Part 2 of Our Lecture
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Transcript 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