a ground-based velocity campaign on procyon tim bedding (univ. sydney) and about 50 others
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A ground-based velocity campaign on Procyon
Tim Bedding (Univ. Sydney)
and about 50 others
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Procyon A• angular diameter = 5.40±0.03 mas (1%;
VLTI)
• parallax = 285.9 ± 0.9 mas (0.5%; Hipparcos)
• radius = 2.04±0.02 (1%)
• mass = 1.46±0.03 (2%; binary orbit)
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Brown et al. (1991)
Martic et al. (2004)
Eggenberger et al. (2005)
Leccio et al. (2006)
Previous velocity observations
Fourier power spectra of Doppler measurements.
All have power centred at about 1 mHz (15-20 minutes)
0 1 2 3Frequency (millihertz)
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n =18
What are stellar oscillations?
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p-mode oscillations are standing sound waves
n =1 n =3n =2
frequencies tell us about internal sound speed
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Pow
er
Fourier power spectrum of solar velocities:
n increases →
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radial modes (ℓ =0)
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ℓ=1 ℓ= 2 ℓ= 3
ℓ > 0 (non-radial)
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Pow
er
Fourier power spectrum of solar velocities:
n increases →
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ℓ=2
ℓ=2
2 0
ℓ=0
ℓ=0 ℓ=1
ℓ=1
ℓ=1
ℓ=33 ℓ=3
n increases →
Dn = 135 mHz
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Brown et al. (1991)
Martic et al. (2004)
Eggenberger et al. (2005)
Leccio et al. (2006)
Previous velocity observations
Fourier power spectra of Doppler measurements.
All have power centred at about 1 mHz (15-20 minutes)
0 1 2 3Frequency (millihertz)
Dn ≈ 55mHz
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2004
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What we knew in 2007
• there is a power excess in velocity• amplitude is lower than predicted theoretically• agreement on Dn ≈ 55mHz.• no agreement on frequencies, presumaby due to
daily aliases/mixed modes/short mode lifetime?
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The Velocity Campaign
Arentoft et al. (2008, ApJ)
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11 telescopes at 8 observatories over 25 days
PROCYON
P
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HARPSCORALIEMcDonaldLickUCLESOkayamaTautenburgSOPHIEEMILIESARGFIES
11 telescopes at 8 observatories over 25 days
10 days
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HARPSSOPHIESARG
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combined
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Note: broad envelope
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Bedding et al. (ApJ,in press)
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ℓ=2
ℓ=2
2 0
ℓ=0
ℓ=0 ℓ=1
ℓ=1
ℓ=1
ℓ=33 ℓ=3
Dn = 135 mHz
What is an echelle diagram? Here is the solar power spectrumdivided into segments of width Dn.
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BISON freq.
échelle diagram
l=3l=1
l=0l=2l=0l=2
dn1
3
dn0
2
Frequency mod Dn
Dn
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Echelle diagram of Procyon (noise-optimized weights)
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Reducing sidelobes
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possible mixed mode (narrow peak)
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Noise-optimizedSidelobe-optimized
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l=3l=1
l=0l=2
which ridge is which?
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Do we have the correct ridge identification?
l=3,1l=2,0
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Ridge structure:
l=3,1l=2,0
YES!
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l=2,0l=1
Absolute model frequencuies:
model(Christensen-Dalsgaard)
NO!
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A new method:scaled echelle diagrams
Bedding & Kjeldsen (2010, Comm. Asteroseismology)
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greyscale = a Cen A Δ = Sun 0.78
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greyscale = Procyon
○=HD 49933 x 0.657(Benomar et al. 2010)
●=HD 49385 x 0.993(Deheuvels et al. 2010)
l=1l=2,0
YES!
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500 mHz
acoustic glitch at t=1000s(He ionization zone)
Asteroseismology using ridge spacings
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Extracting the mode frequencies
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Extracted peaks (“CLEAN”)
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The mixed mode in Procyon
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l=3, 1l=2,0
model with 1.6Msun and Z=3%(Christensen-Dalsgaard 2004)
Avoided crossings in subgiants
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Bedding et al. (in prep.)
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Bedding et al. (in prep.)
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“C-D diagram”
“p-g diagram”Christensen-Dalsgaard (1988,2004)
Bedding et al. (in prep.)
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Procyon: mass = 1.46±0.03 (2%; binary orbit)
Bedding et al. (in prep.)
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Lessons for SONG• combining data from multiple sites works well
(adjust weights to optimize noise and sidelobes)• cannot afford to take 2-3 years to analyse each
star! • low stellar background in velocity allows
detection of wider range of frequencies than may be possible with Kepler. In Procyon, broad envelope allowed us to measure He ionization glitch
• Kepler may not give many sun-like stars (18 Sco) or lower-mass stars (a Cen B, tau Cet)
• SONG will observe nearby stars with good parameters• let’s SING!