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Dust emission from Haebes: Disks and Envelopes
A. Miroshnichenko (Pulkovo/Toledo)
Z. Ivezic (Princeton)
D. Vinkovic (UK)
M. Elitzur (UK)
• ApJ 475, L41 (1997; MIE)• ApJ 520, L115 (1999; MIVE)• in progress (VMIE)
CLOUD COMPRESSION
COLLAPSE
FRAGMENTATION
PROTOSTRAS
M < Mc
PMS STARS
MS STARS
M > Mc
MS STARS
• Envelope evolves on free-fall time scale:
tff = 2x105 (104 cm-3/n)1/2 years
• Hydrostatic PMS low-mass (M 3M) core
evolution:
tpms ~ 3x107(M/M)3 years
M 2 M T-Tauri
2 M M 10 M Herbig Ae/Be
M 10–15 M no PMS
Protostellar Accretion Disks
• R ~ 10 — 100 AU
• M ~ .01 — .1 M
Evidence in pre-main-sequence:
T Tau stars (M 2 M)
? Herbig Ae/Be stars (2 M M 10 – 15 M)
IR ?
Required properties:
Emission from constant-T dust:I = B(T)[1 - exp(-)]
• Optically thick: I = B(T)
• Optically thin: I = B(T)
Protostellar Accretion Disks
Geometrically thin, optically thick:
22
3
R
M~
R
nRnR~
I = B(T), need temperature distribution
Illuminated Disk
• Heating:
• Cooling: Fem = T4
• Balance: T r -3/4 (accretion too!)
yields:
FL
rrabs * sin
4 23
F -4/3
r
Hillenbrand et al ‘92
• Group 1 (30):
F -4/3, disks
• Group 2 (11):
flat or rising SED,
star/disk with
additional shell
• Group 3 (6):
small IR excess
Problems:
• Hartman et al ’93: accretion rates are excessive
• Di Francesco et al ’94: group 1 IR emission is extended!
Spherical, optically thin shell:
T r -1/2
with
r -p, -
get
F -(p - 1)( + 4)/2
Since ~ 1–2, p ~ 3/2 gives
F -4/3
Steady-state accretion to point source:
vr4M 2
Free fall:
rGM2
v2
i.e. v r-½
so
2/32
rvr4
M
SCALINGIvezic & Elitzur ’95,’97
Depends mostly on• type of dust grains• overall optical depth• density profile
DOES NOT depend on• dimensions• density scale• luminosity
The emission from radiatively heated dust
DUSTY: http://www.pa.uky.edu/~moshe/dusty/
MIE ’97:
r -3/2
Mannings & Saregnt ’97:
2.6 mm incompatible with MIE:
V ~ 102–103 — nonsense!
In particular
MWC480 MWC683
MS V > 103 600
MIE V = 0.4 0.3
Conclusion: DISKS!
indeed:
However…
• IR best explained with optically thin shells, inconsistent with mm
• mm emission best explained with optically thick disks, inconsistent with IR
Extrapolate from 2.6 mm with F 1/3 — too little 2.2 m!
Also, MWC 137 imaging:
(50 m) = 66” 2”
(100 m) = 58” 2”
How can that be?
Disk Imbedded in Envelope:
Disk Imbedded in Envelope:
envelope ( -1.5):
T r –0.36
“standard” disk:
T r –0.75
• At the same radius, disk is cooler than envelope
• Smaller disk still contains cooler material
envelope
disk
MIVE ‘99
f = f,disk + (1 - )f,env
Implications:
• Disk + Envelope resolves all discrepancies
• 2 distributions: Disk: compact mm emission Envelope:
• IR emission• Disk heating
• ~ 10-8 M yr –1, Lacc ~ 0.1 L
v ~ 0.1— no molecules
• SED + multi- imaging — essential for finding disks
exM
??? Uniqueness ???
• Disk surface layer may mimic shell
• Equivalent envelope: V R*/Rsub
• However: V ~ 0.1, R*/Rsub ~ 0.01
Chiang & Goldreich ’97:
Images:
Grady et al ‘97 Mannings & Sargent ‘97
NICMOS
Marsh et al ‘95VMIE, in progress
Herbig, 1960:
15 min exposure:
60 min exposure:
3’
AB Aur
SU Aur