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)

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

HD69830 - Lovis et al., Nature, 2006

Long-term precisionσO-C ~ 0.8 m/s rms (raw)

~ 0.3 m/s rms (time-binned)

F. Pepe

Error sourcesStellar noise (p modes, activity)

Contaminants (Earth’s atmosphere, moon, etc.)

Measurement noise

✴Photon noise

✴Instrumental errors (from calibration to measurement)

✴Calibration accuracy (any technique)

Beat the stellar limitations with• good targe selection• clever observational strategy

F. Pepe

23/01/08 - Reunión Plan Estratégico 4

• 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)

E. Martín

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 RVSpot bias 0.25 as 1 m/sEarth @1AU amp 0.3 as 0.09 m/s

• Equiv ast noise ~0.08 as 0.3 as signature• Equiv RV noise ~0.45 m/s 0.09 m/s signature

M. Shao

• 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)

F. Malbet

F. Malbet

Henry 1998

Martín et al. 2004

10 pc sample

E. Martín

ConclusionsInstrumental 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 as level (best performance 300 as)

• Expensive space mission

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

F. Malbet