arXiv · 1809.10376
Multiple Star Systems in the Orion Nebula
Abstract
This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium Cluster with the recently comissioned GRAVITY instrument. We observe a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for $θ^1$ Ori B, $θ^2$ Ori B, and $θ^2$ Ori C. We determine a separation for the previously suspected companion of NU Ori. We confirm four companions for $θ^1$ Ori A, $θ^1$ Ori C, $θ^1$ Ori D, and $θ^2$ Ori A, all with substantially improved astrometry and photometric mass estimates. We refine the orbit of the eccentric high-mass binary $θ^1$ Ori C and we are able to derive a new orbit for $θ^1$ Ori D. We find a system mass of 21.7 $M_{\odot}$ and a period of $53$ days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about 2, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints towards a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We exclude collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.
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GRAVITY collaboration, Martina Karl, Oliver Pfuhl, Frank Eisenhauer, Reinhard Genzel, Rebekka Grellmann, Maryam Habibi, Roberto Abuter, Matteo Accardo, António Amorim, Narsireddy Anugu, Gerardo Ávila, Myriam Benisty, Jean-Philippe Berger, Nicolas Bland, Henri Bonnet, Pierre Bourget, Wolfgang Brandner, Roland Brast, Alexander Buron, Alessio Caratti o Garatti, Frédéric Chapron, Yann Clénet, Claude Collin, Vincent Coudé du Foresto, Willem-Jan de Wit, Tim de Zeeuw, Casey Deen, Françoise Delplancke-Ströbele, Roderick Dembet, Frédéric Derie, Jason Dexter, Gilles Duvert, Monica Ebert, Andreas Eckart, Michael Esselborn, Pierre Fédou, Gert Finger, Paulo Garcia, Cesar Enrique Garcia Dabo, Rebeca Garcia Lopez, Feng Gao, Éric Gandron, Stefan Gillessen, Frédéric Gonté, Paulo Gordo, Ulrich Grözinger, Patricia Guajardo, Sylvain Guieu, Pierre Haguenauer, Oliver Hans, Xavier Haubois, Marcus Haug, Frank Haußmann, Thomas Henning, Stefan Hippler, Matthew Horrobin, Armin Huber, Zoltan Hubert, Norbert Hubin, Christian A. Hummel, Gerd Jakob, Lieselotte Jochum, Laurent Jocou, Andreas Kaufer, Stefan Kellner, Sarah Kandrew, Lothar Kern, Pierre Kervella, Mario Kiekebusch, Ralf Klein, Rainer Köhler, Johan Kolb, Martin Kulas, Sylvestre Lacour, Vincent Lapeyrère, Bernard Lazareff, Jean-Baptiste Le Bouquin, Pierre Léna, Rainer Lenzen, Samuel Lévêque, Chien-Cheng Lin, Magdalena Lippa, Yves Magnard, Leander Mehrgan, Antoine Mérand, Thibaut Moulin, Eric Müller, Friedrich Müller, Udo Neumann, Sylvain Oberti, Thomas Ott, Laurent Pallanca, Johana Panduro, Luca Pasquini, Thibaut Paumard, Isabelle Percheron, Karine Perraut, Guy Perrin, Andreas Pflüger. 2018-09-27. Multiple Star Systems in the Orion Nebula. https://doi.org/10.1051/0004-6361%2F201833575
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