Improving the Effective Spatial Resolution of the HST STIS

As a pos-doc, I helped to work out some of the kinks present in the reduction of the HST STIS data. One advantage of long slit spectroscopy with the Hubble Space Telescope is that the HST, being above the Earth's atmosphere, provides us with better spacial resolution on the cross dispersion axis than any ground based instrument. What does that mean in plain English? Well you are probably aware that HST is able to provide us with sharper pictures of astronomical objects because it is above the atmosphere which normally blurs our view. Because of this we are able to separate the light coming from different parts of Eta Carinae's nebula that, when viewed on Earth, are blurred together. Imagine looking at a blue patch and a green patch next to each other at a distance. Blurred together they will look yellow and you may get the wrong impression. However, when viewed clearly, so that you see the different colored patches, you get a better idea of exactly what you are looking at. In this way the HST gives us a better view of what is happening to Eta Carinae and its nebula. It is a world of difference to be looking at individual knots of material in the nebula versus the entire nebula as one big blob.

The advantage of the HST becomes apparent when you compare the image on the left, which is a color composite of Eta Carinae assembled from HST images, to the image on the right, which was take with a ground based telescope.

Unfortunately, the HST STIS has never been calibrated to its full potential in this area. I'm not putting down the STIS instrument team when I say that. They have done a fantastic job but we think we can do a little better. There are several artifacts that remain in the fully processed images which reduce the effective resolution of the STIS. We feel that careful modeling of these artifacts will allow us to remove them and take advantage of the full resolution promised by the HST. My job is to develop the software that will allow us to take the spacial resolution of the HST STIS one step further, just about doubling it's effective resolution on the cross dispersion axis and allowing a more in depth analysis of not just the Eta Carinae data but all spectra of extended sources which have been gathered with the HST STIS. So my work is not just important to the Hubble Space Telescope Eta Carinae Treasury Project but it has implications for a large fraction of the data which has been gathered by the HST STIS over its lifetime.

Here are some documents with more information:

• A general listing of technical reports generated by the TP

• "Our Adopted Scheme for Subpixel Modeling" by Kris Davidson

• "The STIS/CCD Cross-Dispersion Point Spread Function" by John C Martin

• "Release Notes for Version 1.0 of the Database" by John C Martin

Other projects completed: (in no particular order)

• A method and code to remove the diffuse/scattered light from STIS/CCD images

• A better (new and improved) flux calibration for the STIS CCD (The one STScI has put together is good but I feel with our improved reductions we can in particular clean up the flux calibration on the red-end of the STIS CCD spectral coverag)

• A method and code to remove the ghost images from the STIS/CCD data

• A method and code to deconvolve the PSF from the STIS/CCD images

Last updated 14 Sept 2004