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Astrophysical validation of Gaia parallaxes

Windmark, Fredrik LU (2010) In Lund Observatory Examensarbeten ASTM31 20101
Lund Observatory - Undergoing reorganization
Abstract
The Gaia satellite, to be launched in August 2012, will measure highly accurate absolute parallaxes of hundreds of millions of stars. This is done by comparing parallactic displacement of stars in different parts of the sky. The accuracy of this method highly depends on the stability of the so-called basic angle between the two
fields of view of the Gaia instrument, and periodic variations could lead to a global zero-point error in the measured parallaxes. Small variations of the basic angle are closely monitored by on-board instruments, but independent verification methods are also needed.
In this project, we use Galactic Cepheid variables as standard candles to compare with the observed parallaxes at a wide range of distances. If there... (More)
The Gaia satellite, to be launched in August 2012, will measure highly accurate absolute parallaxes of hundreds of millions of stars. This is done by comparing parallactic displacement of stars in different parts of the sky. The accuracy of this method highly depends on the stability of the so-called basic angle between the two
fields of view of the Gaia instrument, and periodic variations could lead to a global zero-point error in the measured parallaxes. Small variations of the basic angle are closely monitored by on-board instruments, but independent verification methods are also needed.
In this project, we use Galactic Cepheid variables as standard candles to compare with the observed parallaxes at a wide range of distances. If there is a parallax zero-point error, the observed parallaxes will not be consistent with a single Period-Luminosity relation. A model is formulated where the complete Galactic Cepheid
population is generated and observed in a simulated Gaia mission. Using the observed Cepheids, we then make simultaneous fits to the P-L relation and the parallax zero-point in order to determine whether using Cepheids is a viable zero-point verification method.
Our simulations show that Gaia will observe about 9000 Galactic Cepheids, fifteen times the currently known number. Gaia will alone result in large improvements in the accuracy with which the Galactic P-L relation can be determined. Both constants in the relation can be determined with an accuracy of omega a,b < 0.05. We show that using Galactic Cepheids, the parallax zero-point can be determined with an
accuracy of omega c = 0.3 myas, with the largest error contribution coming from the uncertainty with which we can determine the extinction. This is very good, but not enough for the most demanding tasks of Gaia. We conclude that the global verification of the parallax zero-point ultimately will depend on a combination of many
different methods. (Less)
Please use this url to cite or link to this publication:
author
Windmark, Fredrik LU
supervisor
organization
course
ASTM31 20101
year
type
H2 - Master's Degree (Two Years)
subject
publication/series
Lund Observatory Examensarbeten
report number
2010-EXA39
language
English
id
2256295
date added to LUP
2011-12-21 11:21:35
date last changed
2011-12-21 11:21:35
@misc{2256295,
  abstract     = {{The Gaia satellite, to be launched in August 2012, will measure highly accurate absolute parallaxes of hundreds of millions of stars. This is done by comparing parallactic displacement of stars in different parts of the sky. The accuracy of this method highly depends on the stability of the so-called basic angle between the two
fields of view of the Gaia instrument, and periodic variations could lead to a global zero-point error in the measured parallaxes. Small variations of the basic angle are closely monitored by on-board instruments, but independent verification methods are also needed.
In this project, we use Galactic Cepheid variables as standard candles to compare with the observed parallaxes at a wide range of distances. If there is a parallax zero-point error, the observed parallaxes will not be consistent with a single Period-Luminosity relation. A model is formulated where the complete Galactic Cepheid
population is generated and observed in a simulated Gaia mission. Using the observed Cepheids, we then make simultaneous fits to the P-L relation and the parallax zero-point in order to determine whether using Cepheids is a viable zero-point verification method.
Our simulations show that Gaia will observe about 9000 Galactic Cepheids, fifteen times the currently known number. Gaia will alone result in large improvements in the accuracy with which the Galactic P-L relation can be determined. Both constants in the relation can be determined with an accuracy of omega a,b < 0.05. We show that using Galactic Cepheids, the parallax zero-point can be determined with an
accuracy of omega c = 0.3 myas, with the largest error contribution coming from the uncertainty with which we can determine the extinction. This is very good, but not enough for the most demanding tasks of Gaia. We conclude that the global verification of the parallax zero-point ultimately will depend on a combination of many
different methods.}},
  author       = {{Windmark, Fredrik}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Lund Observatory Examensarbeten}},
  title        = {{Astrophysical validation of Gaia parallaxes}},
  year         = {{2010}},
}