title: Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars.
abstract: Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly ∼ 50 seconds) and those that are also burning helium (period spacing ∼ 100 to 300 seconds).
authors: Sydney Institute for Astronomy, School of Physics, University of Sydney, New South Wales 2006, Australia. t.bedding@physics.usyd.edu.au
authors: Timothy R
authors: TR
authors: Bedding
authors: Benoit
authors: B
authors: Mosser
authors: Daniel
authors: D
authors: Huber
authors: Josefina
authors: J
authors: Montalbán
authors: Paul
authors: P
authors: Beck
authors: Jørgen
authors: J
authors: Christensen-Dalsgaard
authors: Yvonne P
authors: YP
authors: Elsworth
authors: Rafael A
authors: RA
authors: García
authors: Andrea
authors: A
authors: Miglio
authors: Dennis
authors: D
authors: Stello
authors: Timothy R
authors: TR
authors: White
authors: Joris
authors: J
authors: De Ridder
authors: Saskia
authors: S
authors: Hekker
authors: Conny
authors: C
authors: Aerts
authors: Caroline
authors: C
authors: Barban
authors: Kevin
authors: K
authors: Belkacem
authors: Anne-Marie
authors: AM
authors: Broomhall
authors: Timothy M
authors: TM
authors: Brown
authors: Derek L
authors: DL
authors: Buzasi
authors: Fabien
authors: F
authors: Carrier
authors: William J
authors: WJ
authors: Chaplin
authors: Maria Pia
authors: MP
authors: Di Mauro
authors: Marc-Antoine
authors: MA
authors: Dupret
authors: Søren
authors: S
authors: Frandsen
authors: Ronald L
authors: RL
authors: Gilliland
authors: Marie-Jo
authors: MJ
authors: Goupil
authors: Jon M
authors: JM
authors: Jenkins
authors: Thomas
authors: T
authors: Kallinger
authors: Steven
authors: S
authors: Kawaler
authors: Hans
authors: H
authors: Kjeldsen
authors: Savita
authors: S
authors: Mathur
authors: Arlette
authors: A
authors: Noels
authors: Victor Silva
authors: VS
authors: Aguirre
authors: Paolo
authors: P
authors: Ventura