Multiple Star Systems in the Orion Nebula
Creators: name: GRAVITY Collaboration
name: Karl, Martina
name: Pfuhl, Oliver
name: Eisenhauer, Frank
name: Genzel, Reinhard
name: Grellmann, Rebekka
name: Habibi, Maryam
name: Abuter, Roberto
name: Accardo, Matteo
name: Amorim, António
name: Anugu, Narsireddy
name: Ávila, Gerardo
name: Benisty, Myriam
name: Berger, Jean-Philippe
name: Bland, Nicolas
name: Bonnet, Henri
name: Bourget, Pierre
name: Brandner, Wolfgang
name: Brast, Roland
name: Buron, Alexander
name: Garatti, Alessio Caratti o
name: Chapron, Frédéric
name: Clénet, Yann
name: Collin, Claude
name: Foresto, Vincent Coudé du
name: de Wit, Willem-Jan
name: de Zeeuw, Tim
name: Deen, Casey
name: Delplancke-Ströbele, Françoise
name: Dembet, Roderick
name: Derie, Frédéric
name: Dexter, Jason
name: Duvert, Gilles
name: Ebert, Monica
name: Eckart, Andreas
name: Esselborn, Michael
name: Fédou, Pierre
name: Finger, Gert
name: Garcia, Paulo
name: Dabo, Cesar Enrique Garcia
name: Lopez, Rebeca Garcia
name: Gao, Feng
name: Gandron, Éric
name: Gillessen, Stefan
name: Gonté, Frédéric
name: Gordo, Paulo
name: Grözinger, Ulrich
name: Guajardo, Patricia
name: Guieu, Sylvain
name: Haguenauer, Pierre
name: Hans, Oliver
name: Haubois, Xavier
name: Haug, Marcus
name: Haußmann, Frank
name: Henning, Thomas
name: Hippler, Stefan
name: Horrobin, Matthew
name: Huber, Armin
name: Hubert, Zoltan
name: Hubin, Norbert
name: Hummel, Christian A.
name: Jakob, Gerd
name: Jochum, Lieselotte
name: Jocou, Laurent
name: Kaufer, Andreas
name: Kellner, Stefan
name: Kandrew, Sarah
name: Kern, Lothar
name: Kervella, Pierre
name: Kiekebusch, Mario
name: Klein, Ralf
name: Köhler, Rainer
name: Kolb, Johan
name: Kulas, Martin
name: Lacour, Sylvestre
name: Lapeyrère, Vincent
name: Lazareff, Bernard
name: Bouquin, Jean-Baptiste Le
name: Léna, Pierre
name: Lenzen, Rainer
name: Lévêque, Samuel
name: Lin, Chien-Cheng
name: Lippa, Magdalena
name: Magnard, Yves
name: Mehrgan, Leander
name: Mérand, Antoine
name: Moulin, Thibaut
name: Müller, Eric
name: Müller, Friedrich
name: Neumann, Udo
name: Oberti, Sylvain
name: Ott, Thomas
name: Pallanca, Laurent
name: Panduro, Johana
name: Pasquini, Luca
name: Paumard, Thibaut
name: Percheron, Isabelle
name: Perraut, Karine
name: Perrin, Guy
name: Pflüger, Andreas
name: Duc, Thanh Phan
name: Plewa, Philipp M.
name: Popovic, Dan
name: Rabien, Sebastian
name: Ramírez, Andrés
name: Ramos, Jose
name: Rau, Christian
name: Riquelme, Miguel
name: Rodríguez-Coira, Gustavo
name: Rohloff, Ralf-Rainer
name: Rosales, Alejandra
name: Rousset, Gérard
name: Sanchez-Bermudez, Joel
name: Scheithauer, Silvia
name: Schöller, Markus
name: Schuhler, Nicolas
name: Spyromilio, Jason
name: Straub, Odele
name: Straubmeier, Christian
name: Sturm, Eckhard
name: Suarez, Marcos
name: Tristram, Konrad R. W.
name: Ventura, Noel
name: Vincent, Frédéric
name: Waisberg, Idel
name: Wank, Imke
name: Widmann, Felix
name: Wieprecht, Ekkehard
name: Wiest, Michael
name: Wiezorrek, Erich
name: Wittkowski, Markus
name: Woillez, Julien
name: Wolff, Burkhard
name: Yazici, Senol
name: Ziegler, Denis
name: Zins, Gérard
Publisher: name: arXiv
Year: 2018
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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.
description: Accepted for publication in A&amp;A