ECLIPSING BINARIES IN OPEN CLUSTERS

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ECLIPSING BINARIESIN OPEN CLUSTERS

• John Southworth
• Dr Pierre Maxted
• Dr Barry Smalley

• Astrophysics Group Keele University

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Eclipsing binaries in open clusters

• EBs are good tests of theoretical stellar models
• EBs in clusters have known age and metal
  abundance
• EBs in clusters are even better tests of
  theoretical models
• EBs are good distance indicators
• Find distance to cluster without using MS fitting

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HD 23642 in the Pleiades

• AO Vp (Si) Am
• Period 2.46 days
  
• mV 5.9 mag
• Shallow eclipses discovered by Torres (2003)
• Munari et al (2004) distance 131.9 2.1 pc

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Distance to the Pleiades

• Long distance scale 132 3 pc
• MS fitting (e.g., Percival et al. 2003)
• HD 23642 (Munari et al. 2004)
• Interferometric binary Atlas (Zwahlen et al.
  2004)
• Short distance scale 120 3 pc
• Hipparcos (van Leeuwen et al. 2004)

• Possible solution Pleiades is metal-poor
• Castellani et al. (2002) Fit for Z 0.012
• But Boesgaard Friel (1990) Fe/H -0.03
  0.02
• Possible solution Hipparcos parallaxes
  correlated
• (Pinsonneault et al. 1998 Makarov 2002)

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HD 23642 light curves

• B and V light curves from Munari et al. (2004)
• We analysed them using EBOP
• Theoretical limb darkening and gravity darkening
• Formal errors very optimistic

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Monte Carlo analysis

• Used Monte Carlo simulations to find light curve
  uncertainties
• Limb darkening coefficients perturbed
• rA 0.151 0.004rB 0.136 0.007
• Problem B and V solutions inaccurate and dont
  agree well
• Solution spectroscopic light ratio (Torres 2003)
• rA 0.154 0.002rB 0.130 0.004

Monte Carlo analysis results for HD 23642 without
spectroscopic light ratio
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HD 23642 effective temperatures

• Compare observations to ATLAS9 spectra
• Temperatures 9750 250 K 7600 400 K
• uvbyß photometry Moon Dworetsky (1985)
  calibration
• 9200 K for system 9870 K for primary only
• Infrared Flux Method 9620 280 K 7510 430 K

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Pleiades is not metal-poor

• HD 23642
• MA 2.19 0.02
• MB 1.55 0.02
• RA 1.83 0.03
• RB 1.55 0.04
• Compare to Granada models
• Z 0.02
• Pleiades distance scales cannot be reconciled
  with low metal abundance

Granada theoretical models 125 Myr Z 0.01
0.02 0.03
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Distance to the Pleiades

• Distance from luminosity bolometric correction
• L 4 p R2 s Teff4 ? Mbol
• Mbol BC V ? MV V ?
  distance
• Problems
• BCs depend on theoretical model atmospheres
• Fundamental effective temperatures are needed
• Consistent solar Mbol and luminosity values needed

• Girardi et al. (2000) BCs (V filter) 139.8
  5.3 pc
• (K filter) 138.8 3.3 pc
• Bessell et al. (1998) BCs give same results
• BCs better in the infrared reddening less
  important
• metallicity less important
• BCs less dependent on Teff

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Distance from surface brightness

• Calibrations of surface brightness vs. colour
  index
• SV surface brightness in V filter
• F angular diameter (mas)
• R linear radius of star (R?)
• SV mV - 5 log F
• distance 9.3048 (R / F) parsecs

• Distance to HD23642 138 19 pc
• Use Di Benedetto (1998) calibration of SV against
  (B - V)
• Problems
• HD 23642 B and V light ratios are inaccurate
• B filter is sensitive to metallicity
• (B - V) is not very sensitive to surface
  brightness
• Reddening is important

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Surface brightness from temperature

• Use zeroth-magnitude angular diameter F(m0)
• SV V0 - 5 log F so F(m0) F 10(0.2
  m) 0.2 SV
• Kervella et al (2004) give F(m0) - log Teff
  calibrations

• Use 2MASS JHK photometry IR relations better
• Distance 139.1 3.5 pc
• Individual uncertainties
• Effective temperatures 0.7 pc 1.4 pc
• Stellar radii 1.4 pc 1.5 pc
• Apparent K magnitude 1.9 pc
• Cosmic scatter in calibration 1.4 pc

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The Pleiades distance is ....?

• Long distance scale 132 3 pc
• main sequence fitting
• study of astrometric binary Atlas
• Short distance scale 120 3 pc
• Hipparcos parallaxes

• Distance to HD 23642 139 4 pc
• only weakly dependent on temperatures and radii
• The Pleiades is not metal-poor
• from comparison between the masses and radii and
  theoretical evolutionary models
• Southworth, Maxted Smalley, astro-ph/0409507

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W W Aurigae

• A4 m A5 m
• Period 2.52 days
  
• mV 5.9 mag
• Discovered by Solviev (1918) and Schwab (1918)
• Hipparcos distance 84.3 7.3 pc

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WW Aur spectral characteristics

• Both components are Am stars
• spectra show strong lines of both components

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WW Aur spectroscopic orbit

• TODCOR two-dimensional cross-correlation
• Cross-correlate against many observed template
  spectra
• Fit spectroscopic orbits using SBOP
• Choose which sets of spectra give good orbits
• Average good orbits to find best orbit

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WW Aur light curves 1

• UBV light curves from Kiyokawa Kitamura (1975)
• 3037 datapoints scanned from paper

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WW Aur light curves 2

• uvby light curves from Etzel (1975) Masters
  Thesis
• 3748 datapoints on a nine-track magnetic tape

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WW Aur light curve analysis

• UBV and uvby light curves fitted using EBOP
• Limb darkening coefficients adjusted
• Uncertainties from Monte Carlo analysis
• Good agreement withvariation between the seven
  light curves
• rA 0.1586 0.0009
• rB 0.1515 0.0009

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WW Aur effective temperatures

• Am stars so spectral analysis unreliable
• Hipparcos parallax gives distance 84.3 7.3 pc
• Get bolometric flux
• UV fluxes from TD-1 satellite
• UBVRI magnitudes
• 2MASS JHK magnitudes
• Convert to separate fluxes using V light ratio
• Temperatures
• Teff (A) 7960 420 K
• Teff (B) 7670 410 K
• almost no dependence on model atmospheres

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WW Aur results

• Masses from cross-correlation against observed
  spectra MA 1.964 0.007 M?
• MB 1.814 0.007 M?
• Radii from EBOP geometrical analysis
• Gravity darkening unimportant
• Limb darkening fitted RA 1.927 0.011 R?
• RB 1.841 0.011 R?
• Effective temperatures from Hipparcos parallax
  and UV-optical-IR fluxes
• Teff (A) 7960 420 K
• Teff (B) 7670 410 K

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Comparison with theoretical models

• Assume common age and chemical composition for
  both stars in WW Aur
• Problem no published theoretical stellar
  models fit the masses and the radii

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Solution Z 0.06

• Claret (2004) models fit for Z 0.06 age
  77?107 Myr

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Metallic-lined eclipsing binaries
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Conclusions

• EBs are excellent distance indicators
• HD 23642 gives Pleiades distance 139 4 pc
• Agrees with MS fitting but not Hipparcos
• Distance from surface brightness is good
• Avoids bolometric corrections from model
  atmospheres
• Best in the infrared (reddening, Teff dependence)
• Eclipsing binaries in open clusters are very
  useful

• WW Aur seems to be very metal-rich
• Masses and radii found to accuracies of 0.4,
  0.6
• Teff s from Hipparcos parallax and UV-optical-IR
  fluxes
• Metal abundance of Z 0.06 not connected to Am
  spectra

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• John Southworth (jkt_at_astro.keele.ac.uk) Keele
  University, UK