HST Astrometric Motions of $\eta$ Carinae from WF2,WF1,PC1

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Session 83 -- Circumstellar Gas and Dust
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[83.11] HST Astrometric Motions of $\eta$ Carinae from WF2,WF1,PC1

D.M.Dowling, D.G.Currie, E.J.Shaya (U.Md.), J.Hester (U.A.), E.Groth (Princeton)

The structure, physics and history of the massive eruptive variable star, $\eta$ Carinae, have been addressed by measuring the proper motion of the numerous dust fragments and condensations. The motions of elements within the Homunculus and of the other debris have been measured using our three WF/PC images obtained over a three-year interval. In this poster we present new astrometric motions based on improved cross-correlation methods.

Data were taken with the F658N [NII] in 1990(WF1),1991(PC1) and 1994(WF2) cameras. We discuss the image restoration procedures and camera distortion correction for each image. In our current analysis we have resampled the HST images to 0.05\arcsec /pixel using cubic interpolation. We have run extensive tests using cosmic-ray pair images from our WF/PC2 observations. By resampling one image with a known expansion rate (2\%) and cross-correlating to the other image, we can understand the systematic errors in our cross-correlation procedure and place limits on the accuracy of measurements. Results show an significant reduction in systematic errors when we use the finer grid.

We also discuss the disappearence of the `ladder' structure seen around the North Jet in the deconvolved WF/PC images from 1990. This structure is not evident in any of the later observations including recent WF/PC2 F656N (H-$\alpha$) images.

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