loredana spezzi inaf-catania astrophysical observatory loredana spezzi inaf-catania astrophysical...
TRANSCRIPT
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