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Advancements in Radial Velocities and Astrometry for Detecting Habitable Planets

This panel discusses the comparative advantages and limitations of radial velocity (RV) and astrometry techniques in identifying habitable planets. Key topics include the performance constraints of RV methods in both visible and near-infrared (NIR) ranges, astrometry's potential in detecting habitable zones, and the impact of stellar noise and contaminants. Expert speakers address the precision challenges, the future prospects of astrometry, and the necessity for new instruments to enhance detection capabilities. The insights aim to guide the designation of habitable planets for follow-up studies.

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Advancements in Radial Velocities and Astrometry for Detecting Habitable Planets

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  1. Satellite meeting - Designating habitable planets for follow-up study: what are the relative parameter spaces of RV and astrometry? (P2 Panel) • Scientific program • Radial velocities to detect habitable planets in the visible: performance and limitations (F. Pepe) • Radial velocities to detect habitable planets in the nIR: performance and limitations (E. Martin) • Astrometry to detect habitable planets: performance and limitations (M. Shao) • Astrometry to detect habitable planets: future prospects (F. Malbet) • Double blind tests (W. Traub)

  2. σO-C~ 0.8 m/s rms (raw) ~ 0.3 m/s rms (time-binned) Long-term precision P1 = 8.67 days M sini = 10.2 M P2 = 31.6 days M sini = 11.8 M P3 = 197 days M sini = 18.1 M F. Pepe HD69830 - Lovis et al., Nature, 2006

  3. Error sources • Beat the stellar limitations with • good targe selection • clever observational strategy • Stellar noise (p modes, activity) • Contaminants (Earth’s atmosphere, moon, etc.) • Measurement noise • Photon noise • Instrumental errors (from calibration to measurement) • Calibration accuracy (any technique) F. Pepe

  4. NIR is full of telluric lines => RV precision limit of 20 m/s • Nearby cool stars are plentiful • HZ planets have stronger RV signal • Current NIR RV precision ~20 m/s • New instruments & calibration methods need to be developed to reach 1 m/s (CRIRES, CARMENES, NAHUAL, PRVS, SPIROU) 4 E. Martín

  5. Impact of Star Spots on Astrometry and RV We find that for the Earth-Sun system, starspots do not appreciably interfere with astrometric detection. impose significant requirements on the number of measurements and duration of an observing campaign needed for radial velocity detection. Example: Spot area 10-3, Sun @ 10pc Astrometry RV Spot bias 0.25 mas 1 m/s Earth @1AU amp 0.3 mas 0.09 m/s • Equiv ast noise ~0.08 mas  0.3 mas signature • Equiv RV noise ~0.45 m/s  0.09 m/s signature • Relative to a planet in a 1yr orbit, the star spot noise for RV is ~10X larger than for Astrometry. (short periods favor RV, long periods favor Astrometry) M. Shao

  6. F. Malbet

  7. F. Malbet

  8. 10 pc sample Henry 1998 Martín et al. 2004 E. Martín

  9. Conclusions • Instrumental considerations: • RV is a time-tested technique, although no proof yet that it can get to a few cm/s (superEarths are better)  but only minimum mass • Prospects seem good (50 cm/s today) • NIR RVs can help for planets in the HZs around cool stars  ~10-20 m/s achieved so far but 1 m/s needed • Astrometry has 2D information and it is not severely affected by inclination degeneracy • Astrometry has not been tested at the mas level (best performance 300 mas) • Expensive space mission

  10. Astrophysical noise • Limitation to visible RVs since only inactive stars (a few 10s within 15 pc) can be observed to the highest accuracy • This is less stringent for NIR RVs  ½ of the jitter and more stars (Ms) • Astrometry is less affected in solar-type stars • Final considerations • Astrometry seems better suited to carry out a census of habitable planets for follow up • Especially so for Earth analogs (i.e., solar-like stars) • RVs are more cost-efficient and can find some valuable systems early on (JWST?) • NIR RVs have good potential for nearby stars

  11. F. Malbet

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