Abell 35 Explained

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.^[1] In the centre of the nebula lies a binary star, composed of a G-type star and a white dwarf.^[2] 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.^{[1] [3]}

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.^[4] The star is estimated to have a radius of 1.5–3.5, indicating it is a subgiant star. It's projected rotational velocity is 55 ± 10 km/s, indicating it is rotating fast.^[5] 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.^[6]

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.^[7] Its effective temperature is estimated to be about 80,000 Kelvin and its mass to be 0.48, too low to form a planetary nebula.^[1] Using the Hubble Space Telescope, the separation of the two stars was estimated to be between 0.08 and 0.14 arcseconds in 1998.^[8]

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.^[9]

Notes and References

1. Ziegler . M. . Rauch . T. . Werner . K. . Köppen . J. . Kruk . J. W. . BD–22°3467, a DAO-type star exciting the nebula Abell 35 . Astronomy & Astrophysics . December 2012 . 548 . A109 . 10.1051/0004-6361/201219536. 1210.7614 .
2. Herald . J. E. . Bianchi . L. . The Binary Central Star of the Planetary Nebula A35 . The Astrophysical Journal . 20 November 2002 . 580 . 1 . 434–446 . 10.1086/343034.
3. Frew . David J. . Parker . Quentin A. . Planetary Nebulae: Observational Properties, Mimics and Diagnostics . Publications of the Astronomical Society of Australia . 2010 . 27 . 2 . 129–148 . 10.1071/AS09040 . 1002.1525 .
4. Jacoby . G. H. . The peculiar planetary nebula Abell 35 . The Astrophysical Journal . March 1981 . 244 . 903 . 10.1086/158765.
5. Thevenin . F. . Jasniewicz . G. . Barium-rich G stars in the nuclei of the planetary nebulae Abell 35 and LoTr5. . Astronomy and Astrophysics . 1 April 1997 . 320 . 913–919 . 1997A&A...320..913T . 0004-6361.
6. Gatti . A. A. . Drew . J. E. . Lumsden . S. . Marsh . T. . Moran . C. . Stetson . P. . A radial velocity study of the companion to the central star of Abell 35 . Monthly Notices of the Royal Astronomical Society . 11 November 1997 . 291 . 4 . 773–779 . 10.1093/mnras/291.4.773. free .
7. Grewing . M. . Bianchi . Luciana . The nucleus of Abell 35: a hot companion to SAO 181201 . ESA, Proceedings of the Celebratory Symposium on a Decade of UV Astronomy with the IUE Satellite . 1 June 1988 . 2 . 177–178 . 1988ESASP.281b.177G .
8. Gatti . A. A. . Drew . J. E. . Oudmaijer . R. D. . Marsh . T. R. . Lynas-Gray . A. E. . The separation of the stars in the binary nucleus of the planetary nebula Abell 35 . Monthly Notices of the Royal Astronomical Society . December 1998 . 301 . 2 . L33–L37 . 10.1046/j.1365-8711.1998.02166.x. free . astro-ph/9809331 .
9. Bond . H. E. . Ciardullo . R. . Meakes . M. G. . The Abell 35-Type Planetary Nuclei . Planetary Nebulae: Proceedings of the 155 Symposium of the International Astronomical Union; Held in Innsbruck; Austria; July 13–17; 1992 . 1 January 1993 . 155 . 397 . 1993IAUS..155..397B .