Andy Boden's Scientific Interests

I've spent a good bit of my career working on long-baseline optical and near-IR interferometers. So it stands to reason that I would be interested in scientific problems these devices can address. For up-to-date publication information please see Andy Boden's ADS references.

Ground-based Interferometry

I'm a long-time collaborator on the Palomar Testbed Interferometer (PTI), the Keck Interferometer (KI), and I am peripherally associated with the CHARA Interferometric Array at Mt. Wilson.

Binary Stars

A lot of what I've done with interferometers is study binary stars. While traditional (read that boring), studies of binary stars are important for at least two distinct reasons:

Besides, if you have an interferometer you have to study binary stars -- it's a moral imperative. [That's a joke folks -- see the work of some poor writer who reads personal web pages rather than interviewing sources -- and who is apparently humor-impaired!]

Several publications in the list below deal with precision determinations of stellar properties from precision studies of binary kinematics -- usually from integrating the results of interferometric and spectroscopic observations. Shown at the right is a cartoon of one of my favorite binary stars, 12 Bootis (HD 123999), a pair of F stars in a 10 d orbit. Even though the two components of the binary are nearly equal mass, there is a rough factor of two difference in the brightness between the two stars -- because of evolutionary effects (the primary is just leaving the main sequence). The two frames of the animation show the relative astrometric and radial velocity orbit of the binary respectively (see Boden, Torres, and Hummel 2005). (Hit reload to run the animation again -- wahoo!). I would also call your attention to our work on pre-main (PMS) sequence binaries (e.g. HD 98800 B (the first!) and V773 Tau (the second!) PMS physical orbits done with long-baseline interferometry), and high proper motion systems (e.g. HD 9939 -- old (9.1 Gyr), yet remarkably metal-rich (solar)!)

Measurements like these help us better understand & constrain the physics of how stars work and evolve. Since stars individually or in ensemble are the fundamental observable objects in optical astronomy, it is critical that our models of stars be as robust and predictive as possible.

Circumstellar & Circumbinary Material in Binary Systems

Associated with binarity as a common product of the star formation process, there are questions of the remaining material in such systems. A natural outgrowth of our PMS work is study of circumstellar and circumbinary material in some of these same systems (e.g. HD 98800 -- Akeson et al 2007, and DQ Tau -- Boden et al 2009). The stellar interaction with and accretion from such material, as well as the possibility of this material as the site for possible planet formation are questions that are fascinating to many of us...

I am also a member of a team that recently announced the detection of circumbinary dust around short-period main-sequence binary stars (see Trilling et al 2007 below). Presumably this dust (in so-called 'debris disks') is produced (and continuously replenished) by collisions of planetesimals orbiting the binary systems. Further, we found that these debris disks were significantly more prevalent in these short-period binaries than in comparable single stars. The implications are profound: it could be that planetesimals -- and even planets -- are common around binary systems!

Exo-Planetary Systems
A lot of us who work in optical interferometry in Pasadena have an interest in exo-planetary systems. The idea that planets could be a pervasive byproduct of the star formation process is attractive one, and has rather profound implications on our place in the grand scheme of things. We like to think of detecting and characterizing planetary systems astrometrically. By measuring the transverse reflex motion of the parent star one can uniquely determine the orbit orientation (especially the all-important inclination Euler angle) and thereby uniquely determine the planet mass rather than only a lower bound on the mass from radial velocity detections.

I have been actively involved with developing relative astrometry technology on the ground with PTI; we have been successful in demonstrating 100 microarcsecond precision relative astrometry on the visual binary 61 Cygni.

I am also a co-investigator on two SIM Key Projects to detect and study exo-planetary systems. The first (EPICS -- PI Shao) will astrometrically survey hundreds of stars down to a precision of a few microarcseconds over a broad range of stellar primary types with a goal of determining the architecture of planetary systems. The second (SIM-YSO -- PI Beichman) will search for planetary companions to pre-main sequence stars to study properties of young planetary systems.

Galactic Dark Matter -- Gravitational Microlensing
Astrometric Microlensing Illustration Gravitational lensing is a property of Einstein's theory of gravitation, and indicates the presence of mass independent of luminosity. Microlensing is gravitational lensing where the individual images of the background source are unresolved by the observer, and typically occurs when the lens is of stellar mass. Astrometric or multiple-perspective observation of microlensing events can break the degeneracies inherent in photometric-only observations of microlensing events, and in particular uniquely determine the mass of and distance to the lens.

The figure at right (from Boden, Shao, and Van Buren 1998) depicts the effects of astrometric gravitational microlensing. The two lensing images change positions and brightness as a function of time. So even though the images are not separately resolved, the photocenter of the two images moves in an apparent elliptical excursion from the nominal source position. (Departures from the elliptical pattern come from the relative parallax between the lens and source.) By jointly measuring the source photometric amplification and apparent astrometric excursion the lens mass and distance are determined uniquely.

I am a co-investigator on a SIM Key Project (SIM Microlensing Key Project -- SMKP -- PI Gould) to measure both the mass function of the Galactic bulge using microlensing events, and to unequivocally establish the Galactic halo nature (or not) of the photometrically detected events seen toward the LMC and SMC.

I am a member of a team that recently announced the first parallax measurement for a lens object (see Dong et al 2007 in the publication list below). For this we used ground-based observations and observations from the Spitzer Space Telescope.

Selected Publications

CV

My CV in PDF...

Acknowledgments

I am very happy to acknowledge financial support from the NSF and NASA /Spitzer Science Center and COO.

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