[email protected] L 4 - Stellar Evolution II: August-September, 20041 L 4: Collapse phase – observational evidence Background image: courtesy Gålfalk &

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



Known Methods & Techniques

What is the problem ?

How to solve it ?



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



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 !


Protostars are the Holy Grail of infrared astronomy

Any observational difficulties ?



(Known) Methods & Techniques

Radiation(1) Continuum

(2) Spectral Lines


(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


(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


(1) Continuum

Spectral Energy Distributions (SEDs)

SED fitting

Observations

Theoretical models

Adams, Lada & Shu 1987ApJ 312, 788

+

protostar


(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 ( ´´ )


(1) Continuum


Shirley et al. 2000 ApJS 131, 249

FIR & submmSCUBA 850 m 450 m

Observations

AzimuthalIntensity

Distribution


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


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 ...


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


(1) Continuum


Firstly and only

directly observed

~ r - 1.5 profile

Keck-I, K band (Hodapp 1998, ApJ 500, L 183)

B 335 FIRS


Harvey et al. 2003, ApJ 583, 809

Infall ? ``YES´´

Inside-out ? ``NO´´

IRAM-PdB Interferometer

1.2 mm

3 mm


(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


(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-


(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


(2) Spectral Lines


Theoretical profiles: cf. L3

Foster & Chevalier 1993, ApJ 416, 303

AmmoniaNH3

(a?)

(b?)

Symmetrical Profiles

no,spatial

resolution


(2) Spectral 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


(2) Spectral Lines

(b) Optically thick lines


Zhou et al. 1993, ApJ 404, 232Shu Infall


fornegative temperature

gradient

cooler:less

intensity

warmer:more

intensity

los


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


(2) Spectral Lines



Hartstein & Liseau 1998, AA 332, 703

Carbon SulfideCS

Observations

+


high blue low red


(2) Spectral Lines


Observed & Theoretical profiles

Hartstein & Liseau 1998, AA 332, 703

Example:Carbon Monoxide

13COCarbon Sulfide

CS

(non-)equilibrium andinformation content

thermalised

C18O13CO


(2) Spectral 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´´


Wilner et al. 2000, ApJ 544, L69

Inside – out collapse: wings

Observation: no wings

B 335

Observed

+Theoretical Profiles

Single Dish

Interferometer


(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


Outflow contamination & confusion!

`` finn fem fel ´´

Current Paradigm - ?



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)


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


Outflow contamination & confusion! Single Stars?

`` finn fem fel ´´

Current Paradigm - ?



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: 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 ?

Documents

[email protected] L 4 - Stellar Evolution II: August-September, 20041 L 4: Collapse phase – observational evidence Background image: courtesy Gålfalk &