EF Eridani

EF Eridani (abbreviated EF Eri, sometimes incorrectly referred to as EF Eridanus) is a variable star of the type known as polars, AM Herculis stars, or magnetic cataclysmic variable stars. Historically it has varied between apparent magnitudes 14.5 and 17.3, although since 1995 it has generally remained at the lower limit. The star system consists of a white dwarf with a substellar-mass former star in orbit.

EF Eridani

Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Eridanus
Right ascension  03h 14m 13.03s[1]
Declination −22° 35′ 41.4″[1]
Apparent magnitude (V) 14.5–17.3[2]
Characteristics
Variable type E+XM[2]
Astrometry
Radial velocity (Rv)70[1] km/s
Distance300[3] ly
Other designations
GSC 6439.00120, X 03116-227[2]
Database references
SIMBADdata

EF Eridani B

The substellar mass in orbit around the white dwarf is a star that lost all of its gas to the white dwarf. What remains is an object with a mass of 0.05 solar masses (M☉), which is too small to continue fusion, and does not have the composition of a super-planet, brown dwarf, or white dwarf. There is no category for such a stellar remnant.[4]

It is theorized that 500 million years ago, the white dwarf started to cannibalize its partner, when they were separated by 7 million km. As it lost mass, the regular star spiralled inward, until now they are separated by a mere 700,000 km.[4]

Another former star orbits the pulsar PSR J1719-1438.[5]

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See also
  • AM Herculis
  • Cataclysmic variable star
  • Polar (cataclysmic variable)
  • Variable stars
  • Stellar remnants
  • PSR J1719-1438 b, a planetary-mass former star that was eroded by its binary star partner, PSR J1719-1438

References
  1. "V* EF Eri – Nova-like Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2009-12-17.
  2. "Query= EF Eri". General Catalogue of Variable Stars. Centre de Données astronomiques de Strasbourg. Retrieved 2009-12-17.
  3. Mystery Object Neither Star Nor Brown Dwarf
  4. Beuermann, K.; Wheatley, P.; Ramsay, G.; Euchner, F.; Gänsicke, B. T. (February 2000). "Evidence for a substellar secondary in the magnetic cataclysmic binary EF Eridani". Astronomy and Astrophysics Letters. 354: L49–L52. arXiv:astro-ph/0001183. Bibcode:2000A&A...354L..49B.
  5. Bailes, M.; Bates, S. D.; Bhalerao, V.; et al. (2011). "Transformation of a Star into a Planet in a Millisecond Pulsar Binary". Science. 333 (6050): 1717–1720. arXiv:1108.5201. Bibcode:2011Sci...333.1717B. doi:10.1126/science.1208890. PMID 21868629.
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