EDP Sciences
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Volume 437, Number 1, July I 2005
Page(s) 339 - 343
Section Celestial mechanics and astrometry
DOI http://dx.doi.org/10.1051/0004-6361:20052878

A&A 437, 339-343 (2005)
DOI: 10.1051/0004-6361:20052878

Research Note

The proper motion of the Magellanic Clouds: The UCAC2-Hipparcos inconsistency

Y. Momany1 and S. Zaggia2

1  Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
    e-mail: momany@pd.astro.it
2  INAF - Osservatrio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy

(Received 2 November 2004 / Accepted 28 March 2005 )

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 $\langle\mu\alpha,\mu\delta\rangle\simeq(+0.84,+4.32$) that is significantly higher, in $\langle\mu\delta\rangle$, than currently accepted Hipparcos-like values; $\langle\mu\alpha,\mu\delta\rangle\simeq(+1.94,-0.14)$. A higher $\langle\mu\alpha\rangle$ 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, AJ, 120, 845) 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.

Key words: astronomical data bases: miscellaneous -- astrometry -- galaxies: Magellanic Clouds -- galaxies: interactions

SIMBAD Objects in preparation

© ESO 2005