Observations of Red Giants in the NGC 6633 cluster by the Space Mission CoRoT

Transcription

1 Observations of Red Giants in the NGC 6633 cluster by the Space Mission CoRoT C. Barban 1 F. Baudin 2, E. Poretti 3, B. Mosser 1, S. Hekker 4, Th. Kallinger 5, A. Miglio 6, J. Montalban 7, T. Morel 7, Ph. Mathias 8 1 LESIA/UFE, Observatoire de Paris, France 2 IAS, Univ. Paris XI, France 3 INAF, Osservatorio Astronomico di Brera, Italy 4 Astronomical Institute Anton Pannekoek, Univ. of Amsterdam, TheNetherlands 5 Institute voor Sterrenkunde, Univ. Leuven, Belgium 6 School of Physics and Astronomy, Univ. of Birmingham, GB 7 Institut d Astrophysique et de Géophysique, Univ. de Liège, Belgium 8 IRAP, Univ. de Toulouse, France 1

2 Solar-like oscillations in red giants Amplitude > 10 ppm or m/s Period > hours Amplitudes larger than for the Sun Interesting targets for studying stars with different internal structure 2

3 However, Red Giants were not among the priority targets of CoRoT! Why? A little bit of history 3

4 During the preparatory phase of the COROT space mission at the beggining of 2000 s Magali Deluil COROT Exoplanet Working Group Eric Michel COROT Seismology Working Group We don t want Red Giants as CoRoT targets since we don t expect earth-like planets around these kind of stars! We don t want Red giants as CoRoT targets because 4

5 Non radial modes strongly damped in Red Giants First clear evidence of solar-like Hya oscillation spectrum oscillations in a red giant by Frandsen et al on Hya: Only radial modes detected. Radial modes are expected to dominate the oscillation spectrum of a Red Giant according to: Dziembowski et al Dziembowski et al Gough & Houdek 2002 non-radial modes strongly damped due to the high density contract between the core and the envelope. 5

6 + controversial results from space Oph oscillation spectrum Only radial modes by Barban et al. (2007) Or radial and non-radial modes by Kallinger et al. (2008) and Hekker et al. (2006) 6

7 leading to a concern about asteroseismology of Red Giants 7

8 And here comes COROT

9 The wealth of results obtained from seismology of red giants by CoRoT and Kepler is an extraordinary and unexpected gift to stellar physics! 9

10 HR diagram of Red Giants observed by CoRoT Chaplin & Miglio

11 HR diagram of Red Giants observed by CoRoT NGC 6633 Chaplin & Miglio

12 The NGC 6633 open cluster Distance = 375 pc (van Leeuwen 2009) <[Fe/H]<-0.04 (Jeffreis et al. 2002, Pauzen et al. 2010) HD

13 Why observing cluster stars? Stars in an open cluster: same distance same age same initial composition See e.g. with Kepler data: Miglio et al. (2012) Stello et al. (2011a) Stello et al. (2011b) Basu et al. (2011), 13

14 Red giants in NGC6633: CoRoT light curves 2 consecutive long Runs ~ 176 days 14

15 ed giants in NGC6633: CoRoT oscillation spectrum 15

16 ed giants in NGC6633: CoRoT oscillation spectrum HD is not a Red Giant with solar-like oscillations BUT a classical pulsator (B)!! 16

17 Mass and radius from seismic indices (e.g. Kjeldsen & Bedding 1995, Kallinger et al. 2010, Belkacem et al. 2011) Sun (Chaplin et al. 2011) : Δν = μhz ν max = 3.15 mhz Teff = 5777 K Chaplin et al

18 Red giants in NGC6633: seismic indices By using an EACF (Envelop Autocorrelation Function) method (Mosser & Appourchaux 2010) In agreement with values obtained by other methods by S. Hekker and Th. Kallinger HD Δν ~ 4.17 μhz ν max ~ μhz M ~ 3M R ~ 14R HD Δν ~ 1.09 μhz ν max ~ 9.18 μhz M ~ 4M R ~ 39R HD Δν ~ 3.87 μhz ν max ~ 39 μhz M ~ 2M R ~ 14R M clump ~2.8M HD is probably a clump star but then has a too low mass HD not a cluster member HD Δν ~ 5.33 μhz ν max ~ 66 μhz M ~ 3M R ~ 13R 18

19 Spectroscopic data ESO, La silla, Chile PI: E. Poretti Simultaneous bi-site observations OHP, France PI: Ph. Mathias Radial velocity of +16 km/s vs -28 km/s for the cluster + Barium abundance HD not a cluster member

20 ed giants in NGC6633: CoRoT oscillation spectrum 3 Red Giants with solar-like oscillations 20

21 Red giants in NGC6633: atmospheric parameters HD Teff (K) logg [Fe/H] HD Teff (K) logg [Fe/H] Spectroscopic data Spectroscopic + seismic data following Morel & Miglio et al HD discrepant in terms of [Fe/H] with logg from spectroscopic data but NOT when logg fixed to seismic data. HD Teff (K) logg [Fe/H] Morel et al. in prep. 21

22 Red giants in NGC6633: individual frequencies By fitting the observed individual modes with Lorentz-like profile. Echelle diagrams l=0 l=1 l=2 22

23 Relative flux Radial Velocity (km/s) Red giants in NGC6633: RV data Search for solar-like oscillations in Radial Velocity data CoRoT Work in progress! 23

24 Conclusion 3 Red Giants with solar-like oscillations + spectroscopic data: - Atmospheric parameters - Seismic indices M,R - Indidividual frequencies Cluster membership test New contrains on the evolution and internal stucture Of Red giants RV + I data : new test on Convection treatment via mode amplitude 24

25 THE END! THANKS 25