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RIPL Radio Interferometric Planet Search

RIPL Radio Interferometric Planet Search. Geoffrey Bower UC Berkeley. Collaborators: Alberto Bolatto (UMD), Eric Ford (UFL), Paul Kalas, Anna Treaster, Vince Viscomi (UCB). MM Wavelength T Tauri Outburst in Orion. 2 nd most luminous stellar radio outburst

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RIPL Radio Interferometric Planet Search

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  1. RIPLRadio Interferometric Planet Search Geoffrey Bower UC Berkeley Collaborators: Alberto Bolatto (UMD), Eric Ford (UFL), Paul Kalas, Anna Treaster, Vince Viscomi (UCB)

  2. MM Wavelength T Tauri Outburst in Orion • 2nd most luminous stellar radio outburst • Briefly, brightest object in nebula • Required long baselines for detection • Magnetized T Tauri outburst • Contemporaneous with X-ray outburst • Many such objects likely to be found by CARMA & ALMA BIMA A configuration images (Bower, Plambeck, Bolatto, Graham, de Pater, McCrady, Baganoff 2004)

  3. Orion Nebula Parallaxw/Star GMR-A D=389 pc +/- 5% <0.1 mas/epoch Sandstrom, Peek, Bower, Bolatto, Plambeck 2007 Astro-ph/0706.2361

  4. Planets are Easy to Detect

  5. Companion to GJ 752B Detected w/Optical Astrometry Pravdo & Shaklan 2009

  6. White et al

  7. Gudel 2002

  8. Requirements of a Planet Survey • Low mass, nearby star • Astrometric displacement ~ 1 mas • Nonthermal radio emission • S ~ 1 mJy • F ~ GHz • Positional stability < 0.1 mas • Stable Image • Active, but not too active

  9. VLA M dwarf Flux Survey • 174 X-ray selected nearby M dwarfs • 10 minute VLA observations with 50 microJy rms • 40 detections of 29 stars • Rough agreement X-ray-radio correlation • No distinction between early and late types Bower, Bolatto, Ford, Kalas 2009, ApJ, in press

  10. Stars are Variable EV Lac Osten et al 2005

  11. Pilot Survey • 7 stars • 3 epochs • < 10 days • Hipparcos errors ~ 1 mas/y • Error over 10 days < 0.1 mas • Test • Detectability • Image stability 8000 km baselines 3 cm wavelength 1 mas resolution Astrometry ~ beam/SNR

  12. Results from Pilot Study:Apparent Motion of GJ 4247 15 mas 26 March 2006 25 March 2006 23 March 2006 Comparison of radio positions (points) with predictions from Hipparcos astrometry (solid line) reveal noise-limited rms residuals ~0.1 milliarcseconds, approximately 1 stellar diameter. Bower, Bolatto, Ford, Kalas 2009, ApJ, in press

  13. Pilot Study Results GJ 4247 GJ 896A Residuals are sensitivity limited ~0.2 mas GJ 65B

  14. VPAS Results

  15. Results from Pilot Study:Constraints on Companion Masses Planet Mass (Mjup) Semi-major Axis (AU) • Agreement with optical astrometry sets upper limit on acceleration and therefore companion masses • Mp < 3 – 10 MJup @ 1 AU • Sensitivity is limited by the short lever arm of VLBA observations: ~10 days • RIPL will extend this lever arm by factor of 100 Bower, Bolatto, Ford, Kalas 2009, ApJ, in press

  16. RIPLRadio Interferometric Planet Search • 30 stars • 12 epochs/4 years • VLBA + GBT • 512 Mb/s • 2 hours on source + 2 hours calibration • 25 microJy rms • 4 x lower than pilot survey • 1392 hours total Key question: What is fraction of long-period planets around low mass stars?

  17. RIPL Sample • 30 Stars • M1 – M8 • V = 9.6 – 15.8 mag • S_6cm = 0.1 – 6 mJy • D = 2.7 – 9.5 pc • 11 are members of known binary or multiple systems

  18. Simulated RIPL Results

  19. RIPL Sensitivity

  20. Current Status • Observing began Oct 2007 • Approximately 4 observations/month • Expected completion in mid-2011 • 40% complete • Pipeline processing underway (see poster by Vince Viscomi) • All stars detected • 60% of stars detected in every epoch

  21. Benefits of Astrometric Detection • Unique method • Breaks degeneracy of RV searches for mass, inclination angle, and ascending node • Probes low mass, active stars that are difficult to study with RV method • Planet fraction of low mass stars poorly determined • Detects planets that can be studied with extreme AO • Ties radio and optical astrometric reference frame

  22. RV Search ResultsFew M dwarf Hosts

  23. RV Search ResultsMost Planets are >10 pc Distant

  24. RV Search ResultsWhat is Mplanet/Mstar?

  25. Microlensing Search Results What is Mplanet/Mstar?

  26. Microlensing Search ResultsPlanets are Very Distant

  27. Comparative Sensitivity of Searches

  28. Future Directions for Radio Astrometry & Planets • Bandwidth upgrade for VLBA • 512 Mb/s  8 Gb/s • 4 x sensitivity • Calibrator density increases by 8 x • In-beam calibrators • 10 microarcsec accuracy  Neptune mass planets • Square Kilometer Array • 100 x sensitivity • 3000-5000 km baselines • 1 microarcsec accuracy  Earth mass sensitivity

  29. Summary • Radio astrometry is sensitive to sub-Jupiter mass planets around M dwarfs • We can already exclude BD companions to three stars based on only three measurements • RIPL survey will probe low mass, active star parameter space

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