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Register a new userTIC 278956474: Two close binaries in one young quadruple system, identified by textit{TESS}
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Pamela Rowden
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We have identified a quadruple system with two close eclipsing binaries in TESS data. The object is unresolved in Gaia and appears as a single source at parallax 1.08~$pm$0.01 mas. Both binaries have observable primary and secondary eclipses and were monitored throughout TESS Cycle 1 (sectors 1-13), falling within the TESS Continuous Viewing Zone. In one eclipsing binary (P = 5.488 d), the smaller star is completely occluded by the larger star during the secondary eclipse; in the other (P = 5.674 d) both eclipses are grazing. Using these data, spectroscopy, speckle photometry, SED analysis and evolutionary stellar tracks, we have constrained the masses and radii of the four stars in the two eclipsing binaries. The Li I EW indicates an age of 10-50 Myr and, with an outer period of $858^{+7}_{-5}$ days, our analysis indicates this is one of the most compact young 2+2 quadruple systems known.
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We report the discovery of a compact, coplanar, quadruply-lined, eclipsing quadruple star system from TESS data, TIC 454140642, also known as TYC 0074-01254-1. The target was first detected in Sector 5 with 30-min cadence in Full-Frame Images and then observed in Sector 32 with 2-min cadence. The light curve exhibits two sets of primary and secondary eclipses with periods of PA = 13.624 days (binary A) and PB = 10.393 days (binary B). Analysis of archival and follow-up data shows clear eclipse-timing variations and divergent radial velocities, indicating dynamical interactions between the two binaries and confirming that they form a gravitationally-bound quadruple system with a 2+2 hierarchy. The Aa+Ab binary, Ba+Bb binary, and A-B system are aligned with respect to each other within a fraction of a degree: the respective mutual orbital inclinations are 0.25 degrees (A vs B), 0.37 degrees (A vs A-B), and 0.47 degrees (B vs A-B). The A-B system has an orbital period of 432 days - the second shortest amongst confirmed quadruple systems - and an orbital eccentricity of 0.3.
KIC 7177553 was observed by the Kepler satellite to be an eclipsing eccentric binary star system with an 18-day orbital period. Recently, an eclipse timing study of the Kepler binaries has revealed eclipse timing variations in this object with an amplitude of about 100 sec, and an outer period of 529 days. The implied mass of the third body is that of a superJupiter, but below the mass of a brown dwarf. We therefore embarked on a radial velocity study of this binary to determine its system configuration and to check the hypothesis that it hosts a giant planet. From the radial velocity measurements, it became immediately obvious that the same Kepler target contains another eccentric binary, this one with a 16.5-day orbital period. Direct imaging using adaptive optics reveals that the two binaries are separated by 0.4 arcsec (about 167 AU), and have nearly the same magnitude (to within 2%). The close angular proximity of the two binaries, and very similar Gamma velocities, strongly suggest that KIC 7177553 is one of the rare SB4 systems consisting of two eccentric binaries where at least one system is eclipsing. Both systems consist of slowly rotating, non-evolved, solar-like stars of comparable masses. From the orbital separation and the small difference in Gamma velocity, we infer that the period of the outer orbit most likely lies in the range 1000 to 3000 years. New images taken over the next few years, as well as the high-precision astrometry of the Gaia satellite mission, will allow us to set much narrower constraints on the system geometry. Finally, we note that the observed eclipse timing variations in the Kepler data cannot be produced by the second binary. Further spectroscopic observations on a longer time scale will be required to prove the existence of the massive planet.
Tidal forces are important for understanding how close binary stars and compact exoplanetary systems form and evolve. However, tides are difficult to model and significant uncertainties exist about the strength of tides. Here, we investigate tidal circularization in close binaries using a large sample of well-characterised eclipsing systems. We searched TESS photometry from the southern hemisphere for eclipsing binaries. We derive best-fit orbital and stellar parameters by jointly modelling light curves and spectral energy distributions. To determine the eccentricity distribution of eclipsing binaries over a wide range of stellar temperatures ($3,000-50,000,$K) and orbital separations $a/R_1$ ($2-300$), we combine our newly obtained TESS sample with eclipsing binaries observed from the ground and by the Kepler mission. We find a clear dependency of stellar temperature and orbital separation in the eccentricities of close binaries. We compare our observations with predictions of the equilibrium and dynamical tides. We find that while cool binaries agree with the predictions of the equilibrium tide, a large fraction of binaries with temperatures between $6,250,$K and $10,000,$K and orbital separations between $a/R_1 sim 4$ and $10$ are found on circular orbits contrary to the predictions of the dynamical tide. This suggests that some binaries with radiative envelopes may be tidally circularised significantly more efficiently than usually assumed. Our findings on orbital circularization have important implications also in the context of hot Jupiters where tides have been invoked to explain the observed difference in the spin-orbit alignment between hot and cool host stars.
We report the discovery in $TESS$ Sectors 3 and 4 of a compact triply eclipsing triple star system. TIC 209409435 is a previously unknown eclipsing binary with a period of 5.717 days, and the presence of a third star in an outer eccentric orbit of 121.872 day period was found from two sets of third-body eclipses and from eclipse timing variations. The latter exhibit signatures of strong 3rd-body perturbations. After the discovery, we obtained follow-up ground-based photometric observations of several binary eclipses as well as another of the third-body eclipses. We carried out comprehensive analyses, including the simultaneous photodynamical modelling of $TESS$ and ground-based lightcurves (including both archival WASP data, and our own follow-up measurements), as well as eclipse timing variation curves. Also, we have included in the simultaneous fits multiple star spectral energy distribution data and theoretical PARSEC stellar isochrones. We find that the inner binary consists of near twin stars of mass 0.90 $M_odot$ and radius 0.88 $R_odot$. The third star is just 9% more massive and 18% larger in radius. The inner binary has a rather small eccentricity while the outer orbit has $e = 0.40$. The inner binary and outer orbit have inclination angles within 0.1$^circ$ and 0.2$^circ$ of 90$^circ$, respectively. The mutual inclination angle is $lesssim 1/4^circ$. All of these results were obtained without radial velocity observations.
We present Keck I/OSIRIS and Keck II/NIRC2 adaptive optics imaging of two member candidates of the Praesepe stellar cluster (d=186.18$pm$0.11 pc; 590-790 Myr), UGC J08451066+2148171 (L1.5$pm$0.5) and UGCS J08301935$+$2003293 (no spectroscopic classification). We resolved UGCS J08451066$+$2148171 into a binary system in the near-infrared, with a $K$-band wavelength flux ratio of 0.89$pm$0.04, a projected separation of 60.3$pm$1.3 mas (11.2$pm$0.7 au; 1$sigma$). We also resolved UGCS J08301935$+$2003293 into a binary system with a flux ratio of 0.46$pm$0.03 and a separation of 62.5$pm$0.9 mas. Assuming zero eccentricity, we estimate minimum orbital periods of $sim$100 years for both systems. According to theoretical evolutionary models, we derive masses in the range of 0.074-0.078 M$_{odot}$ and 0.072-0.076 M$_{odot}$ for the primary and secondary of UGCS J08451066$+$2148171 for an age of 700$pm$100 Myr. In the case of UGCS J08301935$+$2003293, the primary is a low-mass star at the stellar/substellar boundary (0.070-0.078 M$_{odot}$) while the companion candidate might be a brown dwarf (0.051-0.065 M$_{odot}$). These are the first two binaries composed of L dwarfs in Praesepe. They are benchmark systems to derive the location of the substellar limit at the age and metallicity of Praesepe, determine the age of the cluster based on the lithium depletion boundary test, derive dynamical masses, and improve low-mass stellar and substellar evolutionary models at a well-known age and metallicity.
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