ECLIPSING BINARIES IN OPEN CLUSTERS John Southworth Dr Pierre Maxted Dr Barry Smalley Astrophysics...
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Transcript of ECLIPSING BINARIES IN OPEN CLUSTERS John Southworth Dr Pierre Maxted Dr Barry Smalley Astrophysics...
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ECLIPSING BINARIESIN OPEN CLUSTERS
John SouthworthDr Pierre MaxtedDr Barry Smalley
Astrophysics Group Keele University
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• 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
Eclipsing binaries in open clusters
• 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
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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
• 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)
• ‘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)
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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 ± 0.004
rB = 0.136 ± 0.007
• Problem: B and V solutions inaccurate and don’t agree well– Solution: spectroscopic
light ratio (Torres 2003)– rA = 0.154 ± 0.002
rB = 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
• uvbyβ 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 models125 Myr Z = 0.01 0.02 0.03
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Distance to the Pleiades• Distance from luminosity + bolometric correction:
– L = 4 π R2 σ 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
– Φ = angular diameter (mas)
– R = linear radius of star (R)
– SV = mV - 5 log Φ
– distance = 9.3048 (R / Φ) 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 Φ(m=0)
– SV = V0 - 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 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
• RV semiamplitudes:KA = 116.81 ± 0.23 km/sKB = 126.49 ± 0.32 km/s
– Uncertainty is standard deviation of the results from each good orbit
– SBOP uncertainties agree very well
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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) Master’s 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 with
variation between the seven light curves:
– rA = 0.1586 ± 0.0009
– rB = 0.1515 ± 0.0009
HD 23642
WW Aur
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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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• Assume common age and chemical composition for both stars in WW Aur
• Problem: no published theoretical stellar models fit the masses and the radii
Comparison with theoretical models
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Solution: Z = 0.06
Claret (2004) models fit for Z = 0.06 age 77107 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 ([email protected]) Keele University, UK