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Where and How Are Massive Stars Formed in Isolation?

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

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Where and How Are Massive Stars Formed in Isolation?

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  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 

  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 Step 1 (DM of the LMC= 18.5) High-mass YSOs Intermed- Mass YSOs AGB Stars Galaxies Gruendl & Chu 2008, submitted to ApJS

  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 858234 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 CO contours (NANTEN; Fukui et al) H images (MCELS; Smith et al) 15’ = 225 pc

  13. ------------------------------------------------------------------------------------------------------------------------------------------------------------------ OB Ass.HII Region YSO NAME LHDEM demCOHenize --------------------------------------------------------------------------------- 045153.3-692328.6 1 10 ---YN79A 052646.6-684847.2 58 199 ---YN144 053750.3-691107.3 99 263b ---Y30 Dor B 053943.8-693834.0 103 284 ---YN160 051912.3-690907.3 41132b ---YN119 052212.6-675832.4 47152 ---YN44C 050950.5-685305.5 3186 ---YN105A 054004.4-694437.6 105271 ---YN159B 053203.4-674225.7 76229 --- Y N57 053943.3-693854.6 103 284 ---YN160 051325.1-692245.1 35 104 ---YN113 045426.1-691102.3 511 ---Y N83B . . . ( Lucke & Hodge 1970; DEM 1976; Henize 1956 )

  14. On-Going Massive Star Formation near OB Associations Poster Chen et al. N 44 N 206 H image; CO contours; hi-mass YSOs; i-mass YSOs

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

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

  17. On-Going Star Formation near OB Associations N 144 N 51 H 4" = 1 pc H image; CO contours; hi-mass YSOs; i-mass YSOs

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

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

  20. 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. Do SNRs Trigger Star Formation? SNR 0513-69.2 DEM L256 50 pc CO contours (NANTEN; Fukui et al) H images (MCELS; Smith et al) SNe explode in bubbles, did bubbles or SNRs trigger the star formation?

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