Delta Horologii

Delta Horologii (δ Horologii) is a binary star[3] system in the constellation Horologium. It is visible to the naked eye with a combined apparent visual magnitude of 4.93.[2] As of 2014, the pair had an angular separation of 0.20 arc seconds along a position angle of 24°.[9] Based upon an annual parallax shift of 18.24 mas as seen from Earth,[1] it is located 179 ± 4 light years from the Sun.

Delta Horologii
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Horologium
Right ascension 04h 10m 50.58927s[1]
Declination −41° 59′ 36.8537″[1]
Apparent magnitude (V) 4.93[2] (5.15 + 7.29)[3]
Characteristics
Spectral type A9 V[3]
U−B color index +0.084[2]
B−V color index +0.338[2]
Astrometry
Radial velocity (Rv)+38.3±2.6[4] km/s
Proper motion (μ) RA: +199.08[1] mas/yr
Dec.: +70.18[1] mas/yr
Parallax (π)18.24 ± 0.41[1] mas
Distance179 ± 4 ly
(55 ± 1 pc)
Absolute magnitude (MV)1.50[5]
Details
δ Hor A
Mass1.41[6] M☉
Surface gravity (log g)3.71±0.14[6] cgs
Temperature7,033±239[6] K
Metallicity [Fe/H]−0.32[7] dex
Rotational velocity (v sin i)220.1±11.0[5] km/s
Age768[6] Myr
δ Hor B
Rotational velocity (v sin i)51.7±2.6[5] km/s
Other designations
δ Hor, CD−42° 1400, HD 26612, HIP 19515, HR 1302, SAO 216682, WDS J04108-4200AB[8]
Database references
SIMBADdata

The primary, component A, is a magnitude 5.15 A-type main sequence star with a stellar classification of A9 V.[3] At the estimated age of 768 million years,[6] it is spinning rapidly with a projected rotational velocity of 220 km/s,[5] giving the star an oblate shape with an equatorial bulge that is 15% larger than the polar radius.[10] The star has 1.4[6] times the mass of the Sun.

The secondary has an apparent magnitude of 7.29.[3]

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, S2CID 18759600.
  2. Cousins, A. W. J. (1983), "UBV photometry of E region standard stars of intermediate brightness", South African Astronomical Observatory Circular, 7 (7): 36–46, Bibcode:1983SAAOC...7...36C.
  3. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  4. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  5. Ammler-von Eiff, M.; Reiners, A. (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: 31, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672, A116.
  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, S2CID 33401607.
  7. Casagrande, L.; et al. (2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy & Astrophysics, 530 (A138): 21, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276, S2CID 56118016.
  8. "del Hor -- Double or multiple star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-04-25.
  9. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122: 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920
  10. Belle, G. T. (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. S2CID 119273474.
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