Transcript slides_for_cynthia

IRAC/MIPS view of the ISM:
PAHs dominate in IRAC
Li & Draine (2001)
dust emissivity
model; only very
strong (> 103 x avg.)
radiation fields
contribute to
thermal emission at
8 m
Our entire mosaic is remarkably constant in CH4/Ch3 ratio (~ 3) => PAHdominated with a few exceptions near HII regions
Massive stars are rare, but once a single
massive star forms, the game changes.
•L ~ 105 – 106 L
• Intense EUV, FUV
radiation
• Powerful winds
• Supernova
This energy input quickly reshapes
the environment, dominating all that
goes on there, perhaps including lowmass star formation.
Star formation near massive
stars is NOT Taurus-Auriga
writ large!!!!
Disks in Orion
Disks in Taurus-Auriga
Structure of H II region carved by radiation from massive stars.
Dark – Molecular gas
Massive stars
Dense gas compressed
in advance of the
ionization front
Blue – Hot (~104 K),
tenuous (~30 cm-3),
ionized cavity. The
H II region interior.
Red – Ionization front
pushing into and evaporating
dense gas
•
Isolated star formation, such as that seen in Taurus-Auriga is atypical.
The majority of low-mass, Sun-like stars form instead in rich clusters and
in proximity to massive stars.
Direct counts
E.g., Lada & Lada, 2003, Ann. Rev. Astron. Astrophys, 41, 57
Complete survey of embedded clusters out to 2 kpc:
- 70 – 90% of stars form in dense clusters
- Of these, 75% currently near massive stars
•
Short-Lived Radionuclides (SLRs) require that the Sun formed near a
massive star.
•
Solar mass stars form in dense gas, then are soon uncovered by the ionization
front, leaving young disks sitting in a hot, tenuous region near one or more
massive stars.
•
Triggered Star Formation may be the standard mode of star formation, even in
turbulent environments.
Embedded YSOs - 4 kpc*
< 2 Msun
2 < Msun < 5
> 5 Msun
*Assuming
GLIMPSE
sensitivities
Limitations of Color-Color
Analysis
• You need to detect the source in all four
IRAC bands
• Does not work well in crowded regions
• There is significant ambiguity in
interpreting the results
– Does not discriminate different masses well
– Although the effects of extinction are much
smaller at these wavelengths, there are still
degeneracies typical for stars at the GC
• Solution: Fit ALL the SEDs
Tests on
M16
data
Embedded
Disk
Embedded or disk
M16: SED Fitter at Work
(Whitney et al. 2003a,b,2004; Indebetouw et al. 2006; Robitaille et al. 2006)
Stage I: Yellow
Stage II: Green
Stage III: Blue
• A by-product of the fitting program
is a best-fit extinction to each source
• Includes the MS and Giant stars