Lambda Eridani

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λ Eridani
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension 05h 09m 08.78315s[1]
Declination −08° 45′ 14.6908″[1]
Apparent magnitude (V) 4.25[2]
Characteristics
Spectral type B2 IVne[3] or B2 III(e)p[4]
U−B color index −0.88
B−V color index −0.19
Variable type λ Eri
Astrometry
Radial velocity (Rv)−2.51±5.43[5] km/s
Proper motion (μ) RA: +0.25[1] mas/yr
Dec.: −1.97[1] mas/yr
Parallax (π)4.02 ± 0.18[1] mas
Distance810 ± 40 ly
(250 ± 10 pc)
Absolute magnitude (MV)−3.75[3]
Details
Mass8.99±0.69[6] M☉
Radius8.6[3] R☉
Luminosity7,510[6] L☉
Surface gravity (log g)3.6[7] cgs
Temperature21,150[6] K
Rotation1.40346 d[3]
Rotational velocity (v sin i)327±24[5] km/s
Other designations
λ Eridani, 69 Eridani, CD-08° 1040, FK5 190, HD 33328, HIP 23972, HR 1679, SAO 131824.[8]
Database references
SIMBADdata

Lambda Eridani (λ Eri) is a star in the constellation Eridanus. It is visible to the naked eye on a dark night with an apparent visual magnitude of 4.25.[2] The distance to this star, based upon an annual parallax shift of 0.00402 arcseconds,[1] is roughly 810 light years.

λ Eri is classified in the General Catalogue of Variable Stars as a Beta Cephei variable.[9] The AAVSO International Variable Star Index defines a LERI type of variation. λ Eri is classified as LERI + GCAS since it shows both short term periodic variations and longer timescale eruptive variation.[10] It was one of the first stars where short-period variations were found.[3] The line profile variability periods are 0.702d and 0.269d, with intermittently present periods of 0.6d and 0.75d. The photometric amplitude of the variation is 0.010 magnitude.[4]

This is a giant or subgiant Be star with a stellar classification of B2 IVne[3] or B2 III(e)p,[4] depending on the source. It is spinning rapidly with a projected rotational velocity of 327 km/s.[5] Compare this to the estimated break-up velocity of 440 km/s.[7] This rotation is giving the star an oblate shape with an equatorial bulge that is 25% larger than the polar radius.[11] The most likely rotation period is deemed to be twice the period of variation, or 1.4 days.[3] The star also possesses a rotating circumstellar disc, seen edge on, which makes Lambda Eri a "shell star", where the disk appears more opaque than usual. [12]

Like most Be stars, Lambda Eridani emits soft X-rays. In 1993, a giant X-ray flare was observed in which the X-ray luminosity increased by a factor of six over a 39-hour period.[3] Lambda Eridani has about nine times the mass of the Sun,[6] and 8.6[3] times the Sun's radius.[3] It radiates 7,510[6] times the solar luminosity from its outer atmosphere at an effective temperature of 21,150 K.[6]

References[]

  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. ^ a b Crawford, D. L.; et al. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058, Bibcode:1971AJ.....76.1058C, doi:10.1086/111220.
  3. ^ a b c d e f g h i j Balona, L. A.; James, D. J. (May 2002), "Short-period line profile and light variations in the Be star λ Eridani", Monthly Notices of the Royal Astronomical Society, 332 (3): 714–722, Bibcode:2002MNRAS.332..714B, doi:10.1046/j.1365-8711.2002.05336.x.
  4. ^ a b c Rivinius, Th.; et al. (November 2003), "Non-radially pulsating Be stars", Astronomy and Astrophysics, 411 (2): 229–247, Bibcode:2003A&A...411..229R, doi:10.1051/0004-6361:20031285.
  5. ^ a b c Becker, Juliette C.; et al. (April 2015), "Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra", The Astrophysical Journal Supplement Series, 217 (2): 13, arXiv:1503.03874, Bibcode:2015ApJS..217...29B, doi:10.1088/0067-0049/217/2/29, S2CID 33968873, 29.
  6. ^ a b c d e f Hohle, M. M.; et al. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349–360, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355, S2CID 111387483.
  7. ^ a b Frémat, Y.; et al. (2005), "Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars", Astronomy and Astrophysics, 440 (1): 305–320, arXiv:astro-ph/0503381, Bibcode:2005A&A...440..305F, doi:10.1051/0004-6361:20042229, S2CID 19016751.
  8. ^ "lam Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-11-01.CS1 maint: postscript (link)
  9. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR. 1. Bibcode:2009yCat....102025S.
  10. ^ Otero, S. A.; et al. "Variable Star Type Designations in the VSX". AAVSO Website. American Association of Variable Star Observers. Retrieved 19 July 2014.
  11. ^ van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
  12. ^ "Lambda Eridani". stars.astro.illinois.edu. Retrieved 2018-08-20.
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