First determination of the orbit of a Binary L-Dwarf

1. First determination of the orbit of a Binary L-Dwarf H. Bouy, G. Duchêne (LAOG), R. Köhler (MPIA), W. Brandner (MPIA), J. Bouvier (LAOG), E. Martín (IAC), … Hervé Bouy - Cool Stars 13 - Hamburg

2. First determination of the orbit of a Binary L-Dwarf Hervé Bouy 1./ Context of the study 1.1/ Interest of binaries 2.2/ Previous works 2./ 2MASSW J0746+2000 2.1/ Orbit 2.2/ Dynamical mass 3./ Discussion and Future prospects 3.1/ Impact on the models 3.2/ Next candidates Hervé Bouy - Cool Stars 13 - Hamburg

3. Context of the study: About the interest of binaries Binaries as testimonies How do brown dwarfs form, how do they evolve ??? this morning session and Splinter meetings S6 and S7 still few unanswered questions ! Depending on the scenario of formation, the properties of multiple systems change ! Multiple systems provide valuable “tests” and important constrains for the models. Binaries as scales What about the Mass vs. Luminosity relation for BD ??? Still needs to be calibrated ! Binaries offers a unique opportunity to measure dynamical masses independently from any model. The first brown dwarf discovered (Lucas et al., 1983) Hervé Bouy - Cool Stars 13 - Hamburg

4. Previous works Gliese 569b The only brown dwarf/brown dwarf orbit known up to now. Period of ~4 years (see Lane et al. 2001, Zapatero Osorio 2004) DENIS-P J1228-1547 Discovered by Martin et al. 1998. Observations spread over 6 years, but orbital period much longer (~40 years) (See Brandner et al., in prep.) Hervé Bouy - Cool Stars 13 - Hamburg

5. 2MASSW J0746425+200032 2.1./ Introduction L0.5 binary (first resolved by Reid et al. 2001 with WFCP2) Relatively bright: K=10.5  great for A.O and speckle imaging ! Trigonometric parallax with very good precision (12.25±0.05 pc, Dahn et al. 2002) Separation: only ~ 0.”125 only… 2.2/ Observations Need for High Angular Resolution: HST: WFPC2 (Reid et al. 2001), ACS & STIS VLT + NACO Keck + NIRC1 speckle imaging Gemini + Hokupa’a (Close et al. 2002) Hervé Bouy - Cool Stars 13 - Hamburg

6. Hervé Bouy - Cool Stars 13 - Hamburg

7. 2.3/ Orbital parameters: • Total Mass: M • Period: 3850 jours • Eccentricity 0.41 • Semimajor axis: 2.53 A.U • Inclinaison 141.6º Individual masses ???  need the spectroscopic orbit… Problem: v.sin(i) = 25~30 km/s (Bailer-Jones 2004) blend the Doppler shift due to the secondary…  or the astrometric orbit… Problem: no other object in the field of our images… Hervé Bouy - Cool Stars 13 - Hamburg

8. Photometry of the individual components compared to the latest evolutionary DUSTY models Mass Primary: 0.075-0.095 M Mass Secondary: 0.060-0.072 M Hervé Bouy - Cool Stars 13 - Hamburg

9. 2.4/ Spatially resolved spectroscopy with STIS Primary = L0 Secondary = L1.5 H variability (EW x 10)  chromospheric and/or magnetic activity No Lithium in the secondary (EW>1.5Å)  M > 0.060 M (for an age ~ 1 Gyr) Hervé Bouy - Cool Stars 13 - Hamburg

10. Discussion: First dynamical total mass for a L dwarf binary Very interesting object, but limited impacts on the models: - age is not known yet - individual masses from the models Continue follow up observations (2 more NACO and 1 STIS points coming soon) Future Prospects: Follow up other binaries with: - “short” periods (5 to 10 years) - known ages (for example because they orbit a star of know age) - known distances (idem, or via parallax) Good candidates: Eps- Indi B (McCaughrean et al. 2002) Gliese 569b (Lane et al. 2001, Zapatero Osorio et al. 2004) LHS 102b (Golimowski et al. 2004) Gliese 417b (Bouy et al. 2003) Hervé Bouy - Cool Stars 13 - Hamburg

11. Hervé Bouy - Cool Stars 13 - Hamburg