The Proper Motion of the Magellanic Clouds: The UCAC2-Hipparcos Inconsistency

Abstract

Using the USNO CCD Astrograph all-sky Catalog (UCAC2), we measure the mean proper motion of the two Magellanic Clouds. Appropriately selected LMC populations show a proper motion (<μRA>, <μDEC>) ~ (+0.84,+4.32) that is significantly higher, in <μDEC>, than currently accepted Hipparcos-like values, <μRA>, <μDEC> ~ (+1.94,-0.14). A higher <μRA> value is also found for the SMC. Interestingly, the mean UCAC2 LMC proper motion agrees very well with the only work in the literature (Anguita et al. 2000) pointing to an unbound Magellanic Clouds-Milky Way interaction. Nonetheless, the implications of the UCAC2 proper motion are hard to reconcile with our present day understanding of the Clouds-Galaxy interaction unless one assumes a more massive Milky Way. Consequently, although no sources of systematic error have been identified, it is perhaps most likely that the UCAC2 catalog has an as yet unidentified systematic error resulting in an inconsistency between UCAC2 and Hipparcos based results for the Magellanic Clouds.

arXiv commentResearch Note accepted for publication in A&A, 5 pages

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• Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest
• A Chandra/ACIS Study of 30 Doradus II. X-ray Point Sources in the Massive Star Cluster R136 and Beyond
• Proper Motion Study of the Magellanic Clouds using SPM material
• The Proper Motion of the Large Magellanic Cloud: A Reanalysis
• The orbital dynamics of the LMC and SMC about the Milky Way