34 research outputs found
Gaia Science Operations Centre
Brief outline of Science Operations Centre activities for Gaia.Comment: 2 pages no figure
Implementing the Gaia Astrometric Global Iterative Solution (AGIS) in Java
This paper provides a description of the Java software framework which has
been constructed to run the Astrometric Global Iterative Solution for the Gaia
mission. This is the mathematical framework to provide the rigid reference
frame for Gaia observations from the Gaia data itself. This process makes Gaia
a self calibrated, and input catalogue independent, mission. The framework is
highly distributed typically running on a cluster of machines with a database
back end. All code is written in the Java language. We describe the overall
architecture and some of the details of the implementation.Comment: Accepted for Experimental Astronom
Using Java for distributed computing in the Gaia satellite data processing
In recent years Java has matured to a stable easy-to-use language with the
flexibility of an interpreter (for reflection etc.) but the performance and
type checking of a compiled language. When we started using Java for
astronomical applications around 1999 they were the first of their kind in
astronomy. Now a great deal of astronomy software is written in Java as are
many business applications.
We discuss the current environment and trends concerning the language and
present an actual example of scientific use of Java for high-performance
distributed computing: ESA's mission Gaia. The Gaia scanning satellite will
perform a galactic census of about 1000 million objects in our galaxy. The Gaia
community has chosen to write its processing software in Java. We explore the
manifold reasons for choosing Java for this large science collaboration.
Gaia processing is numerically complex but highly distributable, some parts
being embarrassingly parallel. We describe the Gaia processing architecture and
its realisation in Java. We delve into the astrometric solution which is the
most advanced and most complex part of the processing. The Gaia simulator is
also written in Java and is the most mature code in the system. This has been
successfully running since about 2005 on the supercomputer "Marenostrum" in
Barcelona. We relate experiences of using Java on a large shared machine.
Finally we discuss Java, including some of its problems, for scientific
computing.Comment: Experimental Astronomy, August 201
Gaia TGAS search for Large Magellanic Cloud runaway supergiant stars:Candidate hypervelocity star discovery, and the nature of R71
We search for runaway stars in the Large Magellanic Cloud (LMC) by computing
the space velocities of the visually brightest stars in the LMC that are
included in the Gaia TGAS proper motion catalog. We compare with predictions
from stellar dynamical models to obtain (peculiar) velocities relative to their
local stellar environment. Two of the 31 stars have unusually high proper
motions. Of the remaining 29 stars we find that most objects in this sample
have velocities in very good agreement with model predictions of a circularly
rotating disk model. Indeed the excellent fit to the model implies that the
TGAS uncertainty estimates are likely overestimated. The fastest outliers in
this subsample contain the LBV R71 and a few other well known emission line
objects though in no case do we derive velocities consistent with fast (~100
km/s) runaways. Our results imply that R 71 in particular has a moderate
deviation from the local stellar velocity field (40 km/s) lending support to
the proposition that this object cannot have evolved as a normal single star
since it lies too far from massive star forming complexes to have arrived at
its current position during its lifetime. Our findings therefore strengthen the
case for this LBV being the result of binary evolution. Of the two stars with
unusually high proper motions we find that one, the isolated B1.5 Ia+
supergiant Sk-67 2 (HIP 22237), is a candidate hypervelocity star, the TGAS
proper motion implying a very large peculiar transverse velocity (~360 km/s)
directed radially away from the LMC centre. If confirmed, for example by Gaia
Data Release 2, it would imply that this massive supergiant, on the periphery
of the LMC, is leaving the galaxy where it will explode as a supernova.Comment: 7 pages, 5 figures, revised versio
Astronomy and Computing: a New Journal for the Astronomical Computing Community
We introduce \emph{Astronomy and Computing}, a new journal for the growing
population of people working in the domain where astronomy overlaps with
computer science and information technology. The journal aims to provide a new
communication channel within that community, which is not well served by
current journals, and to help secure recognition of its true importance within
modern astronomy. In this inaugural editorial, we describe the rationale for
creating the journal, outline its scope and ambitions, and seek input from the
community in defining in detail how the journal should work towards its
high-level goals.Comment: 5 pages, no figures; editorial for first edition of journa