Contributions of the US Naval Observatory to the Optical Reference Frame - Current and Projected

Corbin T., Gauss S.

With the expected publication of the Hipparcos and Tycho catalogs, astrometrists must determine where their efforts should be directed for the future. The USNO has a long history of observations that have been important in helping to define and densify the optical reference frame. This work is being continued in the form of new astrometric catalogs and new observing programs that will help to both maintain the newest realization (Hipparcos) of the optical frame and will add to the density of stars in that frame.

Current catalogs in preparation include the Twin Catalog (TAC) with a density about 40% greater than that of Tycho and positions accurate to 80 mas. Extending to even greater densities the Precise Measuring Microdensitometer (PMM) catalog is expected to contain about 500 million stars reaching to 20th magnitude with positional accuracies of 150 to 200 mas. Efforts are underway to link the radio and optical systems with programs to provide reference stars around the primary sources of the radio frame and observations of radio stars.

The new observational programs include the Navy Prototype Optical Interferometer (NPOI) that is now beginning operation and will first observe a list of about 1000 stars with an expected accuracy of 1 mas. This will make possible one of the first observational checks on the system of Hipparcos proper motions. The USNO is also proposing an astrographic program to survey the Southern Hemisphere to the 15th magnitude with positions good to 20 to 30 mas. Finally the USNO is a major participant in a proposed astrometric satellite that would survey the entire sky with unprecedented accuracy: positions better than 0.1 mas and reaching to the 16th magnitude.