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Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite

Butkevich, Alexey G.; Klioner, Sergei A.; Lindegren, Lennart LU ; Hobbs, David LU and van Leeuwen, Floor (2017) In Astronomy and Astrophysics 603.
Abstract

Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims. We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods. The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results. In... (More)

Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims. We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods. The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results. In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If these kinds of perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than Hipparcos. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.

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author
organization
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type
Contribution to journal
publication status
published
subject
keywords
Astrometry, Catalogs, Methods: Data analysis, Methods: Statistical, Parallaxes, Space vehicles: Instruments
in
Astronomy and Astrophysics
volume
603
publisher
EDP Sciences
external identifiers
  • scopus:85022214104
  • wos:000406619100139
ISSN
0004-6361
DOI
10.1051/0004-6361/201730781
language
English
LU publication?
yes
id
b284ed0c-adba-4e4a-9d21-f78e5d1f7950
date added to LUP
2017-07-24 11:45:39
date last changed
2017-09-18 11:39:07
@article{b284ed0c-adba-4e4a-9d21-f78e5d1f7950,
  abstract     = {<p>Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims. We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods. The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results. In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If these kinds of perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than Hipparcos. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.</p>},
  articleno    = {30781},
  author       = {Butkevich, Alexey G. and Klioner, Sergei A. and Lindegren, Lennart and Hobbs, David and van Leeuwen, Floor},
  issn         = {0004-6361},
  keyword      = {Astrometry,Catalogs,Methods: Data analysis,Methods: Statistical,Parallaxes,Space vehicles: Instruments},
  language     = {eng},
  month        = {07},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite},
  url          = {http://dx.doi.org/10.1051/0004-6361/201730781},
  volume       = {603},
  year         = {2017},
}