The UK Infrared Telescope M33 monitoring project. IV. Variable red giant stars across the galactic disc

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. In this fourth paper of the series, we present a search for variable red giant stars in an almost square degree region comprising most of the galaxy's disc, carried out with the WFCAM instrument in the K band. These data, taken during the period 2005--2007, were complemented by J- and H-band images. Photometry was obtained for 403 734 stars in this region; of these, 4643 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. The variable stars are concentrated towards the centre of M33, more so than low-mass, less-evolved red giants. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. 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. The photometric catalogue is made publicly available at the Centre de Donnees astronomiques de Strasbourg.

Accepted for publication in MNRAS

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• An Infrared Census Of Dust In Nearby Galaxies With Spitzer (DUSTiNGS): V. The Period-luminosity Relation For Dusty Metal-Poor AGB Stars
• The M33 Synoptic Stellar Survey. II. Mira Variables
• The Isaac Newton Telescope monitoring survey of Local Group dwarf galaxies. I. Survey overview and first results for Andromeda I
• The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies. VI. The Star Formation History and Dust Production in Andromeda IX
• Massive young stellar objects in the Local Group spiral galaxy M33 identified using machine learning
• Infrared variable stars in the compact elliptical galaxy M32
• Monitoring pulsating giant stars in M33: star formation history and chemical enrichment