1 / 4

Current astrometric error is as low as 0.25 mas.

Current astrometric error is as low as 0.25 mas. Individual stars in one night. Galactic Center observed with NIRC2 on Keck astrometric accuracy is a function of atmospheric conditions. astrometric floor at ~0.25 mas What sets the floor?. Nightly averages for 3 different nights.

manton
Download Presentation

Current astrometric error is as low as 0.25 mas.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Current astrometric error is as low as 0.25 mas. Individual stars in one night • Galactic Center observed with NIRC2 on Keck • astrometric accuracy is a function of atmospheric conditions. • astrometric floor at ~0.25 mas • What sets the floor? Nightly averages for 3 different nights. Slides from UCLA Galactic Center Group (Ghez, Lu)

  2. Astrometric accuracy is a function of location in the field. • Use 1 night of GC data: • LGSAO, NIRC2 • 107 exposures • tint = 60 sec each • Strehls: 0.3 - 0.4 • FWHM: 53 - 63 mas • WFE ~ 345 nm (Marechal) • Simultaneous MASS/DIMM (estimated at zenith): • r0 = 10 - 15 cm • theta0 = 1.5’’ - 3.0’’ • Courtesy of Matthew Britton: http://eraserhead.caltech.edu/keck/galactic_center/turbulence_plots/turbulence_plots.html Slides from UCLA Galactic Center Group (Ghez, Lu)

  3. Galactic Center data shows strong isoplanatic effects dependence on astrometric error. • In each frame, measure the position relative to the reference star, which is close to the laser spot. • Take the RMS from all frames. • The RMS positional error can be decomposed into radial and tangential components relative to the laser position (or reference source). Slides from UCLA Galactic Center Group (Ghez, Lu)

  4. PSF elongation seems strongest in elevation direction. • PSF degrades due to both isoplanatic and isokinetic effects. • Isoplanatic effects dominate… isokinetic still under investigation. • Differential tip-tilt jitter masked by larger effects? • anisoplanatism • chromatic differential atmospheric refraction along elevation? • Need an astrometry experiment with the tip-tilt star and a separate guide star in the FOV. Slides from UCLA Galactic Center Group (Ghez, Lu)

More Related