BT Monocerotis

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BT Monocerotis
Observation data
Epoch J2000      Equinox J2000
Constellation Monoceros
Right ascension 06h 43m 47.24s
Declination −02° 01′ 13.9″
Apparent magnitude (V) 15.4
Spectral type D/G8V
Variable type Eclipsing binary[1]
Distance 1,700 ± 300[1] pc
Mass 1.04/0.87[1] M
Rotational velocity (v sin i) —/138[1] km/s
Other designations
BT Mon, Nova Monocerotis 1939

BT Monocerotis (Nova Monocerotis 1939) was a nova, which lit up in the constellation Monoceros in 1939. It was discovered on a spectral plate by Fred L. Whipple on December 23, 1939.[2] BT Monocerotis reached a brightness of 4.5 mag.[citation needed] Its brightness decreased after the outbreak in 36 days by 3 mag.[citation needed] The light curve for the eruption had a long plateau period.[2]

Photographic plates taken for 30 years prior to the eruption show that BT Monocerotis remained visible during that period. Prior to 1933, BT Monocerotis had an average magnitude of 15.52 with a variation of 1.2 magnitudes. It retained the same magnitude up until the eruption, showing a variation of 0.9 magnitudes. Thus it did not show a pre-eruption rise in brightness.[2]

This is an interacting binary star system consisting of a white dwarf primary star and a main sequence star with a stellar classification of G8V. The orbit has a period of 0.33381379 days[2] and an inclination of 88.2° to the line of sight to the Earth, resulting in an eclipsing binary.[1] The nova eruption is believed to have been driven by mass transferred from the secondary star to the white dwarf.[3] It remains uncertain whether the white dwarf has an accretion disk formed by this material. Matter outflowing from the system has a line of sight velocity of 450 km s−1, but may be moving at up to 3,200 km s−1 if the flow is strictly bipolar.[4]


  1. ^ a b c d e Smith, D. A.; Dhillon, V. S.; Marsh, T. R. (1998). "The mass of the white dwarf in the old nova BT MON". In S. Howell, E. Kuulkers, C. Woodward (1998). Wild Stars In The Old West: Proceedings of the 13th North American Workshop on Cataclysmic Variables and Related Objects. ASP Conference Series 137. p. 477. Bibcode:1998ASPC..137..477S. 
  2. ^ a b c d Collazzi, Andrew C. et al. (December 2009). "The Behavior of Novae Light Curves Before Eruption". The Astronomical Journal 138 (6): 1846–1873. arXiv:0909.4289. Bibcode:2009AJ....138.1846C. doi:10.1088/0004-6256/138/6/1846. 
  3. ^ Knigge, Christian (December 2006). "The donor stars of cataclysmic variables". Monthly Notices of the Royal Astronomical Society 373 (2): 484–502. arXiv:astro-ph/0609671. Bibcode:2006MNRAS.373..484K. doi:10.1111/j.1365-2966.2006.11096.x. 
  4. ^ Kafka, S.; Honeycutt, R. K. (November 2004). "Detecting Outflows from Cataclysmic Variables in the Optical". The Astronomical Journal 128 (5): 2420–2429. Bibcode:2004AJ....128.2420K. doi:10.1086/424618. 

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