The star 1SWASP J024743.37−251549.2 was recently discovered to be a binary star in which an A-type dwarf star eclipses the remnant of a disrupted red giant star (WASP 0247−25 B). The remnant is in a rarely-observed state evolving to higher effective temperatures at nearly constant luminosity prior to becoming a very low-mass white dwarf composed almost entirely of helium, i.e., it is a pre-He-WD. We have used the WASP photometric database to find 17 eclipsing binary stars with orbital periods P=0.7 -2.2 d with similar lightcurves to 1SWASP J024743.37−251549.2. The only star in this group previously identified as a variable star is the brightest one, EL CVn, which we adopt as the prototype for this class of eclipsing binary star. The characteristic lightcurves of EL CVn-type stars show a total eclipse by an A-type dwarf star of a smaller, hotter star and a secondary eclipse of comparable depth to the primary eclipse. We have used new spectroscopic observations for 6 of these systems to confirm that the companions to the A-type stars in these binaries have very low masses (≈ 0.2M ⊙ ). This includes the companion to EL CVn which was not previously known to be a pre-He-WD. EL CVn-type binary star systems will enable us to study the formation of very low-mass white dwarfs in great detail, particularly in those cases where the pre-He-WD star shows non-radial pulsations similar to those recently discovered in WASP0247−25 B.

Context. One of the most promising avenues for the detailed study of temperate Earth-sized exoplanets is the detection of such planets in transit in front of stars that are small and near enough to make it possible to carry out a thorough atmospheric characterisation with next-generation telescopes, such as the James Webb Space telescope (JWST) or Extremely Large Telescope (ELT). In this context, the TRAPPIST-1 planets form a unique benchmark system that has garnered the interest of a large scientific community. Aims. The SPECULOOS survey is an exoplanet transit survey targeting a volume-limited (40 pc) sample of ultracool dwarf stars (of spectral type M7 and later) that is based on a network of robotic 1 m telescopes especially designed for this survey. The strategy for brighter and earlier targets leverages the synergy with the ongoing TESS space-based exoplanet transit survey. Methods. We define the SPECULOOS target list as the sum of three non-overlapping sub-programmes incorporating the latest type objects (T eff 3000 K). Programme 1 features 365 dwarfs that are small and near enough to make it possible to detail atmospheric characterisation of an 'Earth-like' planet with the upcoming JWST. Programme 2 features 171 dwarfs of M5-type and later for which a significant detection of a planet similar to TRAPPIST-1b should be within reach of TESS. Programme 3 features 1121 dwarfs that are later than M6-type. These programmes form the basis of our statistical census of short-period planets around ultracool dwarf stars. Results. Our compound target list includes 1657 photometrically classified late-type dwarfs, with 260 of these targets classified, for the first time, as possible nearby ultracool dwarf stars. Our general observational strategy was to monitor each target between 100 and 200 hr with our telescope network, making efficient use of the synergy with TESS for our Programme 2 targets and a proportion of targets in our Programme 1. Conclusions. Based on Monte Carlo simulations, we expect to detect up to a few dozen temperate, rocky planets. We also expect a number of them to prove amenable for atmospheric characterisation with JWST and other future giant telescopes, which will substantially improve our understanding of the planetary population of the latest-type stars.

Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. In this context, TOI-178 has been the subject of particular attention since the first TESS observations hinted at the possible presence of a near 2:3:3 resonant chain. Here we report the results of observations from CHEOPS, ESPRESSO, NGTS, and SPECULOOS with the aim of deciphering the peculiar orbital architecture of the system. We show that TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, with radii ranging from 1.152−0.070+0.073 to 2.87−0.13+0.14 Earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. All planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02−0.23+0.28 to 0.177−0.061+0.055 times the Earth’s density between planets c and d. Using Bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of Laplace resonances. The brightness of TOI-178 (H = 8.76 mag, J = 9.37 mag, V = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. The peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-Earths and mini-Neptunes.

Wastewater disposal wells in southern Texas are disproportionately permitted in areas with higher proportions of people of color and residents living in poverty, a pattern known as "environmental injustice."