EV Lacertae

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EV Lacertae
Nasa EV Lacertae 250408.jpg
Artist's conception of a flare explosion on EV Lacertae.
Observation data
Epoch J2000      Equinox J2000
Constellation Lacerta
Right ascension 22h 46m 49.7323s[1]
Declination +44° 20′ 02.368″[1]
Apparent magnitude (V) 10.09[2]
Spectral type M3.5[3]
U−B color index +0.83[4]
B−V color index +1.36[4]
Variable type Flare star
Radial velocity (Rv) –1.5[5] km/s
Proper motion (μ) RA: –704.65[1] mas/yr
Dec.: –459.41[1] mas/yr
Parallax (π) 198.07 ± 2.05[1] mas
Distance 16.5 ± 0.2 ly
(5.05 ± 0.05 pc)
Mass 0.35[6] M
Radius 0.36[6] R
Temperature 3,400 ± 18[7] K
Metallicity [Fe/H] –0.01 ± 0.17[7] dex
Rotation 4.376 days[8]
Rotational velocity (v sin i) 4.5[6] km/s
Other designations
GJ 873, BD+43 4305, LHS 3853, LTT 16695, HIP 112460.

EV Lacertae (EV Lac, Gliese 873, HIP 112460) is a faint red dwarf star 16.5 light years away in the constellation Lacerta. It is the nearest star to the Sun in that region of the sky, although with an apparent magnitude of 10, it is only barely visible with binoculars. EV Lacertae is spectral type M3.5 flare star that emits X-rays.[9]

On 25 April 2008, NASA's Swift satellite picked up a record-setting flare from EV Lacertae.[10] This flare was thousands of times more powerful than the largest observed solar flare. Because EV Lacertae is much farther from Earth than the Sun, the flare did not appear as bright as a solar flare. The flare would have been visible to the naked eye if the star had been in an observable part of the night sky at the time. It was the brightest flare ever seen from a star other than the Sun.

EV Lacertae is much younger than our Sun,[citation needed] and still spinning rapidly. The fast spin, together with its convective interior, produces a magnetic field that is much more powerful than the Sun's. This strong magnetic field is believed to play a role in the star's ability to produce such bright flares.


  1. ^ a b c d e Perryman, M. A. C.; et al. (April 1997). "The HIPPARCOS Catalogue". Astronomy & Astrophysics 323: L49–L52. Bibcode:1997A&A...323L..49P. 
  2. ^ "V* EV Lac -- Flare Star". SIMBAD. Centre de Données astronomiques de Strasbourg. Retrieved 2010-06-12. 
  3. ^ Montes, D.; López-Santiago, J.; Gálvez, M. C.; Fernández-Figueroa, M. J.; De Castro, E.; Cornide, M. (November 2001). "Late-type members of young stellar kinematic groups - I. Single stars". Monthly Notices of the Royal Astronomical Society 328 (1): 45–63. arXiv:astro-ph/0106537. Bibcode:2001MNRAS.328...45M. doi:10.1046/j.1365-8711.2001.04781.x. 
  4. ^ a b Erro, B. I. (1971). "Infrared photometry of UV CET stars". Boletin Del Instituto De Tonantzintla 6: 143. Bibcode:1971BITon...6..143E. 
  5. ^ Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953QB901.W495..... 
  6. ^ a b c Phan-Bao, Ngoc; Martín, Eduardo L.; Donati, Jean-François; Lim, Jeremy (July 2006). "Magnetic Fields in M Dwarfs: Rapid Magnetic Field Variability in EV Lacertae". The Astrophysical Journal 646 (1): L73–L76. arXiv:astro-ph/0603480. Bibcode:2006ApJ...646L..73P. doi:10.1086/506591. 
  7. ^ a b Rojas-Ayala, Bárbara et al. (April 2012). "Metallicity and Temperature Indicators in M Dwarf K-band Spectra: Testing New and Updated Calibrations with Observations of 133 Solar Neighborhood M Dwarfs". The Astrophysical Journal 748 (2): 93. arXiv:1112.4567. Bibcode:2012ApJ...748...93R. doi:10.1088/0004-637X/748/2/93. 
  8. ^ Testa, Paola; Drake, Jeremy J.; Peres, Giovanni (December 2004). "The Density of Coronal Plasma in Active Stellar Coronae". The Astrophysical Journal 617 (1): 508–530. arXiv:astro-ph/0405019. Bibcode:2004ApJ...617..508T. doi:10.1086/422355. 
  9. ^ Schmitt JHMM, Fleming TA, Giampapa MS (Sep 1995). "The X-ray view of the low-mass stars in the solar neighborhood". Ap J. 450 (9): 392–400. Bibcode:1995ApJ...450..392S. doi:10.1086/176149. 
  10. ^ Dunbar, Brian (May 20, 2008). Smith, Yvette, ed. "Pipsqueak Star Unleashes Monster Flare". NASA. Retrieved 2010-06-12.