EDP Sciences
Free access
Volume 439, Number 2, August IV 2005
Page(s) L5 - L8
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500148

A&A 439, L5-L8 (2005)
DOI: 10.1051/0004-6361:200500148


Searching for merger debris in the Galactic halo: chemodynamical evidence based on local blue HB stars

M. Altmann1, M. Catelan2 and M. Zoccali2

1  Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Correo Central, Santiago, Chile
    e-mail: martin@das.uchile.cl
2  Pontificia Universidad Católica de Chile, Departamento de Astronomía y Astrofísica, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
    e-mail: [mcatelan;mzoccali]@astro.puc.cl

(Received 1 February 2005 / Accepted 26 June 2005)

We report on the discovery of a group of local A-type blue horizontal-branch (HBA) stars moving in a prograde, comet-like orbit with very similar kinematics and abundances. This serendipitously discovered group contains 5 or 6 local HBA stars venturing very close to the Galactic centre; their [Fe/H] is around -1.7, and they seem to present minimum scatter in at least Mg, Si, Ti, Fe, Al, and Cr abundances. This "Cometary Orbit Group" (COG) was found while we were testing a new method to detect the debris associated with the merger of smaller, specific protogalactic entities into our galaxy. The method is primarily intended to identify field HBA stars with similar kinematics and detailed, multi-species abundance patterns as seen among members of a surviving remnant (e.g., $\omega$ Centauri). Quite possibly, the COG is the remnant, on a highly decayed orbit, of a merging event that took place in the relatively remote past (i.e., at least one revolution ago).

Key words: astrometry -- stars: kinematics -- stars: horizontal branch -- Galaxy: halo -- Galaxy: structure

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© ESO 2005