Stellar Astrophysics

Questions

• How are bright planetary nebulae formed?  The PN seen in elliptical galaxies are too bright to be explained by traditional single-star stellar evolution.   Can coalesced binary stars explain the brightest objects?  And why do these bright objects have the exact same luminosity regardless of their parent stellar population?
• 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?
• What are the luminosities and temperatures of the post-asymptotic giant branch stars in globular clusters and other old stellar populations?   Can they be used as a precision standard candle, as stellar evolution theory predicts?
• 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?

Discoveries and Milestones

• 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
• Penn State Astronomy & Astrophysics students and alumni Jacob Luhn and Anna Baum, working with Jason Wright, found the first clear case of a star entering a grand magnetic minimum akin to the Maunder Minimum.
• Howard Bond, Robin Ciardullo, and former Penn State Ph.D. student Brian Davis performed the first complete census of intermediate-temperature Above-the-Horizontal-Branch stars in Milky Way globular clusters.  The 10 post-asymptotic giant branch stars found in the survey have a remarkably small dispersion in luminosity, suggesting that the stars can, indeed, be used as a precision extragalactic distance indicator.

Faculty

Robin Ciardullo
Michael Eracleous
Suvrath Mahadevan
Steinn Sigurdsson
Kevin Luhman
Jason Wright
Howard Bond