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JWST explores enigmatic mid-infrared rings in planetary nebula NGC 1514

Using the James Webb Space Telescope (JWST), astronomers have observed enigmatic rings in the planetary nebula NGC 1514, visible in the mid-infrared band. Results of the new observations, Feb. 28 on the arXiv pre-print server, shed more light on the properties and nature of these rings.

Planetary nebulae (PNe) are expanding shells of gas and dust that have been ejected from a star during the process of its evolution from a main sequence star into a red giant or white dwarf. They are relatively rare, but are important for astronomers studying the chemical evolution of stars and galaxies.

NGC 1514 (also known as Crystal Ball Nebula) is a large and complex elliptical planetary nebula at a distance of about 1,500 light years away. It originated from a binary star designated HD 281679. The bright, visible component of the system is a giant star of spectral type A0III, while the nebula-generating companion is now a hot, sub-luminous O-type star.

Previous observations of NGC 1514 have found that it hosts a pair of infrared-bright, axisymmetric rings lying nearly entirely within the outer shell of the nebula. The rings, dubbed R10, have a diameter of 0.65–1.3 light years and showcase a unique morphology. They are only prominent in the mid-infrared and still very little is known regarding their properties.

That is why a team of astronomers led by Michael E. Ressler of NASA's Jet Propulsion Laboratory (JPL) decided to investigate these mysterious rings with JWST's Mid-Infrared Instrument (MIRI).

"We therefore chose to investigate NGC 1514's rings in more detail using the MidInfrared Instrument on JWST, both through high-spatial-resolution imaging and through spatially resolved medium-resolution spectroscopy where the rings are most prominent," the researchers wrote in the paper.

The observations revealed a wealth of turbulent features in the rings; however, despite that, they still appear as relatively cohesive structures. In the new images, the rings turned out to be very bright with respect to the inner shell of the nebula.

Furthermore, the observations found the existence of faint emission extending outside the ring boundaries at all wavelengths. The astronomers suppose that this is an ejecta from earlier, less intense outflow activity or from later higher-velocity winds that have passed through the rings.

According to the paper, the rings of NGC 1514 appear to be purely dust emission. The color temperature of the ring material was estimated to be 110–200 K.

Trying to explain the origin of the investigated rings, the authors of the study conclude that they were likely formed from material ejected in a slow, heavy mass loss phase from the planetary nebula progenitor. Afterward, they were shaped by faster winds that created the rest of the optically visible nebula.