Transcript Document

Colour Magnitude diagrams and Pre-MainSequence (PMS) populations.
Nathan Mayne
PMS detection mechanisms.
• Class 0,
Deeply embedded stars, 15-30K
black body.
• Class II,
Optically visible, IR excess (disc),
accretion lines. CTTS.
• Class I,
IR source, still embedded.
• Class III,
weak line emissions, less IR excess
(no-disc). WTTS.
WTTS: No Disc
•Thin H-Chromospheric hydrogen (undamped by disc).
BOTH:
•Dust & particulatesReddening of light.
•X-rays-Conversion of g
(accretion).
•Li absorption-Convective,
material mixed, (LDB).
•Continuum radiationAccretion hotspots.
CTTS: Disc
•NIR & UV excess-Inner disc edge heated.
•FIR excess-far disc slower heating.
•Broad H-Magnetically driven accretion (high vel  red/blue shifted).
Colour Magnitude Diagrams.
Large scale surveys of wide fields. WFC on the INT.
Theory.
Isochrones;
From models of stellar interiors.
• Tsurface  Mass relations.
• Convert SED to magnitudes in
different colour bands.
• Account for distance dimming,
Lbol spread over sphere.
• Reddening from ISM.
• Use isochrones to estimate Age, distance or reddening/extinction. Given other
two quantities.
• Theoretical with the above degrees of freedom and degeneracy  large error
budget.
• Difficulty in selecting only members of a cluster/group.
Isolating members of a PMS.
Indirectly;
Directly;
Isolate the cluster, use CMD for PMS;
From T Tauri models.
• Clusters centrally condensed, more massive
objects sink/formed in centre.
• H
• Cut the catalogue at expected OB/massive
star limit.
• Plot positions on the sky to find
conglomerations.
• Variablity
• X-rays
• Li
• Assume a circular distribution, cut full
catalogue, increasing ratio members to nonmembers.
Both include percentage of non-members, BG
or FG. Sequence clearer.
Indirect sequence isolation.
Isochrone application.
Empirical isochrones.
Isochrones formed by fitting a
line through the sequence.
Direct sequence isolation.
Empirical isochrones.
• Sequence isolation
Median used over Mean
• Photometric cut to
clean.
• Tied to real star in population
• Averaging filter
applied to sequence.
• Lessens effect of outliers,
many  from sequence.
• Quadratic fitted
through averages, for
gradient.
• Results in smooth line through
each sequence.
• Cubic spline fitted
through averages.
• Given extinction and distance
modulus-combine.
Empirical isochrones combined diagram.
Inconsistencies/Discoveries.
CepOB3b
IC348
• Age in literature 7 Myrs.
• Studied, as many young groups in IR.
• Actually closer to 3Myrs
• Conversion of reddening IR to V,V-I
incorrect.
• Often cited as spurious, has H2
material at 7 Myr-SSF.
• Sequence tighter in V, V-I.
Conclusion.
• Reduced huge, concurrent
photometric dataset.
• Developed a fitting routine to
provide empirical isochrones.
• Discovered key inconsistencies in
current understanding.
• Developed relative age ladder.
• Increased automation of reduction
process.
WHT Visit.
WYFFOS
•Multi-fibre spectrograph.
• Find continuum flux c.f line flux.
• In many assoc c.f to age in CMD.
Future Plans
Aims
•
•
Finish Paper.
Ambitions
•
Attend/talk at
conferences.
Reduce and analyse
WHT data.
•
Create proposals for
spectroscopy.
•
Examine remaining
INT data (320GB).
•
Visit other
departments/
collaborate.
•
Write thesis.
•
Get a job!!!
y=x3+6 walks into a bar and asks the bartender for the menu.
He says ‘Sorry mate we don’t cater for functions!’