nathan mayne empirical studies of the secular evolution of pre-main-sequence stars background...
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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
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)….
Nathan Mayne
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)
Nathan Mayne
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)
Nathan Mayne
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
Nathan Mayne
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