Rho Leonis

Rho Leonis (ρ Leo) is a binary star in the zodiac constellation of Leo, and, like the prominent nearby star Regulus, is near the ecliptic. With an apparent visual magnitude of 3.9,[4] this star can be readily seen with the naked eye. Parallax measurements give a distance estimate of about 5,400 light-years (1,700 parsecs) from the Earth.[12]

ρ Leonis
Location of ρ Leonis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Leo
Right ascension 10h 32m 48.67168s[1]
Declination +09° 18′ 23.7094″[1]
Apparent magnitude (V) 3.83 - 3.90[2]
Characteristics
Spectral type B1 Iab[3]
U−B color index –0.945[4]
B−V color index –0.153[4]
Variable type α Cyg[2]
Astrometry
Radial velocity (Rv)+42.0[5] km/s
Proper motion (μ) RA: –5.93 ± 0.20[1] mas/yr
Dec.: –3.40 ± 0.11[1] mas/yr
Parallax (π)0.60 ± 0.18[1] mas
Distanceapprox. 5,000 ly
(approx. 1,700 pc)
Absolute magnitude (MV)–6.8[6]
Details
Mass27.1 ± 8.4[7] M☉
Radius37.4[8] R☉
Luminosity295,000[6] L☉
Surface gravity (log g)3.09[9] cgs
Temperature24,200[9] K
Metallicity [Fe/H]–0.89[9] dex
Rotation7 ± 2 days[10]
Rotational velocity (v sin i)60[11] km/s
Age4.5 ± 0.1[7] Myr
Other designations
47 Leo, HR 4133, BD+10 2166, HD 91316, SAO 118355, FK5 396, HIP 51624.
Database references
SIMBADdata

This is an enormous star with about 21 times the Sun's mass (M☉)[13] and 37 times the Sun's radius.[8] Its spectrum matches a stellar classification of B1 Iab,[3] with the 'Iab' luminosity class indicating that it is in the supergiant stage of its evolution. Rho Leonis is radiating about 295,000 times the Sun's luminosity[6] at an effective temperature of 24,200 K,[9] giving it the blue-white hue typical of a B-type star. A strong stellar wind is expelling mass from the outer envelope at a rate of 3.5 × 10−7 M☉ per year, or the equivalent of 1 M☉ every 2.8 million years.[8] The rotation rate is probably about once per 7 days, with an upper limit of 47 days.[10]

Rho Leonis is classified as a runaway star, which means it has a peculiar velocity of at least 30 km s−1 relative to the surrounding stars. It has radial velocity of 42 km s−1 away from the Sun and a proper motion that is carrying it about 1.56 Astronomical Units per year, equivalent to 7 km s−1,[14] in a transverse direction. The star is situated about 2,300 light-years (710 parsecs) above the galactic plane.[15]

Rho Leo is 0.15 degree north of the ecliptic, so it can be occulted by the moon. Unusual light variation during these occultations has been explained as the result of a possible close companion. The companion would be just over one magnitude fainter and separated by 0.01 arcsec.[16] The companion has not been detected by any other means although it should be easily detected with modern observations.[17]

References
  1. van Leeuwen, F. (November 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
  2. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  3. Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179
  4. Gutierrez-Moreno, Adelina; et al. (1966), "A System of photometric standards", Publ. Dept. Astron. Univ. Chile, 1: 1–17, Bibcode:1966PDAUC...1....1G
  5. Wilson, Ralph Elmer (1953), "General Catalogue of Stellar Radial Velocities", Washington, Bibcode:1953GCRV..C......0W
  6. Crowther, P. A.; Lennon, D. J.; Walborn, N. R. (January 2006), "Physical parameters and wind properties of galactic early B supergiants", Astronomy and Astrophysics, 446 (1): 279–293, arXiv:astro-ph/0509436, Bibcode:2006A&A...446..279C, doi:10.1051/0004-6361:20053685
  7. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x
  8. Kraus, M.; Borges Fernandes, M.; Kubát, J. (May 2009), "Parameters of galactic early B supergiants. The influence of the wind on the interstellar extinction determination", Astronomy and Astrophysics, 499 (1): 291–299, Bibcode:2009A&A...499..291K, doi:10.1051/0004-6361/200810319
  9. Gies, Douglas R.; Lambert, David L. (March 10, 1992), "Carbon, nitrogen, and oxygen abundances in early B-type stars", Astrophysical Journal, Part 1, 387: 673–700, Bibcode:1992ApJ...387..673G, doi:10.1086/171116
  10. Kholtygin, A. F.; et al. (November 2007), "Microvariability of line profiles in the spectra of OB stars: III. The supergiant ρ LEO", Astronomy Reports, 51 (11): 920–931, Bibcode:2007ARep...51..920K, CiteSeerX 10.1.1.618.7621, doi:10.1134/S1063772907110054
  11. Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago, 239 (1): 1, Bibcode:1970CoAsi.239....1B
  12. Perryman, M. A. C.; et al. (July 1997), "The HIPPARCOS Catalogue", Astronomy & Astrophysics, 323: L49–L52, Bibcode:1997A&A...323L..49P
  13. Conlon, E. S.; et al. (September 1990), "The runaway nature of distant early-type stars in the galactic halo", Astronomy and Astrophysics, 236 (2): 357–361, Bibcode:1990A&A...236..357C
  14. An Astronomical Unit (AU) is 1.5 × 108 km, while a year is 3.2 × 107 seconds. Thus, 1.56 AU/year = (1.56 AU/yr) × (1.5 × 108 km/AU) / (3.2 × 107 s/yr) = 7 km/s.
  15. Lauroesch, J. T.; Meyer, David M. (July 2003), "Variable Na I Absorption toward ρ Leonis: Biased Neutral Formation in the Diffuse Interstellar Medium?", The Astrophysical Journal, 591 (2): L123–L126, arXiv:astro-ph/0306005, Bibcode:2003ApJ...591L.123L, doi:10.1086/377164
  16. Radick, R. R.; Africano, J. L.; Flores, M. R.; Klimke, D. A.; Tyson, E. T. (1982). "Cloudcroft occulation summary. II - April 1980-December 1981". The Astronomical Journal. 87: 1874. Bibcode:1982AJ.....87.1874R. doi:10.1086/113277. ISSN 0004-6256.
  17. McAlister, H. A. (1978). "Binary stars unresolved by speckle interferometry". Publications of the Astronomical Society of the Pacific. 90: 288. Bibcode:1978PASP...90..288M. doi:10.1086/130327. ISSN 0004-6280.
  • Kaler, James B., "Rho Leonis", Stars, University of Illinois, retrieved 2012-01-11
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