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Register a new userFundamental effective temperature measurements for eclipsing binary stars I. Development of the method and application to AI Phoenicis
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Stars with accurate and precise effective temperature (T$_{rm eff}$) measurements are needed to test stellar atmosphere models and calibrate empirical methods to determine T$_{rm eff}$. There are few standard stars currently available to calibrate temperature indicators for dwarf stars. Gaia parallaxes now make it possible, in principle, to measure T$_{rm eff}$ for many dwarf stars in eclipsing binaries. We aim to develop a method that uses high-precision measurements of detached eclipsing binary stars, Gaia parallaxes and multi-wavelength photometry to obtain accurate and precise fundamental effective temperatures that can be used to establish a set of benchmark stars. We select the well-studied binary AI Phoenicis to test our method, since it has very precise absolute parameters and extensive archival photometry. The method uses the stellar radii and parallax for stars in eclipsing binaries. We use a Bayesian approach to obtain the integrated bolometric fluxes for the two stars from observed magnitudes, colours and flux ratios. The fundamental effective temperature of two stars in AI Phoenicis are $6199pm22$ K for the F7V component and $5094pm16$ K for the K0IV component. The zero-point error in the flux scale leads to a systematic error of only 0.2% ($approx$ 11K) in T$_{rm eff}$. We find that these results are robust against the details of the analysis, such as the choice of model spectra. Our method can be applied to eclipsing binary stars with radius, parallax and photometric measurements across a range of wavelengths. Stars with fundamental effective temperatures determined with this method can be used as benchmarks in future surveys.
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$zeta$ Phoenicis is a bright binary system containing B6V and B8V stars. It has deep total and annular eclipses, a slightly eccentric orbit with a period of 1.669 d, apsidal motion and a third body on a wider orbit. The Transiting Exoplanet Survey Satellite light curve and published radial velocities of this system are analysed to determine masses of 3.91 +/- 0.06 Msun and 2.54 +/- 0.03 Msun and radii of 2.84 +/- 0.02 Rsun and 1.89 +/- 0.01 Rsun. The resulting distance to the system is in agreement with its trigonometric parallax. The physical properties of the stars, with the exception of the effective temperature of the secondary component, can be matched by the predictions of several sets of theoretical stellar evolutionary models for a solar chemical composition and an age of 70 to 90 Myr. A spectroscopic analysis of this system is encouraged for the determination of the photospheric chemical composition of the stars, plus improved measurements of their masses and effective temperatures.
Accurate masses and radii for normal stars derived from observations of detached eclipsing binary stars are of fundamental importance for testing stellar models and may be useful for calibrating free parameters in these model if the masses and radii are sufficiently precise and accurate. We aim to measure precise masses and radii for the stars in the bright eclipsing binary AI Phe, and to quantify the level of systematic error in these estimates. We use several different methods to model the TESS light curve of AI Phe combined with spectroscopic orbits from multiple sources to estimate precisely the stellar masses and radii together with robust error estimates. We find that the agreement between different methods for the light curve analysis is very good but some methods underestimate the errors on the model parameters. The semi-amplitudes of the spectroscopic orbits derived from spectra obtained with modern echelle spectrographs are consistent to within 0.1%. The masses of the stars in AI Phe are $M_1 = 1.1938 pm 0.0008 M_{odot}$ and $M_2 = 1.2438 pm 0.0008M_{odot}$, and the radii are $R_1 = 1.8050 pm 0.0022 R_{odot}$ and $R_2 = 2.9332 pm 0.0023 R_{odot}$. We conclude that it is possible to measure accurate masses and radii for stars in bright eclipsing binary stars to a precision of 0.2% or better using photometry from TESS and spectroscopy obtained with modern echelle spectrographs. We provide recommendations for publishing masses and radii of eclipsing binary stars at this level of precision.
The study of detached eclipsing binaries is one of the most powerful ways to investigate the properties of individual stars and stellar systems. We present preliminary masses, radii and effective temperatures for the eclipsing binary WW Aurigae, which is composed of two metallic-lined A-type stars. We also reanalyse the data on HD 23642, an A-type eclipsing binary member of the Pleiades open cluster with a metallic-lined component, and determine its distance to be 139 +/- 4 pc. This is in agreement with the traditional Pleiades distance, but in disagreement with distance to the Pleiades, and to HD 23642 itself, derived from Hipparcos trigonometrical parallaxes.
We present a detailed photometric and spectroscopic analysis of DD CMa, based on published survey photometry and new spectroscopic data. We find an improved orbital period of $P_mathrm{o}= 2.0084530 pm 0.0000006 ~mathrm{d}$. Our spectra reveal H$beta$ and H$alpha$ absorptions with weak emission shoulders and we also find color excess in the WISE multiband photometry, interpreted as signatures of circumstellar matter. We model the $V$-band orbital light curve derived from the ASAS and ASAS-SN surveys, assuming a semidetached configuration and using the mass ratio and temperature of the hotter star derived from our spectroscopic analysis. Our model indicates that the system consists of a B 2.5 dwarf and a B 9 giant of radii 3.2 and 3.7 $mathrm{R_{odot}}$, respectively, orbiting in a circular orbit of radius 6.75 $mathrm{R_{odot}}$. We also found $M_{mathrm{c}} = 1.7 pm 0.1 ~mathrm{M_{odot}}$, $T_{mathrm{c}} = 11350 pm 100 ~mathrm{K}$ and $M_{mathrm{h}} = 6.4 pm 0.1 ~mathrm{M_{odot}}$, $T_{mathrm{h}} = 20000 pm 500 ~mathrm{K}$, for the cooler and hotter star, respectively. We find broad single emission peaks in H$alpha$ and H$beta$ after subtracting the synthetic stellar spectra. Our results are consistent with mass exchange between the stars, and suggest the existence of a stream of gas being accreted onto the early B-type star.
Binary stellar systems form a large fraction of the Galaxys stars. They are useful as laboratories for studying the physical processes taking place within stars, and must be correctly taken into account when observations of stars are used to study the structure and evolution of the Galaxy. We present a sample of 12760 well-characterised double-lined spectroscopic binaries that are appropriate for statistical studies of the binary populations. They were detected as SB2s using a t-distributed stochastic neighbour embedding (t-SNE) classification and a cross-correlation analysis of GALAH spectra. This sample consists mostly of dwarfs, with a significant fraction of evolved stars and several dozen members of the giant branch. To compute parameters of the primary and secondary star ($T_{rm eff[1,2]}$, $log g_{[1,2]}$, [Fe/H], $V_{r[1,2]}$, $v_{rm mic[1,2]}$, $v_{rm broad[1,2]}$, $R_{[1,2]}$, and $E(B-V)$), we used a Bayesian approach that includes a parallax prior from Gaia DR2, spectra from GALAH, and apparent magnitudes from APASS, Gaia DR2, 2MASS, and WISE. The derived stellar properties and their distributions show trends that are expected for a population of close binaries (a $<$ 10 AU) with mass ratios $0.5 leq q leq 1$. The derived metallicity of these binary stars is statistically lower than that of single dwarf stars from the same magnitude-limited sample.
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