Post on 16-Dec-2015
Relative stellar chronology and Relative stellar chronology and secular evolution.secular evolution.
Nathan MayneNathan Mayne
Exeter University.Exeter University.
Research• Empirical Isochrones
• The R-C (Radiative-Convective) gap 2 Distances
• Extinctions (Q-method v1.1)
• Fitting
• Relative age ladder
Structure:Structure:
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Background• Motivation/Context for research • Stellar chronology
Conclusions
• Summary
• Future work
Motivation:Motivation:Secular Evolution.
*Large timescales and no experimental design.
• Compare properties of clusters, groups etc
• Assume an evolutionary sequence (given chronological order)
• Constrain models using derived parametersCurrent state-Half-full.
• Data precise (~1%), ubiquitous
• Models sophisticated input physics.
Half-empty.
• Ages model dependent, uncertain to a factor two.
• Low resolution on timescales <5Myrs
• Local environment effects missed?
• Population mixing
Model and data need an equal footing!
Example:
Fig: Haisch et al (2001) showing disc indicator against age, t1/2
disc~5Myrs.
• Age uncertainties change ordering
• No local effects.
• Robust relative ages better
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Isochronal fitting:
Model stellar interior & atmospheres
Isochrones in Colour-Magnitude Diagram (CMD).
Fit ‘by eye’ to a sequence.
Problems:• Derived quantities model dependent e.g. mass and age.
- Geneva, Padova, Siess & Dufour, Baraffe and D’AM.
• Shape, Main-Sequence (MS)-Pre-Main-Sequence (PMS) not seen in data.- Bonatto et al (2004), Pinsonneault et al (2004) and Mayne et al (2007)
• Inconsistent across bands.- Naylor et al (2002)
• Intrinsic degeneracy’s of age with distance or extinction.• Selection of a (~)coeval data sequence.
- Unresolved distinct populations, Jeffries et al (2006)- Capture of field stars Pflamm-Altenberg and Kroupa (2007)
Stellar Chronology:Stellar Chronology:
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Empirical Isochrones:Empirical Isochrones:
Why:
• Alternative to theoretical isochrones.
• Necessarily fit the data better.
• Compared to provide relative ages.
Construction:
• Select (~)coeval members.
• Use averaging filter.
• Fit Cubic spline to points.
• Apply distance and extinction.
• Compare on age ladder plot.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Photometry
Members
• X-ray sources
Photometry
Photometry
Members
• X-ray sources
• Periodic variables
Photometry
Members
• X-ray sources
• Periodic variables
• Spectroscopic members
Members
• X-ray sources
• Periodic variables
• Spectroscopic members
• H sources
Photometry
Photometry
Members
• X-ray sources
• Periodic variables
• Spectroscopic members
• H sources
Isochrone
• Isolate members
Photometry
Members
• X-ray sources
• Periodic variables
• Spectroscopic members
• H sources
Isochrone
• Isolate members
• Photometric cut
• Fit cubic spline
Empirical Isochrones-Results:Empirical Isochrones-Results:
Problems:
• Heterogenous photometry.
• PMS degeneracy with distance.
• Distances large source of uncertainty.
Discoveries:
• Age order of several fiducial cluster.
• Local environment effects?
• R-C gap
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Relative age order:
~1Myr (the ONC, NGC6530 and IC5146), ~3Myrs (Cep OB3b, NGC2362, Ori and NGC2264 and ~4-5Myrs ( Ori and IC348)
Updated Disc lifetime:
• New age order.
• Second-order effects achievable.
• IC348, no O stars, local environment effects.
R-C gap?
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
R-C gap:R-C gap:
• Distance independent age indicator.
• Shape factor.
• Size of gap is a function of age.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
R-C gap, Physics:R-C gap, Physics:Using Siess and Dufour (2000) mass tracks. Radiative-Convective gap.
• 1, 3 and 13Myr isochrones.
• 1 and 3Msol evolution shown (red).
• Star from Convective (Hayashi) track to radiative track.
• Moves fast in CMD space.
• Leads to paucity of stars.
• Older clusters R-C gap at lower masses, closer to MS.
Noted in the literature, Stolte et al (2004), not utilised.
Calibration required!
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Calibration:Calibration:
By eye fitting:
• Subjective.
• Uncertainties not well defined.
• Binaries neglected.
2 fitting:
• Statistically meaningful uncertainties.
• Objective fitting statistic.
• Binary stars included.
• Consistent method.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
• Generalised 2 fitting with uncertainties in two-dimensions.
• Massive jump in statistical sophistication, provides first statistically robust uncertainties.
• Use for MS stars to find distances.
• Model dependent, okay for relative ages.
• Extinction dependency for HM fitting.
• 2, extremely sensitive to data, utilise the ~1% photometry.
2 2 Distances:Distances:
Initial Problems:
• Normalisation causing numerical instability?
• Post-MS stars falling outside area of fit, altering 2
• Extinctions from Q-method of spectral types, former inconsistent.
• Filter response?!
dcdmmcmmccU iNi ii ),(),(ln2,1
2
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Extinctions, Q-method:Extinctions, Q-method:
Johnson & Morgan (1953).
• Remarkable piece of work
• From NGC2362, the Pleiades and the Praesepe with nearby stars.
• U-B vs B-V CMD used to calculate extinctions.
• Empirically derived ‘reddening independent’ relationship:
Using: E(U-B)/E(B-V)=0.72±0.03 (empirically derived)
(B-V)0=0.337Q-0.009.
Valid for -0.80<Q<-0.05
For B stars in their sample.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Problems:• Implies intrinsic straight-
line Pseudo-MS in U-B vs B-V.
• Binarity effects ignored. • E(U-B)/E(B-V)=CONST.• Filter response?
Q-method V1.1:Q-method V1.1:
Figure:
• Geneva 1Myr isochrone.
• Intrinsic Q-method Pseudo-MS line.
• Empirical Extinction vector.
Using AV=3.1E(B-V), can lead to an error of ~0.07.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Q-method V1.1:Q-method V1.1:
Problems:• Implies intrinsic straight-
line Pseudo-MS in U-B vs B-V.
• Binarity effects ignored. • E(U-B)/E(B-V)=CONST.• Filter response?
Figure:
• Geneva isochrone 50% binary fraction.
• Q-method implicit line.
• Extinction vector.
Can Lead to an error of AV~0.1.
Errors smaller in the B star range.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Q-method V1.1:Q-method V1.1:
Problems:• Implies intrinsic straight-
line Pseudo-MS in U-B vs B-V.
• Binarity effects ignored. • E(U-B)/E(B-V)=CONST.• Filter response?
Bessels (1998) provides extinction as a function of colour:
AV=(3.26+0.22(B-V)0)*E(B-V)
E(U-B)/E(B-V)=0.71+0.24(B-V)0
(based on E(B-V)~0.3)
• Over range of Q→-0.279<(B-V)0<-0.0259
• Error in AV~0.05
Therefore summed error so far:
In B range: AV~0.2
Errors in different sense.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Q-method V1.1:Q-method V1.1:
• Applied Bessels Extinction functions.
• Limit to binarity E(B-V)<0.03.
• Use Bessels (1998) Col-Teff relation (logg=4.5).
• If AV decereases use a smaller range of B stars.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Fitting:Fitting:
• Use Q-method or spectral types for extinctions.
• Use 2 to find distances.
Filter response:
• Previously used Col-Teff conversion of Flower (1996).
• Updated to Bessels (1998), now consistent.
• Check photometry!
• Naked eye fitting cannot detect the details, and uncertainties meaningless.
Next: Spot the Difference!
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
11.81<dm<11.84
11.84<dm<11.9
NGC2264:
9.35<dm<9.54
• Updated Q
• Extinction=f(B-V)
• Bessels (1998) Col-Teff
The ONC:
8.04<dm<8.16
• Taken Log Teff
• Used Geneva Isochrones for (V-I)0
• Derived E(V-I), AV
• Apply to V.
Spectral types:Spectral types:
Refit using:
• E(V-I)=F(V-I) and AV=F(V-I).
• Use Bessels (1998) Col-Teff relation.
• Check filter responses for data.
Age ladder:Age ladder:
• ZAMS isochrone from Siess and Dufour (2000)
• h and Per, NGC2264 and the ONC.
• Straight line fits to PMS.
• Stop fit at base of R-C gap.
• Distances from 2.
• Substract the ZAMS colour at each magnitude.
• Relative age order clear.
• R-C gap size in colour.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Summary:Summary:
• Developed technique to derive robust relative ages using empirical
isochrones.
• Discovery of R-C gap.
• Derived improved distances to fiducial clusters.
• New method of deriving extinctions.
• Guinea pig for 2-improvements.
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].
Future Work:Future Work:
1. WHT dataset to calibrate the R-C gap.
2. INT (ugri’z), empirical isochrones with homogenous dataset.
3. Use 2 to fit gap?
4. Rinse and repeat/automation.
5. GAIA?
But First….
1. Write Thesis
2. Get a Post-Doc
Intro: [1 2 3] Empirical Isochrones: [3 4 5] R-C gap: [6 7 8] 2 distances: [9] Extinctions: [10 11 12 13 14] Fitting [15] Relative ages [16] Summary [17] Future Work [18].