Why observe M dwarfs?Why observe M dwarfs?

M9V M6V M3V M1V

Due to current technical limits (~ 1m/s ---), the reflex velocities of earth-mass planets in the HZare only observable around mid- to late-M dwarf stars

Why observe in the Why observe in the near-IR?near-IR?GL 406 M6V

PRVS

Y+J+H

Radial velocity precision, v = c Q-1 Ne-0.5

Bouchy et al. (2001)

Although M dwarfs are much brighter inthe NIR than the optical (more photo-electrons Ne), simulations for v must include the measurable amount of Doppler Information (Q) in optical and NIR spectra

(IRTF/SpeX R~2000)

Simulations: Q,Simulations: Q,v v vs v vs v sinsini i (8 m)(8 m)

R=70,000S/N=300

R=70,000S/N=300

R=70,000S/N=300

M3V

M6V

M9V

Theory/Obs ComparisonTheory/Obs Comparison

GL 406 (Wolf 359) M6VJ-band, R=20,000 Keck/NIRSPEC(McLean et al. 2007)Qmodel ~ 800Qdata ~ 1600

From high R data, M dwarf theoretical models (Peter Hauschildt) underestimate the Doppler Information (Q) in the NIR by factors > 2 Considering models + data there is a clear advantage to observing mid- late-M dwarfs in NIR (Y+J+H bands, photon-limited) over the optical

What is the intrinsic RV jitter of What is the intrinsic RV jitter of M dwarfs?M dwarfs?

Causes of intrinsic jitter Rotation + star spots/surface features Activity/variability Turbulence and pulsation

Results from optical RV surveys For non-active M dwarfs, average intrinsic jitter ~ 4 m/s No significant trend with SpT

Expectations for NIR RV surveys Higher v sin i for late-M dwarfs But 2 x better star spot contrast in NIR means intrinsic jitter likely < 4 m/s for non-active M dwarfs

Keck optical sample, Wright et al. (2005)

F stars

G & K stars

M stars

Technical challenges of RV Technical challenges of RV in the NIRin the NIR

Simultaneous wavelength fiducial covering NIR is required for high precision RV spectroscopy

No suitable gas/gases for a NIR absorption cell found Use simultaneously exposed arcs (Th-Ar, Kr, Ne, Xe) and ultra-stable spectrograph

~ 300 bright lines to monitor drift during observing (using super exposures and sub-array reads of arc lines) ~ 1000 lines for PSF and wavelength calibration (daytime)

Use of a laser comb possible following R&D

Significant telluric contamination in the

NIR Mask out 30 km/s around telluric features deeper than 2% At R=70,000 (14,000 ft, 2 mm PWV, 1.2 air-mass) this leaves 87% of Y, 34% of J, and 58% of H Simulations indicate resulting ‘telluric jitter’ ~ 0.5 m/s

PRVS ‘Pathfinder’ instrument being used at

Penn State supports this modeling (see Pathfinder poster below)

Realistic PRVS Realistic PRVS SimulationsSimulations

M6VTeff = 2800 KLog g = 5v sin i = 0 km/s

ModelTelluricOH

Fourier AnalysisFourier Analysis

Doppler info of spectrum F() related to f/.

FT (f/) = k f(k) where spatial freq k = 2/

Plot k f(k) vs k for M6V and v sin i = 0 km/s

Over-plot FT (Gaussian PSF) for R=20k, 50k, 70k, 100k

RESULT: optimum R 70,000

FT (f/)F()

R=70,000 Y

V

J

H

K

Radial Velocity Error Radial Velocity Error BudgetBudget

PRVS SENSITIVITY NICHEPRVS SENSITIVITY NICHE

M9V M6V M3V M1V

PRVSNIR RV

OPTICAL RV(8 m)

Improved intrinsic RV jitter in NIR?

Mean intrinsic RV jitter ~ 4 m/s measured in optical

S/N break-even point between opticaland NIR surveys is early- to mid-M SpT

G2V

Habitable zone is more accessible around Habitable zone is more accessible around M dwarfsM dwarfs

when observed in the NIRwhen observed in the NIR

Kasting et al. (1995)

M Star Planet Habitability: Special issue of Astrobiology (February 2007),including review by Tarter et al.

Required RV precisionto detect 1 ME

1.0 m/s 0.1 m/s