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Trigonometric Parallaxes

William van Altena

Yale UniversityBasic Astrometric Methods

Yale University

July 18-22, 2005

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The Geometry

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More Geometry

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Yes, the Earth moves around the Sun!

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Parallactic motion in Ecliptic Coords

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The Parallactic Ellipse

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Parallax in RA and Dec

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Parallax in RA and Dec (cont.)

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Observational Techniques

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Maximum Parallax Factor

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Ecliptic Latitude Dependence

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Determination of π & µ

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Typical analysis “pipeline”

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Typical analysis “pipeline” (cont.)

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Solving for a single π

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Errors and weights

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Errors and weights (cont.)

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Errors and weights (cont.)

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Reference stars

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Atmospheric Refraction

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Effective wavelength of each star

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Refraction versus star color

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Correction to Absolute π

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Systematic errors

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External error sources

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Deriving external errors

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Parallax ProgramsCatalog Date #stars mas) Comments

YPC 1995 8112 ±15 mas Cat. of all π through 1995

USNO pg To 1992 ~1000 ±2.5 mas Photographic parallaxes

USNO ccd From ‘92 ~150 ±0.5 mas CCD parallaxes

Nstars & GB Current 100? ± 2 mas Southern π programs

Hipparcos 1997 105 ±1 mas First modern survey

HST FGS 1995-2010? 100? ±0.5 mas A few important stars

SIM 2016? 103 ±4 µas Critical targets & exoplanets

Gaia 2016? 109 ±10µas “Ultimate” modern survey

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References for Parallax Programs

Catalog Comments References

YPC Cat. of all π through 1995 van Altena, Lee & Hoffleit 1995

USNO pg Photographic parallaxes Dahn, Harrington, et al

USNO ccd CCD parallaxes Monet, Dahn, et al. AJ,103,638,1992

Nstars & GB Southern π programs Henry, Jao, Ianna, Costa, Mendez, …

Hipparcos First modern survey ESO

HST FGS A few important stars Benedict & HST FGS Team

SIM Critical targets & Exo-planets NASA/JPL

Gaia “Ultimate” modern survey ESO