A near-ultraviolet view of the inner region of M 31 with the large binocular telescope

¹ INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: giacomo.beccari@oabo.inaf.it
² INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy
³ INAF, Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
⁴ INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
⁵ Large Binocular Telescope Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721-0065, USA
⁶ INAF, Osservatorio Astronomico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Received: 3 August 2007
Accepted: 2 October 2007

Abstract

Aims.We present a 900 s, wide-field U image of the inner region of the Andromeda galaxy obtained during the commissioning of the blue channel of the Large Binocular Camera mounted on the prime focus of the Large Binocular Telescope.

Methods.Relative photometry and absolute astrometry of individual sources in the image was obtained along with morphological parameters aimed at discriminating between stars and extended sources, e.g. globular clusters.

Results.The image unveils the near-ultraviolet view of the inner ring of star formation recently discovered in the infrared by the Spitzer Space Telescope and shows in great detail the fine structure of the dust lanes associated with the galaxy inner spiral arms. The capabilities of the blue channel of the Large Binocular Camera at the Large Binocular Telescope (LBC-Blue) are probed by direct comparison with ultraviolet GALEX observations of the same region in M 31. We discovered 6 new candidate stellar clusters in this high-background region of M 31. We also recovered 62 bona-fide globulars and 62 previously known candidates from the Revised Bologna Catalogue of the M 31 globular clusters, and firmly established the extended nature of 19 of them.