78 Ursae Majoris

78 Ursae Majoris is a binary star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye as a faint point of light with a combined apparent visual magnitude of 4.93.^[13] Parallax estimates by Hipparcos put it at a distance of 83 light-years (25 pc),^[1] but it is drifting closer with a radial velocity of −5 km/s.^[2] The system is a candidate member of the Ursa Major Moving Group.^[14]

78 Ursae Majoris

Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	13h 00m 43.69949s[1]
Declination	+56° 21′ 58.8102″[1]
Apparent magnitude (V)	4.93[2] (5.02 + 7.88)[3]
Characteristics
Evolutionary stage	main sequence
Spectral type	F2V[4] + G6V[5]
U−B color index	+0.00[6]
B−V color index	+0.368±0.010[2]
Astrometry
Radial velocity (Rv)	−5.1±0.9[2] km/s
Proper motion (μ)	RA: 107.94[1] mas/yr Dec.: 2.05[1] mas/yr
Parallax (π)	39.30 ± 0.38 mas[1]
Distance	83.0 ± 0.8 ly (25.4 ± 0.2 pc)
Absolute magnitude (MV)	+2.84[7]
Orbit[8]
Period (P)	104.9±0.6 yr
Semi-major axis (a)	1.208±0.010″
Eccentricity (e)	0.388±0.009
Inclination (i)	46.9±0.9°
Longitude of the node (Ω)	88.0±1.1°
Periastron epoch (T)	B 1921.224±0.403
Argument of periastron (ω) (secondary)	119.2±1.5°
Details
78 UMa A
Mass	1.34[9] M☉
Radius	1.62±0.24[10] R☉
Luminosity	5.75[2] L☉
Surface gravity (log g)	4.26±0.14[9] cgs
Temperature	6,908±235[9] K
Metallicity [Fe/H]	0.01±0.05[11] dex
Rotation	19.2 ± 2.9 h[10]
Rotational velocity (v sin i)	91.7±4.6[12] km/s
Age	785[9] Myr
Other designations
78 UMa, BD+57°1408, HD 113139, HIP 63503, HR 4931, SAO 28601, WDS J13007+5622[13]
Database references
SIMBAD	The system
	A
	B

The binary nature of this system was announced by S. W. Burnham in 1894.^[15] The pair orbit each other with a period of 105 years and an eccentricity of 0.39. Their semimajor axis has an angular size of 1.2″ and the orbital plane is inclined by 47°.^[8]

The primary member, designated component A, has a magnitude of 5.02^[3] and is an F-type main-sequence star with a stellar classification of F2V.^[4] It is 785^[9] million years old and is spinning with a projected rotational velocity of 92 km/s.^[12] The star has 1.34^[9] times the mass of the Sun and is radiating 5.75^[2] times the Sun's luminosity from its photosphere at an effective temperature of 6,908 K.^[9]

The secondary, designated component B, has a visual magnitude of 7.88.^[3] It is a G-type main-sequence star with a class of G6V.^[5] The star is a suspected variable.^[16]

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. 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.
3. Fabricius, C.; et al. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
4. Gray, R. O.; et al. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I". The Astronomical Journal. 126 (4): 2048. arXiv:astro-ph/0308182. Bibcode:2003AJ....126.2048G. doi:10.1086/378365. S2CID 119417105.
5. Edwards, T. W. (April 1976), "MK classification for visual binary components", Astronomical Journal, 81: 245–249, Bibcode:1976AJ.....81..245E, doi:10.1086/111879.
6. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
7. Eggen, Olin J. (August 1998), "The Sirius Supercluster and Missing Mass near the Sun", The Astronomical Journal, 116 (2): 782–788, Bibcode:1998AJ....116..782E, doi:10.1086/300465.
8. Drummond, Jack D. (March 2014), "Binary Stars Observed with Adaptive Optics at the Starfire Optical Range", The Astronomical Journal, 147 (3): 10, Bibcode:2014AJ....147...65D, doi:10.1088/0004-6256/147/3/65, 65.
9. 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.
10. Justesen, A. B.; Albrecht, S. (October 2020). "The spin-orbit alignment of visual binaries". Astronomy & Astrophysics. 642: 10. arXiv:2008.12068. Bibcode:2020A&A...642A.212J. doi:10.1051/0004-6361/202039138. S2CID 221340982. A212.
11. Gáspár, András; et al. (2016), "The Correlation between Metallicity and Debris Disk Mass", The Astrophysical Journal, 826 (2): 171, arXiv:1604.07403, Bibcode:2016ApJ...826..171G, doi:10.3847/0004-637X/826/2/171, S2CID 119241004.
12. Ammler-von Eiff, Matthias; Reiners, Ansgar (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
13. "* 78 UMa". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 19 August 2017.
14. Nakajima, Tadashi; Morino, Jun-Ichi (2012), "Potential Members of Stellar Kinematic Groups within 30 pc of the Sun", The Astronomical Journal, 143 (1): 2, Bibcode:2012AJ....143....2N, doi:10.1088/0004-6256/143/1/2.
15. "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 19 August 2017.
16. Baize, P.; Petit, M. (March 1989), "Etoiles doubles orbitales à composantes variables", Astronomy and Astrophysics, Supplemental Series, 77: 497–511, Bibcode:1989A&AS...77..497B.