1 / 36

Breakfast Talk: Views on Star Formation

Breakfast Talk: Views on Star Formation. Current Views on Star Formation. Francesco Palla INAF-Osservatorio di Arcetri, Firenze. 1. From clouds to stars: a unified scenario 2. Star Formation in clusters & associations: SF histories and accelerating SF

kasa
Download Presentation

Breakfast Talk: Views on Star Formation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Breakfast Talk: Views on Star Formation

  2. Current Views on Star Formation Francesco Palla INAF-Osservatorio di Arcetri, Firenze 1. From clouds to stars: a unified scenario 2. Star Formation in clusters & associations: SF histories and accelerating SF 3. Physical origin: slow vs fast mode of SF critical tests on age spreads 4. Conclusions Hamburg, 7 July, 2004

  3. Taurus dense core 5 pc M ~ 5 M N2H+(1-0) 13CO(1-0) Star formation within molecular cloud complexes distribution of molecular gas in the galactic plane CO(1-0) Dame et al. 2001

  4. gravitational collapse 10 000 AU embedded young star 100 AU t =104-105 yr 50 AU Accretion disk jet planetary system T Tauri star main sequence star t >107yr t =106-107 yr dense cores 1pc L1551 binary jet

  5. Star Formation: current views Low & Intermediate mass stars follow the same route whether in clusters or isolated. Problems with initial conditions Next step: from individual to global properties  IMF & SFH Empirical information from study of the distribution of gas & stars in nearby SFRs

  6. SFH solar neighborhood Chamaeleon IC 348 - Perseus

  7. SFH solar neighborhood Rho Ophiuchi

  8. Λ Orionis association interior regions interior: SF 0 external: SF accel exterior

  9. Taurus-Auriga: SF in space & time Distribution of stars 13CO Distribution of dense gas in filaments C18O

  10. Taurus-Auriga Turbolenza accelerating decelerat

  11. SFH of clusters & associations • SF starts at low rates and increases in time • SF accelerateswith e-folding timest~1-3x106 yr both in clusters and associations SF only occurs above threshold NH>N(HIH2) • Lack of stars with ages >107 yr: post-TTS are rare due to limited SF activity • Acceleration followed by rapid dissipation (outflows, UV, X-rays…): OK for massive clusters, but problematic for T associations

  12. Interpretation of SFH: different views on core formation/evolution Case 1: Magnetically controlled quasi-static evolution Cores form as a result of gradual loss of magnetic & turbulent support due to ambipolar diffusion: long times scales(e.g. Ciolek & Basu 2003)

  13. Magnetic Field Diffusion vdrift (F/M)in tad 3-10 Myr F/M<(F/M)in

  14. Interpretation of SFH: different views on core formation/evolution Case 2: Turbulence controlled & dynamic Cores are transient fluctuations induced by shock dissipation at flow intersections (e.g. Mac Low & Klessen 2003) decay time <~ 1 Myr  fresh turbulence SF active only for few crossing times

  15. Turbulence filaments & cores Klessen 2003

  16. Understanding SFH: how to decide? Empirical information from: Dense core lifetimes HI in H2 indicates t≥1-2 Myr(Goldmsith et al.2004) Dynamics of dense cores: velocity gradients inconsistent with shock dissipation (Galli et al. 2004) Age spreads in clusters: Li-depletion as age diagnostic (Palla et al. 2004) Ages of dense cores in Taurus 1 Myr

  17. Predictions on core shape and kinematics magnetically controlled turbulence driven vz +0.2 km s-1 vx vx= vy nz -0.2 km s-1 vy ny vz nx= ny nx nz Fiedler & Mouschovias (1993) Ballesteros-Paredes et al. (2003)

  18. Age spreads: the lithium test • SFRs are not the best sites: SF is taking place and will continue in the futureage spreads are lower limits • Test oftheLithium Depletion Boundary(LDB)in young gas-free clusters, e.g. Orion Cluster, Upp Sco intermediate age open clusters (~10-30 Myr):SF is finished, isochrones are not too crowded, LDB in stellar regime (not BDs as in Pleiades)

  19. Orion Nebula Cluster: HRD & Lithium Depletion Region full depletion

  20. How to test the age spread? Using the lithium line at 6708 Ǻ as a diagnostic of depletion history 1 Myr 20 Myr GTO VLT Flames/Giraffe: Pallavicini, Palla, Randich, Flaccomio

  21. Derived [Li] abundances, veiling corrected M=0.4 Msun

  22. LX vs mass & age for Li-sample:drop at lowest mass & for older stars 10 Myr 1 Myr

  23. The Upper Scorpius Association:evidence for lithium depletion HR diagram Lithium depletion Low-mass sample Preibisch & Zinnecker 2002

  24. Conclusions • Route from molecular clouds to young stars & disk is ~ understood: main phases for low-mass SF have been identified • Importance of initial conditions: rapid vs slow core formation and collapse • In clusters & associations SF accelerates in time  threshold f(AV, NH, xe) • Duration of SF: age spreads & independent tests (lithium…)  long lived

  25. At stellar birth, the IMF is Salpeter from ~0.5 Msun Sun HBL Orion Nebula Cluster K-band image Brown Dwarfs

  26. The IMF in Star Forming Regions & the Pleiades Taurus Chamaeleon I IC 348 Trapezium Bouvier et al. 1998 Hambly et al. 1999 Moraux et al. 2003 Pleiades (100 Myr) Luhman 2004

  27. svir = [GM/5R]1/2 (km s-1) Klessen et al. (2003) 1 Taurus cores 0.3 0.1 0.1 0.3 1 slos(km s-1)

  28. Modo 1: SF lenta… le nubi molecolari sono in equilibrio di forze e autogravitanti: evoluzione quasi-statica tcross~tff & tnube~10 Myr>> tff nascita di stelle localizzata nello spazio & tempo: fenomeno di soglia (NH, G0, xe…) SFR è basso inizialmente e accelera nel tempo SFE è bassa a causa della rapida decelerazione • Modo 2: SF rapida… le nubi molecolari sono entità dinamiche: frammentazione turbolenta & dissipazione,tnube~ tff~2-3 Myr SF avviene in shells create da flussi turbolenti su larga scala SF è rapida, tSF~1-2 tcross SFR è basso a causa della bassa efficienza nelle shells

  29. • stelle giovani • stelle evolute

  30. Distribuzione di età Tau-Aur Turbolenza accelerazione deceleraz

  31. Evolution of the central density t0 t1 t2 Desch & Mouschovias (2001)

  32. The years 2000:Modes of Star Formation Rich Cluster: NGC 3603 Isolated: Taurus Cluster: Orion

  33. Dissipation time Dissipation time of energy Kinetic energy (lateral) The sum of the all Magnetic energy Kinetic energy (vertical) Note that the energy in transverse modes remains much greater than that in generated longitudinal modes. The time we stop driving force

  34. HR diagram of the Orion Cluster most stars formed ~2 Myr ago notice the large age spread: real or not?

  35. Sun HBL At stellar birth, IMF really is given by Salpeter (1955) IMF. Brown Dwarfs Hillenbrand1997

More Related