Dusty Dark Nebulae and the Origin of Stellar Masses

1. Dusty Dark Nebulae and the Origin of Stellar Masses Colloquium: STScI April 08

2. Dusty Dark Nebulae and the Origin of Stellar Masses The Unsolved Problem of Star Formation Boundary Conditions & Initial Conditions Colloquium: STScI April 08

3. BOUNDARY CONDITIONS Colloquium: STScI April 08

4. BOUNDARY CONDITIONS Compositions, Luminosities, Temperatures, Sizes, & Masses Colloquium: STScI April 08

5. BOUNDARY CONDITIONS Compositions, Luminosities, Temperatures, Sizes, & Masses Colloquium: STScI April 08

6. BOUNDARY CONDITIONS Compositions, Luminosities, Temperatures, Sizes, &Masses Colloquium: STScI April 08

7. BOUNDARY CONDITIONS Compositions, Luminosities, Temperatures, Sizes, &Masses The Initial Mass Function (IMF) = first fundamental boundary condition • Once formed, the entire life history of a star is essentially predetermined by a single parameter: the star’s initial mass. • The IMF (the frequency distribution of stellar masses at birth) plays a pivotal role in the evolution of all stellar systems from clusters to galaxies. Colloquium: STScI April 08

8. Fundamental Boundary Conditions Sun HBL DBL 1- The Initial Mass Function (IMF) Muench et al. 2002 The IMF exhibits a broad peak between 0.6 and 0.1 M suggesting a characteristic mass associated with the star formation process. Brown Dwarfs Completeness limit Brown Dwarfs account for only 1 in 5 objects in IMF!

9. Fundamental Boundary Conditions 2- Stellar Multiplicity Multiplicity is a function of stellar mass Most (~70%) stars are single! Lada 2006 Beichman & Tanner

10. INITIAL CONDITIONS

11. Stars form in Dense, Dark Cloud Cores Initial Conditions = Basic physical properties of starless cores: mass, size, temperature density, pressure, kinematics

13. The Team Members: Harvard-Smithsonian CfA: Charles Lada Gus Muench Jill Rathborne Calar Alto Observatory: Joao Alves Carlos Roman-Zuniga European Southern Observatory: Marco Lombardi The Pipe Nebula Project Basic Properties of the Pipe Cloud: Distance: 130 pc Mass: 104 M SIze: ~3 x 14 pc Star Formation Activity: Insignificant Alex Mellinger

14. INITIAL CONDITIONS: Extinction and the Identification and basic properties of dense cores.

15. Seeing the Light Through the Dark

16. Seeing the Light Through the Dark

18. 10 pc

19. 10 pc

20. 10 pc

21. Core Maps after wavelet decomposition RAW Wavelet Decomposed

22. Distribution of core masses (159 cores) Alves, Lombardi, Lada 2007

23. Distribution of core masses Stars Alves, Lombardi, Lada 2007

24. IMFs x 3.3 Pipe CMF Probability Density Function for the Pipe Core Mass Function Star Formation Efficiency is the Key The IMF derives directly from the CMF after modification by a constant SFE Alves, Lombardi & Lada 2007

25. Lada et al. 2007 Mean Core Densities Median Core Density = 7000 cm-3

26. Mass – Radius Relation Constant Column Density: M ~ R2(Larson’s Laws)

27. Radio Molecular Lines and the Nature of the Cores

28. Core to Core Velocity Dispersion (C18O) bowl= 0.28 km/s stem = 0.26 km/s Muench et al. 2007

29. NH3 Line Survey NH3 detections indicate n(H2) > 104 cm-3 Rathborne et al. 2007

30. NH3 Line Survey NH3 detections indicate n(H2) > 104 cm-3 Radially Stratified Cores Rathborne et al. 2007

31. Supersonic Subsonic NT (km/s)

33. Dense cores are thermally supported! Such cores must evolve on ACOUSTIC timescales!!

35. B 68: Radial Density Profile max = 6.9  0.2 Critical Bonnor-Ebert Sphere

36. 0.18 km/s Pthermal / PNT ~ 10-14!! Barnard 68 is a thermally supported Cloud!

37. B68 Core Pulsation Broderick, Keto, Lada & Narayan, 2007

39. Ptotal = Pthermal + PNT ISM

40. Lada et al. 2007 Core structure is set by the requirement of pressure equilibrium with external medium!

41. Pressure and the Origin of Core Masses: From CMF to IMF

42. MBE = 1.15 (ns)-0.5 T1.5 (solar masses) The BE Critical Mass corresponds approximately to the characteristic mass of the core mass function! Origin of Cores: Thermal Fragmentation in a Pressurized Medium Non-equilibrium Equilibrium

43. mBE = C x a4 (Psurface) -0.5 Taurus Luhman 2004 IC 348 Luhman et al. 2003 From CMF to IMF: Setting the Mass Scale of the IMF The effect of increasing External Pressure P/k ~ 105 P/k ~ 106

44. mBE = C x a4 (Psurface) -0.5 x 2 From CMF to IMF: Setting the Mass Scale of the IMF The effect of decreasing internal Pressure Taurus P/k ~ 105 Luhman 2004 IC 348 Luhman et al. 2003 Pinternal = Pthermal + PNT + B2/8π (aeffective)2 = Pinternal

45. High Pressure Regions: Embedded Cluster Cores P/k ~ 106 –107 K cm-3

46. Fundamental Boundary Condition #2: Stellar Multiplicity Multiple Stars Single Stars Multiplicity increases with stellar mass

47. ORIGIN OF THE IMF: • - CMF{logm} = c1 (log{m/m0}, si); m0= mBE** • IMF{logm} = c2(log{m/m0}, sk); m0=SFE mBE **mBE = Constant x a4 (Psurface) -0.5Bonnor-Ebert Mass Scale

48. ORIGIN OF THE IMF: • - CMF{logm} = c1 (log{m/m0}, si); m0= mBE** • IMF{logm} = c2(log{m/m0}, sk); m0=SFE mBE **mBE = Constant x a4 (Psurface) -0.5Bonnor-Ebert Mass Scale

49. Yield = MdgxSFE=b(t) x Δt ORIGIN OF THE IMF: • - CMF{logm} = c1 (log{m/m0}, si); m0= mBE** • IMF{logm} = c2(log{m/m0}, sk); m0=SFEmBE Mdg= mass of dense gas (n>104) b(t) = stellar birthrate **mBE = Constant x a4 (Psurface) -0.5Bonnor-Ebert Mass Scale

50. (E. Lada 1991) What determines the Star Formation Rate? Most stars form in clusters Stars form exclusively in dense (n > 104 cm-3) gas