Active Astrophysics Projects

  • Radial Velocity Follow-Up of Interesting Binaries from NASA's K2 Mission
    Collaborators: Thomas Boudreaux (HPU), Paddy Clancy (HPU)

    Similar to Kepler, NASA's K2 mission has been quite successful at finding new transiting exoplanets and studying variable stars to high photometric precision. Several new eclipsing binaries were recently uncovered by K2 that show ellipsoidal modulations and even Doppler boosting. Some of these systems may consist of A stars with extremely low mass white dwarf companions (EL CVn candidates). Thomas and Paddy have been monitoring the radial velocities of 5 interesting K2 binaries for the last few months using the CHIRON optical spectrograph on the SMARTS 1.5-m telescope.
  • The Eclipsing Reflection Effect Binaries from the OGLE Survey (EREBOS) Project
    Collaborators: Veronika Schaffenoth (PI; Innsbruck), Maja Vuckovic (Valparaiso), Ryan Hegedus (HPU), Thomas Kupfer (CalTech), Thomas Boudreaux (HPU), the EREBOS Team

    Planets and brown dwarfs in close orbits around main sequence stars will interact with their stellar hosts once they ascend the red giant branch. The details of these interactions and their outcomes are currently unclear. Recent discoveries of brown dwarfs orbiting post-red giant branch “hot subdwarf” stars imply that at least some substellar objects are not only sufficient for ejecting the outer layers of a red giant’s atmosphere, they can also survive the engulfment phase. Thirty-six new eclipsing hot subdwarf binaries with cool, low-mass companions were discovered from light curves obtained by the OGLE project, tripling the number of known systems. We recently started the EREBOS porject to obtain spectroscopic observations of these short-period binaries in order to determine their orbital velocities and, ultimately, the companion masses. We will use this unique and homogeneously-selected sample to derive the mass distribution of the companions and determine the minimum mass needed to strip off the red-giant envelope and survive the common envelope phase. Veronika gave a presentation on the EREBOS project at sdOB7.
  • The Disappearing Pulsations of CS 1246
    Collaborators: Alan Vasquez Soto (HPU), Bart Dunlap (UNC)

    At the time of its discovery in 2009, CS 1246 was one of the largest-amplitude pulsating hot subdwarf B stars ever found (Barlow et al. 2009). It exhibited a single p-mode oscillation with a period of 371.7 seconds and amplitude in excess of 3% (likely a radial mode). Since then, its pulsation amplitude has decreased so much that it is barely detectable. We are in the process of analyzing 6 years of SKYNET data to characterize the amplitude change and understand more about the underlying physics leading to such a loss in pulsational power. Alan and Barlow presented tentative results of this work at the 2015 SuRPS Symposium and sdOB7, respectively.
  • The MUCHFUSS Project
    Collaborators: Stephan Geier (PI; ESO), Thomas Kupfer (CalTech), Uli Heber (Dr. Remeis Sternwarte), Veronika Schaffenroth (Innsbruck), the MUCHFUSS Team

    The original aim of the project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) was to find hot subdwarf B stars with massive companions such as white dwarfs, neutron stars, and black holes. Spectra from the Sloan Digital Sky Survey (SDSS) are used to identify candidate binaries from velocity shifts. Follow-up spectroscopy is obtianed of each target in order to determine the full set of orbital periods and the (minimum) mass of the companion. To date, we have discovered and solved for the orbital parameters in over 20 new hot subdwarfs binaries. This campaign will continue for years to come.

What do we do?

Our research group focuses on stellar astrophysics, with emphasis on pulsating stars, stellar remanants, and stellar evolution. Observations of extreme binary systems, especially those containing post-RGB "hot subdwarf" stars, can help constrain parameters in binary population synthesis models. Stellar pulsations in white dwarfs and hot subdwarfs can reveal clues about their interior structure and how physics works at extreme termperature and pressure. Studying the structure and evolution of these objects helps to improve our overall understanding of stellar evolution, along with our ability to model the light from large stellar populations, including globular clusters and galaxies. We also have strong interests in Type Ia supernovae, globular clusters, and pulsars. Additional research details may be found at right and using the links above.

Observing Facilities

   

   

Collaborators

Chris Clemens (Univ. of North Carolina)
Horst Drechsel (Dr. Remeis Sternwarte)
Bart Dunlap (Univ. of North Carolina)
Stephan Geier (ESO)
Patricia Gray (UNCG)
Elizabeth M. Green (Univ. of Arizona)
Bruce Hrivnak (Valparaiso University)
Dave Kilkenny (Univ. of the Western Cape)
Sandra E. Liss (Univ. of Virginia)
Anthony E. Lynas-Gray (Oxford)
Roy Østensen (Katholieke Universiteit Leuven)
Veronique Petit (Florida Inst. of Tech.)
Dan Reichart (Univ. of North Carolina)
Rachel Rosen (NRAO)
Veronika Schaffenroth (Univ. Innsbruck)
John Subasavage (USNO)
Richard A. Wade (Penn State Univ.)