The TESS light curve of AI Phoenicis

Abstract

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 échelle spectrographs are consistent to within 0.1%. The masses of the stars in AI Phe are $M_1 = 1.1938 \pm 0.0008\, \rm M_{\odot }$ and $M_2 = 1.2438 \pm 0.0008\, \rm M_{\odot }$, and the radii are $R_1 = 1.8050 \pm 0.0022\, \rm R_{\odot }$ and $R_2 = 2.9332 \pm 0.0023\, \rm R_{\odot }$. 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 échelle spectrographs. We provide recommendations for publishing masses and radii of eclipsing binary stars at this level of precision.

SPInS, a pipeline for massive stellar parameter inference

“…Then, using these masses and radii, effective temperatures and metallicity from the literature together with stellar evolution models, they estimated the age of the system to be A = 4.39 ± 0.32 Gyr. Recently, Maxted et al (2020) revisited the masses and radii on the basis of the light-curves provided by the TESS mission (Ricker et al 2015).…”

Consequences of parameterization choice on eclipsing binary light curve solutions

“…For the purpose of this paper, we use the soon to be released version 2.3 of PHOEBE to try and reproduce the results from the article by Maxted et al (2020), which examines a number of various methods to accurately estimate the masses and radii for the stars in the binary system AI Phoenicis (AI Phe). This system, which contains two well-separated, sharp-lined stars of comparable luminosity, was first identified as an EB by Strohmeier (1972).…”

“…This system, which contains two well-separated, sharp-lined stars of comparable luminosity, was first identified as an EB by Strohmeier (1972). It is an excellent target for model testing as it is relatively bright (V = 8.6 mag), has a long orbital period (P ≈ 24.59 days), and does not show any distinct spots nor flares associated with increased magnetic activity of the components (e.g., Kirkby-Kent et al, 2016;Maxted et al, 2020).…”

“…To compare the results by Maxted et al (2020), we first carried out a number of runs with varying underlying physical models, free parameters, and their initial values (see Section 2). This further motivated us to design a controlled experiment in order to systematically analyze the effect of parameterization choice on the final light curve resulting from the model (Section 3).…”

Orbital and physical parameters of eclipsing binaries from the ASAS catalogue – XI. CHIRON investigation of long-period binaries

“…The most valuable systems providing stringent tests of theoretical stellar evolutionary models are those with components in different phases of evolution. Literature quotes only a few, including the extensively studied AI Phe (Torres et al 2010;Maxted et al 2020) and TZ For (Higl et al 2018). Evolved systems can be also used to test the absolute calibration of the surface brightness-colour relation for late-type stars (Gallenne et al 2016).…”