1.0 Hubble Space Telescope Astrometry

Who we are.

I don't do this stuff alone. Here is a list of my colleagues.

What we do

We use the Fine Guidance Sensors aboard Hubble Space Telescope to measure star positions and study binary stars unresolvable using ground- based techniques. Primarily, stellar positions yield information on distance. We also work to tie the Hipparchos reference frame to an extragalactic (non- rotating) reference frame.

Problems

While the misfigured primary mirror has caused us some problems, our major irritation was that HST was not as stable a platform as we had hoped. The old solar arrays flexed and wiggled, driven by temperture changes caused by passage from sunlight to dark in each orbit. The new arrays are disturbing our platform far less.

What we've done.

What I do

Proxima Centauri and Barnard's Star

I'm searching for PLANETS near Proxima Centauri and Barnard's Starby detecting wiggles in their motion. Why would Proxima Cen wiggle? It and any associated planet would orbit a common center of mass. No, we have not found any palnets, yet. Here is some information about Proxima Centauri and a status report on our search.

Often in astronomy one looks for one thing and finds another. The FGS are also very good photometers. Proxima Centauri turned out to be a periodic variable star. The announcement paper was based on less than half the data sets we have now. The period may have changed to 82 days from the originally announced 41 days. Finally, here is an example of the periodograms which we use in our search. The only frequency for which there is any power in both x and y is near 0.013 /day. We remain skeptical that it is an astronomical effect.

Hatzes, Kuerster, and Cochran are obtaining high precision (+/- 100 m/s) radial velocity measures of Proxima Cen from ESO. We should know if the planet exists or not by comparing periodicities seen in the astrometry with any found in the radial velocity results. So far, the eight epochs obtained over 2 years are not inconsistent with a variation with a period near 90 days. More data is required to rule out noise as the producer of this variation.

Here is some information about Barnard's Star . We are in the middle of our series of observations of this object. They will continue through 1995-6 (Cycle 5). Thus far, neither astrometric nor radial velocity measurements have yielded a planet.