Stellar Astrophysics

Do most planetary nebulae (PNe) evolve from low-mass single stars, as traditional textbooks describe? Or does the evolution of these objects involve binary stars, as a growing number of astronomers propose?
Can we mitigate or otherwise overcome the limits stellar variations place on the detection of exoplanets?
How well can we determine the ages, compositions, sizes, and masses of field stars?
How do stars' magnetic fields change with time, and how does this influence their surface convective motions?
What are the underlying physical drivers of stellar photometric variations?
Bright PNe in elliptical galaxies are not explained by either of the above two mechanisms; how do they form? Why is the [O III] planetary nebula luminosity function (PNLF) such an excellent standard candle?
What types of stars form novae? How does the production of novae change with stellar population? Are short-period recurrent novae the progenitors of Type Ia supernovae?

Robin Ciardullo has shown that the best explanation for the bright PNe in elliptical galaxies is through the evolution of close-binary stars which have merged while on the main sequence. These merged systems, which are presumed to be blue stragglers, have the correct number density and lifetimes to explain the extragalactic PN observations. Robin's modeling suggests that a considerable fraction of Galactic PNe may form through this blue straggler to planetary nebula scenario.
Jason Wright and his former PhD student Jason Curtis determined that the long-lost open cluster Ruprecht 147 is real, and they established it as an important new benchmark in stellar astrophysics as the oldest nearby cluster.
Robin Ciardullo pioneered the use of H-alpha for extragalactic nova survey. He was also the first to measure luminosity-specific nova rates for different stellar populations and he has used H-alpha observations to explore the physics of the nova phenomenon.
Jacob Luhn, working with Jason Wright, measured the astrophysical component of the radial velocity "noise" in stars, and traced it to distinct magnetic and convective components that change with a star's age. Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars