Solar-like oscillations in intermediate mass stars

Solar-like oscillations in intermediate mass stars Victoria Antoci SAC (Stellar Astrophysics Centre), Aarhus University, Denmark

Why are intermediate mass stars so important? Credit: Kupka & Weiss1999 1.Transition from deep and effective to shallow convective envelope. 2. Rotational boundary. Implications differential rotation activity transport of angular momentum mixing diffusion mass loss pulsation magnetic fields Credit: Royer 2009

Granulation observed in A type stars chromospheric activity (Simon 2002) : boundary at Teff> 8250K convective motion in the the atmospheres of A and Am stars (spectroscopy, e.g. Landstreet et al. 2009) strong evidence from photometry for granulation noise (Kallinger & Matthews 2010) Credit: Kallinger & Matthews 2010 Credit: Hans Kjeldsen

Asteroseismic HRD of pulsating stars κ mechanism acts like a heat engine stochastic excitation by the vigorous convective motion generating acoustic noise, a.k.a. solar-like oscillations convective blocking Credit: J. Christensen-Dalsgaard, G. Handler

Solar-like oscillations Credit: Houdek 2006 Amplitudes can be (more or less) predicted ALL modes in a certain frequency region are damped and re-excited ( by vigorous convective motion) max frequency of maximum power ( ) high radial order p modes (asymptotic relation, Tassoul 1980,1990) => large frequency separation (mean density) => small frequency separation (chemical composition=>age)

max Solar-like oscillations Credit: Houdek 2006 Amplitudes can be (more or less) predicted ALL modes in a certain frequency region are damped and re-excited ( by vigorous convective motion) max frequency of maximum power ( ) high radial order p modes (asymptotic relation, Tassoul 1980,1990) => large frequency separation (mean density) => small frequency separation (chemical composition=>age)

max Solar-like oscillations Credit: Houdek 2006 Amplitudes can be (more or less) predicted ALL modes in a certain frequency region are damped and re-excited ( by vigorous convective motion) frequency of maximum power ( ) Credit: GOLF team, from Aerts et al. 2010 max high radial order p modes (asymptotic relation, Tassoul 1980,1990) => large frequency separation (mean density) => small frequency separation (chemical composition=>age)

Ensemble Asteroseismology of solar-like stars = M M 1 2 R R 3 2 max = M/M (R/R) 2p T e /T e max Kjeldsen & Bedding (1995) Credit: Huber et al. 2011 =(0.263 ± 0.009)µHz( max /µhz) 0.772±0.005 Credit: Chaplin et al., Sci, 2011 Stello et al. (2009)

Solar like pulsation predicted to be excited at the red border of the instability strip by Houdek et al. (1999) and Samadi et al. (2002). A and F type stars: PMS, MS, immediate post MS chemically peculiar and normal stars roap stars Doradus stars δ Scuti stars Credit: J. Christensen-Dalsgaard, G. Handler

(rapidly oscillating) Ap stars strong global magnetic fields: 1-25 kg = large spots strong vertical stratification κ mechanism in the H ionization zone: magnetic field suppresses convection at the magnetic poles reducing the damping (Balmforth et al. 2001) Credit: Lueftinger et al. (2010)

rapidly oscillating Ap (roap) stars high radial order p modes ( ) periods similar to the Sun (4-20 min.) oblique pulsator model (pulsation axes between magnetic and rotation axes; Kurtz (1982), Bigot & Dziembowski (2002) new observations suggest more than one axes of pulsation (Kurtz et al 2011). NO solar-like oscillations in ro Ap stars observed but also not expected

Doradus stars high radial order gravity modes with periods 0.5-3 days (Balona, Krisciunas & Cousins 1994, Kaye et al. 1999, Handler 1999, Uytterhoeven et al. 2011, Balona et al. 2011,... ) convective blocking mechanism: acts also like a heat engine, the base of the convective zone is the driving region (Guzik et al. 2000; Dupret et al. 2005) convective envelope between xx and yy (Guzik et al. 2000). Dors outside the predicted IS => if the convective blocking mechanism is correct then convective envelope MUST have a specific depth => convection up to higher Teffs Credit: Uytterhoeven et al. 2011

Doradus stars from theoretical point of view should be the perfect candidates to show solar-like oscillations. s o f a r n o s o l a r- l i k e oscillations in gamma Dor stars and we do not understand why! observational bias? Tkachenko et al. 2012

δ Scuti stars pre-ms, MS and post-ms 1.5-2.5 M Teff= 6500-8500 K Pop I + II mean v sin i = 100 km/s radial & nonradial pulsation many hybrids ( Sct & Dor) p-,g- and mixed modes coherent pulsation (K mechanism) amplitudes cannot be predicted! not all modes are excited to observable amplitudes mode ID very time consuming

Frequency [c/d] 17.3 34.6 51.9 69.2 17.3 34.6 51.9 69.2 HD 187547 a.k.a. Superstar 47.5 51.9 56.2 60.5 64.8 69.2 73.5 based on Q3.2 data

Can the K-mechanism continuously excite the range 18-70 c/d (180-800 μhz)?

Can the K-mechanism continuously excite the range 18-70 c/d (180-800 μhz)? observed

κ-κ hybrid? Am star (atmospheric under-abundances in Sc and Ca, overabund. in Ba, Sr, Y). No large scale magnetic fields in Am stars (Auriere et al. 2010) => no roap/δ Scuti hybrid. (by the way Carrier et al. 2007 spectroscopic binary Am HD 209625 star (which is not classified as a δ Sct star), but did not detect any Pulsation from companion? Peaks between 43 and 75 c/d from a solar-type star? Unlikely! F type star => would be visible in spectrum, which is not! δ Scuti pulsation from companion? A or F type star => companion would be visible in spectrum, which is not! Contamination from other star <1.5% From RV (7 spectra in 153 days) no indication of binarity either.

No combination frequencies => high radial overtones as expected for solar-like oscillations. but is the driving really the convection in the outer layers? Δν 3.5c/d (40.5 μhz) ~ ν max 50-63 c/d (578-729 μhz) (using the scaling relation from Stello et al. 2009) observed ν max

Temporal behaviour of different modes δ Scuti mode Frequency [c/d] 18.15 56.8 267.8 Sun Solar-like mode in Superstar

strong evidence for solar-like oscillations in δ Scuti stars as predicted by Houdek et al. (1999) & Samadi et al (2002) because of the striking similarities between the observed signal at high frequencies and the properties of stochastically excited pulsation HD 187547 is the first δ Scuti star showing strong evidence for solar-like oscillations.

Q3+Q7+Q8+Q9+Q10+Q11

Stochastic mode? or just amplitude variations...? 450 days cannot resolve the peaks.

Is Superstar a δ Sct/ Dor/ solar-like oscillator???

Is Superstar a δ Sct/ Dor/ solar-like oscillator??? 3rd order combination? unlikely! has high ampli. Due to rotation? =>~2/3 of Vcrit. Remember is an Am star!

Is Superstar a δ Sct/ Dor/ solar-like oscillator??? 3rd order combination? unlikely! has high ampli. Due to rotation? =>~2/3 of Vcrit. Remember is an Am star! independent g-mode

Is Superstar a δ Sct/ Dor/ solar-like oscillator??? 3rd order combination? unlikely! has high ampli. Due to rotation? =>~2/3 of Vcrit. Remember is an Am star! independent g-mode 3rd order combination???

Splittings, splittings! My kingdom for some splittings... I can understand! 0.08 c/d= 0.92muHz Rotation? Yes can be, but there are splittings which cannot be due to rotation. Magnetic fields? Am stars seem not to have large scale magnetic fields. Companion(s)? Every mode would be split, which is not.

Another Superstar?

Thank you! 谢谢