Nathan Mayne

Empirical Studies of the Secular Evolution of Pre-Main-Sequence

Stars

Background picture: http://universe.daylife.com/

Collaborators: Tim Naylor, Rob Jeffries, Stuart Littlefair and Ben Burningham

nathan@astro.ex.ac.uk

Papers: Mayne et al (2007), Mayne and Naylor (2008), Jeffries et al (2007), Naylor and Jeffries (2007)

Nathan Mayne

Structure

Problem

• Theoretical, Timescales

• Observations, ages

• Isochrone fitting

Solution

• 2 fitting

• Empirical isochrones, age orders

Results

• Local environment → Disc dissipation

Conclusions

Nathan Mayne

The Problem: Theory

Timescales: tform & tevolve

tform→ 2 Models, RSF and SSF (rapid- and slow-star-formation)

• SSF, tform~10 Myrs, Shu (1977), Shu et al (1987).

• RSF, tform~1-3 Myrs, Ballesteros-Paredes et al (1999), Hartmann (2001)

tevolve→ Jevolve (Gychronology, Barnes, 2003), ‘Skumanich’ winds

• Winds insufficent, Herbst et al (2007)

• Torque lock-disc? Camenzind (1990) and Edwards et al (1993), as pre-stellar collapse.

• tevolve(J)~5 Myrs (Scholz et al, 2007), tevolve(disc)~5 Myrs (Haisch et al, 2000)….

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The Problem: Observables, assumptions?

Timescales → Ages

• tform≈ Age spread

• Constant SFR, one SF episode

• Coeval ( Ori, Jeffries et al, 2006)

• tevolve (disc), disc %=f(age) (Cieza & Baliber, 2007)

• Initial distribution (e.g. IMF) constant

• EnvironmentHeterogeneous foundation:

• Models/Isochrones

• Accretion effects (Tout et al, 1999, Siess et al, 1999)

• Disc fractions (JHKL, Spitzer)

• Local environment, O stars? (McCaughrean & O’Dell, 1996) (Hollenbach & Gorti, 2005)

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The Problem: Deriving Ages (isochrones)

Turn-on/contraction/Pre-MS

• Model dependent

• Age-Distance degenerate

1, 3, 5 &10 Myr isochrones and ZAMS. Blue=Pre-MS (Siess et al, 2000) . Red=MS (& post-MS) (Geneva)

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The Problem: Deriving Ages (isochrones)

MS?

• ΔPos=slow F(age)

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Unsolved:

• Goodness-of-fit?

• 2, 2-D uncertainties & model

• Extinction

• Binaries

• Spreads?

The Problem: Deriving Ages (isochrones)

Thus,

• dm=MS

• Age=Pre-MS

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The Solution: Distances, 2

iP ln22 2-D, generalised 2 Statistically robust uncertainties

Models Binaries Minimise 2

Rigorous: Bolometric correction, colour-Teff, interpolate surface gravity, extinction vectors etcThe ONC: 7.91<7.96<8.03, 391+12

-

9 pc

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Data + Theory → Evolution=Theory?

Data + Data → Evolution=Theory?

Nathan Mayne

Nathan Mayne

Nathan Mayne

The Solution: Empirical isochrones, age orders

Both: h and Per (black), the ONC (red) & NGC2362 (green). NGC2264 (dashed, blue).

Right hand: ZAMS subtract (minus colour of ZAMS).

Nathan Mayne

The Results: Rotation, tevolve(J)

Period dist (1 mass range)

IC348, NGC2264, NGC2362 and the ONC

• ONC bi-modal

• NGC2264 & NGC2362 uni-modal

Bi-modal → uni-modal (spin up)

IC348, bi-modal, older?

Disc locking

- Old SFR, more discs, less spin up → uni-modal

- IC348 disc are destroyed later?

Nathan Mayne

The Results: tevolve(disc)

Disc Dissipation (add disc fractions)

•IC348 disc %> NGC2362 & NGC2264

Ori, Ori & NGC2264. Age=, disc % ≠

Dissipation from O stars?

• IC348 none.

• NGC2362 13.

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Conclusions:

Parameters:

- Precise distances (& E(B-V)).

- Model dependency negligible (MS)

Pre-MS:

- Modeled pre-MS

Ages:

- Age ordered

- New ages for SFRs

Secular Evolution:

- Local environment effects?

- Disc-locking and tevolve(disc)

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Cep OB3b-younger 3 Myr (5.5Myr)

IC348-older 4-5 Myr (3 Myr)

The ONC-older 2 Myr (0.8 Myr) (distance)

SFR Age (~Myr) dm E(B-V)

NGC2244 1 10.66<10.77<10.81 0.44

IC5146 1 10.4* 0.97*

NGC6530 2 10.49<10.50<10.60 0.33

the ONC 2 7.91<7.96<8.03 0.40 Ori 3 7.99<8.01<8.12 0.10

Cep OB3b 3 9.45<9.65<9.85* 0.93*

NGC2264 3 9.26<9.37<9.52 0.04

Ori 3 7.84<7.94<8.10 0.06

NGC2362 4-5 10.51<10.67<10.70 0.10

IC348 4-5 7.34<7.50<7.64* 0.90*

NGC7160 10 9.77* 0.38*

h Per 13 11.77<11.78<11.84 0.54

Per 13 11.79<11.82<11.88 0.50

NGC1960 20 10.27<10.35<10.46 0.20

NGC2547 40 7.98<8.05<8.09 0.038

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- Noted by Stolte et al (2004)

- Visible in CMDs e.g. Lyra et al (2006a)

R-C gap: ObservationGap or terminus of Pre-MS

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R-C gap: Theory

Theory from Siess and Dufour (2002)

- Mass tracks (dotted lines) 0.8-7M☼

- Isochrones (blue lines) 1, 3, 4 and 13 Myrs and ZAMS

- 1 and 3 M☼ (red dots, and lines)

Phase change

• Convective pre-MS → radiative core

• Hayashi to Henyey track

• Teff

• CMD separation

• Spreads → density, ‘gap’

• Size(gap)=F(age)

Distance independent age indicator

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Lowest M on MS> highest M on pre-MS

h and Per (crosses) 13 Myr Geneva-Bessell isochrone, 13 and 23 Myr Siess and Dufour isochrone.

The ONC (asterisks), Geneva-Bessell 1 Myr and Siess and Dufour 1, 3 and 10 Myrs.

-Stars above turn-off (younger?) - Stars below turn-on (older?)

- Isochronal age spread - Real (SSF) - Accretion history? (RSF)

R-C gap: Overlap