15 Cancri

15 Cancri is an α2 CVn-type variable star in the zodiac constellation of Cancer, located around 980[1] light years away. It has the variable star designation BM Cancri (BM Cnc); 15 Cancri (15 Cnc) is the Flamsteed designation. This system is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of about 5.6. It is moving away from the Earth with a heliocentric radial velocity of 25 km/s.[5]

15 Cancri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Cancer
Right ascension  08h 13m 08.87009s[1]
Declination +29° 39′ 23.5777″[1]
Apparent magnitude (V) 5.53 - 5.65[2]
Characteristics
Spectral type A0:V:spSiSr[3]
B−V color index −0.073±0.002[4]
Variable type α2 CVn[2]
Astrometry
Radial velocity (Rv)25.0±0.8[5] km/s
Proper motion (μ) RA: −12.959[1] mas/yr
Dec.: −22.232[1] mas/yr
Parallax (π)3.3279 ± 0.2458[1] mas
Distance980 ± 70 ly
(300 ± 20 pc)
Absolute magnitude (MV)−0.97[4]
Orbit[5]
Primary15 Cancri A
Companion15 Cancri B
Period (P)635.73±0.53 days[note 1]
Eccentricity (e)0.55±0.08
Periastron epoch (T)2422045±18
Argument of periastron (ω)
(primary)		196±13°
Semi-amplitude (K1)
(primary)		9.6±1.1 km/s
Details
15 Cnc A
Luminosity327.24[4] L☉
Surface gravity (log g)3.22±0.2[6] cgs
Temperature10,080±200[6] K
Rotational velocity (v sin i)25[3] km/s
Other designations
15 Cnc, BM Cnc, BD+30°1664, HD 68351, HIP 40240, HR 3215, GSC 01939-01462[7]
Database references
SIMBADdata

Radial velocity measurements taken at the Dominion Astrophysical Observatory in Victoria, British Columbia Canada in 1918 and 1919 led to the determination that 15 Cancri is a single-lined spectroscopic binary system.[8] The first orbit was calculated in 1973 by Helmut Abt and Michael Snowden with a period of 585 days[9] however later measurements showed that the orbital period was 635 days.[5][note 1]

15 Cancri A, the visible component, is an Ap star, a chemically peculiar star with an over-abundance of iron peak elements, particularly silicon, chromium, and strontium, in its spectrum.[10][3]

Like all Ap stars, 15 Cancri has a strong magnetic field. This magnetic field varies as it rotates and in 1968 the visual brightness of the star was shown to vary regularly over about four days.[11] 15 Cancri was given the variable star designation BM Cancri in 1972 as a member of the α2 CVn class of variable stars.[12] The period has since been measured more accurately at 3.3095 d, believed to be the rotational period of the star.[13]

Notes
  1. An alternate period of 475 days is possible but less likely.

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. 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....102025S.
  3. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
  4. 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.
  5. Stickland, D. J.; Weatherby, J. (1984). "Radial velocities of northern Mercury stars". Astronomy and Astrophysics Supplement Series. 57: 55–67. Bibcode:1984A&AS...57...55S.
  6. Khalack, V.; LeBlanc, F. (2015). "Project VeSElkA: Analysis of Balmer Line Profiles of Slowly Rotating Chemically Peculiar Stars". The Astronomical Journal. 150 (1). 2. arXiv:1505.08158. Bibcode:2015AJ....150....2K. doi:10.1088/0004-6256/150/1/2.
  7. SIMBAD, 15 Cancri (accessed 2012 March 20)
  8. Plaskett, J. S.; et al. (1919). "Fourth list of spectroscopic binaries". Journal of the Royal Astronomical Society of Canada. 13: 372–378. Bibcode:1919JRASC..13..372P.
  9. Abt, Helmut A.; Snowden, Michael S. (1973). "The Binary Frequency for AP Stars". Astrophysical Journal Supplement. 25: 137–162. Bibcode:1973ApJS...25..137A. doi:10.1086/190265.
  10. Renson, P.; Manfroid, J. (2009). "Catalogue of Ap, Hg Mn and Am stars". Astronomy & Astrophysics. 498 (3): 961–966. Bibcode:2009A&A...498..961R. doi:10.1051/0004-6361/200810788.
  11. Stepien, K. (1968). "Photometric behavior of magnetic stars". The Astrophysical Journal. 154: 945. Bibcode:1968ApJ...154..945S. doi:10.1086/149815.
  12. Martins, D. H. (1972). "New Southern Variable Stars". Information Bulletin on Variable Stars. 705: 1. Bibcode:1972IBVS..705....1M.
  13. Wraight, K. T.; Fossati, L.; Netopil, M.; Paunzen, E.; Rode-Paunzen, M.; Bewsher, D.; Norton, A. J.; White, Glenn J. (2012). "A photometric study of chemically peculiar stars with the STEREO satellites - I. Magnetic chemically peculiar stars★". Monthly Notices of the Royal Astronomical Society. 420 (1): 757–772. arXiv:1110.6283. Bibcode:2012MNRAS.420..757W. doi:10.1111/j.1365-2966.2011.20090.x.
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