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A&A 483, L5-L8 (2008)
DOI: 10.1051/0004-6361:200809631
Letter
Resolving stellar populations outside the Local Group: MAD observations of UKS 2323-326
M. Gullieuszik1, L. Greggio1, E. V. Held1, A. Moretti1, C. Arcidiacono1, P. Bagnara1, A. Baruffolo1, E. Diolaiti2, R. Falomo1, J. Farinato1, M. Lombini2, R. Ragazzoni1, R. Brast3, R. Donaldson3, J. Kolb3, E. Marchetti3, and S. Tordo31 Osservatorio Astronomico di Padova, INAF, vicolo dell'Osservatorio 5, 35122 Padova, Italy
e-mail: marco.gullieuszik@oapd.inaf.it
2 Osservatorio Astronomico di Bologna, INAF, via Ranzani 1, 40127 Bologna, Italy
3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
(Received 22 February 2008 / Accepted 18 March 2008)
Abstract
Aims. We present a study aimed at deriving constraints on star formation
at intermediate ages from the evolved stellar populations in the
dwarf irregular galaxy UKS 2323-326. These observations were also
intended to demonstrate the scientific capabilities of the
multi-conjugated adaptive optics demonstrator (MAD) implemented at
the ESO Very Large Telescope as a test-bench of adaptive optics
(AO) techniques.
Methods. We perform accurate, deep photometry of the field using J and 
band AO images of the central region of the galaxy.
Results. The near-infrared (IR) colour-magnitude diagrams clearly show the
sequences of asymptotic giant branch (AGB) stars, red supergiants,
and red giant branch (RGB) stars down to ~1 mag below the RGB
tip. Optical-near-IR diagrams, obtained by combining our data with
Hubble Space Telescope observations, provide the best separation of stars in the
various evolutionary stages. The counts of AGB stars brighter than
the RGB tip allow us to estimate the star formation at intermediate
ages. Assuming a Salpeter initial mass function, we find that the
star formation episode at intermediate ages produced ~6 
of stars in the observed region.
Key words: galaxies: individual: UKS2323-326 -- galaxies: stellar content -- stars: AGB and post-AGB -- stars: carbon -- instrumentation: adaptive optics -- galaxies: individual: ugca438
© ESO 2008