Diffraction-limited Visible Light Images of the Orion Trapezium Cluster With the Magellan Adaptive Secondary AO System (MagAO)

We utilized the new high-order (250-378 mode) Magellan Adaptive Optics system
(MagAO) to obtain very high spatial resolution observations in “visible light”
with MagAO’s VisAO CCD camera. In the good-median seeing conditions of Magellan
(0.5-0.7″) we find MagAO delivers individual short exposure images as good as
19 mas optical resolution. Due to telescope vibrations, long exposure (60s) r’
(0.63 micron) images are slightly coarser at FWHM=23-29 mas (Strehl ~28%) with
bright (R<9 mag) guide stars. These are the highest resolution filled-aperture images published to date. Images of the young (~1 Myr) Orion Trapezium Theta 1 Ori A, B, and C cluster members were obtained with VisAO. In particular, the 32 mas binary Theta 1 Ori C1/C2 was easily resolved in non-interferometric images for the first time. Relative positions of the bright trapezium binary stars were measured with ~0.6-5 mas accuracy. We now are sensitive to relative proper motions of just ~0.2 mas/yr (~0.4 km/s at 414 pc) - this is a ~2-10x improvement in orbital velocity accuracy compared to previous efforts. For the first time, we see clear motion of the barycenter of Theta 1 Ori B2/B3 about Theta 1 Ori B1. All five members of the Theta 1 Ori B system appear likely a gravitationally bound "mini-cluster", but we find that not all the orbits can be both circular and co-planar. The lowest mass member of the Theta 1 Ori B system (B4; mass ~0.2 Msun) has a very clearly detected motion (at 4.1+/-1.3 km/s; correlation=99.9%) w.r.t B1 and will likely be ejected in the future. This "ejection" process of the lowest mass member of a "mini-cluster" could play a major role in the formation of low mass stars and brown dwarfs [caption id="attachment_4889" align="aligncenter" width="1585"]Theta 1 Ori C resolved with VisAO The power of visible light adaptive optics. Here we show (on the left) a “normal” photo of the theta 1 Ori C binary star in red light (in the r’ filter, 630 nm). It just looks an unresolved star. Then the middle image shows how if we remove (in real time) the blurring of the atmosphere with MagAO’s adaptive optics’ the resulting photo becomes ~17 times sharper (corrected resolutions range from 0.019-0.029 arcseconds on theta 1 Ori C). Both photos are 60 seconds long, and no post-detection image enhancement has been applied. These are the highest resolution photos taken by a telescope. Photo credit Laird Close, University of Arizona. [/caption]

For more on high resolution filled-aperture imaging of Trapezium see:
Close, L. M., et al. “Diffraction-limited Visible Light Images of Orion Trapezium Cluster With the Magellan Adaptive Secondary AO System (MagAO)”.
ApJ, 774, 94, 2013    preprint [pdf]    arxiv preprint

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