SONG overview Jørgen Christensen-Dalsgaard Department of Physics and Astronomy Aarhus University
The SONG concept Network of 8 telescopes with a global distribution Long, nearly continuous observations Ultra-precise Doppler-velocity measurements Precise photometry of faint stars in crowded fields SONG is regarded as one scientific instrument
Rationale for SONG project Ultimate asteroseismic precision requires radial velocity observations Continuous extended observations require dedicated facility Optimized instrumentation can reach required sensitivity with 1m telescopes
A little history Early ideas: Spring 2005 With optimized instrumentation, spectroscopy with iodine reference, adequate sensitivity can be reach for bright stars with very modest telescopes Developed further during 2005 Conceptual design phase through 2006 Funded by VKR, Carlsberg,
Early concept (December 2005)
Revised design, mid-2006
ASTELCO sketch, early 2007
Conceptual design review, 1 2 March 2007 Team: Keith Horne, Thomas Augustein, Don Kurtz Conclusion: We commend the SONG team for its remarkable progress in developing the SONG concept to its present level of definition. SONG's unique combination of instrumentation and continuous observing capabilities for timedomain observations will open a new era in asteroseismology and will have a major impact on the discovery and study of extrasolar planets
Prototype funding Villum Fonden, 2007: General funding for prototype development Danish Natural Science Research Council, 2008: Funding of spectrograph Carlsberg Foundation, 2008: Partial funding of telescope Aarhus, Copenhagen Universities: In-kind contributions Instituto de Astrofísica de Canarias, Tenerife: Local infrastructure, local operations
Scientific goals of SONG Asteroseismology of unprecedented resolution and accuracy Radial-velocity observations Characterization of extra-solar planetary systems Radial-velocity observations Gravitational microlensing Additional science
Studies of exo-planets Radial velocity Low-mass planets in short-period orbits Gravitational micro-lensing Characterization of statistics of planetary systems, including low-mass planets in longperiod orbits
Gravitational micro-lensing
Asteroseismology The study of stellar interiors from observations of stellar oscillations Oscillation frequencies can be determined with extremely high precision Frequencies are sensitive to internal structure and rotation Mode amplitudes and lifetimes are sensitive to near-surface physics, including convective dynamics
Goals of asteroseismology Characterize global stellar properties Investigate detailed internal structure and dynamics of stars Improve understanding of the physics of stellar interiors Improve modelling of stellar evolution
Observational requirements Extreme sensitivity Amplitudes down to a few cm/s in velocity and a few parts per million in intensity Very long observation series (weeks or months) Ensure sufficient frequency precision Nearly continuous data Avoid complications in observed oscillation spectrum
An aside: time (or) distance astrophysics Current trend: emphasizing giant telescopes Needed for studying very distant objects, phenomena Needed for studying phenomena on very small scales At the expense of smaller telescopes Allowing dedicated observations to single objects over long time periods Both are obviously needed
An aside: time (or) distance astrophysics Current trend: emphasizing giant telescopes Needed for studying very distant objects, phenomena Needed for studying phenomena on very small scales At the expense of smaller telescopes Allowing dedicated observations to single objects over long time periods Both are obviously needed Hence we need dedicated networks, such as LCOGT or SONG
Basic properties of oscillations
Types of stellar oscillations Acoustic modes (p modes) Standing sound waves Relatively high frequency Depend mainly on sound speed Extend to centre of star, at low degree g modes Standing internal gravity waves Relatively low frequency Depend mainly on the buoyancy frequency, strongly sensitive to composition profile
Observations of solar-like oscillations Radial velocity Amplitudes typically below 1 m/s Sensitive to modes of degree 0, 1, 2, 3 Observe one star at a time Intensity Amplitudes typically of a few ppm Sensitive to modes of degree 0, 1, 2 Observe many stars simultaneously
Observations of solar-like oscillations In both cases: requires continuous observations over many weeks or months Observations from space: intensity CoRoT, Kepler Observations from ground-based network: radial velocity
SONG in the Kepler era Kepler provides very good data for hundreds (thousands) of stars Synasteroseismology (comparison of stellar properties) Population studies Characterization of pulsation properties for broad range of stars SONG will provide exquisite data for a limited number of stars Detailed probing of stellar internal structure Detailed investigations of physics of stellar interiors
Stellar noise vs. oscillations
Asteroseismology across the HR diagram
Solar-like oscillations
Solar-like oscillations
Solar-like oscillations In unevolved stars: acoustic modes In evolved stars: may have mixed g-mode character Generally assumed to be intrinsically damped and stochastically excited by convection. Expected, and now generally observed, in all stars with significant outer convection zones
What we expect: the solar case Grec et al., Nature 288, 541; 1980
Examples of solar-like oscillations
Amplitude distribution
Solar-like oscillators from Kepler Chaplin et al. (2011; Science 332, 213)
Examples of Kepler solar-like pulsators Chaplin et al. (2011; Science 332, 213).
Solar-like oscillations in red giants CoRoT observations De Ridder et al. (2009; Nature 459, 398)
4 months of SONG observations
Asymptotics of p modes
Small frequency separations
Asteroseismic HR diagram
The Sun and its neighbours
Looking for finer details: acoustic glitches Departures from simple asymptotic behaviour Sharp features in the sound speed Edges of convective zones Rapid variations in sound speed caused by ionization Cause oscillatory behaviour of oscillation frequencies as functions of mode order
Sharp features in stellar models HeII ionization No overshoot With overshoot
Oscillatory signals Fit He I He II BCZ Houdek & Gough (2007; MNRAS 375, 861)
Oscillatory signals, SONG 2 x 4 months Needs SONG Fit He I He II BCZ Houdek & Gough (2007; MNRAS 375, 861)
Rotational splitting
Observed splitting pattern Depends on actual amplitudes and inclination i of rotation axis to line of sight For solar-like oscillations reasonable to assume that actual average amplitudes are the same for all m-components Hence obtain estimate of the inclination
Gizon & Solanki (2003; ApJ 589, 1009)
Overall design drivers for SONG instrumentation Optimize the design for the primary science purposes: Ultra-precise radial velocities Photometry in crowded fields High duty-cycle Long lifetime
Telescope and dome 1 m telescope, alt-az mount High-resolution spectrograph Lucky Imaging camera for micro-lensing Contract to Astelco Systems, GmBH, Aug. 2009 Acceptance, Tenerife, late 2011
Summary of status Prototype: well on the way for deployment in 2011 Chinese site, funded by China: under detailed design, deployment in 2013 US site: proposal to be submitted to the NSF Proposal for two additional Danish-funded sites in ongoing evaluation of need for Danish research infrastructure
Strawman sites Izaña: prototype
Almost there!