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„We are not talking about cosmology...“ (A. Sozzetti)

„We are not talking about cosmology...“ (A. Sozzetti). The visitor from an ancient galaxy A planetary companion around an old, metal-poor Red Horizontal Branch star. R. J. Klement, J. Setiawan, Th. Henning, H.-W. Rix, B. Rochau, T. Schulze-Hartung, J. Rodman (ESA/ESTEC,NL).

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„We are not talking about cosmology...“ (A. Sozzetti)

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  1. „We are not talking about cosmology...“ • (A. Sozzetti)

  2. The visitor from an ancient galaxyA planetary companion around an old, metal-poor Red Horizontal Branch star • R. J. Klement, J. Setiawan, Th. Henning, H.-W. Rix, B. Rochau, • T. Schulze-Hartung, J. Rodman (ESA/ESTEC,NL)

  3. Motivational background • Do planets exist in external galaxies? Probably, but can we find out?

  4. Motivational background • Do planets exist in external galaxies? Probably, but can we find out? Yes we can!

  5. Motivational background • Do planets exist in external galaxies? Probably, but can we find out? • Observe nearby halo stream stars! Yes we can!

  6. Target selection The Helmi stream (Helmi et al. 1999)

  7. Target selection The Helmi stream (Helmi et al. 1999) SErGiO

  8. SErGiOStar of Extra-Galactic Origin Stellar parameters Literature & our results • Spectral type • Brightness (V) • Distance • Effective temperature • Radius • Surface gravity (log g) • Stellar mass • Metallicity [Fe/H] • Projected rotational velocity • Confirmed membership • Evolutionary stage • F2 • 9.84 mag • 700 pc • 6025 K • 6.7 RϿ • 2.69 • 0.82 MϿ • -2.09 • 10.3 km/s • Helmi stream • RHB

  9. Radial Velocity FEROS Sept. 2009 – July 2010 36 RV measurements 550 spectral lines for RV computations semi-amplitude 120 m/s uncertainty ~ 50 m/s FAP = 5.5 x 10e-6

  10. Sources of RV variation • Rotational modulation • Stellar pulsations • Rotational modulation • Stellar pulsations • Companion Starspots Line-profile asymmetry (bisector, BVS) Ca IIvariations (K & H, IR triplet) Other spectroscopic activity indicator (Hα, Teff variation, …) Photometric variations If the stellar activity can be excluded

  11. Sources of RV variation periodic variations of - the BVS ~ 5 days - CaII λ8498 ~ 6 days → rotational modulation → Vrot ~60 km/s SuperWASP photometry (~3600 data points) → stellar pulsations

  12. Planet: SerGiO jr.Setiawan, Klement et al., submitted Parameter Value • Period • Amplitude • Eccentricity • Semimajor axis • Minimum mass (m sin i) • 16.2 days • 120 m/s • 0.28 • 0.116 AU • 1.3 M(Jup) The estimated minimum mass places the companion in the substellar regime.

  13. What is interesting? • Sergio has an extra-galactic origin • Sergio has the lowest metallicity among known planet host stars, [Fe/H] = -2.09 ± 0.25 dex

  14. What is interesting? • The planet has survived the RGB phase during the stellar evolution. • Probably, at the beginning the planet had a larger orbit, but then spiraled in to a closer orbit • The star is a fast rotator. Sign that the inner planets have been engulfed already(?)

  15. Conclusions • Planets can indeed form around metal-poor stars as low as [Fe/H] ~ - 2 • Under certain circumtances planets can survive the red giant phase. The orbits may be changed during the stellar evolution. • SErGiO jr is the first planet detected in a tidal stellar stream and probably the first known exoplanetary system with an extragalactic origin.

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