The first 8–13 μm spectra of globular cluster red giants: circumstellar silicate dust grains in 47 Tucanae (NGC 104)

¹ Astrophysics Group, School of Physical & Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG, UK e-mail: jacco@astro.keele.ac.uk
² Department of Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA

Received: 15 November 2005
Accepted: 2 January 2006

Abstract

We present 8–13 μm spectra of eight red giants in the globular cluster 47 Tucanae (NGC 104), obtained at the European Southern Observatory 3.6 m telescope. These are the first mid-infrared spectra of metal-poor, low-mass stars. The spectrum of at least one of these, namely the extremely red, large-amplitude variable V1, shows direct evidence of circumstellar grains made of amorphous silicate.