Survey
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4-8 Maggio 2008 Loredana Spezzi INAF-Catania Astrophysical Observatory J. M. Alcalá E. Covino c2d Spitzer Legacy Team INAF-NAPOLI F. Comerón A. Frasca E. Marilli INAF-CATANIA D. Gandolfi (Evans et al. 2003, PASP 115, 965) Scientific aim: “……..to study the process of star and planet formation from the earliest stages of molecular cores to the epoch of planet-forming disks………” Observations (IRAC, MIPS, IRS@Spitzer): • five nearby molecular clouds: Perseus, Ophiuchus, Serpens, Lupus, Chamaeleon II • 150 compact molecular cores • 300 stars in a wide range of evolutionary states http://astro.berkeley.edu/~stars/bdwarfs Different predictions on BD properties Problem: in the standard cloud fragmentation model self-gravitating objects with mass of only 1 MJ continue to accrete matter from their surrounding cores, usually to the point of reaching stellar masses (Bate et al. 2003, Mon. Not. R.Astron. Soc. 339, 577) Possible explanations: 1) The simulations lack an important piece of physics, e.g. turbulence (Padoan & Nordlund 2004, ApJ 617, 599) 2) BDs are born when cloud fragmentation is modified by an additional process that prematurely halts accretion, i.e. dynamical ejection or photoevaporation by ionizing radiation from massive stars (Reipurth & Clarck 2001, ApJ 122, 432) • • • • • • • disk frequency/characteristics accretion rates clustering properties kinematics binary statistics planetary companions sub-stellar IMF (Spezzi et al., astro-ph 0802.4351 ; Alcalà, Spezzi et al. 2008, ApJ 676, 427) • R, I, z, H7, H12, 856 nm, 914 nm WFI @ ESO 2.2m tel. (Spezzi et al. 2007, A&A 470, 218) • 3.6, 4.5, 5.8 and 8 m IRAC@Spitzer (Young et al. 2005, ApJ 628, 283) • 24, 70 and 160 m MIPS@Spitzer (Porras et al. 2007, ApJ 656, 493) Cha II properties……… T association Age = 1-10 Myr Distance ≈ 180-200 pc Area ≈ 2 deg2 Modest star formation activity (60 members) Alcalà, Spezzi, et al. 2008, ApJ 676, 427 WFI K. Luhman: ‘’Chamaeleon” ASP Conf. Ser., B. Reipurth ed., in press MIPS IRAC (Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) Goals Same as in Cha II, but in a different star-forming environment! Lupus properties……… Complex of T associations Age < 2 Myr Distance ≈ 100-250 pc Area ≈ 20 deg2 High star formation activity (250 members) Location: Scorpius-Centaurus F. Comeròn: ‘’The Lupus clouds” ASP Conf. Ser., B. Reipurth ed., in press Adapted from Cambrèsy 1999 (Spezzi et al. 2007, A&A 470, 281; Alcalà, Spezzi et al. 2008, ApJ 676, 427; Spezzi et al., astro-ph 0802.4351) Instruments: • FORS2@ESO-VLT (R>18 mag): 6000-11000 Å, R~2500 • FLAMES@ESO-VLT (R≲18 mag): MEDUSA: 6400-7200Å, R~9000 UVES: 5800-6800Å, R~47000 Selection of young Contaminant objects with and without IR excess Meyer 1997 • EMMI@NTT (R≲18 mag) 4000-10000 Å, R~8000 Diagnostics of the PMS nature: • LiI 6708Å absorption line (youth indicator) • H emission line (accretion activity indicator) Spectral Type, Teff, Av: • Spectral classification: standard templates (Gandolfi et al., ApJ, submitted) • Teff - Spectral Type tabulation (Kenyon & Hartmann 1995, ApJ 101, 117; Luhman et al. 2003, AJ 593, 1093) • Av = 4.605 E(R-I) (Weingartner & Draine 2001, ApJ 548, 296) Contaminant (Spezzi et al., astro-ph 0802.4351 ; Alcalà, Spezzi et al. 2008, ApJ 676, 427) L DISK / ENVELOPE L STAR,RSTAR NextGen & STARDUSTY Models for stellar atmospheres L*, R* Rhole, Rdisk, Mdisk,Maccr, Grain size, incl. angle, etc… Accreting Disk Models by D’Alessio et al. 2005 (R.M. A. Y A. 41, 61) Passive Disk Models by Dullemond et al. 2001 (AJ 560, 957) Accreting Disk Models by Robitaille et al. 2006 (ApJS 167, 256) (Alcalà, Spezzi et al. 2008, ApJ 676, 427; Spezzi et al., astro-ph 0802.4351; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) Mean Mass 0.52 ± 0.11 M Total Mass 20 – 33 M IMF slope (0.1≤M/M≤2) 0.4 – 1 RSS N (0.02 0.08 N (0.08 10 SFE M) M) M star M star M cloud 6-12% ? (OB associations 26%) 1- 4 % Mean Age 4 ± 2 Myr Star Formation Rate ~ 8 M/Myr Environmental conditions affect the BD formation mechanism dN/dM M- bin=0.2 M 0.1 Mass (M) 1.0 Mean Mass 0.5 M Total Mass 8-62 M IMF slope (0.1≤M/MΘ≤2) 0.9 ? N (0.02 0.08 N (0.08 10 ? RSS SFE M) M) M star M star M cloud 1- 7 % Age 2 Myr Star Formation Rate 4 - 31 M/Myr (Alcalà, Spezzi et al. 2006, A&A 453, L1-L4) STARDUSTY STARDUSTY + BB (Merìn,….Comeròn, Frasca, Alcalà et al. 2007, ApJ 661, 361) FitCGplus fit BDs Very-low mass stars • Twall ≈ 1500 K • Rwall≈ 0.02 AU • Rdisk ≈ 0.4 AU SST-Lup3-1 -4 • Mdisk ≈ 10 M massive stars • IR class = II & Iso-ChaII-13 More Common formation process? •Spectral type: M7 •Teff = 2880±80 K (see also Alcalά •Av et al. 2004; mag = 5.0±0.5 Barrado Y Navascués et0.010±0.001 al. 2004; •L* = L bol = 0.028±0.006 L Luhman •L 2005; •R* = 0.38±0.05 R Preibish et al. 2005) •M = 0.05±0.01 M •Age = 5±3 Myr crystalline silicate features FORS2@VLT (Alcalà, Spezzi et al. 2008, ApJ 676, 427; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) Thick disk fraction peaks ~1 solar mass Do planets preferentially form around solar-mass like stars Thin disk fraction declines with mass See also IC348 (Lada et al. 2006, AJ 131, 1574) ? 1. The Spitzer c2d Survey in Cha II and Lupus 2. Star formation history - Mass spectrum: stellar and sub-stellar IMF - Ages - SFE and SF rate 3. Properties of circumstellar disks - Disks around sub-stellar objects - IR classification and disk fraction Future developments with: II generation VLT intruments (XSHOOTER, SPHERE) and HST Extend these investigations to low-metallicity Enviromments (Magellanic Clouds) Gould’s Belt mapping with Herschel BD and planet formation: constrain the disk parameters (Alcalà, Spezzi et al. 2008, ApJ 676, 427; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) turn-off Rin excess Log () Rin70 AU