HIGH-RESOLUTION IMAGES OF ORBITAL MOTION IN THE ORION TRAPEZIUM CLUSTER WITH THE LBT AO SYSTEM

Journal Article · Fri Apr 20 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/749/2/180· OSTI ID:22020362

Close, L M; Males, J R; Skemer, A; McCarthy, D W; Xompero, M; Kulesa, C ^[1]; Puglisi, A; Busoni, L; Pinna, E; Riccardi, A; Quiros-Pacheco, F; Argomedo, J; Esposito, S; Mannucci, F ^[2]; Arcidiacono, C ^[3]; Guerra, J C; Brusa, G; Miller, D L; Brynnel, J; Boutsia, K ^[4] ; others, and

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1. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
2. INAF-Osservatorio Astrofisico di Arcetri, I-50125 Firenze (Italy)
3. INAF-Osservatorio Astronomico di Bologna, I-40127 Bologna (Italy)
4. LBT Observatory, University of Arizona, Tucson, AZ 85721 (United States)

The new 8.4 m LBT adaptive secondary AO system, with its novel pyramid wavefront sensor, was used to produce very high Strehl ({approx}> 75% at 2.16 {mu}m) near-infrared narrowband (Br{gamma}: 2.16 {mu}m and [Fe II]: 1.64 {mu}m) images of 47 young ({approx}1 Myr) Orion Trapezium {theta}{sup 1} Ori cluster members. The inner {approx}41 Multiplication-Sign 53'' of the cluster was imaged at spatial resolutions of {approx}0.''050 (at 1.64 {mu}m). A combination of high spatial resolution and high S/N yielded relative binary positions to {approx}0.5 mas accuracies. Including previous speckle data, we analyze a 15 year baseline of high-resolution observations of this cluster. We are now sensitive to relative proper motions of just {approx}0.3 mas yr{sup -1} (0.6 km s{sup -1} at 450 pc); this is a {approx}7 Multiplication-Sign improvement in orbital velocity accuracy compared to previous efforts. We now detect clear orbital motions in the {theta}{sup 1} Ori B{sub 2} B{sub 3} system of 4.9 {+-} 0.3 km s{sup -1} and 7.2 {+-} 0.8 km s{sup -1} in the {theta}{sup 1} Ori A{sub 1} A{sub 2} system (with correlations of P.A. versus time at >99% confidence). All five members of the {theta}{sup 1} Ori B system appear likely a gravitationally bound 'mini-cluster'. The very lowest mass member of the {theta}{sup 1} Ori B system (B{sub 4}; mass {approx}0.2 M{sub Sun }) has, for the first time, a clearly detected motion (at 4.3 {+-} 2.0 km s{sup -1}; correlation = 99.7%) w.r.t. B{sub 1}. However, B{sub 4} is most likely in a long-term unstable (non-hierarchical) orbit and may 'soon' be ejected from this 'mini-cluster'. This 'ejection' process could play a major role in the formation of low-mass stars and brown dwarfs.

• OSTI ID: 22020362
• Journal Information: Astrophysical Journal, Vol. 749, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
MASS
OPTICS
ORBITS
PROPER MOTION
SENSORS
SPATIAL RESOLUTION
STAR EVOLUTION
STARS