1. 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)

2. 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

3. 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)

4. MCELS Mosaic of the Large Magellanic Cloud Smith, Points, et al. DM = 18.5 ; 50 kpc; 4” = 1 pc

5. WR Stars in the LMC the LMC 

6. 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%)

7. Spitzer mosaic of the LMC - SAGE Meixner et al.

8. 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

9. Step 2 H  +CO dss-r H  2MASS J 2MASS K 3.6 4.5 5.8 8.0 24 70

10. Massive stars like company Higher-resolution images are needed

11. Massive YSO Candidates in the LMC Source Total [8]<8 YSO  858 234 YSO  303 14 YSO  167 > 4M  > 10M  Neb 126 13 AGB 110 105 PNe 52 9 Galaxy 947 6 Galaxy? 126 Expect ~ 1000 galaxies 98% YSOs confirmed Reliable sample of massive YSOs !!!

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

13. --------------------------------------------------------------------------------- OB Ass. HII Region YSO NAME LH DEM dem CO Henize --------------------------------------------------------------------------------- 045153.3-692328.6 1 10 --- Y N79A 052646.6-684847.2 58 199 --- Y N144 053750.3-691107.3 99 263b --- Y 30 Dor B 053943.8-693834.0 103 284 --- Y N160 051912.3-690907.3 41 132b --- Y N119 052212.6-675832.4 47 152 --- Y N44C 050950.5-685305.5 31 86 --- Y N105A 054004.4-694437.6 105 271 --- Y N159B 053203.4-674225.7 76 229 --- Y N57 053943.3-693854.6 103 284 --- Y N160 051325.1-692245.1 35 104 --- Y N113 045426.1-691102.3 5 11 --- Y N83B... ( Lucke & Hodge 1970; DEM 1976; Henize 1956 )

14. 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.

15. N 144 N 51 H  image; CO contours; hi-mass YSOs; i-mass YSOs On-Going Massive Star Formation near OB Associations

16. N 144 N 51 H  image; CO contours; hi-mass YSOs; i-mass YSOs On-Going Star Formation near OB Associations

17. 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

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

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

20. 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

21. 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.

22. 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 SNRs trigger the star formation?

23. 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

24. 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)

25. 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)