139 research outputs found
Mutual Detectability: A Targeted SETI Strategy That Avoids the SETI Paradox
No full textAs our ability to undertake more powerful Searches for Extraterrestrial Intelligence (SETI) grows, so does interest in the more controversial endeavour of Messaging Extraterrestrial Intelligence (METI). METI proponents point to the SETI Paradox - if all civilisations refrain from METI then SETI is futile. I introduce Mutual Detectability as a game-theoretic strategy aimed at increasing the success potential of targeted SETI. Mutual detectability is embodied by four laws: mutuality, symmetry, opportunity and superiority. These laws establish how SETI participants can engage each other using game theory principles applied to mutual evidence of mutual existence. The law of superiority establishes an "onus to transmit" on the party whom both SETI participants can judge to have better quality evidence, or common denominator information (CDI), thus avoiding the SETI Paradox. I argue that transiting exoplanets within the Earth Transit Zone form a target subset that satisfies mutual detectability requirements. I identify the intrinsic time-integrated transit signal strength as suitable CDI. Civilisations on habitable-zone planets of radius have superior CDI on us, so have game-theory incentive (onus) to transmit. Whilst this implies that the onus to transmit falls on us for habitable planets around L_* > L_{\odot} stars, considerations of relative stellar frequency, main-sequence lifetime and planet occurrence mean such systems are likely a small minority. Surveys of the Earth Transit Zone for Earth-analogue transits around sub-solar luminosity hosts, followed up by targeted SETI monitoring of them, represent an efficient strategy compliant with mutual detectability. A choice to remain silent, by not engaging in METI towards such systems, does not in this case fuel concerns of a SETI Paradox
Euclid: I. Overview of the Euclid mission
No full textThe current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015–2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14 000 deg2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.<br/
Creative Assets and the Changing Economy
Full text linkThis paper evaluates recent claims that art and culture have become more valuable assets in the new economy. Based on conversations with several prominent cultural economists, the author argues that advocates and scholars should be more cautious in their attempts to draw out the implications of the changing economy on culture. Rather than spend time calculating the impact or size of the “creative economy,” the author argues that we should direct our analytical and policy energies toward better understanding how creative work and institutions are changing and what might be done to foster a more robust, creative and diverse cultural life.
Rapidly rotating lenses: Repeating features in the light curves of short-period binary microlenses
Full text linkMicrolensing is most sensitive to binary lenses with relatively large orbital separations, and as such, typical binary microlensing events show little or no orbital motion during the event. However, despite the strength of binary microlensing features falling off rapidly as the lens separation decreases, we show that it is possible to detect repeating features in the light curve of binary microlenses that complete several orbits during the microlensing event. We investigate the light-curve features of such rapidly rotating lens (RRL) events. We derive analytical limits on the range of parameters where these effects are detectable, and confirm these numerically. Using a population synthesis Galactic model, we estimate the RRL event rate for a ground-based and a space-based microlensing survey to be 0.32fb and 7.8fb events per year, respectively, assuming year-round monitoring, where fb is the binary fraction. We detail how RRL event parameters can be quickly estimated from their light curves, and suggest a method to model RRL events using timing measurements of light-curve features. Modelling RRL light curves will yield the lens orbital period and possibly measurements of all orbital elements, including the inclination and eccentricity. Measurement of the period from the light curve allows a mass-distance relation to be defined, which when combined with a measurement of microlens parallax or finite-source effects can yield a mass measurement to a twofold degeneracy. With sub-per cent accuracy photometry, it is possible to detect planetary companions, but the likelihood of this is very small. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS
Detectability of orbital motion in stellar binary and planetary microlenses
Full text linkA standard binary microlensing event light curve allows just two parameters of the lensing system to be measured: the mass ratio of the companion to its host and the projected separation of the components in units of the Einstein radius. However, other exotic effects can provide more information about the lensing system. Orbital motion in the lens is one such effect, which, if detected, can be used to constrain the physical properties of the lens. To determine the fraction of binary-lens light curves affected by orbital motion (the detection efficiency), we simulate light curves of orbiting binary star and star-planet (planetary) lenses and simulate the continuous, high-cadence photometric monitoring that will be conducted by the next generation of microlensing surveys that are beginning to enter operation. The effect of orbital motion is measured by fitting simulated light-curve data with standard static binary microlensing models; light curves that are poorly fitted by these models are considered to be detections of orbital motion. We correct for systematic false positive detections by also fitting the light curves of static binary lenses. For a continuous monitoring survey without intensive follow-up of high-magnification events, we find the orbital motion detection efficiency for planetary events with caustic crossings to be 0.061 ± 0.010, consistent with observational results, and 0.0130 ± 0.0055 for events without caustic crossings (smooth events). Similarly, for stellar binaries, the orbital motion detection efficiency is 0.098 ± 0.011 for events with caustic crossings and is 0.048 ± 0.006 for smooth events. These result in combined (caustic-crossing and smooth) orbital motion detection efficiencies of 0.029 ± 0.005 for planetary lenses and 0.070 ± 0.006 for stellar binary lenses. We also investigate how various microlensing parameters affect the orbital motion detectability. We find that the orbital motion detection efficiency increases as the binary mass ratio and event time-scale increase, and as the impact parameter and lens distance decrease. For planetary caustic-crossing events, the detection efficiency is highest at relatively large values of semimajor axis ∼4 au, due to the large size of the resonant caustic at this orbital separation. Effects due to the orbital inclination are small and appear to significantly affect only smooth stellar binary events. We find that, as suggested by Gaudi, many of the events that show orbital motion can be classified into one of the following two classes. The first class, separational events, typically show large effects due to subtle changes in resonant caustics, caused by changes in the projected binary separation. The second class, rotational events, typically show much smaller effects, which are due to the magnification patterns of close lenses exhibiting large changes in angular orientation over the course of an event; these changes typically cause only subtle changes to the light curve. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS
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