Nathan Mayne Empirical Studies of the Secular Evolution of Pre-Main-Sequence Stars Background picture: 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: t form & t evolve t form → 2 Models, RSF and SSF (rapid- and slow-star-formation) SSF, t form ~10 Myrs, Shu (1977), Shu et al (1987). RSF, t form ~1-3 Myrs, Ballesteros-Paredes et al (1999), Hartmann (2001) t evolve → J evolve (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. t evolve (J)~5 Myrs (Scholz et al, 2007), t evolve (disc)~5 Myrs (Haisch et al, 2000)….

Nathan Mayne The Problem: Observables, assumptions? Timescales → Ages t form ≈ Age spread Constant SFR, one SF episode Coeval (  Ori, Jeffries et al, 2006) t evolve (disc), disc %=f(age) (Cieza & Baliber, 2007) Initial distribution (e.g. IMF) constant Environment Heterogeneous 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)

Nathan Mayne Unsolved: Goodness- of-fit?  2, 2-D uncertainties & model Extinction Binaries Spreads? The Problem: Deriving Ages (isochrones) Thus, dm=MS Age=Pre- MS

Nathan Mayne The Solution: Distances,  2 2-D, generalised  2 Statistically robust uncertainties Models BinariesMinimise  2 Rigorous: Bolometric correction, colour-Teff, interpolate surface gravity, extinction vectors etc The ONC: 7.91<7.96<8.03, pc

Nathan Mayne Data + Theory → Evolution=Theory? Data + Data → Evolution=Theory?

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, t evolve (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: t evolve (disc) Disc Dissipation (add disc fractions) IC348 disc %> NGC2362 & NGC2264 Ori,  Ori & NGC2264. Age=, disc % ≠ Dissipation from O stars? IC348 none. NGC

Nathan Mayne 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 t evolve (disc)

Nathan Mayne Cep OB3b-younger 3 Myr (5.5Myr) IC348-older 4-5 Myr (3 Myr) The ONC-older 2 Myr (0.8 Myr) (distance) SFRAge (~Myr)dmE(B-V) NGC <10.77< IC *0.97* NGC <10.50< the ONC27.91<7.96< Ori 37.99<8.01< Cep OB3b39.45<9.65<9.85*0.93* NGC <9.37<  Ori 37.84<7.94< NGC <10.67< IC <7.50<7.64*0.90* NGC *0.38* h Per <11.78<  Per <11.82< NGC <10.35< NGC <8.05<

Nathan Mayne - Noted by Stolte et al (2004) - Visible in CMDs e.g. Lyra et al (2006a) R-C gap: Observation Gap or terminus of Pre-MS

Nathan Mayne 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 T eff 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