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L 4: Collapse phase – observational evidence

This work presents observational insights into the collapse phase of stellar evolution using infrared techniques. Focused on dense interstellar clouds, it outlines challenges in detecting protostars, which represent a crucial aspect of stellar formation. Various methods such as continuum observations and spectral lines are examined to infer physical conditions and mass distributions in these environments. By integrating theoretical models with observational data, this study addresses complexities in understanding stellar birth, emphasizing the interplay between gas and dust in star formation processes.

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L 4: Collapse phase – observational evidence

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  1. L 4: Collapse phase – observational evidence Background image: courtesy Gålfalk & Liseau, Serpens Core with VLT ANTU and ISAAC L 4 - Stellar Evolution II: August-September, 2004

  2. L 4: Collapse phase – observational evidence What is the problem ? How to solve it ? Known Methods & Techniques L 4 - Stellar Evolution II: August-September, 2004

  3. L 4: Collapse phase – observational evidence What is the problem ? Theories may give different answers what to look for – but predictions include L 4 - Stellar Evolution II: August-September, 2004

  4. L 4: Collapse phase – observational evidence How to solve it ? or - how and where to look ? In dense interstellar clouds with infrared techniques ! L 4 - Stellar Evolution II: August-September, 2004

  5. Protostars are the Holy Grail of infrared astronomy Any observational difficulties ? L 4 - Stellar Evolution II: August-September, 2004

  6. L 4: Collapse phase – observational evidence (Known) Methods & Techniques Radiation (1) Continuum (2) Spectral Lines L 4 - Stellar Evolution II: August-September, 2004

  7. Continuum (Proto-)stellar photospheres Free-free gas emission Thermal radiation from (radiatively) heated dust grains Thermal radiation from (radiatively) heated dust grains To infer the total mass one needs Gas-Dust Relation [ generally assumed: m(g)/m(d) = 100 ] L 4 - Stellar Evolution II: August-September, 2004

  8. notice the spatial scales & time scales • Continuum Observations and Theoretical Models Spectral Energy Distributions SEDs Current Paradigm Astronomical Taxonomy Adapted from van Zadelhoff 2002, PhD thesis L 4 - Stellar Evolution II: August-September, 2004

  9. Continuum Observations + Spectral Energy Distributions (SEDs) SED fitting Theoretical models protostar Adams, Lada & Shu 1987ApJ 312, 788 L 4 - Stellar Evolution II: August-September, 2004

  10. Continuum Observations + Spatial Profile fitting Theoretical models IRS 5 L1551 KAO 50 mm I / Ipeak 100 mm residuals radial offset ( ´´ ) Butner et al. 1991 ApJ 376, 636 L 4 - Stellar Evolution II: August-September, 2004

  11. FIR & submm SCUBA 850 mm 450 mm • Continuum Spatial Profile fitting Observations Azimuthal Intensity Distribution Shirley et al. 2000 ApJS 131, 249 L 4 - Stellar Evolution II: August-September, 2004

  12. Compare to theory of collapse (see L 3) centrally condensed Bonnor 1956 MNRAS 116, 351 flat distribution Shu 1977 extreme case L 4 - Stellar Evolution II: August-September, 2004

  13. See also L 1: Motte et al. made fits at 1.3 mm => mostly Bonnor-Ebert spheres (flat) and r Oph A with I(r) ~ r - 2 and furthermore obtained ... L 4 - Stellar Evolution II: August-September, 2004

  14. Also Johnstone et al. 2000, ApJ 545, 327 Motte et al. 1998, AA 336, 150 Clump Mass Spectrum & IMF 1 clump - 1 star no further Fragmentation ? - see Eduardo (L 3) L 4 - Stellar Evolution II: August-September, 2004

  15. Continuum B 335 FIRS Spatial Profile fitting Firstly and only directly observed r ~ r - 1.5 profile Keck-I, K band (Hodapp 1998, ApJ 500, L 183) L 4 - Stellar Evolution II: August-September, 2004

  16. IRAM-PdB Interferometer 1.2 mm 3 mm Infall ? ``YES´´ Inside-out ? ``NO´´ Harvey et al. 2003, ApJ 583, 809 L 4 - Stellar Evolution II: August-September, 2004

  17. Continuum Observations Theoretical models Major pitfalls/caveats: Geometry - spheres vs disks Calorimetric vs `true´ Luminosities Dust Optical Depths (Properties) Temperatures (Dust and Gas) Inhouse work, see, e.g. : Larsson et al. 2000 White et al. 2000, AA L 4 - Stellar Evolution II: August-September, 2004

  18. (2)Spectral Lines What lines – species ? Physical Conditions of Excitation Cold ( Tk ~ a few x 10 K ~ meV ) Large AV (no / little external radiation) and dense (n > 103 cm -3): collisional excitations dominate level populations ( if t << 1 ) (low-lying) Rotational Transitions in Molecules mostly neutrals but CosmicRays => molecular ions and e- L 4 - Stellar Evolution II: August-September, 2004

  19. (2) Spectral Lines • Optically thin lines • Optically thick lines does not necessarily imply there’s `nothing´ there Why ? L 4 - Stellar Evolution II: August-September, 2004

  20. (2) Spectral Lines Theoretical profiles: cf. L3 Symmetrical Profiles • Optically thin lines • Optically thick lines (a?) no, spatial resolution Ammonia NH3 (b?) Foster & Chevalier 1993, ApJ 416, 303 L 4 - Stellar Evolution II: August-September, 2004

  21. Theoretical profiles (2) Spectral Lines Asymmetrical Profiles • Optically thin lines • Optically thick lines cloud center Carbon monoxide CO =12C16O (a?) and Isotopes (b?) offset ...hmm..., needs to be verified Leung & Brown 1977, ApJ 214, L73 L 4 - Stellar Evolution II: August-September, 2004

  22. (2) Spectral Lines Theoretical profiles warmer: more intensity Asymmetrical Profiles cooler: less intensity (b) Optically thick lines los for negative temperature gradient Shu Infall Zhou et al. 1993, ApJ 404, 232 L 4 - Stellar Evolution II: August-September, 2004

  23. inside-out collapse (Shu 1977, ApJ 214, 488) (see: L 3) B 335 p = -1.5 a = -0.5 p = -2 a = 0 not from Shu model Rinf = cstinf adapted from Hartstein & Liseau 1998, AA 332, 703 L 4 - Stellar Evolution II: August-September, 2004

  24. Theoretical profiles (2) Spectral Lines + Observations (b) Optically thick lines high bluelow red Asymmetrical Profiles Carbon Sulfide CS Hartstein & Liseau 1998, AA 332, 703 L 4 - Stellar Evolution II: August-September, 2004

  25. Observed & Theoretical profiles (2) Spectral Lines 13CO C18O (b) Optically thick lines (non-)equilibrium and information content thermalised Example: Carbon Monoxide 13CO Carbon Sulfide CS Hartstein & Liseau 1998, AA 332, 703 L 4 - Stellar Evolution II: August-September, 2004

  26. (2) Spectral Lines B 335 infall model oH2O (1-0) 10´´ 20´´ 120´´ (b) Optically thick lines Observation: dependence of profiles on spatial resolution (``beam´´) 24´´ 38´´ 51´´ CS (2-1) Carbon Sulfide CS Water Vapour H2O L 4 - Stellar Evolution II: August-September, 2004

  27. Observed + Theoretical Profiles Single Dish B 335 Interferometer Observation: no wings Inside – out collapse: wings Wilner et al. 2000, ApJ 544, L69 L 4 - Stellar Evolution II: August-September, 2004

  28. (3) Continuum and Spectral Lines Theoretical profiles + Observations e.g. Stark et al. 2004, ApJ 608, 341 Inhouse, e.g.: Larsson et al. – Odin H2O + ground based Schöier et al. – ground based inc. chemistry r Oph A IRAS 16293 ( r Oph east ) ... but steady state models .... of a highly dynamic situation... L 4 - Stellar Evolution II: August-September, 2004

  29. Outflow contamination & confusion! Current Paradigm - ? `` finn fem fel ´´ Adapted from van Zadelhoff 2002, PhD thesis L 4 - Stellar Evolution II: August-September, 2004

  30. ISO SWS & LWS + submm/mm FOV = 2.5 X 2.5 amin2 (0.2 X 0.2 pc2) Fitting the observed SED*: Menv = 6 Mo L = 140 Lo * 2-D radiative transfer (Larsson et al. 2002, AA 386, 1055) Serp SMM 1 (S68 FIRS 1)* Infall Candidate Outflow Source Disk Source * D = 310 pc L 4 - Stellar Evolution II: August-September, 2004

  31. Modeling the Line Emission Emission not from Disk Infalling Envelope but Outflow/Shocks L 4 - Stellar Evolution II: August-September, 2004

  32. Outflow contamination & confusion! Single Stars? Current Paradigm - ? `` finn fem fel ´´ Adapted from van Zadelhoff 2002, PhD thesis L 4 - Stellar Evolution II: August-September, 2004

  33. Number of Infall Candidates: Reasonable ? Expected ? * Object Classes and Lifetimes SFR of the solar neighbourhood Consistent picture? Magnus´ IMF talk *High mass starformation – cloud/cluster collapse L 4 - Stellar Evolution II: August-September, 2004

  34. L 4: conclusions • a variety of observational techniques are exploited • a number of collapse candidates have been found • all are strong outflow sources • multiplicity is common • L 4: open questions • How many collapse processes do occur in nature ? • more than one ? which ? • What is the `certain´ collapse tracer ? • What spectral & spatial resolution is needed ? • Are stars/BDs/planets formed differently ? How ? L 4 - Stellar Evolution II: August-September, 2004

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