Letter to the Editor

The Herschel view of star formation in the Rosette molecular cloud under the influence of NGC 2244^*,**

¹ Laboratoire AIM, CEA/DSM – INSU/CNRS – Université Paris Diderot, IRFU/SAp CEA-Saclay, 91191 Gif-sur-Yvette, France e-mail: nschneid@cea.fr
² Laboratoire d'Astrophysique de Bordeaux, CNRS/INSU – Université de Bordeaux, BP 89, 33271 Floirac Cedex, France
³ National Research Council of Canada, Herzberg Institute of Astrophysics, University of Victoria, Department of Physics and Astronomy, Victoria, Canada
⁴ Laboratoire d'Astrophysique de Marseille, CNRS/INSU – Université de Provence, 13388 Marseille Cedex 13, France
⁵ IAS, Université Paris-Sud, 91435 Orsay, France
⁶ CESR & UMR 5187 du CNRS/Université de Toulouse, BP 4346, 31028 Toulouse Cedex 4, France
⁷ IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d'Hères, France
⁸ INAF-IFSI, Fosso del Cavaliere 100, 00133 Roma, Italy
⁹ Cardiff University School of Physics and Astronomy, UK
¹⁰ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China

¹¹ Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot, Oxon OX11 0QX, UK
¹² Herschel Science Centre, ESAC, ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
¹³ CITA & Dep. of Astronomy and Astrophysics, University of Toronto, Toronto, Canada
¹⁴ Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, 10691 Stockholm, Sweden
¹⁵ INAF-IASF, Sez. di Roma, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁶ UPMC Université de Paris 06, UMR7095, IAP, 75014 Paris, France
¹⁷ Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, EH9 3HJ, UK
¹⁸ ESO, Karl Schwarzschild Str. 2, 85748, Garching, Germany
¹⁹ Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK
²⁰ Department of Physics and Astronomy, McMaster University, Hamilton, Canada
²¹ SUPA, Institute for Astronomy, Edinburgh University, Blackford Hill, Edinburgh EH9 3HJ, UK

Received: 31 March 2010
Accepted: 6 May 2010

Abstract

Context. The Rosette molecular cloud is promoted as the archetype of a triggered star-formation site. This is mainly due to its morphology, because the central OB cluster NGC 2244 has blown a circular-shaped cavity into the cloud and the expanding H II-region now interacts with the cloud.

Aims. Studying the spatial distribution of the different evolutionary states of all star-forming sites in Rosette and investigating possible gradients of the dust temperature will help to test the “triggered star-formation” scenario in Rosette.

Methods. We use continuum data obtained with the PACS (70 and 160 μm) and SPIRE instruments (250, 350, 500 μm) of the Herschel telescope during the science demonstration phase of HOBYS.

Results. Three-color images of Rosette impressively show how the molecular gas is heated by the radiative impact of the NGC 2244 cluster. A clear negative temperature gradient and a positive density gradient (running from the H II-region/molecular cloud interface into the cloud) are detected. Studying the spatial distribution of the most massive dense cores (size scale 0.05 to 0.3 pc), we find an age-sequence (from more evolved to younger) with increasing distance to the cluster NGC 2244. No clear gradient is found for the clump (size-scale up to 1 pc) distribution.

Conclusions. The existence of temperature and density gradients and the observed age-sequence imply that star formation in Rosette may indeed be influenced by the radiative impact of the central NGC 2244 cluster. A more complete overview of the prestellar and protostellar population in Rosette is required to obtain a firmer result.