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Radio Continuum Studies of Massive Protostars: Observations and Emission Models

This study explores the radio continuum emission from massive protostars, investigating their evolutionary stages, emission mechanisms, and associated molecular characteristics. Observations of massive protostars in Cygnus and DR21 are discussed, along with emission models such as dust emission, ionized accretion flows, and shocks in flows. The text covers the identification of deeply embedded sources, molecular clumps, and hot molecular cores, providing insights into the formation and characteristics of these massive protostars.

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Radio Continuum Studies of Massive Protostars: Observations and Emission Models

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  1. Radio Continuum Studies of Massive Protostars Peter Hofner New Mexico Tech & NRAO

  2. Collaborators E. Araya NRAO/UNM S. Kurtz, L. Rodriguez CRyA-UNAM M. Goss, D. Shepherd NRAO H. Linz MPIA R. Cesaroni Arcetri Observatory C. Anderson NMT

  3. Outline • Introduction: DR21 • VLA Observations of Massive Protostars: • Jets • Photoevaporating Disks • Accretion Shocks • IR and X-Ray Counterparts

  4. Cygnus at 5 GHz Downes & Rinehart 1966 85 ft single dish telescope at Fort Davis, TX 5GHz, FWHM: 10.8' Many discrete sources: thermal spectra

  5. Cygnus at 5 GHz Downes & Rinehart 1966 85 ft single dish telescope at Fort Davis, TX 5GHz, FWHM: 10.8' Many discrete sources: thermal spectra DR21

  6. Compact HII Region Ryle & Downes 1967: Cambridge 1 mile Interferometer: First Aperture Synthesis, 1.4 GHz, FWHM: 30" DR21: the first compact HII region

  7. Ultracompact HII Regions Harris 1973 Cambridge 5 km Interferometer 5 GHz, FWHM: 3" Component D: Cometary UCHII Region EM= 8.2x107 pc cm-6, ne=6.5x104 cm-3 Central star: B0

  8. Surveys for Massive Protostars Selection Criteria: FIR color L > 103 L dense, hot molecular gas  ‘absence’ of radio continuum > 200 candidates 90 % detection rate of outflows (CO) evolutionary stage of candidates ? Pankonin et al. 2001, Araya et al. 2005, Palla et al. 1991, Molinari et al. 1998, 2000 Sridharan et al. 2002, Beuther et al. 2002

  9. Radio Continuum Emission • Signposts for positions of massive protostars • Emission mechanisms: • How does the intensity of radio continuum • relate to overall luminosity ? •  Evolutionary state • Multiplicity/Cluster vs Accretion Disks

  10. Radio Continuum Emission Models • Dust emission • Ionized accretion flows • Photoevaporating disks • Accretion shocks • H, H2 – e- free-free • Spherical or Equatorial Winds • Shocks in flows • Jets   

  11. Deeply Embedded Sources Molecular Clumps: Size = 1 pc NH = 1023 cm-2 Hot Molecular Cores: Size = 0.1 pc NH 1025 cm-2 Predicted Extinction: AV > 1000  cm observations ! Cesaroni et al. 2005

  12. + 44 GHz CH3OH Masers + + + + + Cesaroni et al. 1999 IRAS 20126+4104 Distance: 1.7 kpc Luminosity: 1.3  104 L HMC: T  200 K nH2  7  108 cm-3 Bipolar Molecular Flow: 2 N-S in CO 30 NW-SE in HCO+ Velocity gradient  Flow  Disk ?

  13. Hofner et al. 2007 IRAS 20126+4104 • VLA A-configuration X-band • Where is the massive protostar ? • a) In between N1 and N2 • b) Near peak of N1 • c) Somewhere else

  14. Hofneret al. 2007 IRAS 20126+4104 Thermal dust at 3 & 1.3 mm  extended dust disk  2.5 M (1500 AU) Ionized gas with density gradient at 3.6, 1.3 & 0.7 cm (< 50 AU) associated with outflow Limit on Disk Mass: < 0.8 M (< 50 AU)

  15. IRAS 20126+4104 Ionization equilibrium: N1 and N2 not photo-ionized by protostar  shock ionization  episodic H2O masers: 100 km/sec proper motion  rotation of molecular jet predicted by magneto- centrifugal jet theory Pudritz et al. 2005 N1  Hofneret al. 2007

  16. G31.41+0.31 Cesaroni et al. , in prep. Araya et al. 2008 CH3OH (44.1 GHz)‏ Distance: 7.9 kpc LIRAS: 2.6 x 105 L (06 ZAMS) NH3(4,4) Size: 2" – 0.08 pc n(H2)  107 cm-3 T= 200 K (CH3CN) Outflow characteristics: L ~ 20L, M > 15 M Tdyn ~ 4 x 103 yr

  17. DR21(OH) Araya et al. 2009 Davis et al. 2007 MM1: L= 1.7 x 104 L, B0.5V ZAMS, M ~ 350 M,T ~ 60 K MM2: Early B ZAMS, M ~ 570 M, T~ 30 K

  18. Photoevaporating Accretion Disks Hollenbach et al. 1994, Yorke et al. 1996, Lizano et al. 1996, Lugo et al. 2004, Originally developed for UCHII/HCHII regions Diffuse Ionization  Static ionized atmosphere within gravitational radius rg Photoevaporative flow for r > rg

  19. Orion Source I Reid et al. 2007 Orion KL Source I d=414 pc VLA: SiO J=1-0, v=0, 1, 2 7mm continuum FWHM: 30 mas Ionized accretion disk (+ Jet ?) H2O

  20. Other Candidates Gibb et al. 2007 S140-IRS1 VLA 7mm S106-IR MERLIN 1.3cm CO Flow CO Flow

  21. Accretion Shocks Neufeld et al. 1994, 1996 Supersonic Infall: vs = 5 – 100 km/sec Pre-Shock Densities: nH = 107.5 – 1012 cm-3  Ionized pre/post-shock layer  cm/mm free-free emission

  22. Accretion Shocks Neufeld et al. 1994, 1996 • High optical depths • High brightness temperatures

  23. Accretion Shocks Neufeld et al. 1994, 1996 Assumptions: Cassen & Moosman 1981 Infall Solution Accretion Rate: 10-4 M/year Accretion Radius: 10 AU Central Mass: 10 M Predicted fluxes: 1.2 Jy (X) dist. = 5 kpc (4 mas) 31 Jy (Q) 7.5 Jy (X) dist. = 2 kpc (10 mas) 200 Jy (Q)

  24. IR Counterparts IRAS18566: SPITZER/IRAC VLA-7mm/2MASS-K Anderson et al. in prep. Araya et al. 2007 Precise Positions of massive protostars: adaptive optics, w/ laser guide star: similar resolution Unclear why detectable at NIR: massive dust condensations predict AV>1000

  25. X-Ray Counterparts IRAS20126: CHANDRA VLA –A conf. 0.5 – 8 keV 3.6 cm Anderson et al. , in prep.

  26. EVLA • Jy sensitivity across a wide range of wavelengths • Observe entire sample of massive protostars • Map brightness distribution, SED • Relative duration of different physical scenarios • Correlate with other age indicators: Evolution • However: want matching resolution: e-MERLIN

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