M dwarfs: Theoretical work

Theoretical work on the atmospheres of M dwarfs has progressed along lines parallel to those followed in the study of other classes of stars. Such models have become increasingly sophisticated as improvements in opacities, in the equation of state, and in the treatment of convection were incorporated during the last 15 to 20 years. As a result, spectrophotometric data on M dwarfs can now be fitted rather well by current models. The various attempts at modeling M dwarf photospheres in purely thermal terms are summarized. Some extensions of these models to include the effects of microturbulence and magnetic inhomogeneities are presented

Magnetic effects and oversized M dwarfs in the young open cluster NGC 2516

By combining rotation periods with spectroscopic determinations of projected rotation velocity, Jackson, Jeffries & Maxted (2009) have found that the mean radii for low-mass M-dwarfs in the young, open cluster NGC 2516 are larger than model predictions at a given absolute I magnitude or I - K color and also larger than measured radii of magnetically inactive M-dwarfs. The relative radius difference is correlated with magnitude, increasing from a few per cent at MI = 7 to greater than 50 per cent for the lowest luminosity stars in their sample at MI about 9.5. Jackson et al (2009) have suggested that a two-temperature star spot model is capable of explaining the observations, but their model requires spot coverage fractions of at least 50 per cent in rapidly rotating M-dwarfs. Here we examine these results in terms of stellar models that include the inhibiting effects of magnetic fields on convective energy transport, with and without the effects of star spots. We find that a pure spot model is inconsistent with the color - magnitude diagram. The observations of radii versus color and radii versus absolute magnitude in NGC 2516 are consistent with models which include only magnetic inhibition or a combination of magnetic inhibition and spots. At a given mass we find a large dispersion in the strength of the vertical component of the magnetic field in the stellar photosphere but the general trend is that the vertical field increases with decreasing mass from a few hundred Gauss at 0.65 Msun to 600 - 900 Gauss, depending on spot coverage, in the lowest mass stars in the sample at 0.25 Msun.Comment: To appear in the Astrophysical Journal. arXiv admin note: text overlap with arXiv:1006.1308 by other author

Corona: Coordinated research on non-thermal processes in astrophysics

Several problems in astrophysics are examined where departures from purely thermal behavior are expected to produce effects which are detectable by a variety of NASA satellites. The problems identified as worthy of study include coronal heating in stars, deposition of non-thermal particle energy in stars from external sources, and turbulence in atmospheres and winds of stars. The progress in solving these problems is summarized

Dynamics of satellites, asteroids, and rings

Work is reported on: (1) the shapes and the internal structures of satellites; (2) the tidal heating of Miranda; (3) the dynamics of arc-like rings; and (4) the structure of the zodiacal cloud that was revealed by the Infrared Astronomy Satellite. Significant progress was made in determining the shape and internal structure of Mimas and in understanding the dynamical evolution of Miranda's orbit

Care and feeding of frogs

"Propellers" are features in Saturn's A ring associated with moonlets that open partial gaps. They exhibit non-Keplerian motion (Tiscareno 2010); the longitude residuals of the best-observed propeller, "Bl\'eriot," appear consistent with a sinusoid of period ~4 years. Pan and Chiang (2010) proposed that propeller moonlets librate in "frog resonances" with co-orbiting ring material. By analogy with the restricted three-body problem, they treated the co-orbital material as stationary in the rotating frame and neglected non-co-orbital material. Here we use simple numerical experiments to extend the frog model, including feedback due to the gap's motion, and drag associated with the Lindblad disk torques that cause Type I migration. Because the moonlet creates the gap, we expect the gap centroid to track the moonlet, but only after a time delay t_diff, the time for a ring particle to travel from conjunction with the moonlet to the end of the gap. We find that frog librations can persist only if t_diff exceeds the frog libration period P_lib, and if damping from Lindblad torques balances driving from co-orbital torques. If t_diff << P_lib, then the libration amplitude damps to zero. In the case of Bl\'eriot, the frog resonance model can reproduce the observed libration period P_lib ~ 4 yr. However, our simple feedback prescription suggests that Bl\'eriot's t_diff ~ 0.01P_lib, which is inconsistent with the observed libration amplitude of 260 km. We urge more accurate treatments of feedback to test the assumptions of our toy models.Comment: 15 pages, 4 figures; AJ in prin

Dynamic Sites:Learning to Design in Techno-Social Landscapes

This paper investigates interdisciplinary research through an urban design project and explores the creation of broader architectural representations of place. It advances the case made by McCarthy and Wright for developing deeper associations between experience and technology. Drawing on artist Janet Cardiff's media representations of space, design students were challenged to represent richer descriptions of place that include factors such as temporal and spatial resistance, experiential laminations, and social linkages and their gaps. Findings support a view of design and transdisciplinarity as potentially compelling modalities for research in these complex contexts, discourage bringing technology to center stage and encourage propositions that recommend looking beyond the functional and attending to personal and social facets of our interaction with technology. </jats:p

The evolution of gender and poverty in Britain: solo-living men are emerging as a new poor group

Esther Dermott examines the relationship between gender, age and living arrangements in Britain over the period of 1999-2012. Her analysis finds that older women have gone from being one of the poorest groups to being relatively advantaged. Meanwhile, men living alone are an emerging poor group in Britain

The parenting and economising practices of lone parents:Policy and evidence

UK governments have historically viewed lone parents as a political and social problem. This article argues that present-day political discourse increasingly positions lone parents as deficient parents, suggesting that they are more likely to fail to engage with good parenting practices than parents in couple households and may lack the resource management skills of successful families. We critique claims of an association between poor parenting and lone parenthood status using data from the UK Poverty and Social Exclusion (PSE) 2012 survey. We find negligible differences in the parenting behaviours of those living in lone and couple households, and lone parents (who are mainly mothers) actually cut back on their own expenditure to a greater extent than other parents in order to provide for children. These findings undermine the viability of links made between ‘poor’ parenting and family living arrangements; such claims are grounded in erroneous individualised accounts of disadvantage