Abundance anomalies in hot horizontal branch stars of the galactic globular cluster NGC 1904

¹ Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy
² : Research School of Astronomy & Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia e-mail: damian@mso.anu.edu.au
³ : Dpt. Cassiopée, UMR 6202, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
⁴ Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy

Received: 15 December 2003
Accepted: 14 December 2004

Abstract

We present abundance measurements, based on high-resolution optical spectroscopic data obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on Kueyen (Very Large Telescope UT2), for ten stars in the extended blue horizontal branch of the Galactic globular cluster NGC 1904 (M79). In agreement with previous findings for other clusters, we obtain normal abundances for stars cooler than  K, and largely anomalous abundances for hotter stars: large He depletions, and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si and Ca are roughly normal, in the hot stars as well as in the cooler ones. This abundance pattern can be attributed to the onset of diffusion and to radiation pressure in the stable atmospheres of hot horizontal branch stars.