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!

Waiting for first light of SONG-OT...Waiting for first light of SONG-OT...