Transcript SINGLE DISH OBSERVATIONS OF STAR FORMING REGIONS

Disks (and outflows) in high-mass YSOs
in collaboration with:
M.T. Beltràn, C. Codella, R. Furuya, P. Hofner, L. Moscadelli,
R. Neri, L. Olmi, L. Testi, C.M. Walmsley and many more…
1) Importance of disks for high-mass star
formation: accretion vs merging
2) Search for disks in massive YSOs: targets
and tracers
3) Results: Keplerian and self-gravitating
disks
Disks and star formation
Star formation  contraction + conserv. of angul.
momentum  rotation and flattening: “disk”
Observer’s definition:
Disk = elongated and rotating structure
• Keplerian disks found in low-mass YSOs
• Disks in high-mass YSOs would be even more
important…
Low-mass vs High-mass
 Lowmass (< 8 M): taccr < tcontr
 Highmass (> 8 M): taccr > tcontr
High-mass stars “switch on” still accreting 
radiation pressure stops accretion  stars > 8
M
cannot form!?
Solutions:
1) non-spherical accretion: disks (and outflows)
2) merging of stars < 8 M
Search for disks in high-mass YSOs
• Target: hot cores (<0.1 pc, 10-103 M, 100 K)
with jet/outflow
• Tracer: “rare” species: CH3CN, NH3, CH3OH
 Test: core with velocity gradient perpendicular
to outflow axis:
outflow
outflow
core
Likely candidates for disks
G24.78
G29.96
G31.41
IRAS20126
LIRAS (L)
7 105
106
3 105
104
MCORE(M)
550
460
2500
10
Gibb et al. 2002
Gibb et al. 2002
Gibb et al. 2002
Gibb et al. 2002
Gibb et al. 2002
Gibb et al. 2002
Higher angular resolution desirable:
• ALMA down to few mas, but only after 2010…
• at present: 7mm cont. with VLA (40 mas) and
masers (H2O, OH, CH3OH) with VLBI (1 mas)
VLA/VLBI observations give ambiguous results
for disks in massive YSOs…
Conclusions
• Disks in high-mass YSOs do exist:
10-1000 M, 100-1000 AU
• Most disks in high-mass YSOs appear to be
unstable
Disks  formation by accretion plausible
Accretion  disks long-lived entities
Search for disks in high-mass YSOs
• Target: hot cores (<0.1 pc, 10-103 M, 100 K)
with jet/outflow
• Tracer: “rare” species: CH3CN, NH3, CH3OH
 Test: core with velocity gradient perpendicular
to outflow axis
Problems:
 large distance (a few kpc): sub-arcsec resolution
 inclination of disk axis: 90° good for disk,
0° good for outflow