Letter to the Editor

Herschel observations of embedded protostellar clusters in the Rosette molecular cloud^*,**

¹ Laboratoire AIM, CEA/IRFU – CNRS/INSU – Université Paris Diderot, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France e-mail: martin.hennemann@cea.fr 

² Laboratoire d'Astrophysique de Bordeaux, CNRS/INSU – Université de Bordeaux, BP 89, 33271 Floirac Cedex, France 

³ Max-Planck-Institut für Astronomie, Königstuhl 17, Heidelberg, Germany 

⁴ National Research Council of Canada, Herzberg Institute of Astrophysics, University of Victoria, Department of Physics and Astronomy, Victoria, Canada 

⁵ Laboratoire d'Astrophysique de Marseille, CNRS/INSU – Université de Provence, 13388 Marseille Cedex 13, France 

⁶ IAS, Université Paris-Sud, 91435 Orsay, France 

⁷ NHSC/IPAC, California Institute of Technology, Pasadena, CA, USA 

⁸ CESR & UMR 5187 du CNRS/Université de Toulouse, BP 4346, 31028 Toulouse Cedex 4, France 

⁹ IRAM, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint-Martin-d'Hères, France

¹⁰ INAF-IFSI, Fosso del Cavaliere 100, 00133 Roma, Italy
¹¹ Cardiff University School of Physics and Astronomy, UK 

¹² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China

¹³ Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0NL, UK 

¹⁴ Herschel Science Centre, ESAC, ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain 

¹⁵ CITA & Dep. of Astronomy and Astrophysics, University of Toronto, Toronto, Canada 

¹⁶ Department of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, 10691 Stockholm, Sweden 

¹⁷ INAF-IASF, Sez. di Roma, via Fosso del Cavaliere 100, 00133 Roma, Italy 

¹⁸ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, EH9 3HJ, UK 

¹⁹ ESO, Karl Schwarzschild Str. 2, 85748 Garching, Germany 

²⁰ Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK

²¹ McMaster University, Hamilton, Canada 


Received: 31 March 2010
Accepted: 2 May 2010

Abstract

The Herschel OB young stellar objects survey (HOBYS) has observed the Rosette molecular cloud, providing an unprecedented view of its star formation activity. These new far-infrared data reveal a population of compact young stellar objects whose physical properties we aim to characterise. We compiled a sample of protostars and their spectral energy distributions that covers the near-infrared to submillimetre wavelength range. These were used to constrain key properties in the protostellar evolution, bolometric luminosity, and envelope mass and to build an evolutionary diagram. Several clusters are distinguished including the cloud centre, the embedded clusters in the vicinity of luminous infrared sources, and the interaction region. The analysed protostellar population in Rosette ranges from 0.1 to about 15  with luminosities between 1 and 150 , which extends the evolutionary diagram from low-mass protostars into the high-mass regime. Some sources lack counterparts at near- to mid-infrared wavelengths, indicating extreme youth. The central cluster and the Phelps & Lada 7 cluster appear less evolved than the remainder of the analysed protostellar population. For the central cluster, we find indications that about 25% of the protostars classified as Class I from near- to mid-infrared data are actually candidate Class 0 objects. As a showcase for protostellar evolution, we analysed four protostars of low- to intermediate-mass in a single dense core, and they represent different evolutionary stages from Class 0 to Class I. Their mid- to far-infrared spectral slopes flatten towards the Class I stage, and the 160 to 70 μm flux ratio is greatest for the presumed Class 0 source. This shows that the Herschel observations characterise the earliest stages of protostellar evolution in detail.