Extrasolar Planet Science with High-Precision Astrometry Johannes Sahlmann Geneva Observatory The First Years Of ESO, Garching, 4.9.212
high-precision astrometry is powerful yields complete information, sensitive to orbit inclination -> ideal tool to determine the accurate planet mass distribution does not require spectral lines -> possible to target faint objects, e.g. brown dwarfs less sensitive to activity than radial velocity & transit method -> adapted to the search for planets around young/active stars
high-precision astrometry is powerful, but yet limited by the achievable precision a 1,min (mas) 1 1.1.1.1 1e 6 HIPPARCOS 1 3 1 2 1 1 1 1 1 1 2 1 3 Period (years) exoplanet.eu
astrometry constrains the true companion mass of RV companions radial velocities yield P, T, e, ω, K1 J. Sahlmann et HIPPARCOS astrometry (van Leeuwen, 27) CORALIE + HIPPARCOS 1 i and Ω from astrometry rch for brown-dwarf companions of stars.. IE 1. CORALIE 1!!1!!1!1 1.1 E.1.2.3.4..6.7.8.9 1. 1.1 2 1! HD43848 M2 sin i = 49 ± 2 MJup!2 Brown dwarf?. CORALIE+MIKE. i 2 = 173.2 ±. deg!!1!1 M2 =.2 ±. M 1!1 Sahlmann et al., 211, A&A, 2!4 1!"* (mas) 2!2!.1..... 1 N M-dwarf! 1 O C (mas) RV [m/s] 1!# (mas)!# (mas) 1 O C (mas) IE HD17289 2 RV [m/s] 2 HD17289!!1
the upper mass limit for planets orbiting Sun-like stars revealed with astrometry RV: 2 candidate brown dwarf companions in uniform sample (CORALIE) Astrometry: 1 companions have true masses > 8 M Jup, thus are M-dwarfs 1 BD companions remain in the sample of 1647 stars..6 ±.2 % of Sun-like stars have a brown dwarf companion within 1 AU. Norm. fraction.1.8.6.4.2 1 2 4 8 16 32 64 M 2 sin i (M Jup ) true masses? µas astrometry Cumulative distribution.9.8.7.6..4.3.2.1 Sahlmann et al., 211, A&A, 2 1 Planets void BDs 13 26 39 2 6 78 M 2 sin i (M J ) upper planet mass limit at ~2-3 M Jup Sahlmann et al., 211, IAUS 276
an IR-interferometer can realise 1 µas astrometry Ref. Target Target 3 arcsec T2 Baseline Beam combination T1 Reference K-band image of an ESPRI target. single-reference relative astrometry within a narrow field (~3 ) in K-band interference fringe separation in delay space is proportional to angular separation atmospheric limit: 1 µas for 3 min integration and a 1 m baseline (Shao & Colavita, 1992) sufficient for exoplanet detection around one of the stars
Exoplanet search with PRIMA PRIMA is the dual-feed facility of the VLTI Delplancke et al., 26 ESPRI = MPIA Heidelberg + LSW Heidelberg + Observatoire de Genève targets: hosts of RV planets, young stars, nearby main-sequence stars ESO/ G. Hüdepohl accuracy requirement: 1-1 µas under commissioning at Paranal observatory Launhardt et al., 28
binary star observations with PRIMA 2 1.22 1.24 1.26 1.28 11.3 1.32 1.34 Δδ (arcsec) 2 4 6 8 1 1.4 4 3 2 HD136 NACO 1. 1 1 2 3 1. 4 Δ α* (arcsec) Δα * (arcsec) HD1361 6 7 1.6 8 WDS PRIMA Δ δ (arcsec) 11.22 11.24 11.3 11.26 11.31 11.28 11.32 11.3 11.32 11.33 11.34 Nov 211 Jul 211 NACO 1.6 1.4 1.8 1. 1.6 Δ α* (arcsec) Nov 21 WDS PRIMA 1.6 1.62 O C (arcsec). 24(18).. 1. 2 4 6 8 1 12 14 16 18 3 µas! Δα* (mas) Years 2(23) since 1826 2(24) 23(12) 2(6) Δδ (mas) 8 2 6 4 2 2 2 4 24(18) (18) (23) (24) (6) 2Δα* (mas) 4 Δα* (mas) 2(23) 2(24) 23(12) 2(6) (12) 6 8 2 2 4 (24) (18) (6) (23) precision is sufficient but biases are yet too large for the planet search 2 4 Δα* (mas) (12) work in progress... 6 8 Sahlmann et al., in prep.
A FORS2/VLT search for planets around late-m and L dwarfs Are the conditions for planet formation met around ultra-cool dwarfs? 4.1 Data reduction ESO 81
FORS2/VLT is capable of 1 micro-arcsec astrometry Principles Lazorenko & Lazorenko 24, Lazorenko 26 - optical imaging with an exquisite camera + large telescope - large number of reference stars - detailed modelling of PSF distortions and atmospheric image motion Performance Lazorenko et al. 27, 29, 211 - precision of ~ µas on time scales of days-years - refuted planet around VB1 Planet search survey of 2 targets (ongoing) 2 late-m and early-l dwarfs close to the galactic plane within 3 pc 2-year programme: 1 epochs per target 1 nights of FORS2 (21-212) Detection limit ( M Neptune ) 2 1 at 3 pc 2 at 1 pc 1 1 2 1 2 Orbital Period (days)
measuring parallax and proper motion 2 Dwarf 4 1 Δ δ (mas) 1 average epoch uncertainty: 11 µas residual dispersion: 14 µas Δ δ (mas) 19 18 17 16 1 1 2 Δ α* (mas) 16 1 14 2 3 3 parallax 6.87 +/-.6 mas (relative) proper motion RA -234.31 +/-.9 mas/yr proper motion DE 8.48 +/-.7 mas/yr 38 37 36 Δ α* (mas) 3 174 17 176 Δ α* (mas) 177
preliminary results Frequency.2.1.1 136 epochs median precision: 11 µas residual dispersion: 134 µas.. 1 1. 2 Modulus (milli arcsec) 1. The long-term accuracy is < 13 µas per epoch. Better than GAIA for faint targets! 2. Exclude planets more massive than Jupiter in intermediate periods (~-4 days) for several targets. Sahlmann et al., in prep.
Conclusions High-precision astrometry is powerful: revealed upper-mass limit for planets around Sun-like stars Better than 1 milli-arcsec astrometry is required to reach into the Jupiter-mass domain: 1. PRIMA/VLTI has the potential: 3 micro-arcsec precision demonstrated, but ESPRI planet search inhibited by systematic errors limiting the astrometric accuracy to > 3 mas (so far!) 2. FORS2/VLT realises 13 micro-arcsec accuracy -> exploring the population of planets around ultra-cool dwarfs (+ ultra-precise distances + BD binaries) General-user ground-based facilities for high-precision astrometry can deliver great science. Synergies (e.g. preparation + follow up) with fixed-duration space missions (GAIA). Unique capabilities present at ESO: Imaging with (extremely) large telescopes + Interferometer