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Black hole binary systems with companion stars are typically found via their x-ray emission, generated by interaction and accretion. Noninteracting binaries are expected to be plentiful in the Galaxy but must be observed using other methods. We combine radial velocity and photometric variability data to show that the bright, rapidly rotating giant star 2MASS J05215658+4359220 is in a binary system with a massive unseen companion. The system has an orbital period of ~83 days and near-zero eccentricity. The photometric variability period of the giant is consistent with the orbital period, indicating star spots and tidal synchronization. Constraints on the giant’s mass and radius imply that the unseen companion is 3.3 − 0.7 + 2.8 solar masses, indicating that it is a noninteracting low-mass black hole or an unexpectedly massive neutron star.

The atmospheres of white dwarfs often contain elements heavier than helium, even though these elements would be expected to settle into the stars’ interiors; observations of the white dwarf WD 1145+017 suggest that disintegrating rocky bodies are orbiting the star, perhaps contributing heavy elements to its atmosphere. A disintegrating planet orbiting a faded white dwarf The atmospheres of white dwarfs often contain elements heavier than helium, even though such elements would be expected to settle into the stars' interiors once they have exhausted their nuclear fuel. Heavy-element abundance ratios in such atmospheres are similar to those of rocky bodies in the Solar System, suggesting that the 'extra' elements may derive from planetary material. This paper presents observations of one or more disintegrating planetesimals in transit across the white dwarf WD 1145+017, with periods ranging from 4.5 to 4.9 hours. The strongest transit signals, occurring every 4.5 hours, are indicative of a small object with a cometary tail of dusty effluent material. This system provides further evidence that the pollution of white dwarfs by heavy elements might originate from disrupted rocky bodies such as asteroids and minor planets. Most stars become white dwarfs after they have exhausted their nuclear fuel (the Sun will be one such). Between one-quarter and one-half of white dwarfs have elements heavier than helium in their atmospheres 1 , 2 , even though these elements ought to sink rapidly into the stellar interiors (unless they are occasionally replenished) 3 , 4 , 5 . The abundance ratios of heavy elements in the atmospheres of white dwarfs are similar to the ratios in rocky bodies in the Solar System 6 , 7 . This fact, together with the existence of warm, dusty debris disks 8 , 9 , 10 , 11 , 12 , 13 surrounding about four per cent of white dwarfs 14 , 15 , 16 , suggests that rocky debris from the planetary systems of white-dwarf progenitors occasionally pollutes the atmospheres of the stars 17 . The total accreted mass of this debris is sometimes comparable to the mass of large asteroids in the Solar System 1 . However, rocky, disintegrating bodies around a white dwarf have not yet been observed. Here we report observations of a white dwarf—WD 1145+017—being transited by at least one, and probably several, disintegrating planetesimals, with periods ranging from 4.5 hours to 4.9 hours. The strongest transit signals occur every 4.5 hours and exhibit varying depths (blocking up to 40 per cent of the star’s brightness) and asymmetric profiles, indicative of a small object with a cometary tail of dusty effluent material. The star has a dusty debris disk, and the star’s spectrum shows prominent lines from heavy elements such as magnesium, aluminium, silicon, calcium, iron, and nickel. This system provides further evidence that the pollution of white dwarfs by heavy elements might originate from disrupted rocky bodies such as asteroids and minor planets.

The interaction of a supernova with a circumstellar medium (CSM) can dramatically increase the emitted luminosity by converting kinetic energy to thermal energy. In ‘superluminous’ supernovae of type IIn—named for narrow hydrogen lines 1 in their spectra—the integrated emission can reach 2 – 6 ~10 51  erg, attainable by thermalizing most of the kinetic energy of a conventional supernova. A few transients in the centres of active galaxies have shown similar spectra and even larger energies 7 , 8 , but are difficult to distinguish from accretion onto the supermassive black hole. Here we present a new event, SN2016aps, offset from the centre of a low-mass galaxy, that radiated ≳5 × 10 51  erg, necessitating a hyper-energetic supernova explosion. We find a total (supernova ejecta + CSM) mass likely exceeding 50−100  M ⊙ , with energy ≳10 52  erg, consistent with some models of pair-instability supernovae or pulsational pair-instability supernovae—theoretically predicted thermonuclear explosions from helium cores >50  M ⊙ . Independent of the explosion mechanism, this event demonstrates the existence of extremely energetic stellar explosions, detectable at very high redshifts, and provides insight into dense CSM formation in the most massive stars. A recent supernova event, SN2016aps, must have involved an extremely energetic explosion and a very massive star, potentially indicating a pair-instability supernova or pulsational pair-instability supernova mechanism.

The giant planet KELT-9b has a dayside temperature of about 4,600 K, which is sufficiently high to dissociate molecules and to evaporate its atmosphere, owing to its hot stellar host. Hot Jupiter-like exoplanet Hot Jupiters are exoplanets that are physically similar to Jupiter, but are strongly irradiated by their host stars. Until now, the most extreme example was WASP-33b, but its atmosphere is still cool enough to contain molecules. Scott Gaudi et al . report the discovery of KELT-9b, which has a dayside temperature of about 4,600 kelvin. This is sufficiently high to dissociate molecules, so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. The atmosphere might be evaporated before the host star reaches the end of its life. The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extrasolar planets now known, only six have been found that transit hot, A-type stars (with temperatures of 7,300–10,000 kelvin), and no planets are known to transit the even hotter B-type stars. For example, WASP-33 is an A-type star with a temperature of about 7,430 kelvin, which hosts the hottest known transiting planet, WASP-33b (ref. 1 ); the planet is itself as hot as a red dwarf star of type M (ref. 2 ). WASP-33b displays a large heat differential between its dayside and nightside 2 , and is highly inflated–traits that have been linked to high insolation 3 , 4 . However, even at the temperature of its dayside, its atmosphere probably resembles the molecule-dominated atmospheres of other planets and, given the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be substantially ablated over the lifetime of its star. Here we report observations of the bright star HD 195689 (also known as KELT-9), which reveal a close-in (orbital period of about 1.48 days) transiting giant planet, KELT-9b. At approximately 10,170 kelvin, the host star is at the dividing line between stars of type A and B, and we measure the dayside temperature of KELT-9b to be about 4,600 kelvin. This is as hot as stars of stellar type K4 (ref. 5 ). The molecules in K stars are entirely dissociated, and so the primary sources of opacity in the dayside atmosphere of KELT-9b are probably atomic metals. Furthermore, KELT-9b receives 700 times more extreme-ultraviolet radiation (that is, with wavelengths shorter than 91.2 nanometres) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star 6 .

This thesis further develops a suite of tools designed for calculating stellar parameters and measuring radial velocities using spectra obtained with the Tillinghast Reflector Echelle Spectrograph (TRES). The standard pipeline was designed for solar-like stars and produces a quick-look summary of stellar parameters and radial velocities. Tools external to the current pipeline have recently been developed to work with hotter or cooler stars. Integrating these tools in the current pipeline extends the capabilities of the pipeline by providing users with the most accurate and precise radial velocities and stellar parameters available for a wider range of stars. A quality flag parameter has been implemented in the stellar parameter classification code to determine the quality of results based on the known capabilities of the classification code. Radial velocities have been corrected to an absolute scale by closely monitoring and correcting for changes in nightly observations of non-variable standard star radial velocities. An additional correction is made by monitoring reflected sunlight using asteroids and daytime sky observations. A complete analysis of all TRES TESS observations have been processed to derive stellar parameters and those parameters have been uploaded and shared with a broad community of users via an exoplanet community repository called ExoFOP. A new TRES instrument front end was installed during this work. The pipeline was edited to accommodate the new changes and additional testing was done to ensure that the pipeline was producing correct results. Finally, as a step to allow ease of use of all the available tools, a TRES Pipeline Results and Analysis Guide was written to give new users a resource to use as they get started working with TRES data.

About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet 1 , 2 . All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii ( R ⊕ ), or apparently rocky planets smaller than 2  R ⊕ . Such lack of planets of intermediate size (the ‘hot Neptune desert’) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6  R ⊕ and a mass of 29  M ⊕ , firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite 3 revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0 − 2.9 + 2.7 % of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness ( V mag  = 9.8). LTT 9779 b is Neptune-sized planet rotating around its star with a period of 0.79 days and an equilibrium temperature of 2,000 K. It is not clear how it retained its atmospheric envelope, which contains ~10% of H/He, as it should have been photoevaporated by now.

We present an asteroseismic analysis of 33 solar-type stars observed in short cadence (SC) during Campaigns (C) 1-3 of the NASA K2 mission. We were able to extract both average seismic parameters and individual mode frequencies for stars with dominant frequencies up to ∼3300 Hz, and we find that data for some targets are good enough to allow for a measurement of the rotational splitting. Modeling of the extracted parameters is performed by using grid-based methods using average parameters and individual frequencies together with spectroscopic parameters. For the target selection in C3, stars were chosen as in C1 and C2 to cover a wide range in parameter space to better understand the performance and noise characteristics. For C3 we still detected oscillations in 73% of the observed stars that we proposed. Future K2 campaigns hold great promise for the study of nearby clusters and the chemical evolution and age-metallicity relation of nearby field stars in the solar neighborhood. We expect oscillations to be detected in ∼388 SC targets if the K2 mission continues until C18, which will greatly complement the ∼500 detections of solar-like oscillations made for SC targets during the nominal Kepler mission. For ∼30-40 of these, including several members of the Hyades open cluster, we furthermore expect that inference from interferometry should be possible.

In Kawahara et al. (2018) and Masuda et al. (2019), we reported the discovery of four self-lensing binaries consisting of F/G-type stars and (most likely) white dwarfs whose masses range from 0.2 to 0.6 solar masses. Here we present their updated system parameters based on new radial velocity data from the Tillinghast Reflector Echelle Spectrograph at the Fred Lawrence Whipple Observatory, and the Gaia parallaxes and spectroscopic parameters of the primary stars. We also briefly discuss the astrophysical implications of these findings.