1 / 18

Accretion Processes in Star Formation Lee Hartmann Cambridge Astrophysics Series, 32

Based on:. Accretion Processes in Star Formation Lee Hartmann Cambridge Astrophysics Series, 32 Cambridge University Press. ACCRETION SIGNATURES IN YSO. Matter transfered from molecular cloud to YSO. The accretion leaves distinctive signatures:

mason
Download Presentation

Accretion Processes in Star Formation Lee Hartmann Cambridge Astrophysics Series, 32

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. Based on: Accretion Processes in Star Formation Lee Hartmann Cambridge Astrophysics Series, 32 Cambridge University Press

  2. ACCRETION SIGNATURES IN YSO Matter transfered from molecular cloud to YSO. The accretion leaves distinctive signatures: . Directly, in velocity field (ex., redshifted absorption in spectra:matter is falling in . Indirectly: energy losses observed in YSO need to be compensated by external sources: Gravitational potential energy is the best candidate to supply this need Visible YSO: (Class II ,III) The emerging flux is characterized by excess over photospheric fluxes appearing in emission lines and continua . T Tauri Stars: 0.02 to 2-3 Msol . Herbig Ae/Be Stars (HAeBe) : M > 1.5 Msol Ages 1-10Myr

  3. Protostars (Class 0,I) Close association with molecular clouds Heavily extincted (undetectable visible/nir wavelength range) Still actively receiving mass from the cloud Powerfull outflows (CO, SiO, H2, [SII], Ha …) Hartmann 2003

  4. PROPERTIES OF YSO “More evolved” YSO (II,III) First spectra (photograph) of TTS (“low-mass” YSO) < 1970

  5. First spectra of Herbig Ae/Be (“Intermediate-mass YSO) Herbig 1960

  6. Observational features: Emergin flux of visible YSO is characterized by excesses over photospheric fluxes, both in emission lines and continua. Emission lines show a wide range of conditions of formation, eg: .Forbidden lines: nH 105cm-3 Optical/NIR : T 104K .Permitted lines: nH 1013cm-3 UV lines from highly ionized species T 105-6 K .v ~ 0 to ~ few x 100 km/s Continuum excess appears as: flux “veiling” in photospheric absorption lines dominates the UV and IR emissions

  7. T Tauri spectra “Modern” data Clase 1 Emission lines H, HeI, NaI, CaII Absorption lines with “veiling” Late spectrum (F-M types Teff 7-3000K) Balmer jump B-V no photospheric Lines with “veiling” Standard photosphere from Hartmann 1998

  8. Veiling Fc Fl Fv Fcl Fl Flf l Flf / Fcf + r Fl Veiling parameter 1 + r Fc r = Fv/ Fcf Fvenergy excess relative to the photospheric flux(Fcf) Hartigan et al 1999

  9. “Veiling” Hartigan et al 1999

  10. Clase 1 SEDS of TTS in Taurus MC Energy excess relative to the photospheric flux in NIR and mm (Dotted curves:SED of LkCa7, classIII with no evidence for accretion) photosphere from Hartmann 1998

  11. UV excess Gullbring et al 2000

  12. Colour-Colour diagrams

  13. NIR excess Reddening lines Kenyon & Hartmann 1995

  14. CTTS locus CTTS loci (Colours corrected from reddening) Meyer, Calvet, & Hillenbrand 1997

  15. CTTS vs WTTS TTS have been classified in two types: Classical (CTTS) Weak (WTTS) Initially, classification based on the equivalent width: for WTTS, EW(Ha) < 10 A (Herbig & Bell 1988) from Hartmann 1998 Classification represented clear physical differences: WTTS : lack NIR excess no veiling excess Narrow emission lines No forbidden lines Weaker FUV lines Comparable Lx (K-L < 0.3 for photospheric colors) K 2.25 mm; L 3.4 mm

  16. CTTS vs WTTS WTTS show no indication of “veiling”. No significant NIR excess r ratio to hot continuum to stellar continuum emission at 5700 A Hartmann 1998

  17. CTTS vs WTTS Emission lines in WTTS are weaker and much narrower than CTTS CTTS

More Related