Download Part 2 of Our Lecture

Formation of stellar systems: The evolution of SED (low mass star formation)
• Class 0
– The core is cold, 20-30K
• Class I
– An infrared excess appears
• Class II
– Classical T Tauri Star
(CTTS)
– The peak shifts as a disk
forms
• Class III
André, 2002, EAS(vol. 3)
– Weak-lined T Tauri Star
(WTTS)
– The disk dissipates
Formation of stellar systems: 5. Class II and Class III (Definitions)
• Class II
Based on the slope (as
previous slides), 1.5   IR  0
– Classical T Tauri Star (CTTS)
– After envelope infall has
ceased, dusty disk produce IR
emission.
SED is much broader than a
single blackbody
• Class III
Based on the slope (as
previous slides),  IR  1.5
– Weak-lined T Tauri Star
(WTTS)
– The disk dust is dissipated or
coagulated. In the SED,
emission from the central star
and only small contribution
from the disk are detectable
- Disk Property
153 disks
in the TaurusAuriga star
formation region
(Andrews &
Williams, 2008)
Based
Formation of stellar systems: CTTS (Class II)
• Classical T Tauri Star
T Tauri Star with strong Hα
emission line - much brighter
than other stars of similar T in
IR
– Dust in disk absorb light from
central star and reradiate @
IR
– ‘reprocessing’ or ‘irradiated’(
or ‘passive’) disk
– Disk accretion produces jets
and winds
Scattered light
Model
SED
• Figure (GM Aur star)
– Scattered light (top left), Model
(top right), and SED (below)
– Model for the stellar
photosphere emission (dark
line)
Model combining the stellar
emission and the disk excess
emission (white line)
Watson et al., ‘Multi-wavelength
imaging of YSO disks...’
Formation of stellar systems: Property of the disk
• Flat disk?
Or Flared disk?
– ‘Flared disk’ :
generally become
proportionately thicker with
increasing radius
c.f)
Spectral
Index (s)
is from
L  s
Lee Hartmann, 2000,
Accretion Processes in Star Formation
Milla-Gabet et al., ‘The circumstellar environments of ..’
Formation of stellar systems: WTTS (Class III)
• Weak-lined T Tauri Star :
T Tauri Star which has no
strong optical excess emission
@ NIR
– Emission from the central star
is only detectable
– No jets or massive outflows
– Solar-type magnetic activity
with low-mass, pre-mainsequence star
– Nominal definition :
Young star with
Class I
Class II
Class III

W ( H ) 10 
– Narrow Hα emission line
Lee Hartmann, 2000,
Accretion Processes in Star Formationis
Formation of stellar systems: CTTS & WTTS (1)
• Hα emission at 656.2 nm
CTTS
• Figure :
Hα profiles (as a function of
the velocity shift from line
center)
• Wide velocity width (± 200
km/s) is contributed to wind
expansion
WTTS
– DF Tau : wide and strong Hα
profile
 CTTS
Lee Hartmann, 2000,
Accretion Processes in Star Formation
– DI Tau : narrow and weak Hα
profile
 WTTS
Formation of stellar systems: CTTS & WTTS (2)
• WTTS nominal definition
Young star with Wλ(Hα) < 10 Å
(K-L) < 0.3
W(Hα) < 10 Å
• Redding-corrected
(K-L) colors
(flux ratios of
3.5 ㎛ emission
to 2.25 ㎛ emissions)
– (K-L) < 0.3
Wλ(Hα) < 10 Å
 WTTS
Lee Hartmann, 2000,
Accretion Processes in Star Formationis
– Otherwise,
 CTTS
Formation of stellar systems: Observations (1)
• Aurora Sicilia-Aguilar,
‘Disk Evolution at the Ages of
Planet Formation’ (doctoral
dissertation)
• Two young clusters in
Cep OB2 association
– Tr 37 (red) is placed at the
edge of bubble (Cep OB2)
containing bright O6 star HD
206267
o
o
~165 low-mass candidate
The age of the cluster
members around 4 Myr
– NGC 7160 (blue) lies near the
center of a bubble.
o
o
~50 low-mass candidates
The age of the cluster
members around 10 Myr
Tr 37
(Red =24 ㎛,
Green=8.0 ㎛,
Blue=3.6 ㎛)
Formation of stellar systems: Observations (2)
• Tr 37 members (upper) and
NGC 7160 members (below)
–
–
–
–
WTTS (green)
CTTS (red)
HD 206267 (blue) in Tr37
High- and intermediate-mass
stars (open stars)
– Filled symbols : confirmed or
those where Li absorption is
detected
– Open figures : Li abs. is not
detectable due to poor signalto-noise
Tr 37
NGC 7160
Formation of stellar systems: Observations (3)
• SEDs of low-mass stars in Tr 37 (avg 4 Myr)  about 40-45% of
the members in Tr 37 (total ~165) have accreting, circumstellar
disks
– black dotted line : similar spectral type derived from Kenyon &
Hartmann (1995)
– magenta dashed line : the median disk emission in Taurus
– light blue line : the median disk emission in Tr 37
ex. CTTS
according to Hα,
even if it shows
no sign of a disk
ex. WTTS according to Hα
ex. CTTS
disk @ 5.8 um and longer
= presence of outer disk
Formation of stellar systems: Observations (4)
• SEDs of low-mass stars in NGC 7160 (about 10 Myr) (according
to the same procedures followed for Tr 37)  only 1 sample
shows indications of active accretion (CTTS).
– black dotted line : similar spectral type derived from Kenyon &
Hartmann (1995)
– magenta dashed line : the median disk emission in Taurus
– light blue line : the median disk emission in Tr 37
ex. WTTS
according to Hα
ex. CTTS
according
to Hα
Formation of stellar systems: Observations (5)
• Evolution of protoplanetary
disks
Tr 37
– Theoretical isochrones from
Siess et al. (2000) for 1, 10
and 100 Myr are shown
together
– CTTS (red circle)
– WTTS (green triangle)
 Significant difference
in the apparent age scatter
between
Tr 37 (dispersion) and
NGC 7160 (mostly located
along the 10 Myr)
NGC 7160
Hot
Cold
Formation of stellar systems: Observations (6)
• Low-mass SED from the
ages 1 to 10 Myr.
1-2 Myr
1 Myr
4.5 Myr
–
–
–
–
–
Taurus (1-2 Myr) - red
Tr 37 globule (1 Myr) - cyan
Tr 37 (avg ~4.5 Myr) - violet
NGC 7160 (10 Myr) – pink
TW Hya (10 Myr) - black
– The steep line slopes of the
SED are shown in NGC 7160
and TW Hya (these are
comparably older than others)
10 Myr
10 Myr