in binaries [1][2][3] . If the orbital period of the binary is short enough, energy losses from gravitational wave radiation can shrink the orbit until the two white dwarfs come into contact and merge 4 . Depending on the masses of the coalescing white dwarfs, the merger can lead to a supernova of type Ia, or it can give birth to a massive white dwarf 5 . In the latter case, the white dwarf remnant is expected to be highly magnetised 6,7 due to the strong dynamo that may arise during the merger, and rapidly rotating due to conservation of the orbital angular momentum of the binary 8 . Here we report the discovery of a white dwarf, ZTF J190132.9+145808.7, which presents all these properties, but to an extreme: a rotation period of 6.94 minutes, one of the shortest measured for an isolated white dwarf 9, 10 , a magnetic field ranging between 600 MG and 900 MG over its surface, one of the highest fields ever detected on a white dwarf 11 , and a stellar radius of 1810 km, slightly larger than the radius of the Moon. Such a small radius implies the star's mass is the closest ever detected to the white dwarf maximum mass, or Chandrasekhar mass 12 . In fact, as the white dwarf cools and its composition stratifies, it may become unstable and collapse due to electron capture, exploding into a thermonuclear supernova or collapsing into a neutron star. Neutron stars born in this fashion could account for ∼10% of their total population.The Zwicky Transient Facility [13][14][15] (ZTF) is a synoptic optical survey that uses the 48-inch Samuel Oschin Telescope of the Palomar Observatory to image the Northern sky on a regular basis.We discovered ZTF J190132.9+145808.7 (hereafter ZTF J1901+1458) during a search for fast variability in massive white dwarfs. To this end, we selected objects in a white dwarf catalogue 16 that lie below the main white dwarf cooling sequence in the Gaia 17 color-magnitude diagram (CMD,

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Heartbeat stars are eccentric (e > 0.2) ellipsoidal variables whose light curves resemble a cardiogram. We present the observations and corresponding model of KIC 3749404, a highly eccentric (e = 0.66), short period (P = 20.3 d) heartbeat star with tidally induced pulsations. A binary star model was created using phoebe, which we modified to include tidally induced pulsations and Doppler boosting. The morphology of the photometric periastron variation (heartbeat) depends strongly on the eccentricity, inclination and argument of periastron. We show that the inclusion of tidally induced pulsations in the model significantly changes the parameter values, specifically the inclination and those parameters dependent on it. Furthermore, we determine the rate of apsidal advance by modelling the periastron variation at the beginning and end of the 4-yr Kepler data set and dividing by the elapsed time. We compare the model with the theoretical expectations for classical and general relativistic apsidal motion and find the observed rate to be two orders of magnitude greater than the theoretical rate. We find that the observed rate cannot be explained by tidally induced pulsations alone and consequently hypothesise the presence of a third body in the system.

The control of military aircraft propulsion and associated aircraft systems continue to become more demanding, in response to the operational needs of new and existing aircraft and missions. High performance aircraft operate in multiple modes. They are complex and require complex propulsion systems that provide precise and repeatable performance: safely, dependably, and cost effectively. To support these requirements, propulsion control systems must manage multiple effectors based on multiple operating parameters through interactive processes. The scopes of control extends beyond the gas turbine engine to the inlet, exhaust, power and bleed extraction, electrical power systems, thermal & environmental management, fuel systems, starting, accessories, and often propellers, rotors or lift fans. Modern propulsion control systems are increasingly integrated with the aircraft flight controls and the distinction is becoming less & less meaningful. Within the gas turbine, variable geometry and active control of turbo-machinery and auxiliary systems proliferate to relax mechanical design constraints and enable designs with increased thrust to weight ratios, reduced fuel burn and increased durability. Digital controls provide crisp and repeatable responses and improve aircraft reliability and availability, but further enhancements are needed as military aircraft become more capable and versatile (e.g., V-22 and F35). The control system must be aware and appropriately respond to component degradation and damage, optimally managing conflicting constraints and goals. Modern propulsion systems are becoming more profoundly multivariable and include multiple effectors to meet multiple goals. They are multivariable because they are cross-coupled, where each effector can affect multiple goals. In addition, these multiple goals, (e.g., performance, life, operating margin) may be conflicting and need to be traded off, and the best trade off will vary with mission. With predictable and rapid increases in computational capability in Full Authority Digital Electronic Controls, the industry is moving forward to address these needs through model based control, control that manages propulsion and aircraft systems with optimal control responses derived from detailed real time models of component behavior. Since the component characteristics change significantly during a service interval, and yet longer time on wing is necessary, these control systems must sense degradation and damage to multiple components and adapt to it. This paper describes current approaches and NAVAIR plans to develop, mature and deploy this technology, while touching on other potential applications.