Where and How Are Massive Stars Formed in Isolation?
You-Hua Chu (U of Illinois)
In collaboration with:R. Gruendl, R. Chen*, M. Gelman, M. Johnson
(Illinois)H. Zinnecker (Potsdam)
Galactic O-Type Stars
70% in clusters or OB associations > 10% runaway stars < 20% formed in isolation Gies 1987; Mason et al. 1998; Maíz-Apellániz et al. 2004
227 O stars with V < 8 mag 43 appear to be field stars 22 are candidate runaway stars 5 are in faint clusters~ 5-10% are true field stars de Wit et al. 2004, 2005
What fraction of massive stars was formed in isolation?
Under what conditions are O stars formed in isolation?
LMC
WR stars - Breysacher, Azzopardi, Testor (1999)
Massive Young Stellar Objects - Gruendl & Chu (2008)
MCELS Mosaic of the Large Magellanic Cloud Smith, Points, et al.
DM = 18.5 ; 50 kpc; 4” = 1 pc
WR Stars inWR Stars in the LMCthe LMC
134 WR stars in the LMC
80 in OB associations 25 near OB associations 6 near GMC and YSOs 14 in supergiant shells
9 truly isolated (~ 7%)
Spitzer mosaic of the LMC - SAGE Meixner et
al.
Identification of YSOs in the LMC
AGB
Stars
Galaxies
Step 1 (DM of the LMC= 18.5)
Gruendl & Chu 2008, submitted to ApJSGruendl & Chu 2008, submitted to ApJS
High-mass YSOs
Intermed-Mass YSOs
Step 2
H+CO dss-r H 2MASS J
2MASS K 3.6 4.5 5.8
8.0 24 70
Massive stars like company Higher-resolution images are needed
Massive YSO Candidates in the LMC
Source Total [8]<8
YSO 858 234YSO 303 14YSO 167 >4M >10M
Neb 126 13AGB 110 105PNe 52 9
Galaxy 947 6Galaxy? 126
Expect ~ 1000 galaxies
98% YSOs confirmed
Reliable sample of
massive YSOs !!!
Massive YSOs and Their Environments
15’ = 225 pcCO contours (NANTEN; Fukui et al) H images (MCELS; Smith et al)
---------------------------------------------------------------------------------OB Ass. HII Region
YSO NAME LH DEM dem CO Henize---------------------------------------------------------------------------------045153.3-692328.6 1 10 --- Y N79A052646.6-684847.2 58 199 --- Y N144053750.3-691107.3 99 263b --- Y 30 Dor B053943.8-693834.0 103 284 --- Y N160051912.3-690907.3 41 132b --- Y N119052212.6-675832.4 47 152 --- Y N44C050950.5-685305.5 31 86 --- Y N105A054004.4-694437.6 105 271 --- Y N159B053203.4-674225.7 76 229 --- Y N57053943.3-693854.6 103 284 --- Y N160051325.1-692245.1 35 104 --- Y N113045426.1-691102.3 5 11 --- Y N83B. . .
( Lucke & Hodge 1970; DEM 1976; Henize 1956 )
N 44 N 206
H image; CO contours; hi-mass YSOs; i-mass YSOs
On-Going Massive Star Formation near OB AssociationsPoster Poster
Chen et al.Chen et al.
N 144 N 51
H image; CO contours; hi-mass YSOs; i-mass YSOs
On-Going Massive Star Formation near OB Associations
N 144 N 51
H image; CO contours; hi-mass YSOs; i-mass YSOs
On-Going Star Formation near OB Associations
N 144 N 51
H image; CO contours; hi-mass YSOs; i-mass YSOs
On-Going Star Formation near OB Associations
4" = 1 pc
H
Massive YSOs Not in CO or OB Associations
15’ = 225 pcCO contours (NANTEN; Fukui et al) H images (MCELS; Smith et al)
Are These Massive YSOs Isolated ?
15’ = 225 pcCO contours (NANTEN; Fukui et al) H images (MCELS; Smith et al)
Massive YSOsMassive YSOsSpitzer observations of the LMC show248 YSOs with [8.0] > 8, or M > 10 M
~ 85% are in molecular cloud
~ 65% are in OB associations
The first star in a molecular cloud appearsisolated until the next star is formed…
~ 7% are neither in OB associations nor in molecular clouds truly isolated
Conclusions
Less than ~ 7% massive stars areformed in isolation.
Isolated massive stars were likelyformed in small dust globulestriggered by ionization front or mild shocks.
50 pc
CO contours (NANTEN; Fukui et al) H images (MCELS; Smith et al)
Do SNRs Trigger Star Formation? SNR 0513-69.2 DEM L256
SNe explode in bubbles, did bubbles or SNRstrigger the star formation?