1. Nicolas Lodieu SAAO, 28 September 2005 Low-mass stars and brown dwarfs in open clusters

2. The BD group @ Leicester  Head: Richard Jameson  Post-docs: Paul Dobbie & Nicolas Lodieu  PhD student: Sarah Casewell  BDs in open clusters  BDs in the field: UKIDSS Large Area Survey { Pleiades, α Per IC2391, Collinder 359 Coma Ber, Praesepe

3. α Per

4. The α Per cluster: previous work ● Lithium test (Stauffer et al. 1999) Distance = 182 pc (Hipparcos) Low galactic latitude (b = -7°) Little extinction  0.3 mag Extended 6°  6° ● Analogue to the Pleiades ● PM and photometric surveys Heckmann et al. (1956) Stauffer et al. (1985, 1989) Prosser (1992, 1994) Down to V = 19; SpT ~ M5 ● Deep optical wide-field survey Barrado y Navascués et al. (2002) ~ 100 new candidates dN/dM α M -0.59  0.05 Mass range 0.3-0.035 M sun  Age = 90  10 Myr

5. Our wide-field near-infrared survey I  Total area of 0.7 deg 2 covered in K' in  Per (Lodieu et al. 2005) ● Wide-field survey conducted with the infrared Omega-Prime camera on the Calar Alto 3.5-m telescope ● Five optical KPNO/MOSA frames covered in the infrared ● Total of 22129 objects common to the optical and to the infrared ● More than 100 new candidates selected from the colour-magnitude (K', I-K') and colour-colour (Rc-Ic, Ic-K') diagrams About 70% are contaminating distant background giants 1 non-member (Barrado y Navascués et al. 2002) 16 probable members (Barrado y Navascués et al. 2002) 16 new infrared-selected candidate members 4 new brown dwarf candidates ● Spectroscopy needed to ascertain the membership

6. Our wide-field near-infrared survey II Colour-magnitude diagram Colour-colour diagram Crosses: distant giants Open hexagons: new infrared-selected candidates (Lodieu et al. 2005) Filled symbols: probable candidates from Barrado y Navascués et al. (2002) 50 Myr 100 Myr

7. Follow-up optical spectroscopy ● Optical spectroscopy (5800-8800 Å) conducted with the Twin spectrograph at Calar Alto 24 probable members ( Barrado et al. 2002) 1 possible member ( Barrado et al. 2002) 4 non-members ( Barrado et al. 2002) 4 new infrared-selected candidates ● All optically-selected candidates with masses 0.4-0.12 M sun are genuine cluster members Spectral types Fluxes consistent with I magnitudes H α in emission (EW = 4-15 Å) Gravity (K I and Na I doublets) ● 4 new infrared-selected candidates are rejected as cluster members ● Possible and non-members are rejected

8. Collinder 359

9. The CFHT Key Programme Main goals of the CFHTKP programme: Targets (age < 200 Myr, d < 500 pc, visible from Hawai'i) CFHTKP: wide-field optical observations: SFRs: Perseus, Taurus, Ophiuchus, and Serpens PMS clusters: IC4665, Collinder 359, Stephenson 1 The Hyades PI: Bouvier in collaboration with the EC network 30 nights over 2 years CFH12K camera offers a 42'*28' FOV with 0.206 arcsec/pix I and z CFH12K filters Completeness and detection limits of 22 and 24 mag in I and z filters How do brown dwarfs form and at which rate? Is the Initial Mass Function sensitive to the environment? How do substellar objects evolve with time? What is the mass distribution of low-mass stars and brown dwarfs?

10. Collinder 359: presentation Unstudied cluster RA=17 h 58 m, Dec=+02°54' Constellation Ophiuchus Located around 67 Oph (Melotte 1915) Galactic latitude = +12.5  Age = 32 Myr (Wielen 1971) Distance = 435 pc [200,650] (Hipparcos) Diameter = 240 arcmin (~ 20 pc)  13 members belonging to the cluster  6 of them confirmed as members Rucínski (1980; 1987), Van't Veer (1980) Collinder (1931)  Latest estimates (Kharchenko et al. 2004) Age = 30 Myr Distance = 650 pc Location of the CFH12K FOV

11. Age of Collinder 359 ● Girardi tracks (Girardi et al. 2002) ● Alpha Persei (open square): ● 67 Ophiuchus (filled hexagon): ● Membership of 67 Ophiuchus: ● Lithium test  age  2  Solar metallicity  Moderate overshoot  50 Myr (Stauffer et al. 2003)  60  20 Myr  P  75% (Baumgardt et al. 2000)  P  95% (Kharchenko et al. 2004)

12. Optical and NIR Observations 1) Optical wide-field survey within the framework of the CFHTKP 2) Near-infrared follow-up photometry of candidates  5 CFH12K fields-of-view covering 42 arcmin x 28 arcmin  1.6 square degree area surveyed in Collinder 359  I and z filters  Completeness limits of I, z  22.0 mag (30 M Jup at 450 pc and 60 Myr)  Detection limits of I, z  24.0 mag (< 30 M Jup at 450 pc and 60 Myr)  2MASS counterparts down to I = 17.0 mag  K'-band follow-up: CFHT 3.6-m/CFHTIR + CAHA 2.2-m/MAGIC 29 + 36 objects spanning I = 17.0-22.0 mag

13. ● Theoretical Isochrones  NextGen + Dusty  Age = 60 Myr  Distance = 450 pc ● Mass scale in solar masses ● HBL @ I = 19.75 mag ● Mass range: 1.3-0.03 Msun (I-z,I) CMD

14. Optical and NIR Observations 1) Optical wide-field survey within the framework of the CFHTKP 2) Near-infrared follow-up photometry of candidates  5 CFH12K fields-of-view covering 42 arcmin x 28 arcmin  1.6 square degree are surveyed in Collinder 359  I and z filters  Completeness limits of I, z  22.0 mag (30 M Jup at 450 pc and 60 Myr)  Detection limits of I, z  24.0 mag (< 30 M Jup at 450 pc and 60 Myr)  2MASS counterparts down to I = 17.0 mag  K'-band follow-up: CFHT 3.6-m/CFHTIR + CAHA 2.2-m/MAGIC 29 + 36 objects spanning I = 17.0-22.0 mag

15. (I-K,I) CMD ● Crosses = 2MASS ● Filled circles = CFHT + CAHA ● Isochrones  NextGen + Dusty  Age = 60 Myr  Distance = 450 pc

16. Optical spectroscopy: H   TNG/DOLORES: 48 candidates  WHT/AF2/WYFFOS: 33 candidates  CAHA 3.5-m/Twin: 74 candidates ==> A dozen candidates confirmed as members out of 100 candidates with optical spectroscopy  Spectral typing  Chromospheric activity: Hα EW  Surface gravity: KI and NaI doublets  Magnitude vs. SpT relationship ● Tests for membership: ● Spectroscopic observations: ● Caveat: What criterion for M  0.3 Msun? Lithium? Radial velocity?  AAT/2dF: several hundreds

17. Collinder 359 & IC4665 Red dots have proper motion consistent with cluster membership Green squares represent a control sample Black boxes represent the coverage in Collinder 359 & IC4665

18. Collinder 359 & IC4665 Red dots have proper motion consistent with cluster membership Green squares represent a control sample Blue dots are within a 2 degree area around Collinder 359 & (B-V) < 1.0 Blue triangles are within a 2 degree area around IC4665 & (B-V) < 1.0

19. Coma Ber

20. Coma Berenices open star cluster  45 known cluster members  Selected via proper motion using the USNO B1.0 catalogue  Photometric selection using 2MASS Point-Source Catalogue  60 new possible members  Stars down to 0.25 M  found  Control field used to estimate membership probability  15 square degrees of cluster surveyed in I and Z  13 brown dwarf candidates  Awaiting UKIRT/WFCAM data

21. Red: NEXTGEN model Green: Dusty model Blue: Known members Black: Our members Magenta: Brown dwarf candidates

22. Future prospects ● Collinder 359: AAT/2dF low-resolution optical spectroscopy (August 2005)  UKIRT/WFCAM with ~0.8 square degree field-of-view  10 open clusters and star-forming regions in ZYJHK  5-σ completeness limits of J = 19.7, H = 18.8, K = 18.4 ● UKIDSS Galactic Cluster Survey: α Per: proper motion + larger coverage Pleiades: proper motion + deeper observations IC4665: infrared counterparts of optically-selected cluster candidates Coma Ber: new candidates over a larger area