Direct imaging of substellar objects around young and nearby stars: The SACY sample

1. Direct imaging of substellar objects around young and nearby stars: The SACY sample N. Huélamo (Laeff-INTA, Spain) H. Bouy (UC Berkeley) C. Torres (LNA, Brazil) C. Melo, M. Sterzik (ESO, Chile) G. Chauvin (LAOG, France) D. Barrado y Navascués (Laeff-INTA, Spain)

2. Motivation of this work Direct images of Substellar/planetary companions Observations are the only way to discriminate betweenformation theories. Put constraints to physical parameters: 1. Frequency of substellar objects in wide orbits 2. Characterize their atmospheres 3.Calibrateevolutionary models

3. Looking for star-companion systems Companion to stars: We can assume similar distance/age High spatial resolution High contrast imaging Adaptive Optics + Large telescope

4. AO ima & spec Population of BD/planets in large orbits Characterize the atmospheres of the objects What can we learn with AO imaging? Targets: Late-type Field stars ~M p *sin(i) orbital parameters Chauvin et al. 2007

5. 7 8 9 log t AO imaging: Where to look…. • Substellar companions are normally searched around young ( < 100 Myr) and nearby (d < 100pc) late-type stars. WHY?CONTRAST Young late-type stars: The younger the substellar object, the brighter Nearby stars: we can probe smaller separations 10 MJup @ 10 Myr

6. Deep surveys to detect substellar/planetary companions And more to come…

7. Confirmed substellar companions Chauvin et al. 2007

8. HN Peg DH Tau HD3651 AB Pic ~475 AU ~795 AU ~100 AU ~ 260 AU ~ 330 AU Confirmed Substellar companions • Most of the substellar companionsto stars detected so far have been found at separations between 100-1000 AU. Neuhauser et al. 2004 Itoh et al. 2005 Chauvin et al. 2005 Burgasser et al. 2005 Luhman et al. 2007 ● 1 planetary-mass companion (substellar binary): sep~60 AU Chauvin et al. 2005 ● No planets (or BDs) detected at very small separations No >2 Mjup at sep. 45-200 AU No >4 Mjup at sep. 20-40 AU No >5 Mjup at sep > 15 AU Lafreniere et al. 2007 Kasper et al. 2007 Biller et al. 2006 Masciadri et al. 2005

9. What is SACY?What is the connection with substellar/planetary searches?

10. The SACY survey • Search for Associations Containing Young stars Torres et al, 2003, Torres et al. 2006 • - Started by Torres et al. in 2000 after the discovery of Tucana & Horologium (Torres et al. 2000, Zuckerman & Webb 2000) • Moving groups of Post- T Tauri stars: How to identify them? • T Tauri Stars (Age ~1 Myr)Post-T Tauri stars (10-100Myr) • Near-IR excess (disks) X-ray emission can persist.. • Forbidden lines (accretion) Lithium • X-ray emission, • Lithium, etc… • - Aim: Search for young and nearby stars as optical counterparts to X-ray (ROSAT) detections d ~30 pc, age~30 Myr

11. Southern ROSAT Sources • SACY [Hip + TYC & (B-V)0.6] • Observed objects (not sources) • Data from literature • 9574 • 1953 • 1750 • 150 The SACY project G0 and later… } Li abundance Radial and Rot. velocity Lithium -- age estimation Dynamical properties + Convergence method: NEW MOVING GROUPS NEW MEMBERS of known assoc. • Torres et al. have identified at least 14 young associations in the SACY database (there are five more possible associations to confirm…) . Torres et al. 2006; Torres et al. 2007 Prime targets for AO surveys to detect subs./planet. companions

12. Our study 1. VLT/NACO survey : Substellar/Planetary companions around new young nearby stars identified in the SACY survey 2. Characterization of nearby (young?) M-type stars in the SACY Catalog that do not belong to any moving group.

13. 1. Search for substellar companions around SACY stars AO survey started on 2006 The sample of 78 targets contains: • I. 18 New identified members of 9 young and nearby loose associations included in Torres et al. 2007 (e.g. TW Hya, Beta Pic, Tuc-Hor) • II. 30 New identified members in other nearby assocs. (e.g. LCC) • III. 15 M-type stars without lithium and/or association but probably young… • IV. 15 Young stars (with lithium) without association

14. Average properties… • Most of them are M,K-type stars • Ages ~ 10 Myr • Hipparcos and/or UCAC2 Proper motions: (Confirm companions in 1-2 yrs)

15. Observations • NACO/VLT • Optical WFS + IB2.27 filter • S27 objective : 27’’ x 27’’ FOV • Typical integrations of 12-15 minutes • Classical AO imaging • Service Observations (April-Sep. 2006)

16. 30 60 90 120 300 (AU) @ 60pc 10MJup M* = 0.8 Msun, 10 Myr Detection limits Δmag ~ 7mag@0.5” Average curve for IB 2.27

17. I: Nearby loose associations

18. Results • 67 detected sources around 12 stars • All of them around BPA and ECA members • 14 sources at separation < 5” • 2 new subarsecond stellar binaries

19. Results

20. Results Targets at separations < 500 AU from host star: 4 in ECA 13 in BPA

21. Sep=0.13” @103 = 13.4 AU 10 MJup 20 MJup The most interesting substellar candidates I. ε Cha Target: K0 star from Є Cha d=103 pc Age=6 Myr Sep=3.8”@103pc= 391AU Galactic latitude ~ -8 deg

22. The most interesting substellar candidates I. ε Cha Target: G8 star from Є Cha d=115 pc Age=6 Myr Sep=1.8”@103pc= 185 AU Companion Candidate: Sep = 210 AU Mass < 10 MJup Galactic latitude ~ -8 deg

23. The most interesting substellar candidates II. BPA Target: M1 star from β Pic d= 54 pc Age=10 Myr Sep=3.9”@54pc= 210 AU 3.9” Companion Candidate: Sep = 210 AU Mass < 10 MJup Galactic Latitude ~ -23 deg

24. The most interesting substellar candidates II. BPA Target: M1 star from β Pic d= 72 pc Age=10 Myr Sep=1.7”@72 pc= 126 AU Galactic Latitude ~ -07 deg Companion Candidate: Sep = 126 AU Mass ~10 MJup 1.7”

25. II: Lower Centaurus Crux (LCC) • 11 new identified members • Distances: 73-110pc • Age ~ 8 Myr (Torres et al., in prep.)

26. Substellar comp. candidates in LCC Results: 130 detected sources 25 at separations < 5” 4 new subarc. binaries Galactic latitudes (~ 0–8 deg)

27. Substellar comp. candidates in LCC 40 MJup @300 AU 15 MJup @260 AU Gal. Latitudes: ~02 deg

28. Subsamples I and II:Nature of the companion candidates? • Wider companions (sep > 10 arcsec): BACKGROUND • cross-correlation with optical, near-IR catalogs • Closer companions (sep < 10 arcsec) Second epoch observations are needed… hopefully next semester

29. III: M-type stars from SACY • Our SACY sample contains 15 M-stars (M0-M3): • With X-ray emission • Without lithium • Do not converge to any moving group • 8 (out of 15) with Hipparcos parallaxes: d ~(14-59 pc) What is the nature of these stars? Are they young or old?

30. AB Dor – 70 Myr β Pic – 10 Myr M-type stars from SACY • Lithium cannot be used as an age estimator since it is depleted too fast. …but gives as a lower limit age ≥ 10Myr

31. M-stars: Age diagnostics? - Comparison with Evol. Tracks - Stellar activity - Surface gravity

32. M-type stars from SACY • Comparison with evolutionary tracks Song et al. 2003

33. M-type stars from SACY • Lx / Lbol as age diagnostic Song et al. 2003

34. M⓪ M-type stars from SACY • Surface Gravity can be used as an age indicator.

35. M-type stars from SACY • Gravity sensitive lines: (e.g. Na I 5900 Å, KI D 7700 Å, Na I D 8200 Å) • Method: • - EW measurement of alkali lines • - Comparison with templates: • Younger and older stars with similar spectral types • (on-going …)

36. He I lines Substellar companion candidates to M-stars? 8.6” companion to a M1 star Sep. ~ 500 AU @ 59pc Mass ~ 20 MJup @ 70 Myr A DB white dwarf ‘companion’ to a nearby star Public Archives: the system is a common proper motion pair (obs from 1910 to 2006). BUT Colors not consistent with a Brown Dwarf but with a White Dwarf.

37. Conclusions SACY Catalog contains prime targets for AO surveys to look for substellar and planetary-mass companions: young and nearby Preliminary results from our NACO/VLT survey: • 17 good substellar/planetary companion candidates to nearby stars in nearby associations. • Several candidates around LCC stars but …at very low galactic latitudes (probably background…) • Second epoch observations necessary… Increase the number of SACY young,nearby M-stars without association via optical, X-ray data (surface gravity, magnetic activity, etc..)