24 Ursae Majoris

24 Ursae Majoris is a variable star in the northern circumpolar constellation of Ursa Major, located 101.5 light-years from the Sun.[1] It has the variable star designation DK Ursae Majoris and the Bayer designation d Ursae Majoris; 24 Ursae Majoris is the Flamsteed designation. This object is visible to the naked eye as a faint, yellow-hued star with an apparent visual magnitude of 4.54.[2] It is moving closer to the Earth with a heliocentric radial velocity of −27 km/s, and is expected to come as close as 51 light-years in around 879,000 years.[2]

This article is about d Ursae Majoris. It is not to be confused with δ Ursae Majoris.
24 Ursae Majoris
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension  09h 34m 28.86175s[1]
Declination +69° 49′ 49.2265″[1]
Apparent magnitude (V) 4.54[2]
Characteristics
Spectral type G4 III-IV[3]
B−V color index 0.781±0.011[2]
Variable type RS CVn[4]
Astrometry
Radial velocity (Rv)−27.0±0.2[2] km/s
Proper motion (μ) RA: −64.785[1] mas/yr
Dec.: +77.214[1] mas/yr
Parallax (π)30.9269 ± 0.1621[1] mas
Distance105.5 ± 0.6 ly
(32.3 ± 0.2 pc)
Absolute magnitude (MV)2.16±0.013[5]
Details
Mass1.9[6] M☉
Radius4.6[6] R☉
Luminosity14.9[6] L☉
Surface gravity (log g)3.44[5] cgs
Temperature5,335[5] K
Metallicity [Fe/H]−0.19[5] dex
Rotation10 d[6]
Rotational velocity (v sin i)5.5[7] km/s
Age1.0±0.1[8] Gyr
Other designations
DK UMa, d UMa, 24 UMa, BD+70°565, FK5 357, HD 82210, HIP 46977, HR 3771, SAO 6897[9]
Database references
SIMBADdata

Description

24 Ursae Majoris has a stellar classification of G4 III-IV,[3] which, at the estimated age of about one billion years,[8] matches the spectrum of an aging giant star blended with features of a subgiant luminosity class. Based upon its position on the H–R diagram, this star has just passed through the Hertzsprung gap and is ready to begin its first ascent along the red-giant branch.[10] It is a suspected RS Canum Venaticorum variable that changes in brightness by up to 0.058 in magnitude with a period of 0.9202 days,[4] and is an X-ray source with a luminosity of 207.4×1028 erg s−1.[11]

This star has 1.9[6] times the mass of the Sun and has expanded to 4.6 times the Sun's radius. It is spinning with a rotation period of 10 days.[6] The star is radiating 14.9[6] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 5,335 K.[5]

Nomenclature

With π1, π2, σ1, σ2, ρ and 2 Ursae Majoris, it composed the Arabic asterism Al Ṭhibā᾽, the Gazelle.[12] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Ṭhibā were the title for seven stars : 2 Ursae Majoris as Althiba I, π1 as Althiba II, π2 as Althiba III, ρ as Althiba IV, σ1 as Althiba V, σ2 as Althiba VI, and this star (d) as Althiba VII.[13]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S.
  5. Park, Sunkyung; et al. (2013), "Wilson-Bappu Effect: Extended to Surface Gravity", The Astronomical Journal, 146 (4): 73, arXiv:1307.0592, Bibcode:2013AJ....146...73P, doi:10.1088/0004-6256/146/4/73.
  6. Gondoin, P. (December 2005), "The relation between X-ray activity and rotation in intermediate-mass G giants", Astronomy and Astrophysics, 444 (2): 531–538, Bibcode:2005A&A...444..531G, doi:10.1051/0004-6361:20053567.
  7. Ayres, Thomas R.; et al. (July 2007), "X-Ray and Ultraviolet Spectroscopy of Intermediate-Mass, First Crossing Giants", The Astrophysical Journal Supplement Series, 171 (1): 304–330, Bibcode:2007ApJS..171..304A, doi:10.1086/516713
  8. Pace, G. (March 2013), "Chromospheric activity as age indicator. An L-shaped chromospheric-activity versus age diagram", Astronomy & Astrophysics, 551: 4, arXiv:1301.5651, Bibcode:2013A&A...551L...8P, doi:10.1051/0004-6361/201220364, L8.
  9. "24 UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-17.
  10. Simon, Theodore (January 1999), "DK UMa: A Star on the Ascent", Technical Report, Honolulu, HI United States: Hawaii University Institute for Astronomy, Bibcode:1999STIN...0116106S.
  11. Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1–3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics, 361: 614–628, Bibcode:2000A&A...361..614P
  12. Allen, Richard Hinckley (1899), Star-Names and Their Meanings, New York: G. E. Stechert, p. 444
  13. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), Jet Propulsion Laboratory, California Institute of Technology.
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