A ground-based velocity campaign on Procyon

Tim Bedding (Univ. Sydney)

and about 50 others

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)

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)

n =18

What are stellar oscillations?

p-mode oscillations are standing sound waves

n =1 n =3n =2

frequencies tell us about internal sound speed

Pow

er

Fourier power spectrum of solar velocities:

n increases →

radial modes (ℓ =0)

ℓ=1 ℓ= 2 ℓ= 3

ℓ > 0 (non-radial)

Pow

er

Fourier power spectrum of solar velocities:

n increases →

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

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

2004

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?

The Velocity Campaign

Arentoft et al. (2008, ApJ)

11 telescopes at 8 observatories over 25 days

PROCYON

P

HARPSCORALIEMcDonaldLickUCLESOkayamaTautenburgSOPHIEEMILIESARGFIES

11 telescopes at 8 observatories over 25 days

10 days

HARPSSOPHIESARG

combined

Note: broad envelope

Bedding et al. (ApJ,in press)

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.

BISON freq.

échelle diagram

l=3l=1

l=0l=2l=0l=2

dn1

3

dn0

2

Frequency mod Dn

Dn

Echelle diagram of Procyon (noise-optimized weights)

Reducing sidelobes

possible mixed mode (narrow peak)

Noise-optimizedSidelobe-optimized

l=3l=1

l=0l=2

which ridge is which?

Do we have the correct ridge identification?

l=3,1l=2,0

Ridge structure:

l=3,1l=2,0

YES!

l=2,0l=1

Absolute model frequencuies:

model(Christensen-Dalsgaard)

NO!

A new method:scaled echelle diagrams

Bedding & Kjeldsen (2010, Comm. Asteroseismology)

greyscale = a Cen A Δ = Sun 0.78

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!

500 mHz

acoustic glitch at t=1000s(He ionization zone)

Asteroseismology using ridge spacings

Extracting the mode frequencies

Extracted peaks (“CLEAN”)

The mixed mode in Procyon

l=3, 1l=2,0

model with 1.6Msun and Z=3%(Christensen-Dalsgaard 2004)

Avoided crossings in subgiants

Bedding et al. (in prep.)

Bedding et al. (in prep.)

“C-D diagram”

“p-g diagram”Christensen-Dalsgaard (1988,2004)

Bedding et al. (in prep.)

Procyon: mass = 1.46±0.03 (2%; binary orbit)

Bedding et al. (in prep.)

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!