The UK Infrared Telescope M33 monitoring project. I. Variable red giant stars in the central square kiloparsec

Abstract

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive dataset was obtained in the K-band with the UIST instrument for the central 4'x 4' (1 square kpc) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18,398 stars in this region; of these, 812 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars, and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the variability survey and the photometric catalogue - which is made publicly available at the Centre de Donnees astronomiques de Strasbourg (CDS) - and discuss the properties of the variable stars. Most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey.

Accepted for publication in MNRAS

References in corpus (8)

• The M33 Metallicity Project: Resolving the Abundance Gradient Discrepancies in M33
• The metallicity gradient of M 33: chemical abundances of HII regions
• RR Lyrae Variables in M33. I. Evidence For a Field Halo Population
• Molecules and dust production in the Magellanic Clouds
• Deep CFHT Photometric Survey of the Entire M33 Galaxy I: Catalogue of 36000 Variable Point Sources
• The M33 Variable Star Population Revealed by Spitzer
• A spectral atlas of post-main-sequence stars in omega Centauri: kinematics, evolution, enrichment and interstellar medium
• Near-Infrared photometry of carbon stars in the Sagittarius dwarf irregular galaxy and DDO 210

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