OH Masers in U Herculis (HD 148206)

Minimum credit line: Image courtesy of NRAO/AUI and H.J. van Langevelde and W. Vlemmings(for details, see Image Use Policy).

About this Image

Circumstellar OH masers are found in the envelope around late type stars. The star itself is obscured by the shell. However, the most blue-shifted spot is thought to be amplified emission from the underlying star. This maser spot would then be a bright beacon, necessarily fixed on the stellar position. Using the maser we can thus trace the stellar trajectory. Using phase referenced VLBA observations of U Her we have obtained very accurate positions for the maser spots in a period of over 4 years. This allows us to determine proper motion and even parallax of the star. The pictures above show the motion of the most blue-shifted maser spot over this 4 year period. The proper motion can clearly be seen. We have also compared the positions of the spots with the optical position determined by the Hipparcos sattelite with unprecedented accuracy (U Her is still faintly visible in the optical). As predicted by the theory the position of the most blue-shifted maser spot matches the Hipparcos position to within 15 mas.

Investigator(s):  H.J. van Langevelde and W. Vlemmings

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Technical Data

    Telescope VLBA 
    Date of Observation 1999-00-00 
    Type of Observation Continuum Observations 
    Band L 
    Wavelength 20 cm 
    Frequency 1.4 GHz 
    Center of Image RA: 16:25:47.47, Dec: 18:53:32.90 (J2000)  

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