Astrometric monitoring of binary Brown Dwarfs with NGS and LGS Adaptive Optics

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1 Astrometric monitoring of binary Brown Dwarfs with NGS and LGS Adaptive Optics Micaela Stumpf Astronomy with LGS AO Ringberg Thomas Henning Wolfgang Brandner MPIA Heidelberg

2 Motivation 86 VLM binaries are resolved BD binaries provide the unique opportunity to determine the dynamical masses of the binary and its components => independent from theoretical models! derive improved spectral types and luminosity study of semi-major axis separation for important clues on formation mechanisms and origins (Umbreit et al. 2005)

3 Previous work Gliese 569 BC: M8.5 + M9 binary with 2.5 year orbit, M tot = ± M sun (Lane et al 2001, Zapatero-Osorio 2004) 2MASS J : L0 + L1 binary with ~ 10 year orbit, M tot = ± M su (Bouy et al. 2004) Gliese 1001 BC: L 4.5 binary with 4 year orbit, M tot = ± 0.023M su (Golimowski et al. 2006,2007) 2MASS J : eclipsing binary (Stassun et al. 2006) M A = ± 0.004M su, M tot = ± 0.002M su play a leading role in verifying their evolutionary models and theories

4 N Kelu 1 E first free floating Brown Dwarf (Ruiz 1998) high proper motion = 285 mas/yr (Dahn 2002) fast rotation period: 1.8 hours (Clarke 2002) distance = 18.7 pc 0.3 HST/NIC1 Martin et al. (1999)

5 Kelu 1 AB E N 31 Jul 2005 first free floating Brown Dwarf (Ruiz 1998) high proper motion = 285 mas/yr (Dahn 2002) fast rotation period: 1.8 hours (Clarke 2002) distance = 18.7 pc 0.3 HST/NIC1 resolved binary (Liu & Leggett 2005, Gelino et al. 2006) Kelu 1A: L1.5 - L3 Kelu 1B: L3- L4.5 relatively bright with K A 12.3 mag and K B 12.7 first meassured separation: arcsec (5.31 AU)

6 Results Date obs. Instrument Filter sep [arcsec ] PA [deg] 04 Mar 2005 Keck 1 K ± ± 0.3 (Gelino et al 2006) 01 May2005 Keck 1 K ± ± 0.26 (Liu et al 2005) 31 Jul 2005 HST/ NIC1 F113N ± ± 0.04 (Stumpf in prep) increasing distance of arcsec in 4 months!

7 Results Keck LGS AO (Gelino et al 2006) Keck LGS AO (Liu et al 2005) HST/NIC1 (Stumpf et al in p rep) VLT/NACO (Stumpf et al in p rep) for precise follow-up high angular resolution observations are necessary!

8 Orbit fitting first rough predictions of period, eccentricity, inclination with datapoints until November 2006 unlikeley, since at least one component would have a mass > 75 M J but both contain lithium

9 Orbit fitting more reliable possibilities but still big uncertainties

10 Best orbit fit including new datapoints from spring 2007 a minimum coverage of ~ 40% of the orbit is needed to receive a reliable fit!

11 PARSEC so far observation with IR-WFS of NACO was limited to a NGS of K < 13 mag out to 55 arcsec. the WFS of SINFONI even to a NGS of R < 14 mag out to 30 arcsec. PARSEC ( only ) needs a Tip/Tilt star with V < 17 mag out to 60 arcsec. provides unique possibility to widely extend the sample of ground-based observable brown dwarf binaries!

12 Instrument + sample selection choose 6 binaries: 2 L/L dwarfs, 2 L/T dwarf binaries and 2 T/T dwarfs, 3 of them just recently resolved. predicted orbital periods of years. beside multi-epoch monitoring, aim to derive improved spectral types and luminosities of individual components. SINFONI: H+K-band with R ~ 1500 and FoV: 0.8 x 0.8 NACO: with S27 camera (FoV: 28 x 28 ) => spatially resolved astrometry and multi-band (H, K) photometry

13 Epsilon Indi Bab epsindi B discovered by Scholz et al 2003 distance to epsindi A (K5 V): 1459 AU approximated age of 1.3 Gyr (0.8-2 Gyr by Lachaume 1999) distance to our sun: pc (M ccaughrean, 2004) resolved into Ba Bb by McCaughrean et al 2004 spectral types T1 (T eff =1276 K) and T6 (T eff = 854K) very bright: K A mag and K B mag first estimated mass of M J 46 and M J 28

14 Preliminary results used Tip/Tilt star with R mag at achieved resolution of 130 mas in H-band

15 Preliminary results CH 4 CH 4 CH 4 H 2 O H 2 O EpsIndi Ba EpsIndi Bb SCR 1845B

16 Preliminary results CH 4 H 2 O CH 4 H 2 O NACO PARSEC/SINFONI

17 Preliminary results H 2 O H 2 O PARSEC/SINFONI: EpsIndi Bb NACO: EpsIndi Bb NACO: SCR 1845B

18 Preliminary results CH 4 Na 12 CO EpsIndi Bb SCR 1845B

19 Future Work ongoing monitoring program of Kelu1 AB at VLT/NACO but: for individual mass determination either astrometric orbit and/or spectroscopic orbit is needed stay tuned for more PARSEC data! :)