15 Cancri is an α2 CVn-type variable star in the zodiac constellation of Cancer, located around 700 light years away.[1] 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.[2]

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.[3] The first orbit was calculated in 1973 by Helmut Abt and Michael Snowden with a period of 585 days[4] however later measurements showed that the orbital period was 635 days.[2][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.[5][6]

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.[7] 15 Cancri was given the variable star designation BM Cancri in 1972 as a member of the α2 CVn class of variable stars.[8] The period has since been measured more accurately at 3.3095 days, believed to be the rotational period of the star.[9]

In Johann Bayer’s Uranometria, this star was designated as Psi Geminorum. When the constellation borders were set in 1930, it was moved to Cancer, so the designation has been dropped.[10]

References

  1. ^
  2. ^ 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
  3. ^ 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
  4. ^ 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
  5. ^ 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
  6. ^ 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
  7. ^ Stepien, K. (1968). "Photometric behavior of magnetic stars". The Astrophysical Journal. 154: 945. Bibcode:1968ApJ...154..945S. doi:10.1086/149815
  8. ^ Martins, D. H. (1972). "New Southern Variable Stars". Information Bulletin on Variable Stars. 705: 1. Bibcode:1972IBVS..705....1M
  9. ^ 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. S2CID 14811051
  10. ^ Ian Ridpath. "Bayer's Uranometria and Bayer letters". Retrieved 2017-11-27.
  1. ^ An alternate period of 475 days is possible but less likely.