84 Ursae Majoris

84 Ursae Majoris, also known as HD 120198, is a star about 300 light years from the Earth, in the constellation Ursa Major.^[2] It is a 5th magnitude star, making it faintly visible to the naked eye of an observer far from city lights. It is an Ap star with an 1,100 gauss magnetic field,^[7] and an α² CVn variable star, varying in brightness from magnitude 5.65 to 5.70, over a period of 1.37996 days.^[3] 84 Ursae Majoris is located just 70 arcseconds from the star LDS 2914, but that star is believed to be a background star not physically associated with 84 Ursae Majoris.^[11]

84 Ursae Majoris

A light curve for CR Ursae Majoris, plotted from TESS data.[1]
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Ursa Major
Right ascension	13h 46m 35.65679s[2]
Declination	+54° 25′ 57.6436″[2]
Apparent magnitude (V)	5.65 - 5.70[3]
Characteristics
Spectral type	B9pe[4]
B−V color index	-0.04[4]
Variable type	α2 CVn[3]
Astrometry
Radial velocity (Rv)	−2.4±1.6[5] km/s
Proper motion (μ)	RA: −18.559±0.041[2] mas/yr Dec.: −4.742±0.039[2] mas/yr
Parallax (π)	10.7417 ± 0.0418 mas[2]
Distance	304 ± 1 ly (93.1 ± 0.4 pc)
Absolute magnitude (MV)	0.98±0.12[6]
Details
Primary
Mass	2.60+0.17 −0.25[7] M☉
Radius	2.28±0.10[7] R☉
Luminosity	44.9±4.3[7] L☉
Surface gravity (log g)	4.07[8] cgs
Temperature	9865±370[7] K
Metallicity [Fe/H]	3.14±0.17[9] dex
Rotation	1.39 d[7]
Age	0.24+0.15 −0.11[7] Gyr
Other designations
CR Ursae Majoris, BD+55 1634, HIP 67231, HD 120198, HR 5187, SAO 28885[10]
Database references
SIMBAD	data

Gerhard Jackisch discovered that 84 Ursae Majoris is a variable star, with a period greater than one day, in 1972.^[12] It was given the variable star designation CR Ursae Majoris in 1974.^[13]

In 1994 John Rice and William Wehlau used Doppler imaging to map the distribution of iron and chromium on the surface of 84 Ursae Majoris. They found that the distribution of those elements across the surface was similar, and the abundances of those elements varied by a factor of 15 across the surface. Chromium was found to be about 600 times more abundant than on the Sun in the regions of the 84 Ursae Majoris surface with the minimum chromium abundance.^[14]

The size of 84 Ursae Majoris was measured in red light during 2015 and 2016, using the CHARA array. The limb darkened angular diameter was 0.226±0.008 milliarcseconds.^[4]

References

1. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 16 January 2023.
2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
3. Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
4. Perraut, K.; Cunha, M.; Romanovskaya, A.; Shulyak, D.; Ryabchikova, T.; Hocdé, V.; Nardetto, N.; Mourard, D.; Meilland, A.; Morand, F.; Tallon-Bosc, I.; Farrington, C.; Lanthermann, C. (October 2020). "Benchmarking the fundamental parameters of Ap stars with optical long-baseline interferometric measurements" (PDF). Astronomy and Astrophysics. 642: A101. Bibcode:2020A&A...642A.101P. doi:10.1051/0004-6361/202038753. S2CID 225158717. Retrieved 20 January 2023.
5. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169. Retrieved 20 January 2023.
6. Kochukhov, O.; Bagnulo, S. (May 2006). "Evolutionary state of magnetic chemically peculiar stars" (PDF). Astronomy and Astrophysics. 450 (2): 763–775. arXiv:astro-ph/0601461. Bibcode:2006A&A...450..763K. doi:10.1051/0004-6361:20054596. S2CID 18596834. Retrieved 20 January 2023.
7. Deal, M.; Cunha, M. S.; Keszthelyi, Z.; Perraut, K.; Holdsworth, D. L. (June 2021). "Fundamental properties of a selected sample of Ap stars: Inferences from interferometric and asteroseismic constraints" (PDF). Astronomy and Astrophysics. 650: A125. arXiv:2104.08097. Bibcode:2021A&A...650A.125D. doi:10.1051/0004-6361/202040234. S2CID 233289688. Retrieved 20 January 2023.
8. Adelman, S. J.; Rayle, K. E. (March 2000). "On the effective temperatures, surface gravities, and optical region fluxes of the CP stars". Astronomy and Astrophysics. 355: 308–314. Bibcode:2000A&A...355..308A. Retrieved 20 January 2023.
9. Sikora, J.; Wade, G. A.; Power, J.; Neiner, C. (February 2019). "A volume-limited survey of mCP stars within 100 pc - I. Fundamental parameters and chemical abundances". Monthly Notices of the Royal Astronomical Society. 483 (2): 2300–2324. arXiv:1811.05633. Bibcode:2019MNRAS.483.2300S. doi:10.1093/mnras/sty3105. Retrieved 20 January 2023.
10. "84 UMa -- alpha2 CVn Variable". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-01-20.
11. Roberts, Lewis C.; Turner, Nils H.; ten Brummelaar, Theo A. (February 2007). "Adaptive Optics Photometry and Astrometry of Binary Stars. II. A Multiplicity Survey of B Stars". The Astronomical Journal. 133 (2): 545–552. Bibcode:2007AJ....133..545R. doi:10.1086/510335. S2CID 10416471. Retrieved 20 January 2023.
12. Jackisch, G. (September 1972). "Über die Veränderlichkeit der Sterne des Spektraltyps A". Astronomische Nachrichten. 294 (1–2): 1–8. Bibcode:1972AN....294....1J. doi:10.1002/asna.19722940102. Retrieved 20 January 2023.
13. Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (January 1975). "60th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 961: 1. Bibcode:1975IBVS..961....1K. Retrieved 20 January 2023.
14. Rice, John; Wehlau, William (February 1994). "Surface Distribution of Iron and Chromium on 84 UMa". Publications of the Astronomical Society of the Pacific. 106: 134–137. Bibcode:1994PASP..106..134R. doi:10.1086/133357. S2CID 119432777. Retrieved 20 January 2023.