65 Ursae Majoris

65 Ursae Majoris, abbreviated as 65 UMa, is a star system in the constellation of Ursa Major. With an apparent magnitude of about 6.5,[2] it is at the limit of human eyesight and is just barely visible to the naked eye. Trigonometric parallax measurements made by the Hipparcos spacecraft put it at a distance of about 690 light years (210 parsecs);[1] this is in close agreement with the dynamical parallax value of 763 ± 95 light-years (234 ± 29 pc).[5]

65 Ursae Majoris
Location of 65 Ursae Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
65 UMa ABC
Right ascension  11h 55m 05.74925s[1]
Declination +46° 28′ 36.6408″[1]
Apparent magnitude (V) +6.54[2] (A/B/C = 6.7 / 8.5 / 8.32)[3]
65 UMa D
Right ascension  11h 55m 11.33152s[1]
Declination +46° 28′ 11.2150″[1]
Apparent magnitude (V) +6.965[4]
Characteristics
65 UMa ABC
Spectral type A7 / A7 / A3 / ? / ?[5]
U−B color index +0.08[2]
B−V color index +0.11[2]
Variable type Algol[5]
65 UMa D
Spectral type A0p[6]
U−B color index +0.01[2]
B−V color index +0.02[2]
Astrometry
65 UMa ABC
Radial velocity (Rv)-3.90 ± 4.4[7] km/s
Proper motion (μ) RA: 10.41[1] mas/yr
Dec.: 2.38[1] mas/yr
Parallax (π)4.72 ± 0.58[1] mas
Distanceapprox. 690 ly
(approx. 210 pc)
65 UMa D
Radial velocity (Rv)-7.00 ± 3.7[8] km/s
Proper motion (μ) RA: 11.82[1] mas/yr
Dec.: 0.39[1] mas/yr
Orbit[5]
Primary65 UMa A
Companion65 UMa B
Period (P)118.209 ± 0.690 yr
Semi-major axis (a)208.2 ± 9.7 mas
Eccentricity (e)0.504 ± 0.006
Inclination (i)38.1 ± 2.4°
Longitude of the node (Ω)92.1 ± 4.2°
Periastron epoch (T)2447516.9 ± 126.8
Argument of periastron (ω)
(secondary)		202.7 ± 1.3°
Details
65 UMa Aa1
Mass1.74 ± 0.06[5] M☉
Radius1.86 ± 0.08[5] R☉
Temperature8000[5] K
65 UMa Aa2
Mass1.71 ± 0.06[5] M☉
Radius1.81 ± 0.08[5] R☉
Temperature7948 ± 20[5] K
65 UMa D
Radius4.39–4.56[6] R☉
Surface gravity (log g)3.5–3.6[6] cgs
Temperature9300–9500[6] K
Other designations
65 UMa, ADS 8347, CCDM J11551+4629
65 UMa ABC: DN UMa, BD+47° 1913, HD 103483, HIP 58112, HR 4560, SAO 43945
65 UMa D: BD+47° 1914, HD 103498, HIP 58117, HR 4561, SAO 43946
Database references
SIMBAD65 UMa
65 UMa AB
65 UMa C
65 UMa D

65 Ursae Majoris is a sextuple star system. It contains six stars in a hierarchical orbit where each star orbits the central system. Such systems are fairly uncommon, with only a few sextuple stars known.[5] Higher-multiplicity star systems are uncommon because they are less stable than their simpler counterparts, and often decay into smaller systems.

Multiplicity
Aa1
Period = 1.73d
a = 0.2 mas
Aa2
Period = 641d
a = 11 mas
Ab
Period = 118y
a = 0.18″
B
3.4″ separation
C
63″ separation
D

Hierarchy of orbits in the 65 Ursae Majoris system

The central pair of stars are both A-type main-sequence stars. These are relatively bright, white-colored stars that typically have masses from 1.6 M☉ to 2.4 M☉.[9] 65 Ursae Majoris Aa1 and Aa2 both have relatively low masses for an A-type main sequence star and have spectral types of A7V.[5] Both components periodically pass in front of each other while orbiting, so they form an eclipsing binary with the variable star designation DN Ursae Majoris. Therefore, the apparent magnitude of the system varies between 6.6 and 6.7 magnitudes.[10] Its orbital period of 1.73 days.[5]

The eclipsing binary pair 65 Ursae Majoris Aa is orbited by another star, designated 65 Ursae Majoris Ab. It is a spectroscopic binary: while the pair cannot be resolved, periodic Doppler shifts in their spectra indicate that there must be orbital motion. 65 Ursae Majoris orbits the inner pair with a period of 641 days (1.76 years) and an eccentricity of 0.169.[5]

65 Ursae Majoris B orbits the three every 118 years. It is separated from the triple by 0.18″, and an astrometric orbit has been calculated. 65 Ursae Majoris C and D are common proper motion companions and are separated 4″ and 63″ away from the central system, respectively.[5] 65 Ursae Majoris D also appears to be a chemically peculiar star with higher amounts of chromium, strontium, and europium than normal.[11] Because of its unusual composition, determination of its stellar parameters is difficult; the effective temperature of this star may be 9300 or 9500 K, with the radius and the surface gravity of the star depending on the effective temperature.[6]


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See also
  • Castor, another multiple star system with six stars
  • Zeta Phoenicis, a multiple star system including an eclipsing binary

References
  1. van Leeuwen, F.; et al. (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.
  2. Tolbert, C. R. (1964). "A UBV Study of 94 Wide Visual Binaries". Astrophysical Journal. 139: 1105. Bibcode:1964ApJ...139.1105T. doi:10.1086/147852.
  3. Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy & Astrophysics Supplement Series. 124: 75. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181.
  4. Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27–L30. Bibcode:2000A&A...355L..27H.
  5. Zasche, P.; Uhlář, R.; Šlechta, M.; Wolf, M.; Harmanec, P.; Nemravová, J. A.; Korčáková, D. (2012). "Unique sextuple system: 65 Ursae Majoris". Astronomy & Astrophysics. 542: A78. arXiv:1207.0651. Bibcode:2012A&A...542A..78Z. doi:10.1051/0004-6361/201219134.
  6. Pandey, Chhavi P.; Shulyak, Denis V.; Ryabchikova, Tanya; Kochukhov, Oleg (2012). "Abundance and stratification analysis of the CP star HD 103498". Astronomical Society of India Conference Series. 6: 225. arXiv:1106.3727. Bibcode:2012ASInC...6..225P.
  7. Gontcharov, G. A. (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.
  8. Kharchenko, N. V.; et al. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776.
  9. Adelman, Saul J. (2004). "The physical properties of normal A stars". Proceedings of the International Astronomical Union. 2004: 1. Bibcode:2004IAUS..224....1A. doi:10.1017/S1743921304004314.
  10. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....1.2025S.
  11. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 95: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.

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