Presentation on theme: "Why observe M dwarfs? Due to current technical limits"— Presentation transcript:
1 Why observe M dwarfs? Due to current technical limits (~ 1m/s ---), the reflex velocitiesof earth-mass planets in the HZare only observable aroundmid- to late-M dwarf starsM9VM6VM3VM1V
2 Why observe in the near-IR? GL 406 M6V(IRTF/SpeX R~2000)Radial velocity precision, v = c Q-1 Ne-0.5Bouchy et al. (2001)Although M dwarfs are much brighter inthe NIR than the optical (more photo-electrons Ne), simulations for v mustinclude the measurable amount ofDoppler Information (Q) in optical andNIR spectraPRVSY+J+H
3 Simulations: Q,v vs v sini (8 m) M3VR=70,000S/N=300M6VR=70,000S/N=300M9VR=70,000S/N=300
4 Theory/Obs Comparison From high R data, M dwarf theoreticalmodels (Peter Hauschildt) underestimatethe Doppler Information (Q) in the NIRby factors > 2Considering models + data there isa clear advantage to observing mid-late-M dwarfs in NIR (Y+J+H bands,photon-limited) over the opticalGL 406 (Wolf 359) M6VJ-band, R=20,000 Keck/NIRSPEC(McLean et al. 2007)Qmodel ~ 800Qdata ~ 1600
5 What is the intrinsic RV jitter of M dwarfs? Keck optical sample, Wright et al. (2005)Causes of intrinsic jitterRotation + star spots/surface featuresActivity/variabilityTurbulence and pulsationResults from optical RV surveysFor non-active M dwarfs,average intrinsic jitter ~ 4 m/sNo significant trend with SpTExpectations for NIR RV surveysHigher v sin i for late-M dwarfsBut 2 x better star spot contrast in NIRmeans intrinsic jitter likely < 4 m/sfor non-active M dwarfsF starsG & K starsM stars
6 Technical challenges of RV in the NIR Simultaneous wavelength fiducial covering NIR is requiredfor high precision RV spectroscopyNo suitable gas/gases for a NIR absorption cell foundUse simultaneously exposed arcs (Th-Ar, Kr, Ne, Xe) and ultra-stable spectrograph~ 300 bright lines to monitor drift during observing (using super exposuresand sub-array reads of arc lines)~ 1000 lines for PSF and wavelength calibration (daytime)Use of a laser comb possible following R&DSignificant telluric contamination in the NIRMask 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 HSimulations indicate resulting ‘telluric jitter’ ~ 0.5 m/sPRVS ‘Pathfinder’ instrument being used at Penn Statesupports this modeling (see Pathfinder poster below)
7 Realistic PRVS Simulations M6VTeff = 2800 KLog g = 5v sin i = 0 km/sModelTelluricOH
8 Fourier Analysis F() FT (f/) Doppler info of spectrum F() related to f/.FT (f/) = k f(k) wherespatial freq k = 2/Plot k f(k) vs k for M6Vand v sin i = 0 km/sOver-plot FT (Gaussian PSF)for R=20k, 50k, 70k, 100kRESULT:optimum R 70,000VR=70,000YJHK
10 PRVS SENSITIVITY NICHE S/N break-even point between opticaland NIR surveys is early- to mid-M SpTOPTICAL RV(8 m)PRVSNIR RVMean intrinsic RV jitter ~ 4 m/s measured in opticalImproved intrinsic RV jitter in NIR?M9VM6VM3VM1VG2V
11 including review by Tarter et al. Habitable zone is more accessible around M dwarfs when observed in the NIR1.0 m/s0.1 m/sRequired RV precisionto detect 1 MEKasting et al. (1995)M Star Planet Habitability: Special issue of Astrobiology (February 2007),including review by Tarter et al.
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