title: The formation of a quadruple star system with wide separation.
abstract: The initial multiplicity of stellar systems is highly uncertain. A number of mechanisms have been proposed to explain the origin of binary and multiple star systems, including core fragmentation, disk fragmentation and stellar capture. Observations show that protostellar and pre-main-sequence multiplicity is higher than the multiplicity found in field stars, which suggests that dynamical interactions occur early, splitting up multiple systems and modifying the initial stellar separations. Without direct, high-resolution observations of forming systems, however, it is difficult to determine the true initial multiplicity and the dominant binary formation mechanism. Here we report observations of a wide-separation (greater than 1,000 astronomical units) quadruple system composed of a young protostar and three gravitationally bound dense gas condensations. These condensations are the result of fragmentation of dense gas filaments, and each condensation is expected to form a star on a timescale of 40,000 years. We determine that the closest pair will form a bound binary, while the quadruple stellar system itself is bound but unstable on timescales of 500,000 years (comparable to the lifetime of the embedded protostellar phase). These observations suggest that filament fragmentation on length scales of about 5,000 astronomical units offers a viable pathway to the formation of multiple systems.
authors: Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland.
authors: Jaime E
authors: JE
authors: Pineda
authors: 1] Department of Astronomy, Yale University, PO Box 208101, New Haven, Connecticut 06520-8101, USA [2] Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, Massachusetts 01003, USA.
authors: Stella S R
authors: SS
authors: Offner
authors: Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK.
authors: Richard J
authors: RJ
authors: Parker
authors: Department of Astronomy, Yale University, PO Box 208101, New Haven, Connecticut 06520-8101, USA.
authors: Héctor G
authors: HG
authors: Arce
authors: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors: Alyssa A
authors: AA
authors: Goodman
authors: Max-Planck-Institut für extraterrestrische Physik (MPE), Gießenbachstrasse 1, D-85741 Garching, Germany.
authors: Paola
authors: P
authors: Caselli
authors: UK ARC Node, Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, Alan Turing Building, Oxford Road, University of Manchester, Manchester M13 9PL, UK.
authors: Gary A
authors: GA
authors: Fuller
authors: 1] SKA Organisation, Jodrell Bank Observatory, Lower Withington, Macclesfield, Cheshire SK11 9DL, UK [2] Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors: Tyler L
authors: TL
authors: Bourke
authors: 1] Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile [2] National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903, USA.
authors: Stuartt A
authors: SA
authors: Corder