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HIGH-PRECISION PHOTOMETRY OF ECLIPSING BINARY STARS

HIGH-PRECISION PHOTOMETRY OF ECLIPSING BINARY STARS. John Southworth + Hans Bruntt + Pierre Maxted + many others. Eclipsing binary stars: why bother?. Eclipsing binary stars: why bother?. Light curve and radial velocity analysis: get masses and radii of two stars to 1%

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HIGH-PRECISION PHOTOMETRY OF ECLIPSING BINARY STARS

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  1. HIGH-PRECISION PHOTOMETRY OF ECLIPSING BINARY STARS John Southworth + Hans Bruntt + Pierre Maxted + many others

  2. Eclipsing binary stars: why bother?

  3. 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?

  4. 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

  5. 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

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

  7. Eclipsing binary stars: how? • Light curve analysis gives: • rA rB radii as fraction of orbital separation • e ω orbital eccentricity and periastron longitude • P i orbital period and inclination

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

  9. Eclipsing binary stars: how? • Light curve analysis gives: • rA rB e ω P i • Radial velocity analysis gives: P e ω • MA sin3i minimum mass of star A • MB sin3i minimum mass of star B • a sin i projected orbital separation

  10. Eclipsing binary stars: how? • Light curve analysis gives: • rA rB e ω P i • Radial velocity analysis gives: • MA sin3i MB sin3i a sin iP e ω • Combine quantities: • MAMBRA RB log gA log gB • get the masses and radii of both stars

  11. Eclipsing binary stars: how? • Light curve analysis gives: • rA rB e ω P i • Radial velocity analysis gives: • MA sin3i MB sin3i a sin iP e ω • Combine quantities: • MAMBRA 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

  12. The WIRE satellite • Launched in 1999 for an IR galaxy survey • electronics problem caused loss of coolant

  13. 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

  14. Eclipsing binaries with WIRE. I. ψ Centauri • V = 4.0 spectral type = B9 V + A2 V • Known spectroscopic binary • WIRE light curve: 41 000 points with 2 mmag scatter

  15. Interlude 1: JKTEBOP • Based on EBOP model (Paul Etzel, 1975) • stars treated as biaxial spheroids • numerical integration includes LD and GD

  16. 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 FORTRAN77

  17. Eclipsing binaries with WIRE. I. ψ Centauri • JKTEBOP fit to the eclipses

  18. Eclipsing binaries with WIRE. I. ψ 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

  19. Eclipsing binaries with WIRE. I. ψ 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, A&A, 456, 651) • We are currently working on new spectroscopy

  20. 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

  21. Eclipsing binaries with WIRE. III. β 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

  22. Interlude 2: more JKTEBOP • Problem: linear limb darkening law too simple • Solution: add log, sqrt, quad, cubic LD laws

  23. 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 FORTRAN77

  24. 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 FORTRAN77

  25. Eclipsing binaries with WIRE. III. β Aurigae • rA = 0.1569 ± 0.0008 P = 3.96004673 (17) • rB = 0.1460 ± 0.0008e = 0.0018 ± 0.0004

  26. Eclipsing binaries with WIRE. III. β 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

  27. Eclipsing binaries with WIRE. III. β 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, A&A, 467, 1215)

  28. Eclipsing binaries: why bother? • Get mass and radius to 1% • accurate distance indicators • compare to theoretical models: get precise age and metal abundance

  29. 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

  30. 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

  31. 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

  32. 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)

  33. Eclipsing binaries in open clusters. III. The distance to the Pleiades • Surface brightness method gives good results • Use zeroth-magnitude angular diameter Φ(m=0) • Kervella et al (2004) give Φ(m=0) - Teff calibrations • Just need RA and RB and apparent magnitudes • See Southworth, Maxted & Smalley (2005, A&A, 429, 645)

  34. 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

  35. 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

  36. JKTEBOP and HD 209458 • JKTEBOP very good for transiting exoplanets • fast and accurate • lots of different limb darkening laws

  37. 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)

  38. 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)

  39. John Southworth jkt@astro.keele.ac.uk University of Warwick, UK

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