70 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
Improving distances to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia
Starting in 2013, Gaia will deliver highly accurate astrometric data, which
eventually will supersede most other stellar catalogues in accuracy and
completeness. It is, however, lim- ited to observations from magnitude 6 to 20
and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall
Japanese astrometry satellite, will observe these bright stars, but with much
lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the
main source of accurate distances to bright nearby stars. We are investigating
how this might be improved by optimally combining data from all three missions
in a joint astrometric solu- tion. This would take advantage of the unique
features of each mission: the historic bright-star measurements of Hipparcos,
the updated bright-star observations of Nano-JASMINE, and the very accurate
reference frame of Gaia. The long temporal baseline between the missions pro-
vides additional benefits for the determination of proper motions and binary
detection, which indirectly improve the parallax determination further. We
present a quantitative analysis of the expected gains based on simulated data
for all three missions.Comment: Final draft for the proceedings of the IAU Symposium 289: Advancing
the physics of cosmic distances, held in Beijing, China, August 2012, eds.
Richard de Grijs and Giuseppe Bono, Cambridge Univ. Pres
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
Combining and comparing astrometric data from different epochs: A case study with Hipparcos and Nano-JASMINE
The Hipparcos mission (1989-1993) resulted in the first space-based stellar
catalogue including measurements of positions, parallaxes and annual proper
motions accurate to about one milli-arcsecond. More space astrometry missions
will follow in the near future. The ultra-small Japanese mission Nano-JASMINE
(launch in late 2013) will determine positions and annual proper motions with
some milli-arcsecond accuracy. In mid 2013 the next-generation ESA mission Gaia
will deliver some tens of micro-arcsecond accurate astrometric parameters.
Until the final Gaia catalogue is published in early 2020 the best way of
improving proper motion values is the combination of positions from different
missions separated by long time intervals. Rather than comparing positions from
separately reduced catalogues, we propose an optimal method to combine the
information from the different data sets by making a joint astrometric
solution. This allows to obtain good results even when each data set alone is
insufficient for an accurate reduction. We demonstrate our method by combining
Hipparcos and simulated Nano-JASMINE data in a joint solution. We show a
significant improvement over the conventional catalogue combination.Comment: 4 pages, 1 figure, 1 table; proceedings of ADASS XXI (Paris, 2011),
ASP Conference Serie
Joint astrometric solution of Hipparcos and Gaia: A recipe for the Hundred Thousand Proper Motions project
The first release of astrometric data from Gaia is expected in 2016. It will
contain the mean stellar positions and magnitudes from the first year of
observations. For more than 100 000 stars in common with the Hipparcos
Catalogue it will be possible to compute very accurate proper motions due to
the time difference of about 24 years between the two missions. This Hundred
Thousand Proper Motions (HTPM) project will be part of the first release. Our
aim is to investigate how early Gaia data can be optimally combined with
information from the Hipparcos Catalogue in order to provide the most accurate
and reliable results for HTPM. The Astrometric Global Iterative Solution (AGIS)
was developed to compute the astrometric core solution based on the Gaia
observations and will be used for all releases of astrometric data from Gaia.
We adapt AGIS to process Hipparcos data in addition to Gaia observations, and
use simulations to verify and study the joint solution method. For the HTPM
stars we predict proper motion accuracies between 14 and 134 muas/yr, depending
on stellar magnitude and amount of Gaia data available. Perspective effects
will be important for a significant number of HTPM stars, and in order to treat
these effects accurately we introduce a scaled model of kinematics. We define a
goodness-of-fit statistic which is sensitive to deviations from uniform space
motion, caused for example by binaries with periods of 10-50 years. HTPM will
significantly improve the proper motions of the Hipparcos Catalogue well before
highly accurate Gaia- only results become available. Also, HTPM will allow us
to detect long period binary and exoplanetary candidates which would be
impossible to detect from Gaia data alone. The full sensitivity will not be
reached with the first Gaia release but with subsequent data releases.
Therefore HTPM should be repeated when more Gaia data become available.Comment: Revised manuscript following referee report. Accepted for publication
in A&
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