L 4: Collapse phase – observational evidence
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Transcript of L 4: Collapse phase – observational evidence
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
L 4: Collapse phase – observational evidence
Background image: courtesy Gålfalk & Liseau, Serpens Core with VLT ANTU and ISAAC
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
L 4: Collapse phase – observational evidence
Known Methods & Techniques
What is the problem ?
How to solve it ?
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
L 4: Collapse phase – observational evidence
What is the problem ?
Theories may give different answers what to look for – butpredictions include
]2 to5.1 [e.g., on distributidensity a (d)
]5.0 [e.g., v field velocity a (c)
pc a offraction aRlength (b)
) :cold , :(dense
few a mass (a)
)o few a(for J
2/3J
2/1J
oJ
rρ(r)
r(r)
TMM
MMM
α
M
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
L 4: Collapse phase – observational evidence
How to solve it ?or - how and where to look ?
m3 :IR
K10 :re temperatu[2]
m2for 1.0 :IR
10 )/( :extinction
mag cm 102 (H) dust gas of
cm1012)H((H) :densitycolumn [1]
(b) and (a)
3
V
3V0
12V
21
]pc2.0,3
cm4
10)2H([ 221
v
T
AA
eII
AN
dlnN
-
Ln
In dense interstellar clouds with infrared techniques !
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Protostars are the Holy Grail of infrared astronomy
Any observational difficulties ?
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
L 4: Collapse phase – observational evidence
(Known) Methods & Techniques
Radiation(1) Continuum
(2) Spectral Lines
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1)Continuum
(Proto-)stellar photospheresFree-free gas emissionThermal radiation from (radiatively) heated dust grains
To infer the total mass one needs
Gas-Dust Relation
[ generally assumed: m(g)/m(d) = 100 ]
Thermal radiation from (radiatively) heated dust grains
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1) Continuum
Spectral Energy Distributions SEDs
Observations
and
Theoretical Models
Current Paradigm
Adapted from van Zadelhoff 2002, PhD thesis
AstronomicalTaxonomy
notice thespatial scales &
time scales
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1) Continuum
Spectral Energy Distributions (SEDs)
SED fitting
Observations
Theoretical models
Adams, Lada & Shu 1987ApJ 312, 788
+
protostar
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1) Continuum
Spatial Profilefitting
Observations
Theoretical models
Butner et al. 1991 ApJ 376, 636
+
KAO50 m
100 m
IRS 5L1551
residuals
I / Ipeak
radial offset ( ´´ )
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1) Continuum
Spatial Profilefitting
Shirley et al. 2000 ApJS 131, 249
FIR & submmSCUBA 850 m 450 m
Observations
AzimuthalIntensity
Distribution
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Compare to theory
of collapse(see L 3)
488 214, ApJ 1977,Shu : max
451.6crit
Bonnor 1956 MNRAS 116, 351
0ext V
P
0ext V
P
centrally condensed
flat distribution
Shu 1977extreme case
max
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
See also L 1:
Motte et al. made fits at 1.3 mm => mostly Bonnor-Ebert spheres (flat) and Oph A with I(r) ~ r - 2
and furthermore obtained ...
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Clump Mass Spectrum & IMF1 clump - 1 star
no further Fragmentation ? - see Eduardo (L 3)
Motte et al. 1998, AA 336, 150
? IMF 5.2d
d
spectrum mass clump
mm
n
Also Johnstone et al. 2000, ApJ 545, 327
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1) Continuum
Spatial Profilefitting
Firstly and only
directly observed
~ r - 1.5 profile
Keck-I, K band (Hodapp 1998, ApJ 500, L 183)
B 335 FIRS
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Harvey et al. 2003, ApJ 583, 809
Infall ? ``YES´´
Inside-out ? ``NO´´
IRAM-PdB Interferometer
1.2 mm
3 mm
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(1) Continuum
Major pitfalls/caveats:
Geometry - spheres vs disks
Calorimetric vs `true´ Luminosities
Dust Optical Depths (Properties)
Temperatures (Dust and Gas)
Observations
Theoretical models
Inhouse work, see, e.g. :Larsson et al. 2000White et al. 2000, AA
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
What lines – species ?
(low-lying) Rotational Transitions in Molecules
Physical Conditions of Excitation
Cold ( Tk ~ a few x 10 K ~ meV )
Large AV (no / little external radiation) and dense (n > 103 cm -3): collisional excitations dominate level populations ( if << 1 )
mostly neutrals but CosmicRays => molecular ions and e-
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(a) Optically thin lines(b) Optically thick lines
1]bg/kin[for kin
mol
bgex
bgex
bgex
] re temperatu [intensity bgex
111
...)1(111
)(
case) normal'' (the emission :
difficult)but - somethingleast (at absorption:
)(oohps! line no:
)(
)1()(
:Jeans)-Rayleigh & LTE(ion approximatSimplest
TT
TI
TTe
NTe
ii
TT
TT
TT
i
eTTT
Why ?
does not necessarily
imply there’s `nothing´ there
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(a) Optically thin lines(b) Optically thick lines
Theoretical profiles: cf. L3
Foster & Chevalier 1993, ApJ 416, 303
AmmoniaNH3
(a?)
(b?)
Symmetrical Profiles
no,spatial
resolution
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(a) Optically thin lines(b) Optically thick lines
Theoretical profiles
Leung & Brown 1977, ApJ 214, L73
Carbon monoxideCO =12C16O (a?)
and Isotopes (b?)
Asymmetrical Profiles
cloudcenter
offset
...hmm...,needs to be verified
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(b) Optically thick lines
Theoretical profiles
Zhou et al. 1993, ApJ 404, 232Shu Infall
Asymmetrical Profiles
fornegative temperature
gradient
cooler:less
intensity
warmer:more
intensity
los
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
inside-out collapse (Shu 1977, ApJ 214, 488) (see: L 3) B 335
not fromShu model
p = -1.5
p = -2
Rinf = cs tinf
= -0.5
= 0
adapted from Hartstein & Liseau 1998, AA 332, 703
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(b) Optically thick lines
Theoretical profiles
Hartstein & Liseau 1998, AA 332, 703
Carbon SulfideCS
Observations
+
Asymmetrical Profiles
high blue low red
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(b) Optically thick lines
Observed & Theoretical profiles
Hartstein & Liseau 1998, AA 332, 703
Example:Carbon Monoxide
13COCarbon Sulfide
CS
(non-)equilibrium andinformation content
thermalised
C18O13CO
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(2) Spectral Lines
(b) Optically thick lines
Carbon SulfideCS
Water VapourH2O
Observation:dependence of profiles
on spatial resolution(``beam´´)
oH2O (1-0)
CS (2-1)
10´´
20´´
120´´
B 335 infall model
24´´38´´51´´
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Wilner et al. 2000, ApJ 544, L69
Inside – out collapse: wings
Observation: no wings
B 335
Observed
+Theoretical Profiles
Single Dish
Interferometer
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
(3) Continuum and Spectral Lines Theoretical profiles
+Observations
Inhouse, e.g.:
Larsson et al. – Odin H2O + ground based
Schöier et al. – ground based inc. chemistry
Oph A
IRAS 16293 ( Oph east )
... but steady state models ....
of a highly dynamic situation...
e.g. Stark et al. 2004, ApJ 608, 341
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Outflow contamination & confusion!
`` finn fem fel ´´
Current Paradigm - ?
Adapted from van Zadelhoff 2002, PhD thesis
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
FOV = 2.5 X 2.5 amin2
(0.2 X 0.2 pc2)
Serp SMM 1 (S68 FIRS 1)*Infall CandidateOutflow Source
Disk Source* D = 310 pc
ISO SWS & LWS+ submm/mm
Fitting the observed SED*:
Menv = 6 Mo
L = 140 Lo
* 2-D radiative transfer(Larsson et al. 2002, AA 386, 1055)
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
dustmol
6o
52o2
o13,12
%1 - %5.0
102 OH)( , 20.0 OH)(
101 O)H( , 21.0 O)H(
37.0CO)(
LL
XLL
XLL
LL
Emission not from
Disk
Infalling Envelope
but
Outflow/Shocks
Modeling the Line Emission
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Outflow contamination & confusion! Single Stars?
`` finn fem fel ´´
Current Paradigm - ?
Adapted from van Zadelhoff 2002, PhD thesis
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
Number of Infall Candidates: Reasonable ? Expected ? *
Object Classes and LifetimesSFR of the solar neighbourhood Consistent picture?
Magnus´ IMF talk
* High mass starformation – cloud/cluster collapse
L 4 - Stellar Evolution II: August-September, 2004 [email protected]
L 4: conclusions• a variety of observational techniques are exploited• a number of collapse candidates have been found• all are strong outflow sources• multiplicity is common
L 4: open questions• How many collapse processes do occur in nature ? more than one ? which ? • What is the `certain´ collapse tracer ?• What spectral & spatial resolution is needed ?• Are stars/BDs/planets formed differently ? How ?