HR 4729

HR 4729 (HD 108250) is a multiple star system located about 95 parsecs (310 ly) from the Sun in the constellation of Crux and part of the asterism known as the Southern Cross. It is a close companion of α Crucis and sometimes called α Crucis C.

HR 4729
Observation data
Epoch J2000      Equinox J2000
Constellation Crux
Right ascension  12h 26m 30.8790s[1]
Declination −63° 07′ 19.993″[1]
Apparent magnitude (V) 4.79[2]
Characteristics
Spectral type B5 V[3]
U−B color index −0.59[4]
B−V color index −0.12[4]
Astrometry
Radial velocity (Rv)+27[5] km/s
Proper motion (μ) RA: −39.593[6] mas/yr
Dec.: −14.537[6] mas/yr
Parallax (π)10.5623 ± 0.2340[6] mas
Distance309 ± 7 ly
(95 ± 2 pc)
Absolute magnitude (MV)−0.98[2]
Orbit[7]
Period (P)1.225155±0.000005 d
Eccentricity (e)0.024±0.014
Periastron epoch (T)2438903.314±0.003 JD
Argument of periastron (ω)
(secondary)		314±34°
Semi-amplitude (K1)
(primary)		43.1±0.6 km/s
Details
Mass9.65[8] M☉
Radius5.5[9] R☉
Rotational velocity (v sin i)131[10] km/s
Age12[11] Myr
Other designations
256 Crucis, HR 4729, CPD−62°2742, GC 16951, 25 G. Crucis, WDS J12266-6306C, CCDM J12266-6306C
Database references
SIMBADdata

Nomenclature

HR 4729 is the star's designation in the Bright Star Catalogue. It is also often referred to by its Henry Draper Catalogue listing of HD 108250. Because of its closeness to α Crucis it is included in many multiple star catalogues as α Crucis C.[12] It is also listed as star 25 in Crux in the Uranometria Argentina, displayed as 25 G. Crucis.[13]

Discovery

HR 4729 was first observed in 1829, as a companion to α Crucis, by James Dunlop from Paramatta in New South Wales.[14] As early as 1916, HR 4729 was reported to have a variable radial velocity indicating a likely binary system, but the orbital elements were not calculated until 1979.[7]

System
α Crucis with HR 4729 close by

HR 4729 lies 90 arcseconds away from the triple star system of α Crucis and shares its motion through space, suggesting it may be gravitationally bound to it, and it is therefore generally assumed to be physically associated. In the context of being a companion to α Crucis it is usually referred to as α Crucis C.[15][16]

HR 4729 is itself a close spectroscopic binary system with a period of 1 day 5 hours. It also has a faint visual companion 2.1" away. A further seven faint stars are also listed as members of the α Crucis group out to a distance of about two arc-minutes.[12] One particular companion very close to HR 4729 has been resolved using adaptive optics at infrared wavelengths. It has been named α Crucis P, or α Crucis CP because it is only 2" from HR 4729.[11]

Rizzuto and colleagues determined in 2011 that the α Crucis system, including HR 4729, was 66% likely to be a member of the Lower Centaurus-Crux sub-group of the Scorpius-Centaurus Association. It was not previously seen to be a member of the group because of confusion over the true radial velocity of the spectroscopic pair.[17]

On 2008 October 2, the Cassini–Huygens spacecraft resolved three of the components (A, B and C) of the multiple star system as Saturn's disk occulted it.[18][19]

Stellar properties

HR 4729 is a hot class B main sequence star nearly ten times as massive as the sun. It is only about twelve million years old, but already shows signs of evolving away from the main sequence. Several studies have assigned a subgiant luminosity class to the star.[7][20]

The spectroscopic companion cannot be seen in the spectrum, therefore little is known about its properties. Analysis of the orbit shows that it has a mass greater than the sun.[8]

The physically associated companion α Crucis D or α Crucis CP is a 15th magnitude star. Its relative faintness suggests an M0 V spectral type.[8] Two other, even fainter stars, lie within 10″ of HR 4729.[12]

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References
  1. Hog, E.; Kuzmin, A.; Bastian, U.; Fabricius, C.; Kuimov, K.; Lindegren, L.; Makarov, V. V.; Roeser, S. (1998). "The TYCHO Reference Catalogue". Astronomy and Astrophysics. 335: L65. Bibcode:1998A&A...335L..65H.
  2. Kaltcheva, N. T.; Golev, V. K.; Moran, K. (2014). "Massive stellar content of the Galactic supershell GSH 305+01-24". Astronomy & Astrophysics. 562: A69. arXiv:1312.5592. Bibcode:2014A&A...562A..69K. doi:10.1051/0004-6361/201321454.
  3. Corbally, C. J. (1984). "Close visual binaries. I - MK classifications". Astrophysical Journal Supplement Series. 55: 657. Bibcode:1984ApJS...55..657C. doi:10.1086/190973.
  4. Stagg, Christopher (1987). "A photometric survey of the bright southern Be stars". Monthly Notices of the Royal Astronomical Society. 227: 213. Bibcode:1987MNRAS.227..213S. doi:10.1093/mnras/227.1.213.
  5. Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953GCRV..C......0W.
  6. 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.
  7. Hernandez, C. A.; De Hernandez, E. B. (1979). "The orbital elements of 25 G Crucis /HD 108250/". Revista Mexicana de Astronomía y Astrofísica. 4: 297. Bibcode:1979RMxAA...4..297H.
  8. Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy and Astrophysics Supplement Series. 124 (1): 75–84. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181. ISSN 0365-0138.
  9. Brown, A. G. A.; Verschueren, W. (1997). "High S/N Echelle spectroscopy in young stellar groups. II. Rotational velocities of early-type stars in SCO OB2". Astronomy and Astrophysics. 319: 811. arXiv:astro-ph/9608089. Bibcode:1997A&A...319..811B.
  10. Tokovinin, A. A.; Chalabaev, A.; Shatsky, N. I.; Beuzit, J. L. (1999). "A near IR adaptive optics search for faint companions to early-type multiple stars". Astronomy and Astrophysics. 346: 481. Bibcode:1999A&A...346..481T.
  11. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  12. Gould, Benjamin Apthorp (1879). "Uranometria Argentina : Brillantez y posicion de las estrellas fijas, hasta la septima magnitud, comprendidas dentro de cien grados del polo austral : Con atlas". Resultados del Observatorio Nacional Argentino en Cordoba ; v. 1. 1. Bibcode:1879RNAO....1.....G.
  13. Dunlop, James (1829). "Approximate Places of Double Stars in the Southern Hemisphere, observed at Paramatta in New South Wales". Memoirs of the Royal Astronomical Society. 3: 257. Bibcode:1829MmRAS...3..257D.
  14. Shatsky, N.; Tokovinin, A. (2002). "The mass ratio distribution of B-type visual binaries in the Sco OB2 association". Astronomy and Astrophysics. 382: 92. arXiv:astro-ph/0109456. Bibcode:2002A&A...382...92S. doi:10.1051/0004-6361:20011542.
  15. Eggleton, Peter; Tokovinin, A. (2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society. 389 (2): 869. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  16. Rizzuto, Aaron; Ireland, Michael; Robertson, J. G. (October 2011), "Multidimensional Bayesian membership analysis of the Sco OB2 moving group", Monthly Notices of the Royal Astronomical Society, 416 (4): 3108–3117, arXiv:1106.2857, Bibcode:2011MNRAS.416.3108R, doi:10.1111/j.1365-2966.2011.19256.x.
  17. NASA/JPL/Space Science Institute. Multimedia - Images - Raw Images Archived 2008-10-25 at the Wayback Machine. Retrieved 2008-10-21
  18. Cassini "Kodak Moments" - Unmanned Spaceflight.com. Retrieved 2008-10-21
  19. Hiltner, W. A.; Garrison, R. F.; Schild, R. E. (1969). "MK Spectral Types for Bright Southern OB Stars". Astrophysical Journal. 157: 313. Bibcode:1969ApJ...157..313H. doi:10.1086/150069.

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