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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 Teff
log
(L/L
)
© JCD
δ Sct and γ Dor stars?
log Teff
log
(L/L
)
δ Sct stars: γ Dor stars:
•Periods of 8h – 3days
•g-modes•flux blocking mechanism
•Teff = 6900-7500K
•Periods of 30min - 6h
•p-modes
•Κ mechanism
•Teff = 6300-8600K
Ground-based discoveries:
δ Sct: # > 630 (Rodriguez et al. 2001)
confirmed γ Dor: # > 70candidate γ Dor: # > 80(Henry et al. 2007; De Cat et al.)
What is the relation between δ Sct and γ Dor stars?
+ δ Scto γ Dor
★ δ Sct+γDor
★ : pre-CoRoT/Kepler hybrid stars
★
★
Probe envelope and deep stellar interior!
Ground-Based: Henry & Fekel 2005; Uytterhoeven et al. 2008
Pre-CoRoT and pre-Kepler: few observational hybrid cases
MOST: King et al. 2006; Rowe et al. 2006
CoRoT: Hareter et al. 2010Kepler: Grigahcène et al. 2010
Many hybrid stars!
First CoRoT / Kepler results
(Uytterhoeven et al. 2008)
(Chapellier et al. 2011)
CoRoT dataHD49434
Ground-based dataHD49434
Space data promise abreakthrough!
- 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 starsShort 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 Teff 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 temperatureδ 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 excitationconvective 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 excitationconvective 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 instruments23 observatories12 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 imagingfilterwheel 6 colours
2 instruments:
Goal: network of 6+ telescopes
Prototype on Teide Observatory, Tenerife
status: installation foreseen in
Feb/March 2012
2nd node at Delingha Observatory, China
status: funding approved
Installation foreseen 2013
3rd node at APO, only spectrograph
attached to 1-m NMSU telescope?
status: NFS funding proposal to
be submitted
4th + 5th node: Danish funding proposal under evaluation
Thank you!
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