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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
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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
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Planets around young stars
Important questions

• Can planets be detected in circumstellar disks?
• How long need planets to be formed?

• What processes affect the formation and evolution
  of planets?
• When and where do planets form?
• How do planets form?

P. Weise RV survey of stars with circumstellar
disks
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Suitable targets?

• Are young stars suitable for precise RV
  measurements?

Accuracy for BD comp.
Accuracy for planetary comp.
FEROS long-term accuracy

• Young (accreating) stars with circumstellar disks
  are usually slow rotators and precise RV is
  possible

P. Weise RV survey of stars with circumstellar
disks
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RV measurements

• Our survey consists of 580 stars
• Selected by youthness (lt300Myr), 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
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Crosscorrelation tool

• MACS is a new tool for crosscorrelating stellar
  spectra with theoretical templates

P. Weise RV survey of stars with circumstellar
disks
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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
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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
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Photometry

• Signals due to stellar spots are quasi-periodic
  and short-lived (for young stars)

• Photometric data is needed to check for
  short-periodic variation due to stellar spots and
  to identify stellar rotation period

Huerta, 2007
P. Weise RV survey of stars with circumstellar
disks
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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
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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
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Analysis strategy

• Analyse RV and Line Shape
• If Bisector does not correlate with RV
• Check other activity indicators
• Ha, 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
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Our Survey

• Targetlist of 580 young (lt600 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
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First results from our survey

• 208 stars have been observed

24 are RV stable
184 show RV variation
34 are SB
133 have vsinilt30km/s
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
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First results from our survey

• RV variation due to stellar spots

K0V star vsini26 km/s Age5 Myr
P. Weise RV survey of stars with circumstellar
disks
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First results from our survey

• Brown Dwarf candidates

Age 3-5Myr M 2.5 M? P 39 d m2sini 41 Mjup
Age 5Myr M 2 M? P 38 d m2sini 31 Mjup
P. Weise RV survey of stars with circumstellar
disks
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First results from our survey

• Planetary candidate

Age 10Myr M 1-2 M? P 34 d m2sini 5-9 Mjup
Age 75Myr M 0.9 M? P 92.7 d m2sini 4 Mjup
P. Weise RV survey of stars with circumstellar
disks
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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