Massive Young Stellar Objects in highmass starforming regions

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Massive Young Stellar Objects in high-mass
star-forming regions

• Arjan Bik
• (ESO, Garching)
• Rens Waters, Lex Kaper (Amsterdam,NL),
• Wing-Fai Thi (ESTEC,NL), Annique Lenorzer
  (SRON,NL), Alex de Koter (Amsterdam,NL), Margaret
  Hanson (Cincinnati, USA), Fernando Comerón (ESO,
  Garching), Elena Puga-Antolin (Leuven, B)

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Conclusions

• A number of objects possessing circumstellar
  disks are found in a sample of high-mass
  star-forming regions
• Are they the remnants of their formation
  process?
• Likely yes!!

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Outline

• Introduction of the sample
• Near infrared survey of 45 UCHII regions
• Modeling of the CO first-overtone emission
• Whats the nature of these objects?
• Are they surrounded by a (remnant) accretion disk?

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Near-infrared survey of UCHII regions with
NTT-SOFI
5x5
5x5
IRAS 11097-6102 NGC 3576
IRAS 08576-4334
5x5
5x5
IRAS 15411-5352
IRAS 16164-5046
Blue Paß Green H2 Red Br?
Kaper et al, to be submitted
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Selection of candidate massive stars
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Spectroscopic follow-up with VLT-ISAAC

• OB stars (40)
• Objects dominated by nebular lines (a lot)
• Objects which show infrared excess (20)
• Late type fore-/background stars (40)

• Bik, Kaper, Waters, submitted to AA
• Bik, Kaper, Hanson, Smits in press
  (astro-ph/0505293, today!)

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Massive Young Stellar Objects
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Massive Young Stellar Objects
Red continuum, IR-excess? Majority of objects
has spectral-type B. Few of them have
spectraltype O. (based on HeI in spectrum)
Broad Hydrogen lines (100 200 km/s)
CO bandheads
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Modeling of the CO-bandheads

• Why are CO bandheads usefull?
• Tracer of dense and hot material
• Velocity information
• A simple model
• Excitation temperature
• Column density
• Velocity profile
• Keplerian disk (Mstar,R,sini )

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Model fits to the data
Bik Thi, AA, 430, 61
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• CO is emitted in a circumstellar disk
• Difference in shape of the bandheads can be
  explained by difference in inclination angle
• CO is emitted in the inner 5 AU of the
  circumstellar disk

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Other indications for disks

• Pfund lines
• Originate in high density ionized gas
  (Ne 108 cm-3)
• Double peaked in one object

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Br? emission

• FWHM 100-200 km/s
• Not correlated with shape CO bandheads
• The objects with steep CO bandheads have broad
  Br?.
• FWHM is smaller than the FWHM of the Pfund lines.

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The origin of the Br? lines

• Surface layer circumstellar disk?
• Br? is formed over a larger area than the Pfund
  lines ? dominated by the velocities in the outer
  parts of the disk
• CO and Br? not formed in same geometry

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The origin of the Br? lines

• Disk wind (e.g. Drew et al 1998)
• Surface layer of the disks evaporates, results in
  a dense, low velocity ionized disk wind
• CO and Pfund require higher densities and are
  formed in the disk
• Br? is formed in the (lower density) disk wind

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Summarizing
Br?
Poster by Thi Bik Water vapor in the
circumstellar disk around a massive YSO
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Are these disks the remnants of the accretion
disks?

• also some main-sequence (MS) and evolved OB
  stars possess disks
• Be and Be stars, fast rotation plays a role
• Young OB stars might rotate faster than MS stars
• CO suggest that disk structure of massive YSOs
  is different from Be stars
• No disk wind observed in Be stars
• Most of the Be stars are supergiants
• (not present in star-forming regions)
• Colors of stars similar to Herbig Be stars

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Conclusions and future perspectives

• A number of objects likely possessing
  circumstellar disks are found
• Are they the remnants of their formation
  process?
• Likely yes, but more study is needed.
• Tracers of the outer regions of the disk CO
• fundamental emission
• Mid-infrared dust emission.
• Extend the sample to find more disks around young
  O stars.