Diapositiva 1

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, 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 (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 ()
Rin70 AU