Trigonometric Parallax

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Trigonometric Parallax

• Joe Eggen

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Overview

• The BASICS
• Past missions
• Current Future missions
• Recent results
• Summary

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Basic info

• Best for close objects
• Currently stars lt 500 pc
• Lowest rung on the distance ladder
• Important calibrator for other methods
• Old idea
• Used as evidence against heliocentric theory
• First successful application by Friedrich Bessel
  in 1838 on 61 Cygni

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Errors

• Small list of possible error sources
• Measurement of an AU (not likely)
• Accurate astrometry
• .
• Ex an accuracy of 0.001 at d 100 pc yeilds
  an error of 10 (Harwit p.54)

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Hipparcos

• ESA mission from 1989 to 1996
• Astrometry parallaxes for gt 1 million stars,
  and parallaxes for gt 100,000 stars to at 0.001
  resolution
• Observed 99 of all stars down to 11th mag
• Maximal precision of 0.001

http//www.rssd.esa.int/index.php?projectHIPPARCO
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Hipparcos
http//www.rssd.esa.int/index.php?projectHIPPARCO
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RECONS

• Census of all objects with a measured parallax of
  more than 100 milliarcseconds
• Current population of 352 objects (2007.4)
• 239 M stars
• 18 WD
• 8 planets
• 28 new objects since 2000

http//www.chara.gsu.edu/RECONS/
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Gaia

• ESA mission to be launched in 2011
• Planned observations of 1 billion stars down to
  20th magnitude
• Resolution of 20 micro-arcseconds
• Spectral photometric measurements of all
  objects

http//www.rssd.esa.int/index.php?projectGAIApag
eindex
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Recent Result Parallax of a Young Planetary
System

• System 2M1207A in TW Hydra cluster
• Consists of an M8 brown dwarf and L-type
  planetary companion
• Distance 58.8-0.7 pc
• Signs of spectral variability -gt young system (lt
  10 Myr)
• 2M1207Ab is self-luminous -gt first direct
  measurement of a distance to a planetary-mass
  object

Biller, B., Close, L. 2007, ApJ, 669 41
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Summary

• Trigonometric parallax is the most accurate
  method available for determining stellar
  distances
• Used to calibrate all other distance methods
• Shortest range due to technical limitations