Download Precision stellar physics from the ground

Precision
stellar physics
from the ground
Andrzej Pigulski
University of Wrocław, Poland
Special Session #13: High-precision tests of stellar physics from high-precision
photometry
Asteroseismology:
satellite observatories
Satellite
WIRE
(tracker)
MOST
CoRoT
Kepler
Launch
1999
2003
2006
2009
Tel. diam. [cm]
5.2
15
27
90/140
9 - 16
V range
<4
<6
5.5 - 9 (sei.)
11.5 - 16 (plan.)
Typical precision*
(single meas.) [ppm]
200
70
150
200
Detection
threshold [ppm]**
80
20
3
3
* bright star, ~1-min (stacked) integration, ** for one-month long observations
Ground-based observing campaigns
DUTY CYCLE
< 60%, typically ~20%
DETECTION THRESHOLD
> 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
Aliasing
problem
Observations:
satellite vs. ground-based
SATELLITE DATA:
•high duty cycle (up to ~100%),
•outstanding precision,
•low noise at low frequencies.
LIGHT
CURVE
SPB star HD 43317, CoRoT
Pápics et al. (2012)
FREQUENCY
SPECTRUM
Do we still need ground-based photometry ?
Asteroseismology:
how it works?
ASTEROSEISMOLOGY
Photometric
observations provide:
• frequencies,
• amplitudes,
• phases.
Mode ID of the
remaining modes
Stability
check
Constraints on
internal rotation,
overshooting, ...
RVs
line profiles
global
parameters
Frequency
matching
Mode identification:
quantum numbers ℓ,m,n
Evolutionary & puls. models,
theoretical frequencies
Asteroseismology:
how modes are identified?
How modes are identified?
1. asymptotic relations &
rotational splitting
2. period ratios
3. multicolour photometry
and/or spectroscopy
(many mode ID methods)
Mode ID:
asymptotic relations
driving
mechanism:
- self-excited pulsations,
- stochastically excited
pulsations (solar-like)
character:
- p modes (acoustic)
- g modes (gravity)
asymptotic relations
(for a given ℓ):
solar-like
oscillations
p modes: equidistant in
frequency
g modes: equidistant in period
J.Christensen-Dalsgaard
Mode ID:
asymptotic relations
The Sun
SOHO/VIRGO
Bedding & Kjeldsen (2003)
Mode ID:
asymptotic relations
Δν = large separation
δν02 = small separation
Chaplin et al. (2010)
Mode ID:
asymptotic relations
echelle diagram: frequency vs. frequency modulo large separation
ℓ= 2 0
White et al. (2011)
1
20 3
1
Bedding et al. (2010)
Mode ID:
asymptotic relations
asymptotic relations
(for a given ℓ):
p modes: equidistant in
frequency
g modes: equidistant in period
rotational splitting:
multiplets with
(2ℓ+1) components
pulsating
(pre)white
dwarfs
+
hot
subdwarfs
solar-like
oscillations
J.Christensen-Dalsgaard
Mode ID:
asymptotic relations
PG 1159 star
RXJ 2117+3412
Average period spacing = 21.618 s
ℓ = 1 modes
Vauclair et al. (2002)
Mode ID:
asymptotic relations
Pulsating hot subdwarf
KIC 5807616
Average period spacing = 242.12 s
ℓ = 1 modes
Reed et al. (2011)
Average period spacing = 139.13 s
ℓ = 2 modes
blue = observed
Mode ID:
rotational splitting
Pulsating hot subdwarf
KIC 10139564
ℓ=2
ℓ=1
Baran et al. (2012)
Asteroseismology:
how modes are identified?
How modes are identified?
1. asymptotic relations &
rotational splitting
2. period ratios
3. multicolour photometry
and/or spectroscopy
(many mode ID methods)
Mode ID:
period ratios
classical
pulsators
period ratios:
double/triple-mode
pulsators,
radial modes
pulsating
(pre)white
dwarfs
+
hot
subdwarfs
solar-like
oscillations
J.Christensen-Dalsgaard
Mode ID:
period ratios
3O/2O
Data: OGLE (LMC)
Soszyński et al. (2008, 2010),
Poleski et al. (2010)
2O/1O
CEPHEIDS
HADS
RRd
1O/F
3O/1O
Asteroseismology:
how modes are identified?
How modes are identified?
1. asymptotic relations &
single-band (satellite)
photometry is
rotational splitting
sufficient for applying
1 and 2
2. period ratios
3. multicolour photometry
and/or spectroscopy
(many mode ID methods)
Mode ID:
multicolour photometry & spectroscopy
driving
mechanism:
main-sequence
pulsators +
hot subdwarfs
- self-excited pulsations,
- stochastically excited
pulsations (solar-like)
classical
pulsators
character:
- p modes (acoustic)
- g modes (gravity)
multicolour
photometry
& spectroscopy
main-sequence pulsators +
hot subdwarfs
pulsating
(pre)white
dwarfs
+
hot
subdwarfs
solar-like
oscillations
J.Christensen-Dalsgaard
Mode ID:
multicolour photometry & spectroscopy
Diagnostic diagrams:
Amplitude ratio vs. phase difference
Cugier et al. (1994)
Mode ID:
multicolour photometry & spectroscopy
Diagnostic diagrams:
Amplitude ratio (RV/phot.) vs. amplitude ratio (colour/band)
Cugier et al. (1994)
Mode ID:
multicolour photometry & spectroscopy
Diagnostic diagrams:
β Cephei star ν Eridani:
goodness-of-fit parameter χ2 vs. ℓ
0
1
0,1,3
1
1
1
1,2,3
2,5
Daszyńska-Daszkiewicz & Walczak (2010)
1,2
Mode ID:
multicolour photometry & spectroscopy
Kepler β Cephei/SPB hybrids
Balona et al. (2011)
Mode ID:
multicolour photometry & spectroscopy
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
Rudolph et al. 2006
Pamyatnykh 1999
Physics to probe
β Cephei star
ν Eridani
Daszyńska-Daszkiewicz & Walczak (2010)
Asteroseismology:
how it works?
ASTEROSEISMOLOGY
Photometric
observations provide:
• frequencies,
• amplitudes,
• phases.
Mode ID of the
remaining modes
Stability
check
Constraints on
internal rotation,
overshooting, ...
RVs
line profiles
global
parameters
Frequency
matching
Mode identification:
quantum numbers
Evolutionary & puls. models,
theoretical frequencies
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
Kepler field
CoRoT „eyes”
(Southern) ASAS sky: δ < +28°, ~300 new β Cephei stars
Pigulski & Pojmański (2010)
Conclusions
1.Ground-based and satellite data are
complementary.
• Ground-based data are crucial for
characterization of all and
asteroseismology of some stars.
• There are good prospects for testing
stellar physics and stellar interiors with
ground-based data.