Phi Leonis

Phi Leonis (φ Leo) is a star in the constellation Leo. It is bright enough to be seen with the naked eye, having an apparent visual magnitude of 4.46.[2] Based upon parallax measurements,[1] the distance to Phi Leo is around 184 light years.

φ Leonis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Leo
Right ascension  11h 16m 39.69960s[1]
Declination −03° 39′ 05.7770″[1]
Apparent magnitude (V) 4.46[2]
Characteristics
Spectral type A7 IVn[3]
U−B color index +0.10[2]
B−V color index +0.22[2]
Astrometry
Radial velocity (Rv)−3.0[4] km/s
Proper motion (μ) RA: −110.37[1] mas/yr
Dec.: −37.16[1] mas/yr
Parallax (π)17.71 ± 0.25[1] mas
Distance184 ± 3 ly
(56.5 ± 0.8 pc)
Absolute magnitude (MV)0.56[5]
Details
Mass1.59[6] M☉
Radius2.9[7] R☉
Luminosity39[8] L☉
Surface gravity (log g)3.56[3] cgs
Temperature7,680±261[3] K
Rotational velocity (v sin i)254[3] km/s
Age432[3] Myr
Other designations
φ Leo, 74 Leo, BD−02°3315, FK5 1292, HD 98058, HIP 55084, HR 4368, SAO 138102[9]
Database references
SIMBADdata

The spectrum of this star fits a stellar classification of A7IVn,[3] which suggests it is an A-type subgiant star that has left the main sequence and is evolving into a giant star. It is being viewed with the plane of the star's equator lying close the line of sight from the Earth,[10] and shows a high rotation rate with a projected rotational velocity of 254 km/s.[3] This rapid spin is giving the star an oblate shape with an equatorial bulge that is 29% larger than the polar radius.[11]

Phi Leonis has been mentioned as a shell star—indicating that there is a circumstellar disk of gas around the star's equator—and may display a slight variability.[5] Sporadic variation of the spectra on the time scale of minutes up to months in duration suggests that solid, cometary bodies are in orbit around the star, with objects approaching close enough for refractory materials to sublimate.[10] Most exocomet hosts do have a circumstellar disk, which can act as an exocomet reservoir. Cold dust around Phi Leonis was not detected and the star is not associated with a warm debris disk.[12]

References
  1. 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.
  2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. Royer, F.; et al. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224.
  4. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic Fundamental Stars with Direct Solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, Astronomisches Rechen-Institut Heidelberg, 35 (35): 1, Bibcode:1999VeARI..35....1W.
  5. Hauck, B.; Jaschek, C. (February 2000), "A-shell stars in the Geneva system", Astronomy and Astrophysics, 354: 157–162, Bibcode:2000A&A...354..157H.
  6. David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146.
  7. Pasinetti Fracassini, L. E.; et al. (2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy & Astrophysics, 367 (2): 521–24, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  8. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  9. "ups Leo". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-09-29.
  10. Eiroa, C.; Rebollido, I.; Montesinos, B.; Villaver, E.; et al. (September 14, 2016), "Exocomet signatures around the A-shell star Φ Leo?" (PDF), Astronomy & Astrophysics, L1: 594, arXiv:1609.04263, Bibcode:2016A&A...594L...1E, doi:10.1051/0004-6361/201629514.
  11. van Belle, Gerard T., 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.
  12. Cataldi, Gianni; Moór, Attila; Ohashi, Nagayoshi; Eiroa, Carlos; Grady, Carol; Rebollido, Isabel (2019-02-22). "No Detection of Cold Dust around the Potential Exocomet Host ϕ Leo". Research Notes of the AAS. 3 (2): 39. doi:10.3847/2515-5172/ab082b. ISSN 2515-5172.
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