Katrien Uytterhoeven The Kepler space mission: New prospects for δ Sct, γ Dor, and hybrid stars Instituto de Astrofísica de Canarias, Tenerife NMSU, January 23, 2012

Uytterhoeven et al., 2011, A&A, 534, A125

  Stellar oscillationsAsteroseismology

© JCD δ Sct and γ Dor stars? log T eff log (L/L  )

© JCD δ Sct and γ Dor stars? log T eff log (L/L  )

δ Sct stars:γ Dor stars: Periods of 8h – 3days g-modes flux blocking mechanism T eff = K Periods of 30min - 6h p-modes Κ mechanism T eff = K Ground-based discoveries: δ Sct: # > 630 (Rodriguez et al. 2001) confirmed γ Dor: # > 70 candidate γ Dor: # > 80 (Henry et al. 2007; De Cat et al.)

What is the relation between δ Sct and γ Dor stars? + δ Sct o γ Dor ★ δ Sct+γDor

★ : pre-CoRoT/Kepler hybrid stars ★ ★  Probe envelope and deep stellar interior! Ground-Based: Henry & Fekel 2005; Uytterhoeven et al Pre-CoRoT and pre-Kepler: few observational hybrid cases MOST: King et al. 2006; Rowe et al CoRoT: Hareter et al Kepler: Grigahcène et al Many hybrid stars! First CoRoT / Kepler results

(Uytterhoeven et al. 2008) (Chapellier et al. 2011) CoRoT data HD49434 Ground-based data HD49434 Space data promise a breakthrough! - sample 1d periods - μmag amplitudes - large sample of stars

More intruiging prospectives! solar-like oscillations are predicted! (Houdek et al. 1999, Samadi et al. 2002) Kepler space mission detects the first δ Sct/solar-like hybrid star! Antoci et al., 2011, Nature, 477, 570

Launch: 7 March 2009 Lifetime: >3.5 years FOV: 10°x10° Instrument: 1.4m mirror, white light,42 CCDs Sampling: Long cadence (30min): ~1500 stars Short cadence (1 min): ~ 150 stars long-term monitoring of the stars! KASC: Kepler Asteroseismic Science Consortium ~5000 stars (8<V<17)

A sample of 750 candidate A-F type Kepler stars:  stars assigned to γ Dor and δ Sct KASC working groups  stars showing δ Sct or γ Dor-like behaviour in survey phase data Survey phase data: Q0,Q1,Q2,Q3,Q4 May 2009 – March 2010 Survey phase data: Q0,Q1,Q2,Q3,Q4 May 2009 – March 2010

best value of parameters from KIC (Kepler Input Catalogue), literature, or Ground-based data (Errors: 290K in T eff and 0.3 dex in log g)

1. Observational Classification Diversity! Lightcurves, periodogram, detected freqs

Observational Classification * δ Sct : only freqs in δ Sct domain (> 5 d -1 = 58 μH) * γ Dor : only freqs in γ Dor domain (< 5 d -1 = 58 μH ) * hybrid stars: freqs in both domains Diversity! Lightcurves, periodogram, detected freqs  comparable amplitudes  > 2 independent freqs in each regime  highest amplitude > 100ppm Beware of rotational/binarity effects! 3 main groups of A-F stars:

δSct

hybrid

γ Dor

* δ Sct stars: 27% * γ Dor stars: 13% * hybrid stars: 23% Total = 63% 23% is a candidate hybrid star!!! (171 stars, i.e. 36% of stars assigned to the 3 groups)

Other classes: No clear periodicity = 16% 10% candidate solar-like ↵ binary = (at least) 5% 3.5% = EB ↵ Rotation/stellar activity = 8% B star = 1% red giant = 6% Cepheid = 1 star

Observational instability strips (Rodríguez & Breger 2001; Handler & Shobbrook 2002)

 Hybrids are not confined to small overlapping region in HR-diagram! Results:  γ Dor pulsations in cooler and hotter stars  δ Sct pulsations beyond red edge of IS

 Hybrids are not confined to small overlapping region in HR-diagram! Results:  γ Dor pulsations in cooler and hotter stars  δ Sct pulsations beyond red edge of IS  revise observational instability strips  Known driving mechanisms do not explain behaviour! 

Effective temperature δ Sct hybrid γ Dor Great concentration of stars near overlap of instability strips Effective Temperature δ Sct, γDor, hybrid stars coincide  what is difference?  What makes a star a δ Sct, γDor, or hybrid?

δ Sct * up to 500 non-combination frequencies detected * Current Instability models: hybrid stars have a ‘frequency gap’ 5-10d -1 Gap not observed in Kepler data! δ Sct hybrid γ Dor 2. Characterization in terms of number of frequencies, amplitudes, frequency range

Summary: 1. variety of variable behaviour * 3 groups (63%): δ Sct, γ Dor and hybrid stars * 23% of the sample shows hybrid behaviour!

Summary: 1. variety of variable behaviour * 3 groups (63%): δ Sct, γ Dor and hybrid stars * 23% of the sample shows hybrid behaviour! 2. γ Dor and δ Sct stars beyond the instability strips? constant stars inside the instability strips?  confirmation of Teff and log g needed!  revision of the instability strips ?!

Summary: 3. What makes a star a δ Sct, γ Dor, or hybrid star? They coincide in the (Teff,logg)-diagram!  pulsation mechanisms to supplement κ mechanism and convective flux blocking to explain the existence of ‘hybrids’ in cool/hot stars? stochastic excitation convective driving cfr. white dwarfs κ Mechanism –related effect effect of radiative levitation (Houdek 1999; Turcotte et al. 2000; Goldreich & Wu 1999; Löffler 2000)

Summary: 3. What makes a star a δ Sct, γ Dor, or hybrid star? They coincide in the (Teff,log g)-diagram!  pulsation mechanisms to supplement κ mechanism and convective flux blocking to explain the existence of ‘hybrids’ in cool/hot stars? stochastic excitation convective driving cfr. white dwarfs κ Mechanism –related effect effect of radiative levitation (Houdek 1999; Turcotte et al. 2000; Goldreich & Wu 1999; Löffler 2000) 4. and many more questions…

rich frequency spectra of tens of δ Sct, γ Dor and hybrid stars are being revealed for the first time!  Many new questions, but also new prospects for seismic studies of AF type stars !

Needed! a)info on Teff, log g, vsini, metallicity,… b)Time-series for mode-ID ground-based support observations! KASC GB follow-up >800 nights 39 instruments 23 observatories 12 countries including ARCES/ARC 3.5m telescope APO!

Addendum: = Network of robotic 1m-telescopes located at different latitudes and longitudes to ensure continuous monitoring project led by Aarhus University, Denmark

Science goals: 1.Asteroseismology of bright stars  RV and line-profile studies 2. follow-up and characterisation of exoplanets  high-resolution imaging: dual-band photometry  precise RV measurements 1. High-resolution échelle spectrograph (R~100,000) Iodine cell: precision <10m/s 2. Dual-colour Lucky imaging filterwheel 6 colours 2 instruments:

Goal: network of 6+ telescopes Prototype on Teide Observatory, Tenerife status: installation foreseen in Feb/March nd node at Delingha Observatory, China status: funding approved Installation foreseen rd node at APO, only spectrograph attached to 1-m NMSU telescope? status: NFS funding proposal to be submitted 4 th + 5 th node: Danish funding proposal under evaluation

Thank you! Waiting for first light of SONG-OT...