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
September 2013
Late stage: Rosette in optical
AFGL 2591
Rosette Nebula, Travis Rector, KPNO
Li et al 2008 ApJL 679, L101
Early emerging: near-infrared, with outflows
Near-Infrared Interferometry: Preibisch, Weigelt et al.
S140 IRS
Mon R2
3
AFGL 2591
S140 IRS 1
R Mon
IRAS
23151+5912
K3-50 A
Numerical telescope: K-band imaging
reflected
shock
AFGL 2591
total
Adapted from Gorti & Hollenbach 2002
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Approach 1: HMCs to UCHii to Hii
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6
Approach 2: IRDCs, ALMA, to Herschel cool cores
Peretto et al 2013, 555, A112
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
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7
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
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Approach 3: two stage stitch-up
Molinari et al 2008 tracks from SED to mm dust masses
Diagnostic tools:
Lbol-Mclump-Tbol
Accelerated accretion
Mclump/Msolar
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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
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Issues for Massive Stars
Most massive? Radiation feedback problem
Environment? Cluster-star evolutions? Efficiency problem.
Global collapse or fragmentation?
IMF: Feedback - radiation and outflow phases? EUV problem
Separate accretion luminosity from Interior luminosity?
Bursts? Luminosity problem
Two phases; accretion followed by clean-up? Dual evolution?
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Recent Simulations
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.
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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.
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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.
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Hosokawa, Omukai, Yorke 2009, 2010
Kuiper & Yorke 2013 ApJ 772
Cold or Hot Accretion?
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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
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The protostar: luminosity
Origin Luminosity as mass accumulates (cold)
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The protostar: adaption
Assumed mass accretion rates + interpolation scheme
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The Low-Mass Scheme: Construction
Clump
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Envelope
Bipolar Outflow
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Evolution:
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systematic and simultaneous
•
Protostar
L(Bolometric)
•
Jet
L(Shock)
•
Outflow
Momentum (Thrust)
•
Clump/Envelope
•
Class
•
Disk
Accretion Disk
Jets
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mass conservation
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prescribed accretion rate
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bifurcation coefficient
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jet speed ~ escape speed
Mass
Temperature
Infrared excess
Protostars
The Capsule Scheme: Construction
Radio: H II region
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Clump
Lyman
Flux
Envelope
Radiative Flux
Accretion Disc
Bipolar Outflow
H2 shocks
Protostar
Jets
thermal
radio jets
Capsule Flow Chart
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The clump mass, isotherms + Herschel data
Origin Luminosity as clump mass declines
Constant slow accretion
Accelerated accretion
(
Accelerated accretion
Power Law deceleration
Data: Elia et al 2010), Hi-GAL
(Data: Molinari et al 2008)
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Bolometric Temperature
Origin Distance dotted line = accelerated accretion
Herschel: <20K: 0.463
<30K: 0.832
<50K: 0.950
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Bolometric Temperature
Clump = cluster x 2
Clump = cluster x 6
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Lbol-Mclump-Tbol results
We find that accelerated accretion is not favoured on the
basis of the often-used diagnostic diagram which
correlates the bolometric luminosity and clump mass.
Instead, source counts as a function of the bolometric
temperature can distinguish the accretion mode.
Specifically, 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%
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The clump mass, isotherms + Herschel data
Or Luminosity as clump mass declines: massive clumps
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GHz data)
Sanchez-Monge et al., 2013, A&A 550, A21
The Lyman Flux (ATCA 18
Orig Accelerated accretion
Lbol /Lsun Bolometric Luminosity
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The Lyman Flux
Origin D COLD accretion + Hot Spots (75%, 5% area)
Distributed accretion
Accretion hotspots
Orig Constant accretion rate
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The Lyman Flux: summary
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.
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Jet speed = keplerian speed
Or Different constant accretion rates………..
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What next?
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Disk – planet formation
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Binary formation, mass transfer etc
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Mass outflows v. radiation feedback
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Feedback routes
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Outbursts
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Thermal radio jets
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???
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Michael D. Smith - Accretion
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Thanks For Listening!
ANY QUESTIONS?
Low-Mass Protostellar
Tracks
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X-Axis: Luminosity
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Y-Axis: Jet Power
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Tracks/Arrows: the scheme
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Diagonal line:
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Class 0/I border
Data: ISO FIR + NIR
(Stanke)
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Above: Class 0
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Under: Class 1
Disk evolution
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Column density as function of radius and time: (r,t)
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Assume accretion rate from envelope
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Assume entire star (+ jets) is supplied through disc
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Angular momentum transport:
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- turbulent viscosity: `alpha’ prescription
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- tidal torques: Toomre Q parameterisation
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Class 0 stage: very abrupt evolution?? Test……
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…to create a One Solar Mass star
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Michael D. Smith - Accretion
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The envelope-disc connection; slow inflow
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Peak accretion at 100,000 yr
Acc rate 3.5 x 10-6 Msun/yr
Viscosity alpha = 0.1
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50,000 yr:
blue
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500,000 yr:
green
2,000,000 yr:
red
Michael D. Smith - Accretion
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The envelope-disc connection; slow inflow; low alpha
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Peak accretion at 200,000 yr
Acc rate 3.5 x 10-6 Msun/yr
Viscosity alpha = 0.01
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50,000 yr: blue
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500,000 yr: green
2,000,000 yr:
red
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Michael D. Smith - Accretion
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