strictness is 'essentially for free'

`First Light' in the Universe; What Ended the "Dark Age"?

The universe would have been completely dark between the epoch of recombination and the development of the first non-linear structure. But at redshifts beyond 5 -- perhaps even beyond 20 -- stars formed within `subgalaxies' and created the first heavy elements; these same systems (together perhaps with `miniquasars') generated the UV radiation that ionized the IGM, and maybe also the first significant magnetic fields. Although we can already probe back to $z \simeq 5$, these very first objects may be so faint that their detection must await next-generation optical and infrared telescopes. Observations in other wavebands may offer indirect clues to when reionization occurred. Despite the rapid improvements in numerical simulations, the processes of star formation and feedback are likely to remain a challenge for the next decade.Comment: For ``Physics Reports'' special issue in memory of D.N. Schram