mdperrin on 27-Nov-2023 16:43:11 GMT about * alf Pic
The listed coordinates for the very bright and high proper motion star Alpha Pictoris have turned out to be incorrect by about 0.7 arcsec. Currently Hipparcos is used as the source for the listed ICRS coordinates; however the Hipparcos and Gaia values are discrepant by about 0.7" when propagated to the same epochs. We suggest updating to use the Gaia DR3 ICRS coordinates for this star.
JWST observations of Alpha Pictoris (used as a PSF calibrator for Beta Pictoris in program 1411) have confirmed that the Gaia astrometry is more correct. Specifically the observed positions of Alpha Pic in 2022 and 2023 appear consistent within ~0.15" with the Gaia astrometry propagated using the Hipparcos proper motion values, but are discrepant by ~0.7" relative to the Hipparcos astrometry similarly propagated. (Gaia does not yet report proper motions for this very bright star, so Hipparcos remains the best source for its proper motion.)
Those JWST observations will be published in papers by Rebollido et al. (submitted) and Kammerer et al. (in prep). Let me know if any further information or details would be helpful. Thanks for all your efforts at CDS!
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