Multiple stellar populations in Magellanic Cloud clusters

II. Evidence also in the young NGC 1844?^{⋆,⋆⋆,⋆⋆⋆}

¹ Instituto de Astrofìsica de Canarias, 38200 La Laguna, Tenerife, Canary Islands, Spain
e-mail: milone@iac.es
² Department of Astrophysics, University of La Laguna, 38200 La Laguna, Tenerife, Canary Islands, Spain
³ Research School of Astronomy and Astrophysics, The Australian National University, Cotter Road, Weston, ACT 2611, Australia
⁴ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
e-mail: luigi.bedin@oapd.inaf.it
⁵ INAF – Osservatorio Astronomico di Collurania, via Mentore Maggini, 64100 Teramo, Italy
e-mail: cassisi@oa-teramo.inaf.it; pietrinferni@oa-teramo.inaf.it; buonanno@oa-teramo.inaf.it
⁶ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, Padova, 35122 Padova, Italy
e-mail: giampaolo.piotto@unipd.it
⁷ Space Telescope Science Institute, 3800 San Martin Drive, Baltimore, MD 21218, USA
e-mail: jayander@stsci.edu

Received: 15 October 2012
Accepted: 5 February 2013

Abstract

We used Hubble Space Telescope observations to study the young cluster NGC 1844 in the Large Magellanic Cloud (LMC). We estimated the fraction and the mass-ratio distribution of photometric binaries and report that the main sequence presents an intrinsic breadth which cannot be explained only in terms of photometric errors, and is unlikely because of differential reddening. We attempted different interpretations of this feature, including stellar rotation, binary stars, and the presence of multiple stellar populations of different ages, metallicity, helium, or C+N+O abundance. Although we have excluded age, helium, and C+N+O variations of being responsible for the main-sequence spread, none of the other interpretations is conclusive.