Loredana Spezzi INAF-Catania Astrophysical Observatory

1. J. M. Alcalá E. Covino INAF-CATANIA F. Comerón A. Frasca E. Marilli INAF-NAPOLI D. Gandolfi c2d Spitzer Legacy Team 4-8 Maggio 2008 Loredana Spezzi INAF-CataniaAstrophysicalObservatory The Spitzer c2d Survey in low-mass star forming regions: Chamaeleon II & Lupus

2. http://astro.berkeley.edu/~stars/bdwarfs Probing the Brown Dwarf formation mechanism Different predictions on BD properties • disk frequency/characteristics • accretion rates • clustering properties • kinematics • binary statistics • planetary companions • sub-stellar IMF 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) The Spitzer c2d survey: “From Molecular Cores to Planet-forming Disks” (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

3. The survey in Cha II (Spezzi et al., astro-ph 0802.4351 ; Alcalà, Spezzi et al. 2008, ApJ 676, 427) • R, I, z, H7, H12, 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(Porraset al. 2007, ApJ 656, 493) Alcalà, Spezzi, et al. 2008, ApJ 676, 427 WFI • Cha II properties……… • T association • Age = 1-10 Myr • Distance ≈ 180-200 pc • Area ≈ 2 deg2 • Modest star formation activity (60 members) IRAC MIPS K. Luhman: ‘’Chamaeleon” ASP Conf. Ser., B. Reipurth ed., in press

4. The survey in Lupus (Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) Adapted from Cambrèsy 1999 Goals Same as in Cha II, but in a different star-forming environment! • Lupus properties……… • Complexof 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

5. Contaminant Contaminant Identification of young stellar objects (Spezzi et al. 2007, A&A 470, 281; Alcalà, Spezzi et al. 2008, ApJ 676, 427; Spezzi et al., astro-ph 0802.4351) Follow-up Spectroscopy Selection of young objects with and without IR excess • 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 • 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) Meyer 1997

6. Stellar and disk parameters (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* Passive Disk Models by Dullemond et al. 2001 (AJ 560, 957) Accreting Disk Models by D’Alessio et al. 2005 (R.M. A. Y A. 41, 61) Accreting Disk Models by Robitaille et al. 2006 (ApJS 167, 256) Rhole, Rdisk, Mdisk,Maccr, Grain size, incl. angle, etc… Masses & Ages

7. Star formation history (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 Mean Mass Cha II Total Mass Total Mass IMF slope (0.1≤M/M≤2) IMF slope (0.1≤M/MΘ≤2) 0.5M 0.52 ± 0.11 M Lupus clouds 20 – 33 M 8-62 M Age Mean Age 0.9 ? 0.4 – 1 Star Formation Rate Star Formation Rate ? 6-12% ? (OB associations 26%) 1- 7 % 1- 4 % 4 ± 2 Myr 2 Myr dN/dM  M- bin=0.2 M 4 - 31 M/Myr ~ 8 M/Myr Environmental conditions affectthe BD formation mechanism 0.1 1.0 Mass (M) M/M

8. STARDUSTYSTARDUSTY + BB FitCGplus fit Brown Dwarfs with disks (Alcalà, Spezzi et al. 2006, A&A 453, L1-L4) (Merìn,….Comeròn, Frasca, Alcalàet al. 2007, ApJ 661, 361) BDs Very-low mass stars & More massive stars Common formation process? (see also Alcalά et al. 2004; Barrado Y Navascués et al. 2004; Luhman 2005; Preibish et al. 2005) • Twall ≈ 1500 K • Rwall≈ 0.02 AU • Rdisk ≈ 0.4 AU • Mdisk ≈ 10-4 M • IR class = II Iso-ChaII-13 SST-Lup3-1 • Spectral type: M7 • Teff = 2880±80 K • Av = 5.0±0.5 mag • L* = 0.010±0.001 L • Lbol = 0.028±0.006 L • R* = 0.38±0.05 R • M = 0.05±0.01 M • Age = 5±3 Myr crystalline silicate features FORS2@VLT

9. Thick disk fraction peaks ~1 solar mass  Do planets preferentially form around solar-mass like stars ? Thindisk fraction declines with mass IR classification and disk fraction (Alcalà, Spezzi et al. 2008, ApJ 676, 427; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) Cha II See also IC348 (Lada et al. 2006, AJ 131, 1574) Lupus clouds

10. Summary 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

11.  turn-off  Rin Log (F×)  excess Log () Rin70 AU “Transition” objects (Alcalà, Spezzi et al. 2008, ApJ 676, 427; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504) Cha II Lupus clouds