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The Small Star Opportunity to Find and Characterize Habitable Planets

The Small Star Opportunity to Find and Characterize Habitable Planets. Jacob Bean. Harvard-Smithsonian Center for Astrophysics. Collaborators:. Texas Fritz Benedict Chris Sneden Barbara McArthur Amber Armstrong (ugrad, now STScI) Germany Andreas Seifahrt (now UC Davis) Ansgar Reiners

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The Small Star Opportunity to Find and Characterize Habitable Planets

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  1. The Small Star Opportunity to Find and Characterize Habitable Planets Jacob Bean Harvard-Smithsonian Center for Astrophysics

  2. Collaborators: Texas Fritz Benedict Chris Sneden Barbara McArthur Amber Armstrong (ugrad, now STScI) Germany Andreas Seifahrt (now UC Davis) Ansgar Reiners Stefan Dreizler Derek Homeier Günter Wiedemann Sweden Henrick Hartman Hampus Nilsson Japan Tomonori Usuda Bunei Sato Ichi Tanaka Harvard David Charbonneau Jean-Michel Désert Zachory Berta (grad) MIT Sara Seager UC Santa Cruz Eliza Miller-Ricci Kempton Jonathan Fortney Princeton Nikku Madhusudhan Georgia State Todd Henry Funding from: NASA, German DFG, ESO, & the EU

  3. Planets detected with RV and transit data compiled by Jean Schneider

  4. Key Results: gas giants in focus • statistical properties • first-order atmospheric characterization of hot planets • feedback to how we view the outer Solar System

  5. Key Results: gas giants in focus • statistical properties • first-order atmospheric characterization of hot planets • feedback to how we view the outer Solar System • Key Questions for the Future: towards other Earths • statistical properties • basic physical properties • atmospheric properties • habitability • inner Solar System in context strongly coupled

  6. Key Results: gas giants in focus • statistical properties • first-order atmospheric characterization of hot planets • feedback to how we view the outer Solar System • Key Questions for the Future: towards other Earths • statistical properties • basic physical properties • atmospheric properties • habitability • inner Solar System in context strongly coupled Low-mass stars offer a shortcut using RV and transit methods

  7. Summary Detecting planets: near-infrared radial velocities • Initiated a comprehensive search for planets around nearby, very low-mass stars (M* < 0.2 Msun) • NIR radial velocities with CRIRES at the VLT and IRCS at Subaru using a new gas cell • Paved the way for a new instrument that will be capable of finding characterizable habitable worlds Characterizing planets: transit spectroscopy • First atmospheric study of a “super-earth” exoplanet – only possible because the planet orbits a very low-mass star • Measurements obtained using a new ground-based technique • First results guide new theoretical and observational work

  8. The shortcut to habitable planets #1 Low-mass advantage for dynamical methods RV signal ∝ M*-2/3 Example – 1 Mearth at 1 AU K = 0.09 m/s for M* = 1.0 Msun K = 0.42 m/s for M* = 0.1 Msun Current state-of-the art is 1 m/s Transit depth ∝ R*-2 R* = 0.2 Rsun for M* = 0.15 Msun

  9. The shortcut to habitable planets #1 Low-mass advantage for dynamical methods Transit Spectroscopy Reflection & Emission both ∝ R*-2 Transmission

  10. The shortcut to habitable planets #2 Low-mass brings in habitable zone (Kasting et al. 1993) better for RV signal ∝ a-1/2 better for transits probability ∝ a-1 frequency ∝ a-3/2 (Selsis et al. 2007) P = 3 d P = 35 d

  11. The shortcut to habitable planets #3 Low-mass stars most numerous 75% M dwarfs 50% M* < 0.2 Msun

  12. The shortcut to habitable planets Low-mass stars… light, small, low luminosity, ubiquitous Best chance to find a transiting habitable planet around a nearby star, and study its atmosphere (Deming et al 2008)

  13. Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

  14. Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

  15. Planet Detection: Technical Approach The problem faintness

  16. Planet Detection: Technical Approach The problem faintness normal RV measurements @ 10 pc Sun V=4.8 M0 V=9.0 M8 V=18.7

  17. Planet Detection: Technical Approach The problem faintness normal RV measurements more flux in the red/NIR

  18. Planet Detection: Technical Approach The solution – the NIR But there is another problem… calibration! No NIR RV precision like in the visible Best previous precision around 200 m/s

  19. Planet Detection: Technical Approach Calibration methods • Emission Lamps • few lines in the NIR (ThAr) • existing instruments have small wavelength coverage • doesn’t track image motion • requires a highly stabilized instrument

  20. Planet Detection: Technical Approach Calibration methods • Emission Lamps • few lines in the NIR (ThAr) • existing instruments have small wavelength coverage • doesn’t track image motion • requires a highly stabilized instrument • Gas Cells • iodine only works in the visible • no existing NIR gas cell • tracks all important effects for non-stabilized instruments with varying illumination

  21. Planet Detection: Technical Approach Calibration methods • Emission Lamps • few lines in the NIR (ThAr) • existing instruments have small wavelength coverage • doesn’t track image motion • requires a highly stabilized instrument • Gas Cells • iodine only works in the visible • no existing NIR gas cell • tracks all important effects for non-stabilized instruments with varying illumination ?

  22. Planet Detection: Technical Approach A NIR gas cell • Important considerations for the gas cell method: • cell should provide lines in a region where stars also have lines • avoid telluric lines • temperature stabilization necessary? • gas mixture not toxic, explosive, or corrosive

  23. Planet Detection: Technical Approach A NIR gas cell filled with 50 mb ammonia (NH3) wedged windows to eliminate fringing 18 cm 5 cm

  24. Planet Detection: Technical Approach First implementation in CRIRES at the VLT ESO

  25. Planet Detection: Technical Approach gas cell goes here • cryogenic, vacuum • λ = 1 – 5 μm, Δλ = 50 nm • R ≤ 100,000 • AO fed • long-slit • no gas cell temperature stabilization possible ESO

  26. Planet Detection: Technical Approach Gas cell lines overlap for in situ calibration stellar lines gas cell lines

  27. Planet Detection: Technical Approach Adaptation of the “iodine cell” method instrumental profile and sampling

  28. Planet Detection: Results Velocity precision tests (Bean et al. 2010b)

  29. Planet Detection: Results A giant planet around VB10? • Star Properties • spectral type: M8V • M* ~ 0.075 Msun • distance = 5.9 pc • V = 17.6 • K = 8.8 • Planet Properties • period = 272 days (0.744 yr) • mass = 6 ± 3 Mjup • inclination ~ edge-on • e, ω, and Tp not constrained • expected K ~ 1 km/s (Pravdo & Shaklan 2009)

  30. Planet Detection: Results A giant planet around VB10? (Bean et al. 2010a)

  31. Planet Detection: Results A giant planet around VB10? (Bean et al. 2010a)

  32. Planet Detection: Results A giant planet around VB10? – probably not (Bean et al. 2010a)

  33. Planet Detection: Results Compare to other results Visible: Anglada-Escudé et al. 2010 Magellan + MIKE rms = 250 m s-1 NIR: Zapatero Osorio et al. 2009 Keck + NIRSPEC rms = 560 m s-1 | 200 m s-1 CRIRES + ammonia cell rms = 10 m s-1

  34. Planet Detection: Outlook • Initial 2 yr VLT survey complete • Identified gas giant planet candidates that need to be followed up • Started a northern hemisphere survey with Subaru + IRCS (Seifahrt PI, with Japanese collaborators) • Next step is to build a specialized instrument to get to 1 m s-1

  35. Planet Detection: Outlook Will enable the large-scale detection of planets down to a few times the mass of the Earth in the habitable zones of nearby M dwarfs PI: A. Quirrenbach, Heidelberg Operational in 2014 Telescope: Calar Alto 3.5m Spectral coverage: 0.5 – 1.7μm Precision: 1 m s-1 for late M dwarfs low-mass planet statistics and characterization

  36. Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

  37. Part I. Planet detection with the radial velocity method Part II. Planet characterization with transit spectroscopy

  38. Planet Characterization Recall small size advantage for transits… Reflection & Emission both ∝ R*-2 Transmission

  39. Planet Characterization Detection of a “super-earth” around a low-mass star planet properties: M = 6.5 Mearth R = 2.7 Rearth Teq < 550 K GJ 1214b star properties: M = 0.16 Msun R = 0.20 Rsun super-earth ≡ 1 < mass < 10 Mearth (Charbonneau et al. 2009)

  40. Planet Characterization Detection of a “super-earth” around a low-mass star planet properties: M = 6.5 Mearth R = 2.7 Rearth Teq < 550 K star properties: M = 0.16 Msun R = 0.20 Rsun Kepler-10b Comparison to models should reveal composition… (Charbonneau et al. 2009)

  41. Planet Characterization Detection of a “super-earth” around a low-mass star 75% H2O / 22% Si / 3% Fe H2O planet properties: M = 6.5 Mearth R = 2.7 Rearth Teq < 550 K H/He Radius of planet (Rearth) Kepler-10b Earth-like star properties: M = 0.16 Msun R = 0.20 Rsun Planet is 0.5 Rearth too large to be 100% solid --> substantial gas envelope (Charbonneau et al. 2009)

  42. Planet Characterization Three models for GJ1214b (Rogers & Seager 2010)

  43. Planet Characterization Three models for GJ1214b Mini-Neptune solar composition H2O FeMgSiO3 Fe Primordial envelope approximately few percent by mass (Rogers & Seager 2010)

  44. Planet Characterization Three models for GJ1214b Water World Mini-Neptune solar composition H2O H2O FeMgSiO3 FeMgSiO3 Fe Fe Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted (Rogers & Seager 2010)

  45. Planet Characterization Three models for GJ1214b Water World true Super-Earth Mini-Neptune solar composition H2O H H2O FeMgSiO3 FeMgSiO3 FeMgSiO3 Fe Fe Fe Primordial envelope approximately few percent by mass Water vapor atmosphere from sublimated ices, H lost or never accreted Secondary atmosphere, formation interior to the snow line (Rogers & Seager 2010)

  46. Planet Characterization Transmission spectroscopy predictions for GJ1214b H-rich Transit Depth (%) “metal”-rich Wavelength (micron) (Miller-Ricci & Fortney 2010)

  47. Planet Characterization Transmission spectroscopy indirectly probes the atmospheric mean molecular weight scale height strength of features (Miller-Ricci, Seager, & Sasselov 2009)

  48. Planet Characterization Transmission spectroscopy indirectly probes the atmospheric mean molecular weight scale height strength of features (Miller-Ricci, Seager, & Sasselov 2009)

  49. Planet Characterization Transmission spectroscopy indirectly probes the atmospheric mean molecular weight scale height low mmw strength of features high mmw (Miller-Ricci, Seager, & Sasselov 2009) Nature

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