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We report the discovery of a detached double white dwarf binary with an orbital period of 20.6 minutes, PTF J053332.05+020911.6. The visible object in this binary, PTF J0533+0209B, is a 0.17 M, K.B.B. thanks the National Aeronautics and Space Administration and the Heising-Simons Foundation for supporting his research. J.F. acknowledges support from an Innovator grant from The Rose Hills Foundation and the Sloan Foundation through grant FG-2018-10515. The KPED team thanks the National Science Foundation and the National Optical Astronomical Observatory for making the Kitt Peak 2.1 m telescope available. The KPED team thanks the National Science Foundation, the National Optical Astronomical Observatory and the Murty family for support in the building and operation of KPED. In addition, they thank the CHIMERA project for use of the Electron Multiplying CCD (EMCCD). Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The research leading to these results has received funding from the European Research Council under the European Unions Horizon 2020 research and innovation program n.677706 (WD3D) This research benefited from interactions at the ZTF Theory Network Meeting that were funded by the Gordon and Betty Moore Foundation through grant GBMF5076 and support from the National Science Foundation through PHY-1748958.

We present 12,155 new differential photometric observations in the V filter made with the Undergraduate Research Studies in Astronomy and NF\Observatory WebScopes, as well as 33 radial velocities from spectroscopic observations of the detached, 4.04 day double-lined eclipsing binary star GX Gem. Absolute dimensions of the components are determined from these new, and also from previously published, data with high precision (less than 0.7% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.488 ? 0.011 solar masses and 2.327 ? 0.012 solar radii for the primary, and 1.467 ? 0.010 solar masses and 2.238 ? 0.012 solar radii for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from the spectra, uvby?, and UBV photometry: 6195 ? 100 K for the primary, 6165 ? 100 K for the secondary, corresponding to spectral types of F7 and F7 V, and 0.068 mag for the color excess Eb ? y . Spectral line widths give rotational velocities that are synchronous with the mean orbital motion in a circular orbit. The components of GX Gem are relatively old main-sequence stars with an age of about 2.8 billion years according to models. Because the components are located right at the end of their main-sequence evolutionary paths, we can place good limits on the convective core overshooting parameter. The lowest value of ?ov consistent with the observations would appear to be approximately ?ov = 0.18. Two different theories of tidal synchronization and circularization agree that the components should be synchronously rotating, but disagree about whether or not the orbits should be circular.

We present 6907 differential photometric observations in the V filter, as well as 52 radial velocities from spectroscopic observations of the detached, eccentric 7.97 day double-lined eclipsing binary star EY Cep. Absolute dimensions of the components are determined with high precision (less than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.523 ± 0.008 M⊙ and 1.463 ± 0.010 R⊙ for the primary and 1.498 ± 0.014 M⊙ and 1.468 ± 0.010 R⊙ for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from the spectra, uvbyβ, and UBV photometry: 7090 ± 150 K for the primary and 6970 ± 150 K for the secondary, corresponding to spectral types of F0 and F0, and 0.036 mag for the color excess Eb-y. Spectral line widths give rotational velocities that are synchronous with the mean orbital motion in a highly eccentric orbit (e = 0.4429). The components of EY Cep are young main-sequence stars with an age of about 40 million years, according to models.

We present 3004 differential observations in the V bandpass measured by a robotic telescope, as well as 36 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, eccentric, EA-type, 10.37 day period, double-lined eclipsing binary star RW Lac. Absolute dimensions of the components are determined with excellent precision (better than 0.7% in the masses and 0.5% in the radii) for the purpose of testing various aspects of theoretical modeling. We obtain 0.928 ± 0.006 M⊙ and 1.186 ± 0.004 R⊙ for the hotter, larger, more massive, and more luminous photometric primary (star A) and 0.870 ± 0.004 M⊙ and 0.964 ± 0.004 R⊙ for the cooler, smaller, less massive, and less luminous photometric secondary (star B). A faint, third component contributes 2.6% of the light in V but is not detected in our spectrograms. The effective temperatures and interstellar reddening of the stars are accurately determined from UBV and uvbyβ photometry and from analysis of the spectrograms: 5760 ± 100 K for the primary and 5560 ± 150 K for the secondary, corresponding to spectral types of G5 and G7, and 0.050 mag for interstellar reddening Eb-y. The orbits are slightly eccentric, and spectral line widths give observed rotational velocities that are not significantly different from synchronous for both components. The components of RW Lac are old, somewhat metal-deficient, low-mass, main-sequence stars with an age of about 11 Gyr, according to models.

We present 6450 differential observations in the V filter measured by a robotic telescope, as well as 28 pairs of radial velocities from high-resolution spectroscopic observations of the detached EA-type, 5.505 day period, double-lined eclipsing binary star V396 Cas. Absolute dimensions of the components are determined with good precision (better than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 2.398 ± 0.022 M⊙ and 2.592 ± 0.013 R⊙ for the hotter, larger, more massive and more luminous photometric primary (star A), and 1.901 ± 0.016 M⊙ and 1.779 ± 0.010 R⊙ for the cooler, smaller, less massive and less luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 9225 ± 150 K for the primary and 8550 ± 120 K for the secondary, corresponding to spectral types of A1 and A3, and 0.119 mag for Eb-y. The metallicity of the stars appears to be significantly less than solar. The stars are located at a distance of about 560 pc near the plane of the Galactic disk. The orbits of the stars are apparently circular, and spectral line widths give observed rotational velocities that are not synchronous with the orbital motion for both components. The components of V396 Cas are main-sequence stars with an age of about 420 Myr according to models.

We present 6151 differential observations in the V filter measured by a robotic telescope, as well as 29 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EA-type, 9.65 day period double-lined eclipsing binary star MU Cas. Absolute dimensions of the components are determined with good precision (better than 2% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 4.57 ? 0.09 M? and 3.67 ? 0.04 R? for the hotter, but smaller, less massive and less luminous photometric primary (star A), and 4.66 ? 0.10 M? and 4.19 ? 0.05 R? for the cooler, larger, more massive and more luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvby? photometry: 15,100 ? 500 K for the primary, 14,750 ? 500 K for the secondary?corresponding to spectral types of B5 and B5?and 0.356 mag for Eb-y. The stars are located at a distance of about 1.7 kpc near the plane of the Galactic disk. The orbits of the stars are eccentric, and spectral line widths give observed rotational velocities that are synchronous with the mean orbital motion for both components. The components of MU Cas are upper main-sequence stars with an age of about 65 Myr according to models.

We present 4179 differential observations in the V filter measured by a robotic telescope, as well as 25 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EB-type, 1.69 day period double-lined eclipsing binary star V885 Cyg. Absolute dimensions of the components are determined with high precision (better than 1.5% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 2.005 ± 0.029 M⊙ and 2.345 ± 0.012 R⊙ for the hotter, but smaller, less massive and less luminous photometric primary (star A), and 2.234 ± 0.026 M⊙ and 3.385 ± 0.026 R⊙ for the cooler, larger, more massive and more luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 8375 ± 150 K for the primary, 8150 ± 150 K for the secondary—corresponding to spectral types of A3m and A4m—and 0.058 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvbyβ photometry. The orbits are circular, and spectral line widths give observed rotational velocities that are synchronous with the orbital motion for both components. The components of V885 Cyg are main-sequence stars with an age of about 500 Myr according to models. Our estimate of the age of this system would seem to favor the hydrodynamic damping formalism of Tassoul & Tassoul in this particular case, since both the components' spins are synchronous and the orbit is circular.

We present 5064 differential observations in the V filter measured by a robotic telescope, as well as 30 pairs of radial velocities from high-resolution spectroscopic observations, of the detached, EA-type, 8.46 day period double-lined eclipsing binary star V459 Cas. Absolute dimensions of the components are determined with good precision (better than 1.6% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 2.02 ± 0.03 M⊙ and 2.009 ± 0.013 R⊙ for the hotter, larger, more massive and more luminous photometric primary (star A), and 1.96 ± 0.03 M⊙ and 1.965 ± 0.013 R⊙ for the cooler, smaller, less massive and less luminous photometric secondary (star B). The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 9140 ± 300 K for the primary, 9100 ± 300 K for the secondary—corresponding to spectral types of A1—and 0.186 mag for Eb-y. The orbits are eccentric, and spectral line widths give observed rotational velocities that are much faster than synchronous for both components. The components of V459 Cas are main-sequence stars with an age of about 525 Myr according to models.

We present 5236 differential observations in the V filter measured by a robotic telescope, as well as radial velocities from spectroscopic observations, of the detached, eccentric 1.9 day double-lined eclipsing binary star BP Vul. Absolute dimensions of the components are determined with high precision (better than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.737 ± 0.015 M⊙ and 1.852 ± 0.014 R⊙ for the primary, and 1.408 ± 0.009 M⊙ and 1.489 ± 0.014 R⊙ for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from uvbyβ photometry: 7700 ± 150 K for the primary, 6800 ± 150 K for the secondary—corresponding to spectral types of A7m and F2m—and 0.022 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvbyβ photometry. Spectral line widths give rotational velocities that are synchronous with the orbital motion for the secondary component, but subsynchronous for the primary component, in a slightly eccentric orbit (e = 0.0345). Apsidal motion based on times of minimum light appears to be negative with a period of about 75 years based on recent observations of minima, but this result is not confirmed by the radial velocity measurements, and it is indeterminate when older photographic and visual data are included. The components of BP Vul are main-sequence stars with an age of about 1 Gyr according to models.

We present absolute photometric observations in uvby? and 5759 differential observations in the V filter (the most complete light curve ever obtained) measured by a robotic telescope, as well as radial velocities from spectroscopic observations of the detached, eccentric, 2.3 day, double-lined, eclipsing binary star WW Camelopardalis. Absolute dimensions of the components are determined with high precision (better than 1% in the masses and radii) for the purpose of testing various aspects of theoretical modeling. We obtain 1.920 ? 0.013 M? and 1.911 ? 0.016 R? for the primary, and 1.873 ? 0.018 M? and 1.808 ? 0.014 R? for the secondary. The effective temperatures and interstellar reddening of the stars are accurately determined from new uvby? photometry: 8350 ? 135 K for the primary and 8240 ? 135 K for the secondary, corresponding to a spectral type of A4m for both, and 0.294 mag for Eb-y. The metallic-lined character of the stars is revealed by high-resolution spectroscopy and uvby? photometry. Spectral line widths give rotational velocities that are synchronous with the orbital motion in a slightly eccentric orbit (e = 0.0098). The components of WW Cam are main-sequence stars with an age of about 490 Myr according to models.

We present photometric observations in B and V as well as spectroscopic observations of the 1.9 day¨ period, double-lined main-sequence eclipsing binary FS Mon. From the analysis of the light curves and radial velocity curves, we have determined the masses and radii of the components: 1.631 ^ 0.012 M _ and 2.051 ^ 0.012 for the primary component; 1.461 ^ 0.010 and 1.629 ^ 0.012 for the sec- R _ M _ R _ ondary component. The formal uncertainties are all less than 1%. Based on our light curves as well as on the combined-light photometry of the system, we estimate eUective temperatures of 6715 ^ 100 K for the primary and 6550 ^ 100 K for the secondary component, corresponding to spectral types of F2 and F4, respectively. Projected rotational velocities (v sin i) from the spectograms are measured as 52 ^ 2k m s~1 and 43 ^ 3k m s~1, respectively, from the spectrograms and are consistent with rotation that is synchronous with the orbital motion. Evolutionary tracks from current models are in good agreement with the observations for a system age of about 1.6 ) 109 yr with slightly nonsolar chemical composi- tion. We —nd the best match for models with a slightly lower helium abundance and a higher metal abundance than the Sun. An accurate metallicity determination for FS Mon is needed to constrain the models further.

We present photoelectric observations in B and V, as well as spectroscopic observations of the 7.3 day period double-lined eclipsing binary V364 Lacertae. From the analysis of the light curves and the radial velocity curves we have determined the absolute dimensions of the components with high precision (1%). The masses for the primary and secondary are MA = 2.333 ± 0.015 M⊙ and MB = 2.296 ± 0.025 M⊙, respectively, and the radii are RA = 3.307 ± 0.038 R⊙ and RB = 2.985 ± 0.035 R⊙. We derive also effective temperatures of T = 8250 ± 150 K and T = 8500 ± 150 K, and projected rotational velocities of vA sin i = 45 ± 1 km s-1 and vB sin i = 15 ± 1 km s-1. Evolutionary tracks from current stellar evolution models are in good agreement with the observations for a system age of log t = 8.792 (6.2 × 108 yr) and for solar metallicity. Hints of a lower metallicity from spectroscopy and photometry appear to be ruled out by these models, but a definitive comparison must await a more accurate spectroscopic abundance determination. Analysis of all available eclipse timings along with our radial velocities of this moderately eccentric system (e = 0.2873 ± 0.0014) has revealed a small but significant motion of the line of apsides of = 0.00258 ± 0.00033 deg cycle-1, corresponding to an apsidal period of U = 2810 ± 360 yr. The contribution from general relativity effects is significant (~17%). A comparison with predictions from interior structure models shows the real stars to be less concentrated in mass than expected. Our measurements of the projected rotational velocities indicate that the primary star is essentially pseudosynchronized (synchronized at periastron), while the secondary is spinning 3 times more slowly and is not yet synchronized. Both the rotational status of the stars and the nonzero eccentricity of the orbit are consistent with the predictions from tidal theory, specifically for the radiative damping mechanism.

CF Tau is now known to be an eclipsing triple star with relatively deep total and annular eclipses. New light and radial velocity curves as well as new times of minima were obtained and used for further modeling of the system. Very accurate (better than 0.9%) masses and radii of the eclipsing pair are determined from analysis of the two new light curves, the radial velocity curve, and the times of minimum light. The mass and luminosity of the distant third component is accurately determined as well. Theoretical models of the detached, evolved eclipsing pair match the observed absolute properties of the stars at an age of about 4.3 Gy and [Fe/H] = -0.14.

V335 Ser is now known to be an eccentric double-lined A1+A3 binary star with fairly deep (0.5 mag) partial eclipses. Previous studies of the system are improved with 7456 differential photometric observations from the URSA WebScope and 5666 from the NFO WebScope, and 67 high-resolution spectroscopic observations from the Tennessee State University 2 m automatic spectroscopic telescope. From dates of minima, the apsidal period is about 880 years. Accurate (better than 2%) masses and radii are determined from analysis of the two new light curves and the radial velocity curve. Theoretical models match the absolute properties of the stars at an age of about 380 Myr, though the age agreement for the two components is poor. Tidal theory correctly confirms that the orbit should still be eccentric, but we find that standard tidal theory is unable to match the observed asynchronous rotation rates of the components' surface layers.

BF?Dra is now known to be an eccentric double-lined F6+F6 binary star with relatively deep (0.7?mag) partial eclipses. Previous studies of the system are improved with 7494 differential photometric observations from the URSA WebScope and 9700 from the NFO WebScope, 106 high-resolution spectroscopic observations from the Tennessee State University 2?m automatic spectroscopic telescope and the 1?m coud?-feed spectrometer at Kitt Peak National Observatory, and 31 accurate radial velocities from the CfA. Very accurate (better than 0.6%) masses and radii are determined from analysis of the two new light curves and four radial velocity curves. Theoretical models match the absolute properties of the stars at an age of about 2.72?Gyr and [Fe/H] = ?0.17, and tidal theory correctly confirms that the orbit should still be eccentric. Our observations of BF?Dra constrain the convective core overshooting parameter to be larger than about 0.13 Hp . We find, however, that standard tidal theory is unable to match the observed slow rotation rates of the components' surface layers.

WOS: 000290518500022, Accurate absolute properties are determined for the first time for the 3.15 day period eccentric eclipsing binary star FT Ori based on new absolute photometry, five differential light curves, and a radial velocity curve. The stars appear to be normal for their spectral types, A0 + A2. The orbit is highly eccentric (e = 0.409) and shows apsidal motion with a period of 536 years. The absolute properties and the degree of central mass concentration of the stars are consistent with current theoretical models at an age of 190 Myr.