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?