Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite
(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 shortterm stability of the socalled 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 shortterm stability of the socalled 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.
(Less)
 author
 Butkevich, Alexey G.; Klioner, Sergei A.; Lindegren, Lennart ^{LU} ; Hobbs, David ^{LU} and van Leeuwen, Floor
 organization
 publishing date
 20170701
 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
 00046361
 DOI
 10.1051/00046361/201730781
 language
 English
 LU publication?
 yes
 id
 b284ed0cadba4e4a9d21f78e5d1f7950
 date added to LUP
 20170724 11:45:39
 date last changed
 20170918 11:39:07
@article{b284ed0cadba4e4a9d21f78e5d1f7950, abstract = {<p>Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the shortterm stability of the socalled 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 = {00046361}, 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/10.1051/00046361/201730781}, volume = {603}, year = {2017}, }