Precision stellar physics from the ground

Precisionstellar physics

from the ground

Andrzej PigulskiUniversity of Wrocław, Poland

Special Session #13: High-precision tests of stellar physics from high-precision photometry

Asteroseismology:satellite observatories

SatelliteWIRE

(tracker)MOST CoRoT Kepler

Launch 1999 2003 2006 2009

Tel. diam. [cm] 5.2 15 27 90/140

V range < 4 < 6 5.5 - 9 (sei.)11.5 - 16 (plan.) 9 - 16

Typical precision*(single meas.) [ppm] 200 70 150 200

Detectionthreshold [ppm]** 80 20 3 3

* bright star, ~1-min (stacked) integration, ** for one-month long observations

Ground-based observing campaigns

DUTY CYCLE DETECTION THRESHOLD

< 60%, typically ~20% > 0.08 mmag, typically ~1 mmag

In comparison with satellite data: lower duty cycle, worse detection

threshold

Ground-based observing campaigns

NGC 6910 campaign: single-site data, 81 observing nights

Aliasingproblem

Observations:satellite vs. ground-based

SATELLITE DATA:•high duty cycle (up to ~100%),•outstanding precision,•low noise at low frequencies.

Do we still need ground-based photometry ?

LIGHTCURVE

FREQUENCYSPECTRUM

Pápics et al. (2012)

SPB star HD 43317, CoRoT

Evolutionary & puls. models,theoretical frequencies

global parameters

Asteroseismology:how it works?

Photometricobservations provide:• frequencies,• amplitudes,• phases.

Mode identification:quantum numbers ℓ,m,n

RVsline profiles

Frequency matching

Constraints on internal rotation, overshooting, ...

Mode ID of the remaining modes

Stabilitycheck

ASTEROSEISMOLOGY

Asteroseismology:how modes are identified?

How modes are identified?

1. asymptotic relations &rotational splitting

2. period ratios3. multicolour photometry

and/or spectroscopy(many mode ID methods)

Mode ID:asymptotic relations

J.Christensen-Dalsgaard

driving mechanism:- self-excited pulsations,- stochastically excited pulsations (solar-like)

character:- p modes (acoustic)- g modes (gravity)

asymptotic relations(for a given ℓ):p modes: equidistant in frequency g modes: equidistant in period

solar-likeoscillations


Bedding & Kjeldsen (2003)

The Sun

SOHO/VIRGO


Chaplin et al. (2010)

Δν = large separation

δν02 = small separation


White et al. (2011)

echelle diagram: frequency vs. frequency modulo large separation

Bedding et al. (2010)

ℓ= 2 0 1 2 0 3 1



asymptotic relations(for a given ℓ):p modes: equidistant in frequency g modes: equidistant in period

solar-likeoscillationspulsating

(pre)whitedwarfs

+hot

subdwarfs

rotational splitting:multiplets with (2ℓ+1) components


PG 1159 starRXJ 2117+3412

Average period spacing = 21.618 s ℓ = 1 modes

Vauclair et al. (2002)


Pulsating hot subdwarfKIC 5807616

Reed et al. (2011)



blue = observed

Mode ID:rotational splitting

Pulsating hot subdwarfKIC 10139564

Baran et al. (2012)

ℓ = 2

ℓ = 1



1. asymptotic relations & rotational splitting2. period ratios3. multicolour photometry


Mode ID:period ratios



(pre)whitedwarfs

+hot

subdwarfs

period ratios: double/triple-mode pulsators, radial modes

classicalpulsators

3O/1O

2O/1O

3O/2O

Mode ID:period ratios

Data: OGLE (LMC)Soszyński et al. (2008, 2010),Poleski et al. (2010)

HADS RRd

CEPHEIDS

1O/F



1. asymptotic relations & rotational splitting2. period ratios3. multicolour photometry


single-band (satellite)photometry is

sufficient for applying 1 and 2

Mode ID:multicolour photometry & spectroscopy


driving mechanism:- self-excited pulsations,- stochastically excited pulsations (solar-like)

character:- p modes (acoustic)- g modes (gravity)


(pre)whitedwarfs

+hot

subdwarfs

classicalpulsators

multicolour photometry& spectroscopy main-sequence pulsators + hot subdwarfs

main-sequencepulsators +

hot subdwarfs


Diagnostic diagrams:

Amplitude ratio vs. phase difference

Cugier et al. (1994)


Diagnostic diagrams:

Amplitude ratio (RV/phot.) vs. amplitude ratio (colour/band)

Cugier et al. (1994)


Diagnostic diagrams:β Cephei star ν Eridani:

goodness-of-fit parameter χ2 vs. ℓ

Daszyńska-Daszkiewicz & Walczak (2010)

0 1 1 1 1,2

1

0,1,3 1,2,3

2,5


Kepler β Cephei/SPB hybrids

Balona et al. (2011)


The methods using multicolour photometry and spectroscopy for mode ID require ground-based data.

A lot of interesting physics to study:

- internal (core) rotation,- amount of overshooting from the core,- diffusion,- testing stellar opacities.

An example: Z-effect

Pamyatnykh 1999

Rudolph et al. 2006

Physics to probe

Daszyńska-Daszkiewicz & Walczak (2010)

β Cephei star ν Eridani

Evolutionary & puls. models,theoretical frequencies

global parameters

Asteroseismology:how it works?

Photometricobservations provide:• frequencies,• amplitudes,• phases.

Mode identification:quantum numbers

RVsline profiles

Frequency matching

Constraints on internal rotation, overshooting, ...

Mode ID of the remaining modes

Stabilitycheck

ASTEROSEISMOLOGY

Ground-based vs. satellite

SATELLITE:•higher duty cycle (up to ~100%),•better precision,•low noise at low frequencies (?).

GROUND-BASED:•cheaper,•multicolour photometry (exc. BRITE, however),•spectroscopy,•all sky available.

Do we still need ground-based photometry ?

YES, WE DO...

β Cephei stars: ASAS contribution

(Southern) ASAS sky: δ < +28°, ~300 new β Cephei stars Pigulski & Pojmański (2010)

CoRoT „eyes”

Kepler field

Conclusions

1.Ground-based and satellite data are complementary.

• Ground-based data are crucial for characterization of all and asteroseismology of some stars.

2.There are good prospects for testing stellar physics and stellar interiors with ground-based data.

Precision stellar physics from the ground

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