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Search for Extrasolar Planets

Search for Extrasolar Planets. Artie P. Hatzes Thüringer Landessternwarte Tautenburg. RV (m/s). Indirect Techniques. Radial Velocity Astrometry Microlensing Transits. Direct Techniques. 4. Spectroscopy/Photometry: Reflected or Radiated light 5. Imaging.

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Search for Extrasolar Planets

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  1. Search for Extrasolar Planets Artie P. Hatzes Thüringer Landessternwarte Tautenburg RV (m/s)

  2. Indirect Techniques • Radial Velocity • Astrometry • Microlensing • Transits Direct Techniques • 4. Spectroscopy/Photometry: Reflected or Radiated light • 5. Imaging Summary Search Techniques

  3. How many confirmed extrasolar planets are there? 169? (Extrasolar planet enyclopaedia) Answer: 13 Reason: A extrasolar planet is confirmed only if we know the true mass Transits + RV: OGLE-TR-10,56,113,132, TrES-1, HD 209458 Astrometry + RV: GL 876b-d, 55 CnC e-d, e Eri

  4. Extrasolar planet detections are mostly indirect detections, therefore you need 2 techniques to get the mass Radial Velocity + Transits Radial Velocity + Astrometry Direct imaging + Astrometry Keep in mind that most of the 160+ extrasolar planet candidates are just that…candidates

  5. A0 Interferometry Imaging RV C5,C6,C8 A5 A0 F3 Differential Imaging A5 M5 K5 Transits M7 Astrometry G0 M9 M0 M8 G2 M6 Darwin M5 COROT/Kepler Astrometry w/interferometry M7 Microlensing M9 Filling the parameter space requires ALL search techniques 2.0 Brown Dwarf 1.0 Jupiter 0.0 Log MJupiter Saturn -1.0 Uranus -2 Earth -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 Log Semi-major axis (AU)

  6. The words of Donald Rumsfeld, U.S. Secretary of Defense: „There are things we know that we know“ (known known) „There are things we know that we don‘t know“ (known unknown) „There are things we don‘t know we know“ (unknown known) „There are things we don‘t know that we don‘t know“ (unknown unknown) Maybe Mr. Rumsfeld was really talking about extrasolar planets

  7. Known Known: Global Statistics • 169 Extrasolar Planets around „normal“ stars • 18 Multiple Systems • 55 Cnc: 4 planets • 3 systems in resonant orbits (2:1, 3:1) • 9 transiting systems • 4 Pulsar planets

  8. Mass Distribution The Brown Dwarf Desert

  9. An Oasis: The Brown Dwarf around HD 137510 Endl et al. 2004 RV (m/s)

  10. Semi-major axis distribution ~20% at 1 AU !!

  11. Eccentricities • Period (days)

  12. RV=10 m/s RV=50 m/s Mass versus Orbital Distance Eccentricities

  13. The Dependence of Planet Formation on Stellar Mass Setiawan et al. 2005 A known unknown!

  14. Too faint (8m class tel.). Poor precision Ideal for 3m class tel. Main Sequence Stars RV Error (m/s) M0 K5 F0 K0 A5 G0 G5 A0 F5 Spectral Type

  15. Exoplanets around low mass stars • Ongoing programs: • ESO UVES program (Kürster et al.): 40 stars • HET Program (Endl & Cochran) : 100 stars • Keck Program (Marcy et al.): 200 stars? • HARPS Program (Mayor et al.): ??? • Results: • Giant planets (2) around GJ 876 • Hot neptune around GJ 436, GJ 876

  16. Exoplanets around massive stars Difficult on the main sequence, easier (in principle) for evolved stars

  17. Hatzes & Cochran (1993) M sin i = 3 MJupiter „If true, then it would seem that planetary companions around K giants have been detected.“

  18. Setiawan et al. 2005: P = 711 d Msini = 8 MJ M* = 1.9 s.m.

  19. HD 13189 P = 471 d Msini = 14 MJ M* = 3.5 s.m.

  20. HD 13189 : Short Term Variations

  21. Döllinger Ph.D. work: Another planet around a K giant star

  22. Period (days) Worry: All periods are in a narrow range TLS Sample (60 stars): 25-35 % show evidence for long period variations

  23. The Planet-Metallicity Connection? Valenti & Fischer

  24. The K giants with planets have low metallicities: HD 13189: [Fe/H] = –0.58

  25. The Planet-Metallicity Connection? Valenti & Fischer According to this trend 10% of all Hyades stars should have planets Problem: Paulson et al. (2004) surveyed 100 stars in the Hyades for 5 years and found no planets! Unknown Unknown

  26. Transit Searches Finally Producing results... rJupiter = 1.25

  27. HD 209458 b

  28. Mazeh, Zucker, and Pont (2004)

  29. Transits: Lots of known knowns* • True mass • Radius versus mass relationship • Composition of the atmosphere • Temperature (IR eclipses) In near future: COROT and Kepler will make significant contributions (hot neptunes, radii of giant planets at greater distances) * In combination with spectroscopy

  30. Center of mass D Astrometric Measurements of Spatial Wobble • Since D ~ 1/d can only look at nearby stars • Need interferometry for high precision • In near future should have an impact D = 8 mas at a Cen D = 1 mas at 10 pcs Current limits: 1-2 mas (ground) 0.1 mas (HST)

  31. q = P2/3 m D M2/3 Astrometry Example: The astrometric signature of Jupiter around a star at 10 pcs is 0.5 mas (1 mas peak-to-peak) The astrometric signal is given by: m r q = M D m = mass of planet M = mass of star r = orbital radius D = distance of star

  32. Jupiter only 1 milliarc-seconds for a Star at 10 parsecs

  33. Astrometry…not quite there Astrometric measurements need a 100-1000 times increase in the precision to have a major impact. RV method: • Year Precision No. of exoplanets • 300 m/s 0 • 2005 1-3 m/s 160+

  34. Astrometry Best astrometric measurements: HST: 0.1 mas 3 planets detected Ground based: ~1 mas 0 planets detected Ground based (VLTI)/ Space based (SIM, GAIA) interferometry should achieve a precision of 1– 100 mas Impact is in the near future

  35. S s • B = sin q q A2 x2 A1 x1 Beam Combiner Delay Line 2 d2 Delay Line 1 d1 A simple 2-telescope interferometer

  36. The astrometric error for interferometer measurements (mostly due to the Earth’s atmosphere): sdq = 300 B–2/3q t –1/2 B = baseline t = integration time q = star separation thus for a 20-arcsec separation and 100 m baseline the atmospheric error in one hour integration is 20 mas

  37. Space Interferometry Mission Precision 1– 4 mas

  38. Jupiter only 1 milliarc-seconds for a Star at 10 parsecs

  39. Direct Imaging Neuhäuser et al. 2005 100 AU Have we found the first image of an extrasolar planet?

  40. Direct Imaging Confirmation • Establish that the pair has a common proper motion • Establish that the companion is indeed a cool object • Derive a dynamical mass put less faith in Baraffe, Burrows, Wuchterl, etc And more faith in Kepler and Newton! Unknown Known Is a giant planet at 100 AU still a planet?

  41. The Search for a Second Earth • Radial Velocity signal: 9 cm/s • Transit depth: 8.4 x 10–5 • Astrometric signal (10pc) : 3 x 10–5 mas • Brightness contrast: 10–9 – 10–10 • Microlensing amplitude: >0.1 mag Kepler may find the first terrestrial planet at 1 AU, but how do you confirm this?

  42. M = 14 Mearth McArthur, Endl, Cochran, et al. 2004 55 CnC

  43. Searching for the Blue Dot Indirect methods are fine, but what we really would like is a picture! But how do we know it is an Earth-like planet

  44. Summary • Radial Velocity Method • Pros: • Most successful detection method • Is often needed to get the true mass • Distance independent • Will provide the bulk (~1000) discoveries in the next 10+ years • Cons: • Only for late-type stars • Most effective for short (< 10 – 20 yrs) periods • Only high mass planets • Other phenomena (pulsations, spots) can mask as an RV signal

  45. Summary • Astrometry • Pros: • Effective for long period planets • Is needed to get the true mass • Cons: • Precision is not sufficient yet • Other phenomena (pulsations, spots) can mask as an RV signal • Only nearby stars

  46. Summary • Photometric transits • Pros: • Gives you the planet radius • With RV gives you the true mass • Studies of the atmosphere composition and albedo via in-transit spectroscopy and secondary eclipses • Space-based transit searches can find Earth-like planets • Cons: • Only effective for short period planets • Spectroscopic follow-up on faint targets can be difficult • Requires exquisite photometric precision • Stellar noise can easily mask signal

  47. Summary • Microlensing • Pros: • One of the few techniques that can detect an Earth-like planet • Good for statistical studies of extrasolar planets • Cons: • One shot event, cannot go back to study host star • Orbital parameters not well known

  48. Summary • Direct imaging • Pros: • Seeing is believing • Lots of press coverage • Studies of the extrasolar planet itself • Cons: • Very very difficult • Mass is unknown, unless looking at ones found by RV method first

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