Astronomy:Rho Leonis

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Short description: Variable star in the constellation Leo
ρ Leonis
Location of ρ Leonis (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Leo
Right ascension  10h 32m 48.67168s[1]
Declination +09° 18′ 23.7094″[1]
Apparent magnitude (V) 3.83 - 3.90[2]
Characteristics
Evolutionary stage Blue loop[3]
Spectral type B1 Iab[4]
U−B color index −0.945[5]
B−V color index −0.153[5]
Variable type α Cyg[2]
Astrometry
Radial velocity (Rv)+42.0[6] km/s
Proper motion (μ) RA: −5.93±0.20[1] mas/yr
Dec.: −3.40±0.11[1] mas/yr
Distance2,900±230 ly
(900±70 pc)
Absolute magnitude (MV)−6.19±0.2[7]
Details
Mass19.9±1.0[7] M☉
Radius28±3[7] R☉
Luminosity151,000+30,600
−25,500[7] L☉
Surface gravity (log g)2.87±0.04[7] cgs
Temperature21,700±200[7] K
Metallicity [Fe/H]−0.06[8] dex
Rotation12.5±0.7[3] days
Rotational velocity (v sin i)49.0±2.4[3] km/s
Age9.12+0.88
−0.91[7] Myr
Other designations
Shaomin, ρ Leo, 47 Leo, BD+10 2166, FK5 396, HD 91316, HIP 51624, HR 4133, SAO 118355
Database references
SIMBADdata

Rho Leonis, also named Shaomin,[9] is a 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,[5] this star can be readily seen with the naked eye. Spectroscopic measurements give a distance estimate of about 2,930 light-years (900 parsecs) from the Earth.[7] Rho Leonis is an Alpha Cygni-type variable star, showing 0.032 magnitude brightness variations with a period of 3.427 days, in Hipparcos data.[10]

Nomenclature

ρ Leonis (Latinized to Rho Leonis, abbreviated ρ Leo, Rho Leo) is the star's Bayer designation.

Rho Leonis has the traditional Chinese name Shaomin (少民); it and ο Leonis (Taimin, 太民) are the two southernmost stars of the Xuanyuan (轩辕) constellation. The IAU Working Group on Star Names approved the name Shaomin for ρ Leonis on 18 July 2024 and it is now so entered in the IAU Catalog of Star Names; ο Leonis has the IAU-approved name Subra.[9]

Characteristics

A light curve for Rho Leonis, plotted from Hipparcos data[11]

The spectrum of Rho Leonis matches a stellar classification of B1 Iab,[4] with the 'Iab' luminosity class indicating that it is a supergiant star. Rho Leonis is a former red supergiant that shifted back to hotter temperatures, being in the evolutionary stage known as blue loop.[3]

This is an enormous star with about 20 times the Sun's mass (M☉) and 28 times the Sun's radius (R☉). Rho Leonis is radiating about 150,000 times the Sun's luminosity (L☉) at an effective temperature of 21,700 K,[7] 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.[12] The rotation rate is about once per 12.5 days. The star rotates at an angle of 21.7°+0.5°
−0.4° relative to Earth.[3]

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,[lower-alpha 1] in a transverse direction. The star is situated about 2,300 light-years (710 parsecs) above the galactic plane.[13]

The star is 0.15 degree north of the ecliptic, so it can be occulted by the moon.[14] Unusual light variation during these occultations has been explained as the result of a possible close companion, which would be just over one magnitude fainter and separated by 0.01 arcsec.[15] It has not been detected by any other means although it should be easily detected with modern observations.[16] Speckle interferometry observations made during 2009 to 2023 did not detect the companion, strongly indicating that it does not exist.[17] However, there is evidence for a companion from spectroscopic observations, which could be interpreted as radial pulsations or the presence of a secondary star that periodically exchange mass with the primary and has its own circumstellar disk.[3]

Notes

  1. ↑ An Astronomical Unit (AU) is 1.5×108 km, while a year is 3.2×107 s. Thus, 1.56 AU/year = (1.56 AU/yr) × (1.5×108 km/AU) / (3.2×107 s/yr) = 7 km/s.

References

  1. ↑ 1.0 1.1 1.2 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 Samus, N. N. 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. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Checha, V. A.; Aret, A.; Kolka, I.; Liimets, T.; Araya, I.; Christen, A.; Marín, G. F. Avila; Levenhagen, R. S.; Cidale, L. (2025-12-17). "Photometric and spectroscopic variability of blue supergiant ρLeo". arXiv:2512.15345 [astro-ph.SR].
  4. ↑ 4.0 4.1 Lesh, Janet Rountree (December 1968). "The Kinematics of the Gould Belt: an Expanding Group?". Astrophysical Journal Supplement 17: 371. doi:10.1086/190179. Bibcode: 1968ApJS...17..371L. 
  5. ↑ 5.0 5.1 5.2 Gutierrez-Moreno, Adelina et al. (1966). "A System of photometric standards". Publ. Dept. Astron. Univ. Chile 1: 1–17. Bibcode: 1966PDAUC...1....1G. 
  6. ↑ Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities". Washington. Bibcode: 1953GCRV..C......0W. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Weßmayer, D.; Przybilla, N.; Ebenbichler, A.; Aschenbrenner, P.; Butler, K. (2023-09-01). "The blue supergiant Sher 25 revisited in the Gaia era". Astronomy and Astrophysics 677: A175. doi:10.1051/0004-6361/202347253. ISSN 0004-6361. Bibcode: 2023A&A...677A.175W. 
  8. ↑ Koleva, M.; Vazdekis, A. (2012). "Stellar population models in the UV. I. Characterisation of the New Generation Stellar Library". Astronomy & Astrophysics 538: A143. doi:10.1051/0004-6361/201118065. Bibcode: 2012A&A...538A.143K. 
  9. ↑ 9.0 9.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/. 
  10. ↑ Lefèvre, L.; Marchenko, S. V.; Moffat, A. F. J.; Acker, A. (November 2009). "A systematic study of variability among OB-stars based on HIPPARCOS photometry". Astronomy and Astrophysics 507 (2): 1141–1201. doi:10.1051/0004-6361/200912304. Bibcode: 2009A&A...507.1141L. 
  11. ↑ "Light Curve". ESA. https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve. 
  12. ↑ 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. doi:10.1051/0004-6361/200810319. Bibcode: 2009A&A...499..291K. 
  13. ↑ 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. doi:10.1086/377164. Bibcode: 2003ApJ...591L.123L. 
  14. ↑ Herr, Richard B. (April 1969). "Identification List of Spectroscopic and Eclipsing Binaries Subject to Occultations by the Moon". Publications of the Astronomical Society of the Pacific 81 (479): 105. doi:10.1086/128748. Bibcode: 1969PASP...81..105H. 
  15. ↑ Radick, R. R.; Africano, J. L.; Flores, M. R.; Klimke, D. A.; Tyson, E. T. (1982). "Cloudcroft occultation summary. II - April 1980-December 1981". The Astronomical Journal 87: 1874. doi:10.1086/113277. ISSN 0004-6256. Bibcode: 1982AJ.....87.1874R. 
  16. ↑ McAlister, H. A. (1978). "Binary stars unresolved by speckle interferometry". Publications of the Astronomical Society of the Pacific 90: 288. doi:10.1086/130327. ISSN 0004-6280. Bibcode: 1978PASP...90..288M. 
  17. ↑ Tokovinin, Andrei; Mason, Brian D.; Mendez, Rene A.; Costa, Edgardo (2024-06-24). "Speckle Interferometry at SOAR Telescope in 2023". The Astronomical Journal 168 (1): 28. doi:10.3847/1538-3881/ad4d56. ISSN 0004-6256. Bibcode: 2024AJ....168...28T. 



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