1. Accretion Processes in Star Formation
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: 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. < 1970 PROPERTIES OF YSO First spectra (photograph) of
“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 105 cm Optical/NIR : T 104K
.Permitted lines: nH 1013 cm UV lines from highly ionized species T 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. Clase 1 T Tauri spectra Standard Emission lines H, HeI, NaI, CaII
“Modern” data
T Tauri spectra
Clase 1
Emission lines
H, HeI, NaI, CaII
Absorption lines with “veiling”
Late spectrum
(F-M types Teff K)
Balmer jump
B-V no photospheric
Lines with “veiling”
Standard
photosphere
from Hartmann 1998

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

9. “Veiling”
Hartigan et al 1999

10. Clase 1 photosphere from Hartmann 1998 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 Meyer, Calvet, & Hillenbrand 1997
(Colours corrected from reddening)
Meyer, Calvet, & Hillenbrand 1997

16. 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

17. 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

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