Abell 35
Nebula located in the constellation of Hydra
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Abell 35, also known as Sh 2-313, is a nebula located in the constellation of Hydra, at a distance of 400 light years. The nebula is characterised by its unusual appearance, which features a central bow shock surrounded by symmetric emission.[2] In the centre of the nebula lies a binary star, composed of a G-type star and a white dwarf.[3] Although it is commonly referred to as a planetary nebula, it has been suggested that the nebula wasn't created by a post-AGB star shedding its outer shells but it is interstellar medium photoionised by the passing binary system, leading also to the creation of the bow shock.[2][4]
| Emission nebula | |
|---|---|
| Planetary nebula | |
| |
| Observation data: J2000.0 epoch | |
| Right ascension | 12h 53m 32.8s[1] |
| Declination | −22° 52′ 23″[1] |
| Distance | 400 ly |
| Apparent magnitude (V) | 9.69[1] |
| Apparent dimensions (V) | 12.87′[1] |
| Constellation | Hydra |
| Designations | PN G303.6+40.0, BD-22 3467, HIP 62905, SH 2-313, LW Hya |
The optical spectrum of the central star is dominated by a G8 III–IV star which travels through the interstellar medium with a transverse velocity of 150 km/s.[5] The star is estimated to have a radius of 1.5–3.5 R☉, indicating it is a subgiant star. It's projected rotational velocity is 55 ± 10 km/s, indicating it is rotating fast.[6] The star has a visual apparent magnitude of 9.6 and exhibits short term variability every 0.765 days, indicating this is its rotational period, and has the variable star designation LW Hydrae.[7]
When observed in ultraviolet wavelengths by the International Ultraviolet Explorer, a very hot companion star was discovered, which was categorised as a DAO white dwarf based on the strong absorption features of HI and He II.[8] Its effective temperature is estimated to be about 80,000 Kelvin and its mass to be 0.48 M☉, too low to form a planetary nebula.[2] Using the Hubble Space Telescope, the separation of the two stars was estimated to be between 0.08 and 0.14 arcseconds in 1998.[9]
Planetary nebulae with similar binary systems, comprising a fast rotating late-type subgiant or giant star and a very hot companion are referred to as having Abell 35-type nuclei.[10]