ECLIPSING BINARIES IN OPEN CLUSTERS John Southworth Dr

ECLIPSING BINARIES IN OPEN CLUSTERS John Southworth Dr Pierre Maxted Dr Barry Smalley Astrophysics Group Keele University

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 • Two EBs in one cluster: – four stars with same age and chemical composition – excellent test of models – find metal and helium abundance of cluster – 2004, MNRAS, 349, 547

HD 23642 in the Pleiades • • • AO Vp (Si) + Am Period 2. 46 days m. V = 5. 9 mag Shallow eclipses discovered by Torres (2003) Munari et al (2004) distance: 131. 9 ± 2. 1 pc

Distance to the Pleiades • ‘Long’ distance scale: 132 ± 3 pc – MS fitting – HD 23642 – Interferometric binary Atlas (e. g. , Percival et al. 2003) (Munari et al. 2004) (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): – But Boesgaard & Friel (1990): Fit for Z = 0. 012 [Fe/H] = -0. 03 ± 0. 02 • Possible solution: Hipparcos parallaxes correlated – (Pinsonneault et al. 1998; Makarov 2002)

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

Monte Carlo analysis • Used Monte Carlo simulations to find light curve uncertainties – Limb darkening coefficients perturbed – r. A = 0. 151 ± 0. 004 r. B = 0. 136 ± 0. 007 • Problem: B and V solutions inaccurate and don’t agree well – Solution: spectroscopic light ratio (Torres 2003) – r. A = 0. 154 ± 0. 002 r. B = 0. 130 ± 0. 004 Monte Carlo analysis results for HD 23642 without spectroscopic light ratio

HD 23642 effective temperatures • Compare observations to ATLAS 9 spectra: – Temperatures: 9750 ± 250 K 7600 ± 400 K • uvbyβ photometry + Moon & Dworetsky (1985) calibration: – 9200 K for system 9870 K for primary only • Infrared Flux Method: 9620 ± 280 K 7510 ± 430 K

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 Granada theoretical models 125 Myr Z = 0. 01 0. 02 0. 03 – Pleiades distance scales cannot be reconciled with low metal abundance

Distance to the Pleiades • Distance from luminosity + bolometric correction: – L = 4 π R 2 σ Teff 4 – Mbol + BC + V Mbol 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

Distance from surface brightness • Calibrations of surface brightness vs. colour index – – – SV = surface brightness in V filter Φ = angular diameter (mas) R = linear radius of star (R ) SV = m. V - 5 log Φ distance = 9. 3048 (R / Φ) parsecs • Distance to HD 23642: 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

Surface brightness from temperature • Use zeroth-magnitude angular diameter Φ(m=0) – SV = V 0 - 5 log Φ so Φ(m=0) = Φ 10(0. 2 m) = 0. 2 SV – Kervella et al (2004) give Φ(m=0) - log Teff calibrations • Use 2 MASS JHK photometry: IR relations better – Distance : – Individual uncertainties: • • 139. 1 ± 3. 5 pc 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

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

W W Aurigae • • • A 4 m + A 5 m Period 2. 52 days m. V = 5. 9 mag Discovered by Solviev (1918) and Schwab (1918) Hipparcos distance: 84. 3 ± 7. 3 pc

WW Aur spectral characteristics • Both components are Am stars – spectra show strong lines of both components

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 • RV semiamplitudes: KA = 116. 81 ± 0. 23 km/s KB = 126. 49 ± 0. 32 km/s – Uncertainty is standard deviation of the results from each good orbit – SBOP uncertainties agree very well

WW Aur light curves 1 • UBV light curves from Kiyokawa & Kitamura (1975) – 3037 datapoints scanned from paper

WW Aur light curves 2 • uvby light curves from Etzel (1975) Master’s Thesis – 3748 datapoints on a nine-track magnetic tape

WW Aur light curve analysis • UBV and uvby light curves fitted using EBOP – Limb darkening coefficients adjusted • Uncertainties from Monte Carlo analysis – Good agreement with variation between the seven light curves: – r. A = 0. 1586 ± 0. 0009 – r. B = 0. 1515 ± 0. 0009 HD 23642 WW Aur

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 – 2 MASS 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

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

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

Solution: Z = 0. 06 Claret (2004) models fit for Z = 0. 06 age 77 107 Myr

Metallic-lined eclipsing binaries

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

John Southworth (jkt@astro. keele. ac. uk) Keele University, UK