Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: email@example.com
2 Initiative in Innovative Computing at Harvard University, 60 Oxford Street, 02138 Cambridge, MA, USA
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, 02138 Cambridge, MA, USA
4 Argelander Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
5 Department of Astronomy, University of Texas at Austin, 1 University Station C1400, 78712 Austin, TX, USA
6 Korea Astronomy and Space Science Institute, 61-1 Hwaam-dong, Yusung-gu, Daejeon 305-348, Korea
Accepted: 15 May 2008
Aims. To study the structure of nearby (<500 pc) dense starless and star-forming cores with the particular goal to identify and understand evolutionary trends in core properties, and to explore the nature of Very Low Luminosity Objects (≤0.1 ; VeLLOs).
Methods. Using the MAMBO bolometer array, we create maps unusually sensitive to faint (few mJy per beam) extended (≈5) thermal dust continuum emission at 1.2 mm wavelength. Complementary information on embedded stars is obtained from Spitzer, IRAS, and 2MASS.
Results. Our maps are very rich in structure, and we characterize extended emission features (“subcores”) and compact intensity peaks in our data separately to pay attention to this complexity. We derive, e.g., sizes, masses, and aspect ratios for the subcores, as well as column densities and related properties for the peaks. Combination with archival infrared data then enables the derivation of bolometric luminosities and temperatures, as well as envelope masses, for the young embedded stars.
Conclusions. Starless and star-forming cores occupy the same parameter space in many core properties; a picture of dense core evolution in which any dense core begins to actively form stars once it exceeds some fixed limit in, e.g., mass, density, or both, is inconsistent with our data. A concept of necessary conditions for star formation appears to provide a better description: dense cores fulfilling certain conditions can form stars, but they do not need to, respectively have not done so yet. Comparison of various evolutionary indicators for young stellar objects in our sample (e.g., bolometric temperatures) reveals inconsistencies between some of them, possibly suggesting a revision of some of these indicators. Finally, we challenge the notion that VeLLOs form in cores not expected to actively form stars, and we present a first systematic study revealing evidence for structural differences between starless and candidate VeLLO cores.
Key words: stars: formation / ISM: evolution / ISM: structure / ISM: dust, extinction / ISM: clouds
Figure 1, Tables 3–5 and Appendices A, B are only available in electronic form at http://www.aanda.org
© ESO, 2008