(AO) Observations of the Galactic Center Seth Hornstein (UCLA) CfAO Summer School on Adaptive Optics

Why Study the Galactic Center? Is there a super massive black hole? What are the interactions of the black hole with its environment? Lensing Modified stellar formation Accretion of material August 6, 2001 CfAO Summer School on Adaptive Optics

Courtesy of the Keck Observatory

Courtesy of the Keck Observatory

CfAO Summer School on Adaptive Optics Proof of a Black Hole Proper Motion Studies If point mass exists, objects should follow Keplerian (elliptical) orbits Velocities yield enclosed mass as a function of radius August 6, 2001 CfAO Summer School on Adaptive Optics

CfAO Summer School on Adaptive Optics Proof of a Black Hole High resolution is required to get to stars closest to the black hole (possibly with the shortest periods) Ghez et al., 2000 August 6, 2001 CfAO Summer School on Adaptive Optics

More Proof of a Black Hole Rschwarzschild≈3km*M For a 3x106 M black hole = 9x106km=0.05 AU!! In order to prove there is a black hole at the Galactic Center, we must constrain the mass to a very small area. Again, this requires very high resolution. Enclosed Mass Plot Ghez et al., 1998 August 6, 2001 CfAO Summer School on Adaptive Optics

Effects of the Black Hole on Its Environment Variability Stellar population Accretion disk August 6, 2001 CfAO Summer School on Adaptive Optics

Variability

CfAO Summer School on Adaptive Optics Variability Lensing Excellent probe of black hole mass & location. Modified Stellar formation How does a 2.6x106 M object effect formation of nearby stars? Accretion Rate increase Stationary variability at the position of Sgr A* could be coming from the black hole itself. August 6, 2001 CfAO Summer School on Adaptive Optics

Current Work Variability August 6, 2001 CfAO Summer School on Adaptive Optics

Current/Future Work High resolution spectroscopy Previous low-res spectroscopy was able to establish the lack of CO bandhead absorption in several of the stars. However, when looking at features intrinsic to early-type stars, it was unable to distinguish between absorption from the stellar sources and emission from background gas. Lack of bandheads means not late type. Possibly Early type. Doppler shifts from the stellar emission lines will allow calculation of the radial velocities of the central cluster of stars. Thus allowing an actual estimate of the enclosed mass. Gezari et al., 2001 August 6, 2001 CfAO Summer School on Adaptive Optics

Current/Future Work Proper Motion Radial velocities & accelerations Radial velocities will allow 3-D orbits to be fit. Thus giving estimates of both the positional location of the central dark matter and the enclosed mass. Acceleration provides another method of confining the center of mass. Ghez et al., 2000 August 6, 2001 CfAO Summer School on Adaptive Optics

Problems With Adaptive Optics at the Galactic Center Natural guide stars are severely lacking Keck guide star: Very far off axis (30” from central cluster) Dim (Vmag=13.2) Gemini guide star: Off axis (18” from central cluster) Very dim (Vmag=13.8) Anisoplanatism August 6, 2001 CfAO Summer School on Adaptive Optics

Ohio State image - guide stars Courtesy of OSU (OSIRIS)

CfAO Summer School on Adaptive Optics Solutions Infrared Wavefront Sensor This would allow the use of IRS 7 as the guide star Kmag=6.6 Distance from GC = 6” Laser guide star Larger target audience. Would be disabled by even a small amount of clouds. August 6, 2001 CfAO Summer School on Adaptive Optics