Astrophysics and Space Science

, Volume 308, Issue 1–4, pp 225–230 | Cite as

The trigonometric parallax of the neutron star Geminga

  • Jacqueline FahertyEmail author
  • Frederick M. Walter
  • Jay Anderson
Original Article


We obtained a series of four observations of the isolated neutron star Geminga over an 18 month period using the Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) on the Hubble Space Telescope in order to determine its trigonometric parallax. We find the parallax π=4.0±1.3 mas, corresponding to a distance to Geminga of 250 −62 +120  pc, a result 60% larger than the previously published value. The proper motion is 178.2±1.8 mas/year. In this paper, we describe the analysis techniques in detail since the amplitude of the parallactic shift is smaller than the camera’s pixel size. We fit each star in the images with an appropriate effective PSF and applied a distortion correction to generate stellar positions accurate to 0.01 pixels (∼0.5 mas). The 134 stars common to all images serve to establish a reference frame for alignment of the image series. Our observations were made around the times of maximum parallactic shift. We discuss the implications of this new distance measurement for the inferred radius of Geminga, and the neutron star equation of state.


Astrometry Geminga Parallax Neutron star 


95.10.Jk 97.60.Jd 


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Copyright information

© Springer Science+Business Media B.V. 2007

Authors and Affiliations

  • Jacqueline Faherty
    • 1
    Email author
  • Frederick M. Walter
    • 1
  • Jay Anderson
    • 2
  1. 1.Stony Brook UniversityStony BrookUSA
  2. 2.Rice UniversityHoustonUSA

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