Editing Helix Nebula (section)

==Central star==
[[File:HelixCentralStarLightCurve.png|thumb|left|A light curve for the Helix Nebula central star, adapted from Iskandarli et al. (2024)<ref name="Iskandarli2024"/>]]
The central star of the Helix Nebula is a [[white dwarf]] of spectral type DAO.<ref name="Iskandarli2024"/> It has the designations WD 2226-210, PHL 287, and GJ 9785.<ref name="simbad"/> The star has a radius of {{convert|0.025|solar radius|km}}, a mass of {{Solar mass|0.678}}, a temperature of 120,000 [[Kelvin]] and has an apparent magnitude of 13.5.<ref name="Iskandarli2024"/>

A mid-infrared excess suggest a disk with a size of 35 to 150 AU, formed from [[Kuiper belt|Kuiper-belt]] like objects.<ref name="Su2007"/> The size was later revised to be a ring between 30 and 100 AU. The non-detection at longer wavelengths allowed a research team to reject a series of scenarios. The researchers think the mid-IR excess comes from a replenishment of dust particles from thousands of [[exocomets]] at high eccentricities, with an origin from an [[Oort cloud]]-like structure.<ref name="Marshall2023"/>

A 2024 study hypothesized that the central star might be orbited by a planet based on periodic variations in its [[light curve]], but it cannot be ruled out that these variations are due to intrinsic stellar variability. Assuming an inclination of 25° (aligned with the nebula itself), this hypothetical planet is estimated to have a radius of {{convert|0.021|solar radius|km}}, or about 2.3 times the [[Earth radius|radius of Earth]].<ref name="Iskandarli2024"/>

Another study from 2025 found from X-ray observation that the central star may be accreting the remains of a Jupiter-like planet. This would be closer than the planet found via optical variability.<ref name="Estrada-Dorado2025"/>

{{OrbitboxPlanet begin
| table_ref = <ref name="Iskandarli2024"/><ref name="Estrada-Dorado2025"/><ref name="Marshall2023"/>
}}
{{OrbitboxPlanet hypothetical
| exoplanet = c
| mass = 1
| semimajor = 0.004
| period = 0.12
| eccentricity = 
| inclination = 
| radius_earth = 
}}
{{OrbitboxPlanet hypothetical
| exoplanet = b
| mass_earth = 
| semimajor = 0.034
| period = 2.79
| eccentricity = 
| inclination = ~25?
| radius_earth = ~2.3?
}}
{{OrbitboxPlanet disk
| disk = debris disk
| periapsis = 30
| apoapsis = 100
| inclination = <!--Inclination from the plane of the sky, in degrees-->
}}
{{Orbitbox end}}