Neutron Star Planets: Atmospheric processes and habitability

Of the roughly 3000 neutron stars known, only a handful have sub-stellar companions. The most famous of these are the low-mass planets around the millisecond pulsar B1257+12. New evidence indicates that observational biases could still hide a wide variety of planetary systems around most neutron stars. We consider the environment and physical processes relevant to neutron star planets, in particular the effect of X-ray irradiation and the relativistic pulsar wind on the planetary atmosphere. We discuss the survival time of planet atmospheres and the planetary surface conditions around different classes of neutron stars, and define a neutron star habitable zone. Depending on as-yet poorly constrained aspects of the pulsar wind, both Super-Earths around B1257+12 could lie within its habitable zone.Comment: Submitted to A&

Proceedings of the Conference on Human and Economic Resources

There has been an increasing number of literature on globalization and its effects on labour markets. With increasing global economic competition employment conditions have changed. Evidence shows that greater trade openness is associated with increase in women’s share of paid employment. In this paper, we concentrate on the aspects of trade on gender discrimination and particularly Turkey’s situation on this context. In the period of 1970-2005 there was substantial overall improvement in women’s quality of life, as reflected in social indicators. Women lived longer, had fewer children and more schooling. From the statistics, we can say that there is a moderate rise in women’s participation in the labour force. Usually, schooling, participation in politics and work and earnings can be used to measure women’s achievement in comparison with men’s. Focusing on Turkish economy, we know that in 24th January 1980 Turkey announced to follow a far reaching program of stabilization with structural change. The main objective of the program was to shift from an inward to an outward oriented development strategy. With an increase in trade, women transferred from the non productive housework economy to the productive economy. So, it is possible to say that trade create jobs for women but what about the gender gap? There is a quite number of literature for believing that the effect of globalisation may act to widen the gender pay gap. As long as women remain less qualified than men, they are likely to remain lower paying jobs, even if better-paying jobs become available through trade expansion.trade liberalization, gender gap, turkey

A dearth of small particles in debris disks: An energy-constrained smallest fragment size

A prescription for the fragment size distribution resulting from dust grain collisions is essential when modelling a range of astrophysical systems, such as debris disks and planetary rings. While the slope of the fragment size distribution and the size of the largest fragment are well known, the behaviour of the distribution at the small size end is theoretically and experimentally poorly understood. This leads debris disk codes to generally assume a limit equal to, or below, the radiation blow-out size. We use energy conservation to analytically derive a lower boundary of the fragment size distribution for a range of collider mass ratios. Focussing on collisions between equal-sized bodies, we apply the method to debris disks. For a given collider mass, the size of the smallest fragments is found to depend on collision velocity, material parameters, and the size of the largest fragment. We provide a physically motivated recipe for the calculation of the smallest fragment, which can be easily implemented in codes for modelling collisional systems. For plausible parameters, our results are consistent with the observed predominance of grains much larger than the blow-out size in Fomalhaut's main belt and in the Herschel cold debris disks.Comment: 5 pages, 3 figures, Accepted for publication as a Letter in Astronomy & Astrophysic

Spirals in protoplanetary disks from photon travel time

Spiral structures are a common feature in scattered-light images of protoplanetary disks, and of great interest as possible tracers of the presence of planets. However, other mechanisms have been put foward to explain them, including self-gravity, disk-envelope interactions, and dead zone boundaries. These mechanisms explain many spirals very well, but are unable to easily account for very loosely wound spirals and single spiral arms. We study the effect of light travel time on the shape of a shadow cast by a clump orbiting close (within ${\sim}1\,$au) of the central star, where there can be significant orbital motion during the light travel time from the clump to the outer disk and then to the sky plane. This delay in light rays reaching the sky plane gives rise to a variety of spiral- and arc-shaped shadows, which we describe with a general fitting formula for a flared, inclined disk.Comment: Accepted for publication in A&A Letters. Videos available at dl.dropboxusercontent.com/u/3526708/spiralmovies.zi

Fingerprints of giant planets in the photospheres of Herbig stars

Around 2% of all A stars have photospheres depleted in refractory elements. This is hypothesized to arise from a preferential accretion of gas rather than dust, but the specific processes and the origin of the material -- circum- or interstellar -- are not known. The same depletion is seen in 30% of young, disk-hosting Herbig Ae/Be stars. We investigate whether the chemical peculiarity originates in a circumstellar disk. Using a sample of systems for which both the stellar abundances and the protoplanetary disk structure are known, we find that stars hosting warm, flaring group I disks typically have Fe, Mg and Si depletions of 0.5 dex compared to the solar-like abundances of stars hosting cold, flat group II disks. The volatile, C and O, abundances in both sets are identical. Group I disks are generally transitional, having radial cavities depleted in millimetre-sized dust grains, while those of group II are usually not. Thus we propose that the depletion of heavy elements emerges as Jupiter-like planets block the accretion of part of the dust, while gas continues to flow towards the central star. We calculate gas to dust ratios for the accreted material and find values consistent with models of disk clearing by planets. Our results suggest that giant planets of ~0.1 to 10 M_Jup are hiding in at least 30% of Herbig Ae/Be disks.Comment: 5 pages, 3 figures, accepted for publication in A&A Letter

Growth, Environment and Uncertain Future Preferences

The attitude of future generations towards environmental assets may well be different from ours, and it is necessary to take into account this possibility explicitly in the current debate about environmental policy. The question we are addressing here is: should uncertainty about future preferences lead to a more conservative attitude towards environment? Previous literature shows that it is the case when society expects that on average future preferences will be more in favor of environment than ours, but this result relies heavily on the assumption of a separability between consumption and environmental quality in the utility function. We show that things are less simple when preferences are non-separable: the attitude of the society now depends not only on the expectation of the change in preferences but also on the characteristics of the economy (impatience, intertemporal flexibility, natural capacities of regeneration of the environment, relative preference for the environment), on its history (initial level of the environmental quality) and on the date at which preferences are expected to change (near or far future).Growth ; Environment ; Preferences ; Uncertainty c ° 2002 Kluwer Academic Publishers. Printed in the Netherlands.

Optimal Nuclear Waste Burial Policy under Uncertainty

The aim of this paper is to study the optimal nuclear waste burial policy under an uncertainty : the possibility that an accident might occur in the future. The framework is an optimal growth model with pollution disutility. We show, under some conditions on the waste burial policy, that nuclear power may be a long-term solution for the world energy demand. Under uncertainty on the future safety of the buried waste, the social planner will decide to decrease the rate of waste burying, but the evolution of consumption and hence the evolution of the level of buried waste, are ambiguous. Depending on some simple conditions on the balanced growth rate of the economy and on the preference parameters of the households, the optimal amount of buried waste may increase, even if there is a risk of accident in the future.Nuclear waste; pollution; growth; uncertainty

Near-infrared emission from sublimating dust in collisionally active debris disks

Hot exozodiacal dust is thought to be responsible for excess near-infrared (NIR) emission emanating from the innermost parts of some debris disks. The origin of this dust, however, is still a matter of debate. We test whether hot exozodiacal dust can be supplied from an exterior parent belt by Poynting-Robertson (P-R) drag, paying special attention to the pile-up of dust that occurs due to the interplay of P-R drag and dust sublimation. Specifically, we investigate whether pile-ups still occur when collisions are taken into account, and if they can explain the observed NIR excess. We compute the steady-state distribution of dust in the inner disk by solving the continuity equation. First, we derive an analytical solution under a number of simplifying assumptions. Second, we develop a numerical debris disk model that for the first time treats the complex interaction of collisions, P-R drag, and sublimation in a self-consistent way. From the resulting dust distributions we generate thermal emission spectra and compare these to observed excess NIR fluxes. We confirm that P-R drag always supplies a small amount of dust to the sublimation zone, but find that a fully consistent treatment yields a maximum amount of dust that is about 7 times lower than that given by analytical estimates. The NIR excess due this material is much smaller (<10^-3 for A-type stars with parent belts at >1 AU) than the values derived from interferometric observations (~10^-2). Pile-up of dust still occurs when collisions are considered, but its effect on the NIR flux is insignificant. Finally, the cross-section in the innermost regions is clearly dominated by barely bound grains.Comment: 18 pages, 10 figures, A&A accepte

Optimal Emission Policy under the Risk of Irreversible Pollution

We consider an optimal consumption and pollution problem that has two important features. Environmental damages due to economic activities may be irreversible and the level at which the degradation becomes irreversible is unknown. Particular attention is paid to the situation where agents are relatively impatient and/or do not care a lot about the environment and/or Nature regenerates at low rate. We show that the optimal policy of the uncertain problem drives the economy in the long run toward a steady state while, when ignoring irreversibility, the economy follows a balanced growth path accompanied by a perpetual decrease in environmental quality and consumption, both asymptotically converging toward zero. Therefore, accounting for the risk of irreversibility induces more conservative decisions regarding consumption and polluting emissions. In general, however, we cannot rule out situations where the economy will optimally follow an irreversible path and consequently, will also be left, in the long run, with an irreversibly degraded environment.Optimal Control, Irreversibility Threshold, Uncertainty, Optimal Reversible, Irreversible Policy