Delta Doradus
δ Doradus (often Latinised to Delta Doradus, abbreviated to δ Dor or delta Dor) is a star in the southern constellation of Dorado. Based upon an annual parallax shift of 21.80 mas as seen from Earth, it is located around 150 light years from the Sun. The star is visible to the naked eye with an apparent visual magnitude of +4.34.[2]
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Dorado |
| Right ascension | 05h 44m 46.37811s[1] |
| Declination | −65° 44′ 07.9011″[1] |
| Apparent magnitude (V) | +4.34[2] |
| Characteristics | |
| Spectral type | A7 V[3] |
| U−B color index | +0.11[2] |
| B−V color index | +0.22[2] |
| Astrometry | |
| Radial velocity (Rv) | −8.3±0.8[4] km/s |
| Proper motion (μ) | RA: −28.91[1] mas/yr Dec.: +5.17[1] mas/yr |
| Parallax (π) | 21.80 ± 0.14 mas[1] |
| Distance | 149.6 ± 1.0 ly (45.9 ± 0.3 pc) |
| Absolute magnitude (MV) | +1.03[5] |
| Details | |
| Mass | 1.85[6] M☉ |
| Radius | 2.1[7] R☉ |
| Luminosity | 29[8] L☉ |
| Surface gravity (log g) | 3.89[6] cgs |
| Temperature | 7,828±266[6] K |
| Metallicity [Fe/H] | −0.40[9] dex |
| Rotational velocity (v sin i) | 172[3] km/s |
| Age | 940[6] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is an A-type main sequence star with a stellar classification of A7 V.[3] The star is spinning rapidly with a projected rotational velocity of 172 km/s.[3] This is giving the star an oblate shape with an equatorial bulge that is 12% larger than the polar radius.[11] Although A-type stars are not expected to harbor a magnetic dynamo needed to power X-ray emission, an X-ray flux of 3.6×1027 erg/s has been detected at these coordinates. This may indicate that the star has an unseen companion.[12] δ Doradus displays an infrared excess suggesting it may be a Vega-like star with an orbiting debris disk.[9]
Currently this star is the Moon's south pole star, which occurs once every 18.6 years.[13] The pole star status changes periodically, because of the precession of the Moon's rotational axis. When δ Doradus is the pole star, it is better aligned than Earth's Polaris (α Ursae Minoris), but much fainter. It is also the south pole star of Jupiter.[citation needed]
References edit
- ^ a b c d e 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.
- ^ a b c d Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
- ^ a b c d 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, S2CID 18475298.
- ^ 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.
- ^ 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, S2CID 119257644.
- ^ a b c d 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.
- ^ Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics, 367 (3rd ed.): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451, S2CID 425754.
- ^ 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, S2CID 118665352.
- ^ a b Saffe, C.; Gómez, M.; Pintado, O.; González, E. (October 2008), "Spectroscopic metallicities of Vega-like stars", Astronomy and Astrophysics, 490 (1): 297–305, arXiv:0805.3936, Bibcode:2008A&A...490..297S, doi:10.1051/0004-6361:200810260, S2CID 15059920.
- ^ "del Dor". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-04-17.
{{cite web}}: CS1 maint: postscript (link) - ^ van Belle, 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, S2CID 119273474.
- ^ Schröder, C.; Schmitt, J. H. M. M. (November 2007), "X-ray emission from A-type stars", Astronomy and Astrophysics, 475 (2): 677–684, Bibcode:2007A&A...475..677S, doi:10.1051/0004-6361:20077429.
- ^ Patrick Moore (1983), The Guinness Book of Astronomy Facts & Feats, p. 29,
In 1968 the north pole star of the Moon was Omega Draconis; by 1977 it was 36 Draconis. The south pole star is Delta Doradus.