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 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 in the LMC the 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 ApJS High-mass YSOs Intermed- Mass YSOs

Step 2 H  +CO dss-r H  2MASS J 2MASS K

Massive stars like company Higher-resolution images are needed

Massive YSO Candidates in the LMC Source Total [8]<8 YSO  YSO  YSO  167 > 4M  > 10M  Neb AGB PNe 52 9 Galaxy Galaxy? 126 Expect ~ 1000 galaxies 98% YSOs confirmed Reliable sample of massive YSOs !!!

Massive YSOs and Their Environments 15’ = 225 pc CO contours (NANTEN; Fukui et al) H  images (MCELS; Smith et al)

OB Ass. HII Region YSO NAME LH DEM dem CO Henize Y N79A Y N b --- Y 30 Dor B Y N b --- Y N Y N44C Y N105A Y N159B Y N Y N Y N 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 Associations Poster 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H

Massive YSOs Not in CO or OB Associations 15’ = 225 pc CO contours (NANTEN; Fukui et al) H  images (MCELS; Smith et al)

Are These Massive YSOs Isolated ? 15’ = 225 pc CO contours (NANTEN; Fukui et al) H  images (MCELS; Smith et al)

Massive YSOs Massive YSOs Spitzer observations of the LMC show 248 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 appears isolated until the next star is formed… ~ 7% are neither in OB associations nor in molecular clouds  truly isolated

Conclusions Less than ~ 7% massive stars are formed in isolation. Isolated massive stars were likely formed in small dust globules triggered 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 DEM L256 SNe explode in bubbles, did bubbles or SNRs trigger the star formation?

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. Johnnson (Illinois) H. Zinnecker (Potsdam) 100 pc

In collaboration with: R. Gruendl, R. Chen, M. Gelman, M. Johnnson (Illinois) H. Zinnecker (Potsdam) Where and How Are Massive Stars Formed in Isolation? You-Hua Chu (U of Illinois)

100 pc In collaboration with: R. Gruendl, R. Chen, M. Gelman, M. Johnnson (Illinois) H. Zinnecker (Potsdam) Where and How Are Massive Stars Formed in Isolation? You-Hua Chu (U of Illinois)