The Distance to the Perseus Spiral Arm in the Milky Way

doi:10.1126/science.1120914

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Published Online December 8, 2005
Science DOI: 10.1126/science.1120914

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Submitted on October 3, 2005
Accepted on November 16, 2005

The Distance to the Perseus Spiral Arm in the Milky Way

Y. Xu ¹, M. J. Reid ², X. W. Zheng ³, K. M. Menten ⁴

¹ Department of Astronomy, Nanjing University, Nanjing 210093, China; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA; Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 20030, China.
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
³ Department of Astronomy, Nanjing University, Nanjing 210093, China; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.

We have measured the distance to the massive star-forming regionW3OH in the Perseus spiral arm of the Milky Way to be 1.95 ±0.04 kiloparsecs (5.86 x 10¹⁶ km). This distance was determinedby triangulation, with the Earth's orbit as one segment of atriangle, using the Very Long Baseline Array. This resolvesa long-standing problem of a factor of two discrepancy betweendifferent techniques to determine distances. The reason forthe discrepancy is that this portion of the Perseus arm hasanomalous motions. The orientation of the anomalous motion agreeswith spiral density-wave theory, but the magnitude is somewhatlarger than most models predict.

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