Loredana Spezzi INAF-Catania Astrophysical Observatory

4-8 Maggio 2008

INAF-CATANIA

A. FrascaE. Marilli

INAF-NAPOLI

J. M. AlcaláE. Covino

F. Comerón

c2d Spitzer Legacy Team 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

• disk frequency/characteristics• accretion rates• clustering properties• kinematics• binary statistics• planetary companions• sub-stellar IMF

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)

http://astro.berkeley.edu/~stars/bdwarfs

MIPS

WFI

IRAC

• 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)Alcalà, Spezzi, et al. 2008, ApJ 676, 427

Cha II properties……… T association Age = 1-10 Myr Distance ≈ 180-200 pc Area ≈ 2 deg2

Modest star formation activity (60 members)

K. Luhman: ‘’Chamaeleon”ASP Conf. Ser., B. Reipurth ed., in press

(Spezzi et al., astro-ph 0802.4351 ; Alcalà, Spezzi et al. 2008, ApJ 676, 427)

Adapted from Cambrèsy 1999

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

(Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504)

(Spezzi et al. 2007, A&A 470, 281; Alcalà, Spezzi et al. 2008, ApJ 676, 427; Spezzi et al., astro-ph 0802.4351)

Meyer 1997

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)

Contaminant

Contaminant

(Spezzi et al., astro-ph 0802.4351 ; Alcalà, Spezzi et al. 2008, ApJ 676, 427)

L STAR,RSTAR

L DISK / ENVELOPE

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…

(Alcalà, Spezzi et al. 2008, ApJ 676, 427; Spezzi et al., astro-ph 0802.4351; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504)

Star Formation Rate

Mean Age

IMF slope (0.1≤M/M≤2)

Total Mass

Mean Mass

cloudstar

star

MM

MSFE

)1008.0(

)08.002.0(

MN

MNRSS

0.52 ± 0.11 M

20 – 33 M

0.4 – 1

6-12% ?(OB associations 26%)

1- 4 %

4 ± 2 Myr

~ 8 M/Myr

0.1 1.0 Mass (M)

dN/dM M- bin=0.2 M

Environmental conditions affect the

BD formation mechanism

Star Formation Rate

Age

IMF slope (0.1≤M/MΘ≤2)

Total Mass

Mean Mass

cloudstar

star

MM

MSFE

)1008.0(

)08.002.0(

MN

MNRSS

0.5 M 8-62 M

0.9 ?

?

1- 7 %

2 Myr

4 - 31 M/Myr

(Alcalà, Spezzi et al. 2006, A&A 453, L1-L4) (Merìn,….Comeròn, Frasca, Alcalà et al. 2007, ApJ 661, 361)

•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

• Twall ≈ 1500 K• Rwall≈ 0.02 AU• Rdisk ≈ 0.4 AU• Mdisk ≈ 10-4 M

• IR class = II

STARDUSTY STARDUSTY + BB FitCGplus fit

FORS2@VLT

Iso-ChaII-13 SST-Lup3-1

crystalline silicate features

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)

(Alcalà, Spezzi et al. 2008, ApJ 676, 427; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504)

Thin disk fraction

declines with mass

Thick disk fraction

peaks ~1 solar mass

Do planets preferentially form

around solar-mass like stars ?

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

turn-off Rin

Log ()

excess

(Alcalà, Spezzi et al. 2008, ApJ 676, 427; Merìn, Jørgensen, Spezzi et al. , astro-ph 0803.1504)

Rin70 AU