How do massive stars form? A comparison of model tracks with Herschel data Michael D Smith CAPS...
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Transcript of How do massive stars form? A comparison of model tracks with Herschel data Michael D Smith CAPS...
How do massive stars form?
A comparison of model tracks with Herschel data
Michael D Smith CAPS
University of Kent
Available at: http://astro.kent.ac.uk/mds/capsule.pdf
October 2013
K3-50 AIRAS 23151+5912
AFGL 2591Mon R2
R MonS140 IRS 1S140 IRS 3
Near-Infrared Interferometry: Preibisch, Weigelt
et al.
● 7
Approach 2: IRDCs, ALMA, to Herschel cool cores
IRDCs: initial states imprinted - SDC335
Accelerated accretion
a) Mid-infrared Spitzer composite image (red: 8 μm; green: 4.5 μm; blue: 3.6 μm)
b) ALMA-only image of the N2H+(1−0) integrated intensity,
c) ALMA N2H+(1−0) velocity field
Pere
tto e
t al 2
013
, 555
, A
112
● 8
Approach 3: two stage stitch-up
Molinari et al 2008
noted: lack of diagnostic tools.
Stage 1: Accretion phase
Stage 2: Clean up,
cluster forms + sweep out
Early protostar: Accelerated accretion
model (Mckee & Tan 2003)
Clump mass and final star mass
simply related):
Accelerated accretion
● 9
Approach 3: two stage stitch-up
Molinari et al 2008 tracks from SED to mm dust masses
Diagnostic tools:
Accelerated accretion
Lbol-Mclump-Tbol
L bol/L
sola
r
Mclump/Msolar
● 10
Alternative evolutions
Dark cloud fragments into cores/envelopes.
Envelope accretion: from fixed bound envelope, bursts etc
Global collapse.
Accretion evolutions: from clumps, competitive, turbulent. Cores and protostars grow simultaneously
Mergers, harrassment, cannabolism, disintegration
● 11
Issues for Massive StarsGlobal collapse or fragmentation?
Most massive? Radiation feedback problem + solutions
Environment? Cluster-star evolutions? Which forms first?
Efficiency problem.
IMF: Feedback - radiation and outflow phases? EUV problemSeparate accretion luminosity from Interior luminosity?
Bursts? Luminosity problem: under-luminous?
Two phases; accretion followed by clean-up? Dual evolution?
● 12
Krumholz et al. 2007 , 2009 ; Peters et al. 2010a , 2011 ; Kuiper et al. 2010a , 2011 , 2012 ; Cunningham et al. 2011 ; Dale & Bonnell 2011
Kuiper & Yorke 2013: 2D RHD, core only: spherical solid-body rotation + protostellar structure.
Conclusion: diverse, depends on disk formation, bloating and feedback coordination.
Recent Simulations
● 13
Objective: Model for Massive Stars
Piece together evolutionary algorithms for the protostellar structure, the environment, the inflow and the radiation feedback.
The framework requires the accretion rate from the clump to be specified.
We investigate constant, decelerating and accelerating accretion rate scenarios.
We consider both hot and cold accretion, identified with spherical free-fall and disk accretion, respectively.
● 14
Objective: Model for Massive Stars
Piece together evolutionary algorithms for the protostellar structure, the environment, the inflow and the radiation feedback.
The framework requires the accretion rate from the clump to be specified.
We investigate constant, decelerating and accelerating accretion rate scenarios.
We consider both hot and cold accretion, identified with spherical free-fall and disk accretion, respectively.
● 15
Cold or Hot Accretion?
Kuip
er
& Y
ork
e 2
01
3 A
pJ 77
2
Hoso
kaw
a, O
muka
i, Y
ork
e 2
009,
20
10
● 16
The protostar: radius
Stellar radius as mass accumulates
(I) adiabatic, (II) swelling/bloating,
(III) Kelvin–Helmholtz contraction, and (IV) main sequence
Hot accretion Cold accretion
● mass conservation
● prescribed accretion rate
● bifurcation coefficient
● jet speed ~ escape speed
The Low-Mass Scheme: Construction● Clump Envelope Accretion Disk Protostars
● Bipolar Outflow Jets ● Evolution:
● systematic and simultaneous
• Protostar L(Bolometric)
• Jet L(Shock)
• Outflow Momentum (Thrust)
• Clump/Envelope Mass
• Class Temperature
• Disk Infrared excess
The Capsule Scheme: Construction
● Clump Envelope Accretion Disc Protostar
Bipolar Outflow Jets
Lyman Flux
thermal radio jets
H2 shocks
Radiative Flux
Radio: H II region
Origin Luminosity as clump mass declines
● 22
The clump mass, isotherms + Herschel data
Accelerated accretion Power Law deceleration (Data: Molinari et al 2008)
Constant slow accretion Accelerated accretion
( Data: Elia et al 2010), Hi-GAL
Origin Distance dotted line = accelerated accretion
● 23
Bolometric Temperature
Herschel: <20K: 0.463 <30K: 0.832 <50K: 0.950
● 25
Lbol-Mclump-Tbol results
Accelerated accretion is not favoured
Source counts as a function of the bolometric temperature can distinguish the accretion mode.
Accelerated accretion yields a relatively high number of low-temperature objects.
On this basis, we demonstrate that evolutionary tracks to fit Herschel Space Telescope data require the generated stars to be three to four times less massive than in previous interpretations.
This is consistent with star formation efficiencies of 10-20%
● 27
The Lyman Flux (ATCA 18 GHz data)
Orig Accelerated accretion
N(L
y),
Lym
an
Con
tin
uu
m p
hoto
ns/
s
Lbol /Lsun Bolometric Luminosity
Sanch
ez-
Monge e
t al., 2
013,
A&
A 5
50
,
A21
Origin D COLD accretion + Hot Spots (75%, 5% area)
Distributed accretion Accretion hotspots
● 28
The Lyman Flux
Orig Constant accretion rate
Neither spherical nor disk accretion can explain the high radio luminosities of many protostars.
Nevertheless, we discover a solution in which the extreme ultraviolet flux needed to explain the radio emission is produced if the accretion flow is via free-fall on to hot spots covering less than 20% of the surface area.
Moreover, the protostar must be compact, and so has formed through cold accretion.
This suggest that massive stars form via gas accretion through disks which, in the phase before the star bloats, download their mass via magnetic flux tubes on to the protostar.
● 29
The Lyman Flux: summary
● Michael D. Smith - Accretion Discs
● 31
What next?
● Disk – planet formation
● Binary formation, mass transfer etc● Mass outflows v. radiation feedback● Feedback routes● Outbursts ● Thermal radio jets● ???
● X-Axis: Luminosity
● Y-Axis: Jet Power
● Tracks/Arrows: the scheme
● Diagonal line:
● Class 0/I border
● Data: ISO FIR + NIR (Stanke)
● Above: Class 0
● Under: Class 1
Low-Mass Protostellar Tracks
● Michael D. Smith - Accretion Discs
● 34
Disk evolution
● Column density as function of radius and time: (r,t)
● Assume accretion rate from envelope
● Assume entire star (+ jets) is supplied through disc
● Angular momentum transport:
● - turbulent viscosity: `alpha’ prescription
● - tidal torques: Toomre Q parameterisation
● Class 0 stage: very abrupt evolution?? Test……
● …to create a One Solar Mass star
● Michael D. Smith - Accretion Discs
● 35
The envelope-disc connection; slow inflow
● Peak accretion at 100,000 yr● Acc rate 3.5 x 10-6 Msun/yr● Viscosity alpha = 0.1
● 50,000 yr: blue
● 500,000 yr: green
● 2,000,000 yr: red