Doug WelchMcMaster University

Citizen Sky WorkshopAugust 2009

Image credit: Kerry Ann Lecky-HepburnImage credit: Kerry Ann Lecky-Hepburn

• Stars are not Stars are not created equal in the created equal in the information they information they provide to observersprovide to observers• eps Aur is a rare eps Aur is a rare combination of combination of extra observablesextra observables• This eclipse This eclipse isis at a at a tipping point in our tipping point in our ability to understand ability to understand it.it.

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Image credit: Hans Hillewaert (Image credit: Hans Hillewaert (Lycaon) )

• Rare massive star• Rare supergiant• Rare long-period• Rare orbital alignment• Rare opportunity

=?• Good observational constraint• Clearer understanding

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2.035 day pulsation period2.035 day pulsation period

800.4 day orbital period800.4 day orbital period

D. Lepischak M.Sc. Thesis and papersD. Lepischak M.Sc. Thesis and papers

18 nights on 18 nights on the Mt the Mt Stromlo 74”Stromlo 74”

Complete Complete phase phase coverage in coverage in BVIBVI

Several

pulsational cycles within single eclipse.

CepheidCepheid CompanionCompanionRadiusRadius 0.0365 ± 0.0365 ±

0.00090.00090.047 ± 0.047 ± 0.0010.001

Radial Radial Ampl.Ampl.

0.0015 ± 0.0015 ± 0.00020.0002

<V> [mags]<V> [mags] 17.2 ± 0.217.2 ± 0.2 20.5 ± 0.620.5 ± 0.6 <R> <R> 16.5 ± 0.216.5 ± 0.2 19.0 ± 0.619.0 ± 0.6 <I><I> 15.9 ± 0.215.9 ± 0.2 17.7 ± 0.617.7 ± 0.6 <V-R><V-R> 0.63 ± 0.010.63 ± 0.01 1.4 ± 0.11.4 ± 0.1

Results:Results:

χχνν22 = 1.4 = 1.4

Relative to Relative to orbital orbital

separationseparation

Inconsistent with isolated single-star evolution?

Observed

Cepheid

Companion

De-reddened

M–type. Mass loss? M–type. Mass loss?

Image credit: Sky & TelescopeImage credit: Sky & Telescope

Watching the Detections Watching the Detections ……

“The Force has a strong effect on weak minds” – Obiwan Kenobi

OR (translated) Most of the previous interpretations are

wrong in one (or more!) important ways Look at the actual observational data with

fresh eyes Separate findings from suspicions Keep track of the dominant signals

Monoliths could reproduce the eclipse Monoliths could reproduce the eclipse lightcurve, too! lightcurve, too!

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1. eps Aur has a “timescale”, not a period2. Nobody has factored in the effects of

radial pulsation of the supergiant during the eclipse

3. We have been blind to more common analogues.

Predictions1. There won’t be a central peak this eclipse2. The peaks in eclipse are due to the

primary, not details of the secondary

This eclipse and observing campaign will likely be definitive.

Outcome 1: The scales will fall from our eyes and we will extract new, important understanding from this system.

OR Outcome 2: It will become clear that this system

is too much of a mess to provide improvements in our understanding of evolutionary issues.

Part of the scientific process is knowing your efforts are providing diminishing returns!