Journal
ASTRONOMY & ASTROPHYSICS
Volume 564, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201323191
Keywords
stars: formation; stars: massive; stars: pre-main sequence; ISM: clouds; ISM: individual objects: Orion A
Categories
Funding
- Spanish Ramon y Cajal fellowship program [RYC-2009-04497]
- European Space Astronomy Centre (ESAC)
- Spanish grant [AYA2010-21161-C02-02, AYA2012-38897-C02-01]
- Austrian Science Fund (FWF)
- National Science Foundation
- US Department of Energy Office of Science
- University of Arizona
- Brazilian Participation Group
- Brookhaven National Laboratory
- University of Cambridge
- University of Florida
- French Participation Group
- German Participation Group
- Instituto de Astrofisica de Canarias
- Michigan State/Notre Dame/JINA Participation Group
- Johns Hopkins University
- Lawrence Berkeley National Laboratory
- Max Planck Institute for Astrophysics
- New Mexico State University
- New York University
- Ohio State University
- Pennsylvania State University
- University of Portsmouth
- Princeton University
- Spanish Participation Group
- University of Tokyo
- University of Utah
- Vanderbilt University
- University of Virginia
- University of Washington
- Yale University
- National Aeronautics and Space Administration
- Canadian Space Agency
- Robert Martin Ayers Sciences Fund
- Alfred P. Sloan Foundation
- US Department of Energy
- Ministry of Education and Science (Spain)
- Science and Technology Facilities Council (UK)
- Higher Education Funding Council (England)
- National Center for Supercomputing Applications
- Kavli Institute for Cosmological Physics
- Financiadora de Estudos e Projetos
- Fundacao Carlos Chagas Filho de Amparo a Pesquisa
- Conselho Nacional de Desenvolvimento Cientifico e Tecnologico
- Ministerio da Ciencia e Tecnologia (Brazil)
- German Research Foundation
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Aims. Following the recent discovery of a large population of young stars in front of the Orion nebula, we carried out an observational campaign with the DECam wide-field camera covering approximate to 10 deg(2) centered on NGC 1980 to confirm, probe the extent of, and characterize this foreground population of pre-main-sequence stars. Methods. We used multiwavelength wide-field images and catalogs to identify potential foreground pre-main-sequence stars using a novel probabilistic technique based on a careful selection of colors and luminosities. Results. We confirm the presence of a large foreground population towards the Orion A cloud. This population contains several distinct subgroups, including NGC 1980 and NGC 1981, and stretches across several degrees in front of the Orion A cloud. By comparing the location of their sequence in various color-magnitude diagrams with other clusters, we found a distance and an age of 380 pc and 5 similar to 10 Myr, in good agreement with previous estimates. Our final sample includes 2123 candidate members and is complete from below the hydrogen-burning limit to about 0.3 M-circle dot, where the data start to be limited by saturation. Extrapolating the mass function to the high masses, we estimate a total number of approximate to 2600 members in the surveyed region. Conclusions. We confirm the presence of a rich, contiguous, and essentially coeval population of about 2600 foreground stars in front of the Orion A cloud, loosely clustered around NGC 1980, NGC 1981, and a new group in the foreground of the OMC-2/3. For the area of the cloud surveyed, this result implies that there are more young stars in the foreground population than young stars inside the cloud. Assuming a normal initial mass function, we estimate that between one to a few supernovae must have exploded in the foreground population in the past few million years, close to the surface of Orion A, which might be responsible, together with stellar winds, for the structure and star formation activity in these clouds. This long-overlooked foreground stellar population is of great significance, calling for a revision of the star formation history in this region of the Galaxy.
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