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

Early emerging: near-infrared, with outflows

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2008

ApJ

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101

K3-50 AIRAS 23151+5912

AFGL 2591Mon R2

R MonS140 IRS 1S140 IRS 3

Near-Infrared Interferometry: Preibisch, Weigelt et al.

Numerical telescope: K-band imaging

reflected

shock

totalAFGL 2591

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Approach 1: HMCs to UCHii to Hii

●Ad

apte

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m G

orti

& Ho

llenb

ach

2002

● 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

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Approach 3: two stage stitch-upMolinari et al 2008 noted: lack of diagnostic tools.

Stage 1: Accretion phaseStage 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-upMolinari et al 2008 tracks from SED to mm dust massesDiagnostic tools:

Accelerated accretionLbol-Mclump-Tbol

L bol/L

sola

r

Mclump/Msolar

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Alternative evolutionsDark 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 StarsMost massive? Radiation feedback problem

Environment? Cluster-star evolutions? Efficiency problem.

Global collapse or fragmentation?

IMF: Feedback - radiation and outflow phases? EUV problemSeparate accretion luminosity from Interior luminosity?

Bursts? Luminosity problem

Two phases; accretion followed by clean-up? Dual evolution?

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Krumholz et al. 2007 , 2009 ; Peters et al. 2010a , 2011 ; Kuiper et al. 2010a , 2011 , 2012 ; Cunningham et al. 2011 ; Dale & Bonnell 2011Kuiper & Yorke 2013: 2D RHD, core only: spherical solid-body rotation + protostellar structure.Conclusion: diverse, depends on disk formation, bloating and feedback coordination.

Recent Simulations

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Objective: Model for Massive StarsPiece 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 StarsPiece 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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Cold or Hot Accretion?

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The protostar: radiusStellar 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: luminosityOrigin Luminosity as mass accumulates (cold)

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The protostar: adaptionAssumed mass accretion rates + interpolation scheme

● 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

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Capsule Flow Chart

Origin Luminosity as clump mass declines

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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

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Bolometric Temperature

Herschel: <20K: 0.463 <30K: 0.832 <50K: 0.950

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Bolometric Temperature

Clump = cluster x 6

Clump = cluster x 2

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Lbol-Mclump-Tbol resultsWe 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%

Or Luminosity as clump mass declines: massive clumps

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The clump mass, isotherms + Herschel data

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The Lyman Flux (ATCA 18 GHz data)

Orig Accelerated accretion

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), Lym

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Lbol /Lsun Bolometric LuminositySa

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Origin D COLD accretion + Hot Spots (75%, 5% area)Distributed accretion Accretion hotspots

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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.

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The Lyman Flux: summary

Or Different constant accretion rates………..

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Jet speed = keplerian speed

● Michael D. Smith - Accretion Discs

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What next?● Disk – planet formation● Binary formation, mass transfer etc● Mass outflows v. radiation feedback● Feedback routes● Outbursts ● Thermal radio jets● ???

Thanks For Listening!

ANY QUESTIONS?

● 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

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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

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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

● Michael D. Smith - Accretion Discs

● 36

The envelope-disc connection; slow inflow; low alpha

● Peak accretion at 200,000 yr● Acc rate 3.5 x 10-6 Msun/yr● Viscosity alpha = 0.01

● 50,000 yr: blue● 500,000 yr: green

● 2,000,000 yr: red