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Tim Kendall's Extreme Astrophysics

Constraints on companions to nearby stars by proper motion anomalies

28 Nov 2018, 15:39 UTC
Constraints on companions to nearby stars by proper motion anomalies
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Both the Hipparcos satellite in the 90s and the recent Gaia mission measured the absolute position of stars to an accuracy measured in micro-arcseconds, and they also observed stars more than once. From space, enough positional accuracy can be obtained to measure the apparent or proper motion of the star on the sky as it is observed over the duration of the mission. Relatively nearby and bright stars with quite large proper motions were observed by both Hipparcos and Gaia, yielding a timeline of around 25 years over which to additionally deduce the long-term proper motion vector of the star. The proper motion anomaly is any difference between the individual measurements and the long-term measurement. Any regular variation of the anomaly with time may be caused by the orbital motion of unseen companions. I do not generally call attention to papers which have not yet been refereed but I will make an exception for this recent preprint by Pierre Kervella et al. which has exploited this technique and data by measuring the proper motion anomalies of a sample of nearby objects to constrain the properties of any low-mass stellar, brown dwarf or giant exoplanet companions orbiting around them. While the ...

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