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Radial-velocity planet-search survey of stars with circumstellar disks

Radial-velocity planet-search survey of stars with circumstellar disks. Patrick Weise Johny Setiawan, Ralf Launhardt, André Müller, Thomas Henning Max-Planck-Institute for Astronomy, Heidelberg. Overview. Why are young planets important? Are precise RV measurements possible?

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Radial-velocity planet-search survey of stars with circumstellar disks

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  1. Radial-velocity planet-search survey of stars with circumstellar disks Patrick Weise Johny Setiawan, Ralf Launhardt, André Müller, Thomas Henning Max-Planck-Institute for Astronomy, Heidelberg

  2. Overview • Why are young planets important? • Are precise RV measurements possible? • MACS - A new Crosscorrelation tool • Stellar activity and its effects on RV measurements • First results from our survey P. Weise – RV survey of stars with circumstellar disks

  3. Planets around young stars • What processes affect the formation and evolution of planets? • When and where do planets form? • How do planets form? Important questions: • Can planets be detected in circumstellar disks? • How long need planets to be formed? P. Weise – RV survey of stars with circumstellar disks

  4. Suitable targets? • Are young stars suitable for precise RV measurements? • Young (accreating) stars with circumstellar disks are usually slow rotators and precise RV is possible Accuracy for BD comp. Accuracy for planetary comp. FEROS long-term accuracy P. Weise – RV survey of stars with circumstellar disks

  5. RV measurements • Our survey consists of 580 stars • Selected by youthness (<300Myr), dwarf stars, single stars • RV measurements are obtained by crosscorrelating stellar spectra with theoretical templates • The crosscorrelation profile gives RV and vsini of the star • Data reduction tools to crosscorrelate spectra of very young stars do not exists • We are currently developing a new tool P. Weise – RV survey of stars with circumstellar disks

  6. Crosscorrelation tool • MACS is a new tool for crosscorrelating stellar spectra with theoretical templates P. Weise – RV survey of stars with circumstellar disks

  7. Stellar activity • Stellar spectral line shapes are affected by • Cold and hot spots on the surface • Granulation • Non-radial pulsations • Stellar winds P. Weise – RV survey of stars with circumstellar disks

  8. Effect on RV • Spots and stellar winds alter spectral line shape • Measurable by line bisector variation Müller, 2008 • Line bisector varies with RV Huerta, 2007 P. Weise – RV survey of stars with circumstellar disks

  9. Photometry • Photometric data is needed to check for short-periodic variation due to stellar spots and to identify stellar rotation period • Signals due to stellar spots are quasi-periodic and short-lived (for young stars) Huerta, 2007 P. Weise – RV survey of stars with circumstellar disks

  10. NIR spectroscopy • Amplitude of RV signal decreases with wavelength when signal is due to spots • Observationally not yet proven. First results are inconclusive • This is an effect of lowered contrast between spot and photosphere P. Weise – RV survey of stars with circumstellar disks

  11. Observing strategy • More than 1 period has to be well sampled • To verify that amplitude and period of the signal are stable over time • Stellar spots are short-lived and amplitude changes • Several exposures in one night needed • To identify short-period stellar activity jitter • Rotational period from activity indicators (for young stars ~2-4 days) P. Weise – RV survey of stars with circumstellar disks

  12. Analysis strategy • Analyse RV and Line Shape • If Bisector does not correlate with RV: • Check other activity indicators • Hα, CaII, NaI, HeI, Line depth ratio FeI/VI, Veiling, photometric data • Check them for periodicity • If stellar activity indicators show no periodicity or other than RV measurements • Obtain NIR spectroscopy data P. Weise – RV survey of stars with circumstellar disks

  13. Our Survey • Targetlist of 580 young (<600 Myr) stars • 208 have been observed with FEROS and analysed for stellar parameters • 58 stars have multi-epoch data • 27 stars show signs of circumstellar disks and 8 are still accreating P. Weise – RV survey of stars with circumstellar disks

  14. First results from our survey • 208 stars have been observed 24 are RV stable 184 show RV variation 133 have vsini<30km/s 34 are SB 58 with more data 33 carefully analysed Signal due to stellar activity 8 Planetary comp. 2 BD comp. 4 P. Weise – RV survey of stars with circumstellar disks

  15. First results from our survey • RV variation due to stellar spots K0V star vsini=26 km/s Age=5 Myr P. Weise – RV survey of stars with circumstellar disks

  16. First results from our survey • Brown Dwarf candidates Age: 3-5Myr M*: 2.5 Mʘ P: 39 d m2sini: 41 Mjup Age: 5Myr M*: 2 Mʘ P: 38 d m2sini: 31 Mjup P. Weise – RV survey of stars with circumstellar disks

  17. First results from our survey • Planetary candidate Age: 10Myr M*: 1-2 Mʘ P: 34 d m2sini: 5-9 Mjup Age: 75Myr M*: 0.9 Mʘ P: 92.7 d m2sini: 4 Mjup P. Weise – RV survey of stars with circumstellar disks

  18. Summary • RV surveys of young stars are possible and very important for planet formation and early evolution • Stellar activity indicators have to be analysed very carefully • To improve data reduction for young stars, we are currently developing a new crosscorrelation tool • Our survey has just started to find potential planetary host stars with age  10 Myr • NIR spectroscopy has to be obtained to verify planetary companions P. Weise – RV survey of stars with circumstellar disks

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