HIGH-PRECISION PHOTOMETRY OF ECLIPSING BINARY STARS

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HIGH-PRECISION PHOTOMETRY OF ECLIPSING BINARY
STARS

• John Southworth
• Hans Bruntt Pierre Maxted many others

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Eclipsing binary stars why bother?
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Eclipsing binary stars why bother?

• Light curve and radial velocity analysis get
  masses and radii of two stars to 1
• where else could we get this from?

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Eclipsing binary stars why bother?

• Light curve and radial velocity analysis get
  masses and radii of two stars to 1
• where else could we get this from?
• Accurate mass, radius, Teff, luminosity
• use as high-precision distance indicators
• check that theoretical models work

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Eclipsing binary stars why bother?

• Light curve and radial velocity analysis get
  masses and radii of two stars to 1
• where else could we get this from?
• Accurate mass, radius, Teff, luminosity
• use as high-precision distance indicators
• check that theoretical models work
• Comparison with theoretical models
• get metal abundance and age
• investigate overshooting, mixing length, helium
  abundance, diffusion

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Eclipsing binary stars how?
WW Aurigae Southworth et al. (2005)
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Eclipsing binary stars how?

• Light curve analysis gives
• rA rB radii as fraction of orbital separation
• e ? orbital eccentricity and periastron
  longitude
• P i orbital period and inclination

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Eclipsing binary stars how?
WW Aurigae Southworth et al. (2005)
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Eclipsing binary stars how?

• Light curve analysis gives
• rA rB e ? P i
• Radial velocity analysis gives P e ?
• MA sin3 i minimum mass of star A
• MB sin3 i minimum mass of star B
• a sin i projected orbital separation

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Eclipsing binary stars how?

• Light curve analysis gives
• rA rB e ? P i
• Radial velocity analysis gives
• MA sin3 i MB sin3 i a sin i P
  e ?
• Combine quantities
• MA MB RA RB log gA log gB
• get the masses and radii of both stars

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Eclipsing binary stars how?

• Light curve analysis gives
• rA rB e ? P i
• Radial velocity analysis gives
• MA sin3 i MB sin3 i a sin i P
  e ?
• Combine quantities
• MA MB RA RB log gA log gB
• get the masses and radii of both stars
• Spectral modelling or photometric colours
• get effective temperatures
• get luminosities
• get distance

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The WIRE satellite

• Launched in 1999 for an IR galaxy survey
• electronics problem caused loss of coolant

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The WIRE satellite

• Launched in 1999 for an IR galaxy survey
• electronics problem caused loss of coolant
• Star tracker used since 1999 as a high-speed
  photometer
• aperture 5 cm
• cadence 2 Hz
• 5 targets at once

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Eclipsing binaries with WIRE. I. ? Centauri

• V 4.0 spectral type B9 V A2 V
• Known spectroscopic binary
• WIRE light curve 41 000 points with 2 mmag
  scatter

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Interlude 1 JKTEBOP

• Based on EBOP model (Paul Etzel, 1975)
• stars treated as biaxial spheroids
• numerical integration includes LD and GD

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Interlude 1 JKTEBOP

• Based on EBOP model (Paul Etzel, 1975)
• stars treated as biaxial spheroids
• numerical integration includes LD and GD
• JKTEBOP retains original model
• new input / output
• Levenberg-Marquardt optimisation algorithm
• bootstrapping and Monte Carlo simulations to find
  parameter uncertainties

http//www.astro.keele.ac.uk/jkt/codes.html FORT
RAN77
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Eclipsing binaries with WIRE. I. ? Centauri

• JKTEBOP fit to the eclipses

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Eclipsing binaries with WIRE. I. ? Centauri

• Best fit and Monte Carlo simulation results
• rA 0.043984 0.000045
• rB 0.021877 0.000032
• e 0.55408 0.00024
• P 38.81252 0.00029
• And limb darkening too
• uA 0.256 0.009
• uB 0.362 0.041

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Eclipsing binaries with WIRE. I. ? Centauri

• Best fit and Monte Carlo simulation results
• rA 0.043984 0.000045
• rB 0.021877 0.000032
• e 0.55408 0.00024
• P 38.81252 0.00029
• And limb darkening too
• uA 0.256 0.009
• uB 0.362 0.041
• See Bruntt et al. (2006, AA, 456, 651)
• We are currently working on new spectroscopy

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Eclipsing binaries with WIRE. II. AR Cas

• P 6.07 days B4 V A6 V V 4.9
• variation at primary star rotation period
• several pulsation frequencies

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Eclipsing binaries with WIRE. III. ß Aurigae

• V 1.9 P 3.960 days A1m A1m
• First known double-lined binary 1889 (Maury)
• First known double-lined eclipsing binary
  Stebbins (1911)
• WIRE light curve 30 000 points 0.3 mmag scatter

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Interlude 2 more JKTEBOP

• Problem linear limb darkening law too simple
• Solution add log, sqrt, quad, cubic LD laws

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Interlude 2 more JKTEBOP

• Problem linear limb darkening law too simple
• Solution add log, sqrt, quad, cubic LD laws
• Problem ratio of the radii poorly determined
• Solution allow spectroscopic light ratio to be
  included directly as another observation

http//www.astro.keele.ac.uk/jkt/codes.html FORT
RAN77
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Interlude 2 more JKTEBOP

• Problem linear limb darkening law too simple
• Solution add log, sqrt, quad, cubic LD laws
• Problem ratio of the radii poorly determined
• Solution allow spectroscopic light ratio to be
  included directly as another observation
• Problem difficult to get good times of minimum
  light from the WIRE data
• Solution include old times of minimum light
  directly as additional observations

http//www.astro.keele.ac.uk/jkt/codes.html FORT
RAN77
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Eclipsing binaries with WIRE. III. ß Aurigae

• rA 0.1569 0.0008 P 3.96004673 (17)
• rB 0.1460 0.0008 e 0.0018 0.0004

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Eclipsing binaries with WIRE. III. ß Aurigae

• Combine light curve result with spectroscopic
  orbit of Smith (1948)
• MA 2.376 0.027 M?
• MB 2.291 0.027 M?
• RA 2.762 0.017 R?
• RB 2.568 0.017 R?

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Eclipsing binaries with WIRE. III. ß Aurigae

• Combine light curve result with spectroscopic
  orbit of Smith (1948)
• MA 2.376 0.027 M?
• MB 2.291 0.027 M?
• RA 2.762 0.017 R?
• RB 2.568 0.017 R?
• Distance to system
• Hipparcos parallax 25.2 0.5 pc
• Orbital parallax 24.8 0.8 pc
• Surface brightness 25.0 0.4 pc
• Bolometric corrections 24.8 0.3 pc
• Southworth, Bruntt Buzasi (2007, AA, 467, 1215)

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Eclipsing binaries why bother?

• Get mass and radius to 1
• accurate distance indicators
• compare to theoretical models get precise age
  and metal abundance

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Eclipsing binaries why bother?

• Get mass and radius to 1
• accurate distance indicators
• compare to theoretical models get precise age
  and metal abundance
• Now apply to EBs in open clusters
• get accurate distance
• get precise age and metallicity
• no need for MS fitting

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Eclipsing binaries why bother?

• Get mass and radius to 1
• accurate distance indicators
• compare to theoretical models get precise age
  and metal abundance
• Now apply to EBs in open clusters
• get accurate distance
• get precise age and metallicity
• no need for MS fitting
• Combined study of cluster and binary
• stronger test of theoretical models

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Eclipsing binaries in open clusters. I. V615 and
V618 Per

• Both members of the young h Per cluster
• have same age and chemical composition
• compare all four stars to models using a
  mass-radius diagram
• h Per has low metal abundance Z 0.01

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Eclipsing binaries in open clusters. II. V453 Cyg

• Member of sparse young cluster NGC 6871
• Comparison to theoretical models
• age 10.0 0.2 Myr
• metal abundance Z 0.01 (half solar maybe)

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Eclipsing binaries in open clusters. III. The
distance to the Pleiades

• Surface brightness method gives good results
• Use zeroth-magnitude angular diameter F(m0)
• Kervella et al (2004) give F(m0) - Teff
  calibrations
• Just need RA and RB and apparent magnitudes
• See Southworth, Maxted Smalley (2005, AA, 429,
  645)

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Eclipsing binaries in open clusters. III. HD
23642 in the Pleiades

• V 6.8 P 2.46 AO Vp (Si) Am
• Light curves from Munari et al. (2004)
• We find distance 139.1 3.5 pc

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Eclipsing binaries in open clusters what next?

• V1481 Cyg and V2263 Cyg in NGC 7128
• 14 nights of INT / WFC photometry
• 7 nights of INT / IDS spectroscopy
• watch this space

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JKTEBOP and HD 209458

• JKTEBOP very good for transiting exoplanets
• fast and accurate
• lots of different limb darkening laws

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JKTEBOP and HD 209458

• JKTEBOP very good for transiting exoplanets
• fast and accurate
• lots of different limb darkening laws
• Results for HD 209458
• rA 0.11405 0.00042
• rB 0.01377 0.00008
• gB 9.28 0.15 m s-2

Southworth et al. (2007, MNRAS, 379, L)
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Extrasolar planet surface gravity

• The known transiting extrasolar planets have a
  significant correlation between orbital period
  and suface gravity
• the closer planets are more bloated

Southworth et al. (2007, MNRAS, 379, L)
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• John Southworth jkt_at_astro.keele.ac.uk
  University of Warwick, UK