Robert McMillan Radial Velocity papers

Dr. McMillan leads the SPACEWATCH® Project which recovers and makes astrometric observations of Near-Earth Objects (NEOs). He is also a Co-Investigator on the Science Team of the NEO Wide-field Infrared Survey Explorer (NEOWISE) spacecraft mission that surveys the sky in the near-infrared. The Spacewatch Project's role for that mission is follow-up observations of asteroids and comets detected by that spacecraft. Spacewatch contributes the majority of the recovery observations of NEOs recently discovered by NEOWISE.

McMillan's career has included studies of variable stars, statistics of stellar populations, interstellar dust, interstellar magnetic fields, planetary atmospheres, Doppler shift spectroscopy of stars, astronomical instrumentation, and surveys of asteroids. He has worked in the last four disciplines from 1979 to the present while at the Lunar and Planetary Laboratory at the University of Arizona. Some of McMillan's peer-reviewed first-author papers from the 1970s were still being cited and used as many as 40 years later.

McMillan's group at LPL was the first to publish stellar Doppler shift (radial velocity; RV) measurements better than +/-20 meters per second (m/s) in a refereed journal. They also made the first reliable detection of p-mode oscillations in a star other than the Sun (Arcturus), discovered the spectroscopic binary of then-longest known period, and established a new upper limit on the RV stability of the Sun observed as a point source. That limit was published in 1993 and as of 2014 has been neither challenged nor surpassed. McMillan also further investigated techniques to measure the RVs of stars in ways that minimize confusion of Doppler shift measurements by effects intrinsic to stellar atmospheres. He returned to the field in 2007 as a collaborator with a group who used a prototype of a newly designed dispersed Fourier Transform Spectrometer to measure the RVs of binary stars with the 2.3-meter Bok Telescope of the Steward Observatory.

As Co-Investigator, Deputy Principal Investigator, Project Scientist, and Project Manager of Prof. Tom Gehrels' Spacewatch Project from 1980-1997, McMillan guided the physical realization of CCD surveying as a productive method of exploring the solar system for asteroids and comets. McMillan became the Principal Investigator of Spacewatch in mid-1997. In 2000 McMillan discovered large Trans-Neptunian Object 2000 WR106, now known as Minor Planet (20000) Varuna. On 2005 Dec 28 he discovered minor planet 2005 YU55, a 300-meter diameter Earthcrossing asteroid that made a close approach to Earth on 2011 Nov 8. The 1.8-m telescope was completed in 2002 and the 0.9-m telescope was completely rebuilt with all new optics and detectors under McMillan's leadership. The 0.9-m telescope was fully automated in 2006. The 1.8-m telescope received a new imaging camera in 2011 October, which has increased the rate of observations by 50% and improved astrometric accuracy by a factor of 2. In 2015 October, the Spacewatch Project further boosted its rate of observations with a new CCD camera at the cassegrain focus of the Bok 2.3-meter telescope of the Steward Observatory and converting the operation of the Spacewatch 0.9-meter telescope from surveying to targeted followup observations.

The Radial Velocity Project was started by Krzysztof Serkowski around 1973 to detect planets orbiting other stars. Detection requires specialized equipment for measuring the polarization of light that is more accurate than conventional Doppler shift equipment. The instrument required a great deal of careful calibration and lots of photons to make measurements with ground-based telescopes.

Robert S. McMillan began collaborating with Serkowski in 1979 because his dissertation topic, interstellar polarization, related to his work. Serkowski was suffering from Lou Gehrig's Disease and the project was passed to McMillan in 1980. Serkowski passed away in 1981. At the time the project had run out of money so McMillan had to restart the project from scratch. Funding was secured from the National Science Foundation and the National Aeronautics and Space Administration.

The specialized instrument, the University of Arizona radial velocity spectrometer (RVS), was redesigned and new software was written before ovservations commenced. It was successful and the team was the first to publish radial velocity measurements of starts better than 20 meters per second accuracy. They also discovered pulsations in Arcturus, a different, new type of pulsation that had never been seen before in any other stars but the Sun. They also discovered the longest period of a spectroscopic binary.

The program was successful, but suffered from "photon starvation". It required vast amounts of light to work effectively and due to various constraints sufficient large telescope time wasn't available for the project. With a small telescope the project wasn't able to discover planets as it set out to, but it proved the measurement concept and achieved the desired accuracy.

In the 1990s McMillan and the Radial Velocity Project partnered with George David Gatewood, of Allegheny Observatory, Univ. of Pittsburgh, to make ovservations with an instrument called the Multichannel Astrometric Photometer and Spectrograph (MAPS). Observing runs were conducted in 1997 at the Keck II telescope on Mauna Kea in Hawaii.