Constraint on brown dwarf formation: radial variation of the stellar and sub- stellar mass function of IC 2391 ( and mass function of Praesepe)

Transcription

1 BD 2009, ESTEC, Noordwijk Thursday 10 th of September 2009 Constraint on brown dwarf formation: radial variation of the stellar and sub- stellar mass function of IC 2391 ( and mass function of Praesepe) Steve Boudreault Coryn Bailer-Jones, Bertrand Goldman, Thomas Henning and Wei Wang ( Max-Planck-Institut für f Astronomie ) José Caballero ( (Universidad Complutense de Madrid )

2 BD 2009, ESTEC, Noordwijk Thursday 10 th of September 2009 Constraint on brown dwarf formation: radial variation of the stellar and sub- stellar mass function of IC 2391 ( and mass function of Praesepe) ( justification of project ) Future work

3 : previous radial/spatial study of cluster(s) BDs with v > v e these BDs would have escaped after a few t c Muench et al. (2002) BDs v δ and spatial distribution very similar to stars Moraux & Clarke (2005) Kumar & Schmeja (2007) - for IC 348 ( data from Muench et al ) Bate et al. (2003) if v δ ~2-3km/s Kroupa & Bouvier (2003) in favor of ejection scenario 80-25M J : 14% in core / 16% in halo ( +/- 10% ) whether IMF variation primordial or via dynamical evolution, does not acting on substellar population

4 : why survey in IC2391? IC2391 is an interesting targets because near : distance is 146pc ( Robichon et al., 1999 ) age of 50Myr ( Barrado y Navascues et al [ Li ] ) ( 40Myr from Platais et al [ MS fitting ] ) not too young ( extinction due to molecular gaz, models ) not too old ( dynamical evaporation, optical data ) low reddening : E ( B V ) = 0.01 ( Randoch et al., 2001 ) previous study of MF : completness limit of 0.072M no radial study of IC 2391 yet

5 : determination of the mass function for very low mass stars and brown dwarfs population in IC 2391 Wide bands R c and J Medium 35 ESO/WFI bands fields at 770, of 815, 34 x and 914 nm ( ~ 10.9 sq. deg. ) ESO/WFI (optical data) CTIO/CPAPIR (IR data) 10δ detection limit at ~0.03Mʘ Fields chosen to avoid bright stars Those bands were chosen avoid MF gradient due to to sample spectra of M and low galactic latitude b~-6º L-dwarfs to minimize Earth-sky background

6 : determination of the mass function for very low mass stars and brown dwarfs population in IC Colour-magnitude diagrams - Colour-colour diagrams - Astrometry - M [obs] VS M [model] ( from Teff and mass )

7 : no radial variation below 0.15 M ʘ of the mass function of IC 2391, but observed for M ʘ Future work In favor of v δbd > v δs? ( Kroupa & Bouvier 2003 ) or BDs are already gone ( Moraux & Clarke 2005 )? simply other formation process involved?

8 Future work : spectroscopic follow-up to confirm/refute the radial variation of the mass function of IC 2391 To confirm the radial variation of the MF of IC 2391 VLT/VIMOS for IC2391 ( from up to 0.9M ʘ )

9 : why survey in Praesepe? Praesepe is an interesting target because with age 500 My 1 Gy ( like IC2391 ; no interstellar gaz, model ) My ( Fossati et al ) and Hyades at 625±50 My ( Bouvier et al ) not too far : pc, van Leeuwen (2009) low reddening : E ( B - V ) = 0.027±0.004 ( Taylor 2006 ) we may investigate how the BDs and population itself evolves (e.g. efficiency with which BDs are evaporated and populate the field)

10 : determination of the mass function for very low mass stars and brown dwarfs population in Praesepe Fields and area of the survey total coverage of ~3.2 sq. deg. 47 fields of Omega x 7 fields of Omega 2000 ( 14.5' x 14.5' ) centred on J and α=08:40:04 K s ( 3.1 and sq. δ=+19:40:00 deg. ) other 9 fields survey of goes WFI from ~0.3 sq. deg. I c ( 2.8 González-García sq. deg. ) et al ) >300 5σ sq. detection deg. ( Kraus limit & Hillenbrand of M )

11 : VLMS and BDs mass function of Praesepe What we have For the Hyades ( Bouvier et al ) m 0 = 0.60M σ = 0.39 Miller & Scallo (1979) m 0 = 0.15M σ = 0.51

12 : VLMS and BDs mass function of Praesepe For the Hyades we have Lognormal fit of Galactic field MF from Chabrier (2003) - age = 625±50My ( Perryman et al ) - [Fe/H] = +0.14±0.10 ( Pace et al ) Reid & Hawley (1999) - tidal radii = 10.3pc ( Perryman et al ) - core radii = ~ pc ( Perryman et al ) THEREFORE different initial conditions? ( and IMF? ) binaries? ( Thies & Kroupa 2007 ) For Praesepe we have - age = My ( Fossati et al ) [Fe/H] = ±0.039 (Friel & Boesgaard 1992) to +0.27±0.10 ( Pace et al ) - tidal radii = 11.5±0.3pc ( Kraus & Hillenbrand 2007) - core radii = 0.8±0.1pc ( Piskunov et al ) - mass = 550±40M ʘ ( Kraus & Hillenbrand 2007 ) - binarity : % for M, ʘ 44±6% for M, 47 ʘ - mass = 400M ʘ ( Perryman et al ) evolution of Praesepe differ from the Hyades? [ merged clusters (Holland( et al. 2000) - binarity = 0.41±0.05 ( Patience et al ) but Adams et al. (2002) find no evidence of subclusters ] % for M ʘ ( Pinfield et al )

13 Future work : spectroscopic follow-up to confirm/refute the radial variation of the mass function of IC 2391 and the mass function of Praesepe To confirm the radial variation of the MF of IC 2391 VLT/VIMOS for IC2391 ( from up to 0.9M ʘ ) Photometry from LBTC-red and blue r, i, z and Y band 4 pointing ( 0.61 sq. deg. ) and from 0.1 M ʘ down to 0.04 M ʘ Spectroscopic follow up of candidates with I c < 18.5 HYDRA at 3.5m WYIN telescope at KPNO MOSCA at 3.5m telescope at Calar Alto WHYFOS at 4.2m telescope at La Palma

14 CONCLUSIONS AND REVIEW We wanted to study the radial distribution and the evolution of the BD population in IC 2391 and Praesepe respectively radial photometric survey of ~10.9 sq. deg. of IC 2391 ( 0.03M ) ʘ using WFI ( R c, 770, 815, 856 and 913), CPAPIR ( J ) no significant variation < 0.15 M ʘ photometric survey of ~3.6 sq. deg. of Praesepe using WFI ( I c ), O2K ( J, K c ) but observed for > 0.15 M ʘ ejection scenario with different velocity dispersion... or BDs gone from cluster ( Moraux & Clarke 2003 ) and contamination? analysis of spectroscopic follow-up rise down from 0.6 to 0.1M ʘ, then drop at the substellar regime not consistent with Hyades different evolution, IMF, binaries ratio?