Cool carbon stars in the halo

II. A study of 25 new objects

¹ Groupe d'Astrophysique, UMR 5024 CNRS, Case CC72, Place Bataillon, 34095 Montpellier Cedex 5, France e-mail: mauron@graal.univ-montp2.fr
² Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
³ 378433 Byurakan Astrophysical Observatory & Isaac Newton Institute of Chile, Armenian Branch, Ashtarak d-ct, Armenia

Received: 4 February 2005
Accepted: 29 March 2005

Abstract

We present new results from an ongoing survey of carbon-rich asymptotic giant (AGB) stars in the halo of our Galaxy. After selecting candidates primarily through their 2MASS colours, slit spectroscopy was achieved at the ESO NTT telescope. Twenty-one new AGB carbon stars were discovered, increasing the total of presently known similar AGB C stars to ~120. A further four were observed again in order to confirm their carbon-rich nature and measure radial velocities. Two main findings emerge from this work. First, we found a C star located at ≈130 kpc from the Sun and at . This distant star is remarkably close (5 kpc) to the principal plane of the Stream of the Sagittarius dwarf galaxy, and is likely to be a tracer of a distant poorly populated southern warp of the Stream. Such a warp is predicted by model simulations, but it passes ~45 kpc from that star. The second result is that, mainly in the North, several already known or newly discovered AGB carbon stars lie far, up to 60 kpc, from the mean plane of the Sagittarius Stream.