Lambda 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 mas[1] |
| Distance | 810 ± 40 ly (250 ± 10 pc) |
| Absolute magnitude (MV) | −3.75[3] |
| Details | |
| Mass | 8.99±0.69[6] M☉ |
| Radius | 8.6[3] R☉ |
| Luminosity | 7,510[6] L☉ |
| Surface gravity (log g) | 3.6[7] cgs |
| Temperature | 21,150[6] K |
| Rotation | 1.40346 d[3] |
| Rotational velocity (v sin i) | 327±24[5] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
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
- ^ 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.
- ^ 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.
- ^ 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.
- ^ a b c Rivinius, Th.; et al. (November 2003), "Non-radially pulsating Be stars", Astronomy and Astrophysics, 411: 229–247, Bibcode:2003A&A...411..229R, doi:10.1051/0004-6361:20031285.
- ^ 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, 29.
- ^ 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.
- ^ 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.
- ^ "lam Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-11-01.
{{cite web}}: CS1 maint: postscript (link) - ^ 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.
- ^ Otero, S. A.; et al. "Variable Star Type Designations in the VSX". AAVSO Website. American Association of Variable Star Observers. Retrieved 19 July 2014.
- ^ 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.
- ^ "Lambda Eridani". stars.astro.illinois.edu. Retrieved 2018-08-20.
