Properties of the Remnant Clockwise Disk of Young Stars in the Galactic Center

Using high precision kinematic measurements and modeling of 116 young stars in the central 1 pc of the Galaxy, we derive the ensemble properties of the clockwise stellar disk. The disk is made up of ~20% of the young stars, which revolve around the supermassive black hole on non-circular orbits. The estimated eccentricities can be achieved through dynamical relaxation in an initially circular disk with a moderately top-heavy mass function, which has been recently found by Lu et al. (2013). We also find that the B stars have similar kinematic properties as the more massive O and WR stars, suggesting a common star formation event. For more details, see the full manuscript.

Is G2 a gas cloud or a star?

Recently, Gillessen et al. discovered the exotic Galactic center object G2. G2 in unique because of its very red near infrared color, which could be indicative of warm dust or a realtively cool star, and emission lines which trace excited hyrdrogen gas. The line emission exhibit marginal spatial extent and strong evidence of temporal evolution which is consistent with a tidal interaction with our Galaxy's supermassive black hole. We suggest the realtively compact nature of this object is indicative that G2 is a star. Furthermore, we present a new orbit for G2, which predicts it will go through periapse in March of 2014. For more details, see the full manuscript. For other publicationa about G2, see the G2 wiki.

Discovery of the shortest period star, S0-102

Over the past 17 years, we have used the W. M. Keck Observatory to image the Galactic center at the highest angular resolution possible today. By adding to this data set and advancing methodologies, we have detected S0-102, a star orbiting our galaxy's supermassive black hole with a period of just 11.5 years.
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Keck I and II laser guide stars pointing at the Galactic center
(Photo credit: Dan Birchall).

Adaptive Optics Technology

Our best views of the night sky are afforded by the world's largest telescopes, such as those at the W. M. Keck Observatory that have been equipped for the last decade with Adaptive Optics. This revolutionary hardware technology corrects for the blurring effects of the Earth's atmosphere by measuring aberrations in the wavefront of a bright guide star and subsequently adjusting the shape of a deformable mirror. These corrections can be made on either a bright natural guide star (NGS) or a laser guide star (LGS), as shown in the image.
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Three-color (HKL) image of the central 10'' of the Galaxy.

Stellar Populations

Adaptive optics spectroscopy has allowed for spectral identifications of bright (K < 16) stars within ~1 pc of the supermassive black hole and has revealed two very unexpected results. The first surprise was the detection of a wealth of young (< 10 Myr) stars in a region where none were expected due to the strong tidal field of the supermassive black hole and the low present day gas densities. The second surprise was the unanticipated dearth of late-type stars near the SMBH. The radial profile of these old stars is significantly flatter than that predicted by theoretical models.
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Black Hole Accretion

Sgr A*, the radio source associated with the central supermassive black hole, is quite underluminous as compared to black holes at the centers of other galaxies. However, with the increased sensitivity provided by adaptive optics, the infrared emission from material accreting onto Sgr A* has been detected. The emission is variable, and the luminosity of Sgr A* can increase by a factor of a few over the stellar background during a single night.
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Three-color images showing the variable emission of Sgr A*

NIRC2 Distortion Solution

We have constructed a new optical distortion model for the W. M. Keck II 10 m telescope's adaptive optics camera, NIRC2, in its narrow field mode. Using on-sky measurements of a globular cluster, we have improved the distortion solution by a factor of ~3 over the previous solutions. Download the distortion solution here.
Download the distortion solution here.