Rediscussion of eclipsing binaries. Paper XXVII. The totally-eclipsing system UZ Draconis

Abstract

UZ Dra is a detached and totally-eclipsing binary containing two late-F stars in a circular orbit of period 3.261 d. It has been observed by the Transiting Exoplanet Survey Satellite in 41 sectors, yielding a total of 664,809 high-quality flux measurements. We model these data and published radial velocities to determine the physical properties of the system to high precision. The masses of the stars are 1.291 +/- 0.012 Msun and 1.193 +/- 0.009 Msun, and their radii are 1.278 +/- 0.004 Rsun and 1.122 +/- 0.003 Rsun. The high precision of the radius measurements is made possible by the (previously unrecorded) total eclipses and the extraordinary amount of data available. The light curves show spot modulation at the orbital period, and both stars rotate synchronously. Our determination of the distance to the system, 185.7 +/- 2.4 pc, agrees very well with the parallax distance of 185.39 +/- 0.39 pc from Gaia DR3. The properties of the system are consistent with theoretical predictions for an age of 600 +/- 200 Myr and a slightly super-solar metallicity.

Figures (6)

• Figure 1: TESS sector 84 photometry of UZ Dra. The flux measurements have been converted to magnitude units after which the median was subtracted. The other sectors used in this work are very similar so are not plotted.
• Figure 2: jktebop best fit to the light curves of UZ Dra from TESS sector 84 for the primary eclipse (left panels) and secondary eclipse (right panels). The data are shown as filled red circles and the best fit as a light blue solid line. The residuals are shown on an enlarged scale in the lower panels.
• Figure 3: The best fit to selected photometric parameters of UZ Dra from TESS sectors 1 to 86. The times used in the plot are those presented in the next section. The errorbars are from Monte Carlo simulations.
• Figure 4: RVs of UZ Dra compared to the best fit from jktebop (solid blue lines). The RVs for star A are shown with filled symbols, and for star B with open symbols. The residuals are given in the lower panels separately for the two components. RVs from Imbert Imbert86aas are shown with green triangles, and those from L89 with dark red circles.
• Figure 5: Comparison between the observed spectrum of UZ Dra and a synthetic spectrum around the Ca ii H and K lines. The observed spectrum has been shifted to zero velocity and normalised to approximately unit flux (blue line with points). The synthetic spectrum is for $T_{\rm eff} = 6450$ K, $\log g = 4.3$ and solar metallicity from the BT-Settl model atmospheres Allard+01apjAllard++12rspta (orange line). A composite synthetic spectrum has been made by duplicating and shifting the original one to the velocities of the two components of UZ Dra then adding them using the light ratio from Table \ref{['tab:jktebop']}.