18 Ursae Majoris

Star in the constellation Ursa Major e Ursae Majoris epsilon Ursae Majorisε Ursae Majoris Ursa Major constellation map.svg center 280 right Red circle.svg 10 18 Ursae Majoris 845 400 Location of 18 Ursae Majoris (circled in red) J2000.0 Ursa Major 09 16 11.32784 +54 01 18.6878 4.832 main sequence A6 V 0.186 0.087 δ Sct −16.13 1.30 +49.43 +59.92 27.90 0.20 2.03 1.72 0.02 12.83 7450 150 commas 3.98 0.2 158 17 1.05 0.10 0.15 DD UMa e UMa 18 UMa +54°1285 2734 3541 79439 45493 3662 27191 e UMa 2018-02-22 e+UMa 18 Ursae Majoris, or e Ursae Majoris, is a single star in the northern circumpolar constellation of Ursa Major. It is faintly visible to the naked eye with an apparent visual magnitude of 4.832. The annual parallax shift measured from Earth's orbit is 27.90 mas, which provides a distance estimate of 117 light years. It is moving closer to the Sun with a heliocentric radial velocity of −16 km/s, and is an unbound and older member of the Ursa Major Moving Group. The stellar classification assigned to this star is A6 V, which indicates it is an A-type main-sequence star that is generating energy through hydrogen fusion at its core. The star's variability was first noticed by American astronomer Frank Schlesinger in 1914, and the variable star designation DD UMa was given to it. This is a low amplitude Delta Scuti variable with a magnitude change of around 0.4 and pulsation cycles of 9.4 and 15.0 cycles per day. It is rotating rapidly with a projected rotational velocity of about 158 km/s. This is giving the star an oblate shape with an equatorial bulge that is an estimated 6% larger than the polar radius. 18 UMa is about a billion years old with 1.72 times the mass of the Sun. It is radiating around 13 times the Sun's luminosity from its photosphere at an effective temperature of about 7,450 K. Naming With τ, h, υ, φ, θ and f, it composed the Arabic asterism Sarīr Banāt al-Na'sh, the Throne of the daughters of Na'sh, and Al-Haud, the Pond. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al-Haud were the title for seven stars: f as Alhaud I, τ as Alhaud II, this star (e) as Alhaud III, h as Alhaud IV, θ as Alhaud V, υ as Alhaud VI and φ as Alhaud VII. References Zorec J. Royer F. Rotational velocities of A-type stars. IV. Evolution of rotational velocities Astronomy and Astrophysics 2012 537 A120 10.1051/0004-6361/201117691 free 1201.2052 2012A&A...537A.120Z Validation of the new Hipparcos reduction van Leeuwen F. Astronomy and Astrophysics 474 2 653–664 2007 0708.1752 2007A&A...474..653V 10.1051/0004-6361:20078357 18759600 . XHIP: An extended hipparcos compilation Anderson E. Francis Ch. Astronomy Letters 38 5 331 2012 2012AstL...38..331A 10.1134/S1063773712050015 1108.4971 119257644 . A spectroscopic study of DD UMa: Ursa Major group member and candidate for BRITE 1 Elmaslı A. Fossati L. Folsom C. P. Albayrak B. Izumiura H. New Astronomy 17 2 221−226 February 2012 10.1016/j.newast.2011.07.006 2012NewA...17..221E 1107.4856 119183478 . 1 Boyajian Tabetha S. McAlister Harold A. van Belle Gerard Gies Douglas R. ten Brummelaar Theo A. von Braun Kaspar Farrington Chris Goldfinger P. J. O'Brien David Parks J. Robert Richardson Noel D. Ridgway Stephen Schaefer Gail Sturmann Laszlo Sturmann Judit Touhami Yamina Turner Nils H. White Russel Stellar Diameters and Temperatures. I. Main-sequence A, F, and G Stars The Astrophysical Journal 746 1 101 February 2012 10.1088/0004-637X/746/1/101 2012ApJ...746..101B 1112.3316 18993744 . Interferometric observations of rapidly rotating stars Belle G. T. The Astronomy and Astrophysics Review 20 51 2012 1 10.1007/s00159-012-0051-2 2012A&ARv..20...51V 1204.2572 119273474 . 1 Rodriguez David R. Duchêne Gaspard Tom Henry Kennedy Grant M. Matthews Brenda Greaves Jane Butner Harold Stellar multiplicity and debris discs: an unbiased sample Monthly Notices of the Royal Astronomical Society 449 3 3160–3170 May 2015 10.1093/mnras/stv483 free 1503.01320 2015MNRAS.449.3160R 119237891 . Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra Becker Juliette C. Johnson John Asher Vanderburg Andrew Morton Timothy D. The Astrophysical Journal Supplement Series 217 2 29 13 April 2015 10.1088/0067-0049/217/2/29 2015ApJS..217...29B 1503.03874 33968873 1 . Abt Helmut A. Morrell Nidia I. The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars Astrophysical Journal Supplement 99 135 July 1995 . 10.1086/192182 1995ApJS...99..135A free Star-Names and Their Meanings Allen Richard Hinckley Richard Hinckley Allen 1899 G. E. Stechert . New York 442 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720005197_1972005197.pdf Jack W. Rhoads Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars Jet Propulsion Laboratory, California Institute of Technology November 15, 1971 . Category:A6V stars Category:Delta Scuti variables Category:Ursa Major Ursae Majoris, e BD+54 1285 Ursae Majoris, 18 3541 079439 045493 3662 Ursae Majoris, DD Alhaud III