High-Contrast Observations in Optical and Infrared Astronomy

High-contrast observations in optical and infrared astronomy are defined as any observation requiring a technique to reveal a celestial object of interest that is in such close angular proximity to another source brighter by a factor of at least 10^5 that optical effects hinder or prevent the collection of photons directly from the target of observation. This is a relatively new type of observation that enables research on previously obscured parts of the Universe. In particular, it is most applicable to Comparative Planetary Science, a field that directly attacks such questions as "how common are planetary systems? What types of planets exist, and are there planets other than Earth that are capable of supporting life as we know it?" We survey the scientific motivations for high-contrast observations, provide an overview of the techniques currently being used or developed, and discuss some ideas and studies for future prospects.Comment: In press for Annual Review of Astronomy and Astrophysics (Vol. 47). 46 pages, 15 figure

Constraints on Nucleon Decay via "Invisible" Modes from the Sudbury Neutrino Observatory

Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to ``invisible'' modes, such as n -> 3 nu. The analysis was based on a search for gamma-rays from the de-excitation of the residual nucleus that would result from the disappearance of either a proton or neutron from O16. A limit of tau_inv > 2 x 10^{29} years is obtained at 90% confidence for either neutron or proton decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton decay modes and 400 times more stringent than similar neutron modes.Comment: Update includes missing efficiency factor (limits change by factor of 2) Submitted to Physical Review Letter

First Neutrino Observations from the Sudbury Neutrino Observatory

The first neutrino observations from the Sudbury Neutrino Observatory are presented from preliminary analyses. Based on energy, direction and location, the data in the region of interest appear to be dominated by 8B solar neutrinos, detected by the charged current reaction on deuterium and elastic scattering from electrons, with very little background. Measurements of radioactive backgrounds indicate that the measurement of all active neutrino types via the neutral current reaction on deuterium will be possible with small systematic uncertainties. Quantitative results for the fluxes observed with these reactions will be provided when further calibrations have been completed.Comment: Latex, 7 pages, 10 figures, Invited paper at Neutrino 2000 Conference, Sudbury, Canada, June 16-21, 2000 to be published in the Proceeding

Variability of Brown Dwarfs

Brown dwarfs constitute a missing link between low-mass stars and giant planets. Their atmospheres display chemical species typical of planets, and one could wonder whether they also have weather-like patterns. While brown dwarf surface features cannot be directly resolved, the photometric and spectroscopic modulations induced by these features, as they rotate in and out of view, provide a wealth of information on the evolution of their atmosphere. A review of brown dwarfs variability through the L, T and Y spectral types sequence is presented, as well as the constraints that they set on the nature of weather-like patterns on their surface.Comment: Accepted chapter in the "Handbook of Exoplanets"; Springe

Formation, evolution and multiplicity of brown dwarfs and giant exoplanets

This proceeding summarises the talk of the awardee of the Spanish Astronomical Society award to the the best Spanish thesis in Astronomy and Astrophysics in the two-year period 2006-2007. The thesis required a tremendous observational effort and covered many different topics related to brown dwarfs and exoplanets, such as the study of the mass function in the substellar domain of the young sigma Orionis cluster down to a few Jupiter masses, the relation between the cluster stellar and substellar populations, the accretion discs in cluster brown dwarfs, the frequency of very low-mass companions to nearby young stars at intermediate and wide separations, or the detectability of Earth-like planets in habitable zones around ultracool (L- and T-type) dwarfs in the solar neighbourhood.Comment: "Highlights of Spanish Astrophysics V", Proceedings of the VIII Scientific Meeting of the Spanish Astronomical Society (SEA) held in Santander, 7-11 July, 2008. Edited by J. Gorgas, L. J. Goicoechea, J. I. Gonzalez-Serrano, J. M. Diego. Invited oral contribution to plenary sessio

Pediatric DXA: clinical applications

Normal bone mineral accrual requires adequate dietary intake of calcium, vitamin D and other nutrients; hepatic and renal activation of vitamin D; normal hormone levels (thyroid, parathyroid, reproductive and growth hormones); and neuromuscular functioning with sufficient stress upon the skeleton to induce bone deposition. The presence of genetic or acquired diseases and the therapies that are used to treat them can also impact bone health. Since the introduction of clinical DXA in pediatrics in the early 1990s, there has been considerable investigation into the causes of low bone mineral density (BMD) in children. Pediatricians have also become aware of the role adequate bone mass accrual in childhood has in preventing osteoporotic fractures in late adulthood. Additionally, the availability of medications to improve BMD has increased with the development of bisphosphonates. These factors have led to the increased utilization of DXA in pediatrics. This review summarizes much of the previous research regarding BMD in children and is meant to assist radiologists and clinicians with DXA utilization and interpretation

Observing Exoplanets with the James Webb Space Telescope

The census of exoplanets has revealed an enormous variety of planets or- biting stars of all ages and spectral types: planets in orbits of less than a day to frigid worlds in orbits over 100 AU; planets with masses 10 times that of Jupiter to planets with masses less than that of Earth; searingly hot planets to temperate planets in the Habitable Zone. The challenge of the coming decade is to move from demography to physical characterization. The James Webb Space Telescope (JWST) is poised to open a revolutionary new phase in our understanding of exoplanets with transit spectroscopy of relatively short period planets and coronagraphic imaging of ones with wide separations from their host stars. This article discusses the wide variety of exoplanet opportunities enabled by JWSTs sensitivity and stability, its high angular resolution, and its suite of powerful instruments. These capabilities will advance our understanding of planet formation, brown dwarfs, and the atmospheres of young to mature planets