27,838 research outputs found
Observational Constraints on Pulsar Wind Theories
Two-dimensional, relativistic, MHD simulations of pulsar-wind powered nebulae
provide strong constraints on the properties of the winds themselves. In
particular, they confirm that Poynting flux must be converted into particle
energy close to or inside the termination shock front, emphasising the puzzle
known as the paradox. To distinguish between the different possible
resolutions of this paradox, additional observational constraints are required.
In this paper, I briefly discuss two recents developments in this respect: the
modelling of high time-resolution optical polarimetry of the Crab pulsar, and
the detection of the pulsar/Be star binary PSR 1259-63 in TeV energy
gamma-rays.Comment: Paper presented at the workshop on "Stellar End Products", Granada
13-15 April 200
Catalogue of Be/X-ray binary systems in the Small Magellanic Cloud: X-ray, optical & IR properties
This is a catalogue of approximately 70 X-ray emitting binary systems in the
Small Magellanic Cloud (SMC) that contain a Be star as the mass donor in the
system and a clear X-ray pulse signature from a neutron star. The systems are
generally referred to as Be/Xray binaries. It lists all their known binary
characteristics (orbital period, eccentricity), the measured spin period of the
compact object, plus the characteristics of the Be star (spectral type, size of
the circumstellar disk, evidence for NRP behaviour). For the first time data
from the Spitzer Observatory are combined with ground-based data to provide a
view of these systems out into the far-IR. Many of the observational parameters
are presented as statistical distributions and compared to other similar
similar populations (eg isolated Be & B stars) in the SMC, and to other
Be/X-ray systems in the Milky Way. In addition previous important results are
re-investigated using this excellently homogeneous sample. In particular, the
evidence for a bi-modality in the spin period distribution is shown to be even
stronger than first proposed, and the correlation between orbital period and
circumstellar disk size seen in galactic sources is shown to be clearly present
in the SMC systems and quantised for the first time.Comment: 10 pages, 10 figures, 4 tables. Accepted for publication in MNRA
Climate change: carbon losses in the Alps
The response of the terrestrial carbon cycle to global change is one of the main uncertainties in current climate change predictions1. Most terrestrial carbon is held in soils as organic matter derived from the decay of plant material (Fig. 1). Soil organic matter accounts for roughly three times more carbon than living vegetation, and for more carbon than vegetation and the atmosphere combined. Because elevated atmospheric CO2 concentrations have a fertilizing effect on plant growth, anthropogenic CO2 emissions have triggered increases in the land carbon sink2. However, models predict that other factors — such as water and nutrients — will eventually become limiting to plant growth, and hence to the land carbon sink. In contrast, the turnover of soil organic matter producing CO2 is expected to increase as the Earth warms. As a result, simulations using coupled carbon–climate models predict that the land surface will become a net source of CO2 before the end of the century, leading to a feedback loop between climate and soil carbon losses: increased emissions of CO2 from soil organic matter will lead to enhanced warming, which may then feedback to cause further soil organic matter losses. Prietzel and colleagues3, writing in Nature Geoscience, now provide evidence that warming has already caused a decline in soil organic matter in the German Alps
An Annotated Checklist of Scarab Beetles (Coleoptera: Scarabaeidae) from Northeastern Iowa
A survey of scarab beetles (Coleoptera: Scarabaeidae) was conducted during 2009 in the geographically distinct area of Winneshiek and Allamakee counties in extreme Northeast Iowa. Four plant communities distributed among 10 locations, including tallgrass prairie, mixed grassland and forest, oak-hickory forest, and pasture were sampled during 2009 using black light traps, banana- beer traps, rodent burrow pitfalls, manure-baited pitfalls, and gleaning. Additionally, previous specimen records were examined. Forty-nine scarab species were documented for Winneshiek and Allamakee counties, including five species not previously reported in Iowa. Mixed grassland and forest habitat contained the greatest scarab species richness (n=31); black light trapping yielded the greatest number of individual beetles and collected the most species
The "sigma" problem of the Crab pulsar wind
The conversion of the Crab pulsar wind from one dominated by Poynting flux
close to the star to one dominated by particle-born energy at the termination
shock is considered. The idea put forward by Coroniti (1990) and criticised by
Lyubarsky & Kirk (2001) that reconnection in a striped wind is responsible, is
generalised to include faster prescriptions for the a priori unknown
dissipation rate. Strong acceleration of the wind is confirmed, and the higher
dissipation rates imply complete conversion of Poynting flux into particle-born
flux within the unshocked wind.Comment: 4 pages, to appear in "Young Neutron Stars and Their Environments"
(IAU Symposium 218, ASP Conference Proceedings), eds F. Camilo and B. M.
Gaensle
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