arXiv subjects

Roy Williams

Publications and source records attributed to Roy Williams.

18 recordsLinked to original sources

arXiv2016

Astronomical Catalogs for Locating Gravitational-wave Events

Gravitational wave transients are caused by some of the most energetic events in the Universe, and a precise location would allow deep examination of the counterpart by electromagnetic waves (telescopes collecting light), the combination of GW and EM resulting in very much improved science return (multi-messenger Astronomy). Since the GW detectors do not provide good localization on the sky, the faint counterpart will be very difficult to find. One strategy to help the search is to look first where mass is concentrated and thus the prior probability of GW events is highest. In the first part of this paper, we present methods used to estimate stellar masses and metallicities of galaxies and galaxy clusters in different catalogs. In the second part of the paper, we test our estimation accuracy by comparing our results with stellar masses given in Stripe 82 Massive Galaxy Catalogue (S82-MGC). The relation between stellar mass we found and that from S82-MGC is provided for GWGC, 2MASS-GLADE, and WISExSCOS catalog in the last part of the paper. Our results are used in an interactive web-based tool (Skymap Viewer) for astronomers to decide where to look first in EM follow-up observations of GW events in the future.

astro-ph.GA↗

arXiv2016

IVOA Identifiers Version 2.0

An IVOA Identifier is a globally unique name for a resource within the Virtual Observatory. This name can be used to retrieve a unique description of the resource from an IVOA-compliant registry or to identify an entity like a dataset or a protocol without dereferencing the identifier. This document describes the syntax for IVOA Identifiers as well as how they are created. The syntax has been defined to encourage global-uniqueness naturally and to maximize the freedom of resource providers to control the character content of an identifier.

astro-ph.IM↗

arXiv2014

The LIGO Open Science Center

The LIGO Open Science Center (LOSC) fulfills LIGO's commitment to release, archive, and serve LIGO data in a broadly accessible way to the scientific community and to the public, and to provide the information and tools necessary to understand and use the data. In August 2014, the LOSC published the full dataset from Initial LIGO's "S5" run at design sensitivity, the first such large-scale release and a valuable testbed to explore the use of LIGO data by non-LIGO researchers and by the public, and to help teach gravitational-wave data analysis to students across the world. In addition to serving the S5 data, the LOSC web portal (losc.ligo.org) now offers documentation, data-location and data-quality queries, tutorials and example code, and more. We review the mission and plans of the LOSC, focusing on the S5 data release.

gr-qc↗

arXiv2012

Astronomy with Cutting-Edge ICT: From Transients in the Sky to Data over the Continents (India-US)

Astronomy has always been at the forefront of information technology, moving from the era of photographic plates, to digital snapshots and now to digital movies of the sky. This has brought about a data explosion with multi- terabyte surveys already happening and upcoming petabyte scale surveys. By scanning the sky repeatedly and automatically, astronomers find rapidly changing phenomena - transients - of a great variety. Surveys like the Catalina Real-time Transient Survey (CRTS) publish details on the transients right away since many of these fade in a matter of minutes and it is important to get additional observations in order to determine their nature. This involves being able to combine a variety of datasets, small and large, in real-time. With networks like the Asia Pacific Advanced Network (APAN) and India's National Knowledge Network (NKN) we are in the realm where such a data transfer is possible in real time across continents. Here we describe the live demonstration we were able to carry out at data transfer speeds of several hundred megabits per second (Mbps) between California Institute of Technology (Caltech, USA) and the Inter-University Centre for Astronomy and Astrophysics (IUCAA, India). This project illustrates how machines can make rapid decisions in response to complex, heterogeneous data, using sophisticated software and networking. While the broader impact covers all aspects of society (disaster response, power grids, earthquakes, and many more), we have used astronomy to show how the APAN and NKN make this possible.

astro-ph.IM↗

arXiv2012

Using the VO to Study the Time Domain

Just as the astronomical "Time Domain" is a catch-phrase for a diverse group of different science objectives involving time-varying phenomena in all astrophysical regimes from the solar system to cosmological scales, so the "Virtual Observatory" is a complex set of community-wide activities from archives to astroinformatics. This workshop touched on some aspects of adapting and developing those semantic and network technologies in order to address transient and time-domain research challenges. It discussed the VOEvent format for representing alerts and reports on celestial transient events, the SkyAlert and ATELstream facilities for distributing these alerts, and the IVOA time-series protocol and time-series tools provided by the VAO. Those tools and infrastructure are available today to address the real-world needs of astronomers.

astro-ph.IM↗

arXiv2011

The VAO Transient Facility

The time domain community wants robust and reliable tools to enable production of and subscription to community-endorsed event notification packets (VOEvent). The VAO Transient Facility (VTF) is being designed to be the premier brokering service for the community, both collecting and disseminating observations about time-critical astronomical transients but also supporting annotations and the application of intelligent machine-learning to those observations. This distinguishes two types of activity associated with the facility: core infrastructure and user services. In this paper, we will review the prior art in both areas and describe the planned capabilities of the VTF. In particular, we will focus on scalability and quality-of-service issues required by the next generation of sky surveys, such as LSST and SKA.

astro-ph.IM↗

arXiv2011

Gravitational Waves and Time Domain Astronomy

The gravitational wave window onto the universe will open in roughly five years, when Advanced LIGO and Virgo achieve the first detections of high frequency gravitational waves, most likely coming from compact binary mergers. Electromagnetic follow-up of these triggers, using radio, optical, and high energy telescopes, promises exciting opportunities in multi-messenger time domain astronomy. In the next decade, space-based observations of low frequency gravitational waves from massive black hole mergers, and their electromagnetic counterparts, will open up further vistas for discovery. This two-part workshop at featured brief presentations and stimulating discussions on the challenges and opportunities presented by gravitational wave astronomy. Highlights from the workshop, with the emphasis on strategies for electromagnetic follow-up, are presented in this report.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: An IVOA Standard for Unified Content Descriptors Version 1.1

This document describes the current understanding of the IVOA controlled vocabulary for describing astronomical data quantities, called Unified Content Descriptors (UCDs). The present document defines a new standard (named UCD1+) improving the first generation of UCDs (hereafter UCD1). The basic idea is to adopt a new syntax and vocabulary requiring little effort for people to adapt softwares already using UCD1. This document also addresses the questions of maintenance and evolution of the UCD1+. Examples of use cases within the VO, and tools for using UCD1+ are also described.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: Maintenance of the list of UCD words Version 1.20

According to what is stated in the IVOA Recommendation "An IVOA standard for Unified Content Descriptors", a procedural document should be created in order to maintain (add, change, suppress words) the standard list of UCD1+ words "The UCD1+ Controlled Vocabulary". This document describes the procedure to maintain the standard list of UCD1+ words.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: IVOA Identifiers Version 1.12

An IVOA Identifier is a globally unique name for a resource. This name can be used to retrieve a unique description of the resource from an IVOA-compliant registry. This document describes the syntax for IVOA identifiers as well as how they are created. An IVOA identifier has two separable components that can appear in two equivalent formats: an XML-tagged form and a URI-compliant form. The syntax has been defined to encourage global-uniqueness naturally and to maximize the freedom of resource providers to control the character content of an identifier.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: The UCD1+ controlled vocabulary Version 1.23

This document describes the list of controlled terms used to build the Unified Content Descriptors, Version 1+ (UCD1+). The document describing the UCD1+ can be found at the URL: http://www.ivoa.net/Documents/latest/UCD.html. This document reviews the structure of the UCD1+ and presents the current vocabulary.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: Simple Cone Search Version 1.03

This specification defines a simple query protocol for retrieving records from a catalog of astronomical sources. The query describes sky position and an angular distance, defining a cone on the sky. The response returns a list of astronomical sources from the catalog whose positions lie within the cone, formatted as a VOTable. This version of the specification is essentially a transcription of the original Cone Search specification in order to move it into the IVOA standardization process.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: VOTable Format Definition Version 1.3

This document describes the structures making up the VOTable standard. The main part of this document describes the adopted part of the VOTable standard; it is followed by appendices presenting extensions which have been proposed and/or discussed, but which are not part of the standard.

astro-ph.IM↗

arXiv2011

IVOA Recommendation: Sky Event Reporting Metadata Version 2.0

VOEvent defines the content and meaning of a standard information packet for representing, transmitting, publishing and archiving information about a transient celestial event, with the implication that timely follow-up is of interest. The objective is to motivate the observation of targets-of-opportunity, to drive robotic telescopes, to trigger archive searches, and to alert the community. VOEvent is focused on the reporting of photon events, but events mediated by disparate phenomena such as neutrinos, gravitational waves, and solar or atmospheric particle bursts may also be reported. Structured data is used, rather than natural language, so that automated systems can effectively interpret VOEvent packets. Each packet may contain zero or more of the "who, what, where, when & how" of a detected event, but in addition, may contain a hypothesis (a "why") regarding the nature of the underlying physical cause of the event. Citations to previous VOEvents may be used to place each event in its correct context. Proper curation is encouraged throughout each event's life cycle from discovery through successive follow-ups. VOEvent packets gain persistent identifiers and are typically stored in databases reached via registries. VOEvent packets may therefore reference other packets in various ways. Packets are encouraged to be small and to be processed quickly. This standard does not define a transport layer or the design of clients, repositories, publishers or brokers; it does not cover policy issues such as who can publish, who can build a registry of events, who can subscribe to a particular registry, nor the intellectual property issues.

astro-ph.IM↗

arXiv2010

Montage: a grid portal and software toolkit for science-grade astronomical image mosaicking

Montage is a portable software toolkit for constructing custom, science-grade mosaics by composing multiple astronomical images. The mosaics constructed by Montage preserve the astrometry (position) and photometry (intensity) of the sources in the input images. The mosaic to be constructed is specified by the user in terms of a set of parameters, including dataset and wavelength to be used, location and size on the sky, coordinate system and projection, and spatial sampling rate. Many astronomical datasets are massive, and are stored in distributed archives that are, in most cases, remote with respect to the available computational resources. Montage can be run on both single- and multi-processor computers, including clusters and grids. Standard grid tools are used to run Montage in the case where the data or computers used to construct a mosaic are located remotely on the Internet. This paper describes the architecture, algorithms, and usage of Montage as both a software toolkit and as a grid portal. Timing results are provided to show how Montage performance scales with number of processors on a cluster computer. In addition, we compare the performance of two methods of running Montage in parallel on a grid.

astro-ph.IM↗

arXiv2009

Highly Variable Objects in the Palomar-QUEST Survey: A Blazar Search using Optical Variability

We identify 3,113 highly variable objects in 7,200 square degrees of the Palomar-QUEST Survey, which each varied by more than 0.4 magnitudes simultaneously in two broadband optical filters on timescales from hours to roughly 3.5 years. The primary goal of the selection is to find blazars by their well-known violent optical variability. Because most known blazars have been found in radio and/or X-ray wavelengths, a sample discovered through optical variability may have very different selection effects, elucidating the range of behavior possible in these systems. A set of blazars selected in this unusual manner will improve our understanding of the physics behind this extremely variable and diverse class of AGN. The object positions, variability statistics, and color information are available using the Palomar-QUEST CasJobs server. The time domain is just beginning to be explored over large sky areas; we do not know exactly what a violently variable sample will hold. About 20% of the sample has been classified in the literature; over 70% of those objects are known or likely AGN. The remainder largely consists of a variety of variable stars, including a number of RR Lyrae and cataclysmic variables.

astro-ph.CO↗

arXiv2004

Grist: Grid-based Data Mining for Astronomy

The Grist project (http://grist.caltech.edu/) is developing a grid-technology based system as a research environment for astronomy with massive and complex datasets. This knowledge extraction system will consist of a library of distributed grid services controlled by a workflow system, compliant with standards emerging from the grid computing, web services, and virtual observatory communities. This new technology is being used to find high redshift quasars, study peculiar variable objects, search for transients in real time, and fit SDSS QSO spectra to measure black hole masses. Grist services are also a component of the ``hyperatlas'' project to serve high-resolution multi-wavelength imagery over the Internet. In support of these science and outreach objectives, the Grist framework will provide the enabling fabric to tie together distributed grid services in the areas of data access, federation, mining, subsetting, source extraction, image mosaicking, statistics, and visualization.

astro-ph↗

arXiv2004

Palomar-QUEST: A case study in designing sky surveys in the VO era

The advent of wide-area multicolour synoptic sky surveys is leading to data sets unprecedented in size, complexity and data throughput. VO technology offers a way to exploit these to the full but requires changes in design philosophy. The Palomar-QUEST survey is a major new survey being undertaken by Caltech, Yale, JPL and Indiana University to repeatedly observe 1/3 of the sky (~15000 sq. deg. between -27 < Dec <27 in seven passbands. Utilising the 48-inch Oschin Schmidt Telescope at the Palomar Observatory with the 112-CCD QUEST camera covering the full 4 x 4 sq. deg. field of view, it will generate \~1TB of data per month. In this paper, we review the design of QUEST as a VO resource, a federated data set and an exemplar of VO standards.

astro-ph↗