1,088 research outputs found
Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008–2009 using the CRIRES spectrograph mounted on the 8 m UT 1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in He i λ10833 extending up to -1900 km s-1 across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s-1) in the ultraviolet resonance lines of Si iv λλ1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si ii λλ1527, 1533 and C ii λλ1334, 1335, show absorption only up to -1200 km s-1, indicating that the absorption with velocities -1200 to -2100 km s-1 originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6 m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989–2009) also show high-velocity absorption in He i λ10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s-1 is present in the phase range 0.976 ≤ ϕ ≤ 1.023 of the spectroscopic cycle, but absent in spectra taken at ϕ ≤ 0.94 and ϕ ≥ 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of ω ~ 240°–270°. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40°–60°.JHG thanks the Max-Planck-Gesellschaft for financial support
for this work. AD and MT thanks the FAPESP foundation for continuous support.
TIM is supported by a NASA GSRP fellowshi
The Nuts and Bolts of Einstein-Maxwell Solutions
We find new non-supersymmetric solutions of five-dimensional ungauged
supergravity coupled to two vector multiplets. The solutions are regular,
horizonless and have the same asymptotic charges as non-extremal charged black
holes. An essential ingredient in our construction is a four-dimensional
Euclidean base which is a solution to Einstein-Maxwell equations. We construct
stationary solutions based on the Euclidean dyonic Reissner-Nordstrom black
hole as well as a six-parameter family with a dyonic Kerr-Newman-NUT base.
These solutions can be viewed as compactifications of eleven-dimensional
supergravity on a six-torus and we discuss their brane interpretation.Comment: 29 pages, 3 figure
A Schwarz lemma for K\"ahler affine metrics and the canonical potential of a proper convex cone
This is an account of some aspects of the geometry of K\"ahler affine metrics
based on considering them as smooth metric measure spaces and applying the
comparison geometry of Bakry-Emery Ricci tensors. Such techniques yield a
version for K\"ahler affine metrics of Yau's Schwarz lemma for volume forms. By
a theorem of Cheng and Yau there is a canonical K\"ahler affine Einstein metric
on a proper convex domain, and the Schwarz lemma gives a direct proof of its
uniqueness up to homothety. The potential for this metric is a function
canonically associated to the cone, characterized by the property that its
level sets are hyperbolic affine spheres foliating the cone. It is shown that
for an -dimensional cone a rescaling of the canonical potential is an
-normal barrier function in the sense of interior point methods for conic
programming. It is explained also how to construct from the canonical potential
Monge-Amp\`ere metrics of both Riemannian and Lorentzian signatures, and a mean
curvature zero conical Lagrangian submanifold of the flat para-K\"ahler space.Comment: Minor corrections. References adde
High Energy Neutrinos from Quasars
We review and clarify the assumptions of our basic model for neutrino
production in the cores of quasars, as well as those modifications to the model
subsequently made by other workers. We also present a revised estimate of the
neutrino background flux and spectrum obtained using more recent empirical
studies of quasars and their evolution. We compare our results with other
thoeretical calculations and experimental upper limits on the AGN neutrino
background flux. We also estimate possible neutrino fluxes from the jets of
blazars detected recently by the EGRET experiment on the Compton Gamma Ray
Observatory. We discuss the theoretical implications of these estimates.Comment: 14 pg., ps file (includes figures), To be published in Space Science
Review
Worm Grunting, Fiddling, and Charming—Humans Unknowingly Mimic a Predator to Harvest Bait
Background: For generations many families in and around Florida’s Apalachicola National Forest have supported themselves by collecting the large endemic earthworms (Diplocardia mississippiensis). This is accomplished by vibrating a wooden stake driven into the soil, a practice called ‘‘worm grunting’’. In response to the vibrations, worms emerge to the surface where thousands can be gathered in a few hours. Why do these earthworms suddenly exit their burrows in response to vibrations, exposing themselves to predation? Principal Findings: Here it is shown that a population of eastern American moles (Scalopus aquaticus) inhabits the area where worms are collected and that earthworms have a pronounced escape response from moles consisting of rapidly exiting their burrows to flee across the soil surface. Recordings of vibrations generated by bait collectors and moles suggest that ‘‘worm grunters’ ’ unknowingly mimic digging moles. An alternative possibility, that worms interpret vibrations as rain and surface to avoid drowning is not supported. Conclusions: Previous investigations have revealed that both wood turtles and herring gulls vibrate the ground to elicit earthworm escapes, indicating that a range of predators may exploit the predator-prey relationship between earthworms and moles. In addition to revealing a novel escape response that may be widespread among soil fauna, the results sho
Binary and Millisecond Pulsars at the New Millennium
We review the properties and applications of binary and millisecond pulsars.
Our knowledge of these exciting objects has greatly increased in recent years,
mainly due to successful surveys which have brought the known pulsar population
to over 1300. There are now 56 binary and millisecond pulsars in the Galactic
disk and a further 47 in globular clusters. This review is concerned primarily
with the results and spin-offs from these surveys which are of particular
interest to the relativity community.Comment: 59 pages, 26 figures, 5 tables. Accepted for publication in Living
Reviews in Relativity (http://www.livingreviews.org
Multifrequency Strategies for the Identification of Gamma-Ray Sources
More than half the sources in the Third EGRET (3EG) catalog have no firmly
established counterparts at other wavelengths and are unidentified. Some of
these unidentified sources have remained a mystery since the first surveys of
the gamma-ray sky with the COS-B satellite. The unidentified sources generally
have large error circles, and finding counterparts has often been a challenging
job. A multiwavelength approach, using X-ray, optical, and radio data, is often
needed to understand the nature of these sources. This chapter reviews the
technique of identification of EGRET sources using multiwavelength studies of
the gamma-ray fields.Comment: 35 pages, 22 figures. Chapter prepared for the book "Cosmic Gamma-ray
Sources", edited by K.S. Cheng and G.E. Romero, to be published by Kluwer
Academic Press, 2004. For complete article and higher resolution figures, go
to: http://www.astro.columbia.edu/~muk/mukherjee_multiwave.pd
GLAST: Understanding the High Energy Gamma-Ray Sky
We discuss the ability of the GLAST Large Area Telescope (LAT) to identify,
resolve, and study the high energy gamma-ray sky. Compared to previous
instruments the telescope will have greatly improved sensitivity and ability to
localize gamma-ray point sources. The ability to resolve the location and
identity of EGRET unidentified sources is described. We summarize the current
knowledge of the high energy gamma-ray sky and discuss the astrophysics of
known and some prospective classes of gamma-ray emitters. In addition, we also
describe the potential of GLAST to resolve old puzzles and to discover new
classes of sources.Comment: To appear in Cosmic Gamma Ray Sources, Kluwer ASSL Series, Edited by
K.S. Cheng and G.E. Romer
Accreting Millisecond X-Ray Pulsars
Accreting Millisecond X-Ray Pulsars (AMXPs) are astrophysical laboratories
without parallel in the study of extreme physics. In this chapter we review the
past fifteen years of discoveries in the field. We summarize the observations
of the fifteen known AMXPs, with a particular emphasis on the multi-wavelength
observations that have been carried out since the discovery of the first AMXP
in 1998. We review accretion torque theory, the pulse formation process, and
how AMXP observations have changed our view on the interaction of plasma and
magnetic fields in strong gravity. We also explain how the AMXPs have deepened
our understanding of the thermonuclear burst process, in particular the
phenomenon of burst oscillations. We conclude with a discussion of the open
problems that remain to be addressed in the future.Comment: Review to appear in "Timing neutron stars: pulsations, oscillations
and explosions", T. Belloni, M. Mendez, C.M. Zhang Eds., ASSL, Springer;
[revision with literature updated, several typos removed, 1 new AMXP added
“Medically unexplained” symptoms and symptom disorders in primary care: prognosis-based recognition and classification
Background: Many patients consult their GP because they experience bodily symptoms. In a substantial proportion of
cases, the clinical picture does not meet the existing diagnostic criteria for diseases or disorders. This may be because
symptoms are recent and evolving or because symptoms are persistent but, either by their character or the negative
results of clinical investigation cannot be attributed to disease: so-called “medically unexplained symptoms” (MUS).
MUS are inconsistently recognised, diagnosed and managed in primary care. The specialist classification systems
for MUS pose several problems in a primary care setting. The systems generally require great certainty about
presence or absence of physical disease, they tend to be mind-body dualistic, and they view symptoms from a
narrow specialty determined perspective. We need a new classification of MUS in primary care; a classification
that better supports clinical decision-making, creates clearer communication and provides scientific underpinning
of research to ensure effective interventions.
Discussion: We propose a classification of symptoms that places greater emphasis on prognostic factors.
Prognosis-based classification aims to categorise the patient’s risk of ongoing symptoms, complications, increased
healthcare use or disability because of the symptoms. Current evidence suggests several factors which may be
used: symptom characteristics such as: number, multi-system pattern, frequency, severity. Other factors are:
concurrent mental disorders, psychological features and demographic data. We discuss how these characteristics may
be used to classify symptoms into three groups: self-limiting symptoms, recurrent and persistent symptoms, and
symptom disorders. The middle group is especially relevant in primary care; as these patients generally have reduced
quality of life but often go unrecognised and are at risk of iatrogenic harm. The presented characteristics do not
contain immediately obvious cut-points, and the assessment of prognosis depends on a combination of several factors.
Conclusion: Three criteria (multiple symptoms, multiple systems, multiple times) may support the classification into
good, intermediate and poor prognosis when dealing with symptoms in primary care. The proposed new classification
specifically targets the patient population in primary care and may provide a rational framework for decision-making in
clinical practice and for epidemiologic and clinical research of symptoms
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