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Cambridge, MA, United States

Mink J.D.,Smithsonian Astrophysical Observatory
Astronomy and Computing | Year: 2015

Despite almost all being acquired as photons, astronomical data from different instruments and at different stages in its life may exist in different formats to serve different purposes. Beyond the data itself, descriptive information is associated with it as metadata, either included in the data format or in a larger multi-format data structure. Those formats may be used for the acquisition, processing, exchange, and archiving of data. It has been useful to use similar formats, or even a single standard to ease interaction with data in its various stages using familiar tools. Knowledge of the evolution and advantages of present standards is useful before we discuss the future of how astronomical data is formatted. The evolution of the use of world coordinates in FITS is presented as an example. © 2015. Source

Kenyon S.J.,Smithsonian Astrophysical Observatory | Bromley B.C.,University of Utah
Astronomical Journal | Year: 2014

Motivated by the New Horizons mission, we consider how Pluto's small satellites - currently Styx, Nix, Kerberos, and Hydra - grow in debris from the giant impact that forms the Pluto-Charon binary. After the impact, Pluto and Charon accrete some of the debris and eject the rest from the binary orbit. During the ejection, high-velocity collisions among debris particles produce a collisional cascade, leading to the ejection of some debris from the system and enabling the remaining debris particles to find stable orbits around the binary. Our numerical simulations of coagulation and migration show that collisional evolution within a ring or a disk of debris leads to a few small satellites orbiting Pluto-Charon. These simulations are the first to demonstrate migration-induced mergers within a particle disk. The final satellite masses correlate with the initial disk mass. More massive disks tend to produce fewer satellites. For the current properties of the satellites, our results strongly favor initial debris masses of 3-10 × 1019g and current satellite albedos A 0.4-1.We also predict an ensemble of smaller satellites,R ≲1-3 km, and very small particles, R 1-100 cm and optical depth τ ≲ 10-10. These objects should have semimajor axes outside the current orbit of Hydra. © 2014.The American Astronomical Society.All rights reserved. Source

Kenyon S.J.,Smithsonian Astrophysical Observatory | Bromley B.C.,University of Utah
Astrophysical Journal, Supplement Series | Year: 2010

We describe comprehensive calculations of the formation of icy planets and debris disks at 30-150 AU around 1-3M · stars. Disks composed of large, strong planetesimals produce more massive planets than disks composed of small, weak planetesimals. The maximum radius of icy planets ranges from ∼ 1500km to 11,500km. The formation rate of 1000km objects - "Plutos" - is a useful proxy for the efficiency of icy planet formation. Plutos form more efficiently in massive disks, in disks with small planetesimals, and in disks with a range of planetesimal sizes. Although Plutos form throughout massive disks, Pluto production is usually concentrated in the inner disk. Despite the large number of Plutos produced in many calculations, icy planet formation is inefficient. At the end of the main sequence lifetime of the central star, Plutos contain less than 10% of the initial mass in solid material. This conclusion is independent of the initial mass in the disk or the properties of the planetesimals. Debris disk formation coincides with the formation of planetary systems containing Plutos. As Plutos form, they stir leftover planetesimals to large velocities. A cascade of collisions then grinds the leftovers to dust, forming an observable debris disk. In disks with small (≲1-10km) planetesimals, collisional cascades produce luminous debris disks with maximum luminosity ∼ 10-2 times the stellar luminosity. Disks with larger planetesimals produce debris disks with maximum luminosity 5 × 10-4 (10km) to ∼ 5 × 10-5 (100km) times the stellar luminosity. Following peak luminosity, the evolution of the debris disk emission is roughly a power law, f α t -n with n ≈ 0.6-0.8. Observations of debris disks around A-type and G-type stars strongly favor models with small planetesimals. In these models, our predictions for the time evolution and detection frequency of debris disks agree with published observations. We suggest several critical observations that can test key features of our calculations. © 2010. The American Astronomical Society. All rights reserved. Source

Bromley B.C.,University of Utah | Kenyon S.J.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2011

We describe an updated version of our hybrid N-body-coagulation code for planet formation. In addition to the features of our 2006-2008 code, our treatment now includes algorithms for the one-dimensional evolution of the viscous disk, the accretion of small particles in planetary atmospheres, gas accretion onto massive cores, and theresponse of N-bodies to the gravitational potential of the gaseous disk and the swarm of planetesimals. To validate the N-body portion of the algorithm, we use a battery of tests in planetary dynamics. As a first application of the complete code, we consider the evolution of Pluto-mass planetesimals in a swarm of 0.1-1 cm pebbles. In a typical evolution time of 1-3 Myr, our calculations transform 0.01-0.1 M ⊙ disks of gas and dust into planetary systems containing super-Earths, Saturns, and Jupiters. Low-mass planets form more often than massive planets; disks with smaller α form more massive planets than disks with larger α. For Jupiter-mass planets, masses of solid cores are 10-100 M ⊕. © 2011. The American Astronomical Society. All rights reserved. Source

Schwartz D.A.,Smithsonian Astrophysical Observatory
Review of Scientific Instruments | Year: 2014

The Chandra X-ray Observatory is an orbiting x-ray telescope facility. It is one of the National Aeronautics and Space Administration's four "Great Observatories" that collectively have carried out astronomical observations covering the infrared through gamma-ray portion of the electromagnetic spectrum. Chandra is used by astronomers world-wide to acquire imaging and spectroscopic data over a nominal 0.1-10 keV (124-1.24 Å) range. We describe the three major parts of the observatory: the telescope, the spacecraft systems, and the science instruments. This article will emphasize features of the design and development driven by some of the experimental considerations unique to x-ray astronomy. We will update the on-orbit performance and present examples of the scientific highlights. © 2014 AIP Publishing LLC. Source

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