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Gaia reference frame amid quasar variability and proper motion patterns in the data

Bachchan, Rajesh Kumar LU ; Hobbs, David LU and Lindegren, Lennart LU (2016) In Astronomy & Astrophysics p.1-12
Abstract
Context. Gaia’s very accurate astrometric measurements will allow the optical realisation of the International Celestial Reference System to be improved by a few orders of magnitude. Several sets of quasars are used to define a kinematically stable non-rotating reference frame with the barycentre of the solar system as its origin. Gaia will also observe a large number of galaxies. Although they are not point-like, it may be possible to determine accurate positions and proper motions for some of their compact bright features. Aims. The optical stability of the quasars is critical, and we investigate how accurately the reference frame can be recovered. Various proper motion patterns are also present in the data, the best known is caused by... (More)
Context. Gaia’s very accurate astrometric measurements will allow the optical realisation of the International Celestial Reference System to be improved by a few orders of magnitude. Several sets of quasars are used to define a kinematically stable non-rotating reference frame with the barycentre of the solar system as its origin. Gaia will also observe a large number of galaxies. Although they are not point-like, it may be possible to determine accurate positions and proper motions for some of their compact bright features. Aims. The optical stability of the quasars is critical, and we investigate how accurately the reference frame can be recovered. Various proper motion patterns are also present in the data, the best known is caused by the acceleration of the solar system barycentre, presumably, towards the Galactic centre. We review some other less well-known effects that are not part of standard astrometric models.
Methods. We modelled quasars and galaxies using realistic sky distributions, magnitudes, and redshifts. Position variability was introduced using a Markov chain model. The reference frame was determined using the algorithm developed for the Gaia mission, which also determines the acceleration of the solar system. We also tested a method for measuring the velocity of the solar system barycentre in a cosmological frame.
Results. We simulated the recovery of the reference frame and the acceleration of the solar system and conclude that they are not significantly disturbed by quasar variability, which is statistically averaged. However, the effect of a non-uniform sky distribution of the quasars can result in a correlation between the parameters describing the spin components of the reference frame and the acceleration components, which degrades the solution. Our results suggest that an attempt should be made to astrometrically determine the redshift- dependent apparent drift of galaxies that is due to our velocity relative to the cosmic microwave background, which in principle could allow determining the Hubble parameter. (Less)
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author
organization
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type
Contribution to journal
publication status
published
in
Astronomy & Astrophysics
pages
12 pages
publisher
EDP Sciences
external identifiers
  • Scopus:84964867077
ISSN
0004-6361
language
English
LU publication?
yes
id
e9eadfb6-5915-4857-be30-0956382061eb
date added to LUP
2016-06-23 11:03:13
date last changed
2017-01-01 08:28:52
@article{e9eadfb6-5915-4857-be30-0956382061eb,
  abstract     = {Context. Gaia’s very accurate astrometric measurements will allow the optical realisation of the International Celestial Reference System to be improved by a few orders of magnitude. Several sets of quasars are used to define a kinematically stable non-rotating reference frame with the barycentre of the solar system as its origin. Gaia will also observe a large number of galaxies. Although they are not point-like, it may be possible to determine accurate positions and proper motions for some of their compact bright features. Aims. The optical stability of the quasars is critical, and we investigate how accurately the reference frame can be recovered. Various proper motion patterns are also present in the data, the best known is caused by the acceleration of the solar system barycentre, presumably, towards the Galactic centre. We review some other less well-known effects that are not part of standard astrometric models.<br/>Methods. We modelled quasars and galaxies using realistic sky distributions, magnitudes, and redshifts. Position variability was introduced using a Markov chain model. The reference frame was determined using the algorithm developed for the Gaia mission, which also determines the acceleration of the solar system. We also tested a method for measuring the velocity of the solar system barycentre in a cosmological frame.<br/>Results. We simulated the recovery of the reference frame and the acceleration of the solar system and conclude that they are not significantly disturbed by quasar variability, which is statistically averaged. However, the effect of a non-uniform sky distribution of the quasars can result in a correlation between the parameters describing the spin components of the reference frame and the acceleration components, which degrades the solution. Our results suggest that an attempt should be made to astrometrically determine the redshift- dependent apparent drift of galaxies that is due to our velocity relative to the cosmic microwave background, which in principle could allow determining the Hubble parameter.},
  articleno    = {A71},
  author       = {Bachchan, Rajesh Kumar and Hobbs, David and Lindegren, Lennart},
  issn         = {0004-6361},
  language     = {eng},
  month        = {04},
  pages        = {1--12},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Gaia reference frame amid quasar variability and proper motion patterns in the data},
  year         = {2016},
}