BT Monocerotis


BT Monocerotis
Location of BT Monocerotis (circled in red)
Observation data
Epoch J2000      Equinox J2000
Constellation Monoceros
Right ascension 06h 43m 47.242s[1]
Declination −02° 01′ 13.88″[1]
Apparent magnitude (V) 4.5 – 15.8[2]
Spectral type D/G8V
Variable type Eclipsing binary[3]
Distance1,413 ± 97[4] pc
Mass1.04/0.87[3] M
Rotational velocity (v sin i)—/138[3] km/s
Other designations
BT Mon, Nova Monocerotis 1939, 2MASS J06434723-0201139, AAVSO 0638-01, Gaia DR2 3106991818813980416
Database references

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.[5] BT Monocerotis is believed to have reached mag 4.5, which would have made it visible to the naked eye, but that value is an extrapolation; the nova was not observed at peak brightness[2] Its brightness decreased after the outbreak by 3 magnitudes in 182 days, making it a "slow nova".[6] The light curve for the eruption had a long plateau period.[5]

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 until the eruption, showing a variation of 0.9 magnitudes. Thus it did not show a pre-eruption rise in brightness.[5]

This is an interacting binary star system consisting of a 1.04±0.06M white dwarf primary star and a 0.87±0.06M main sequence star with a stellar classification of G8V.[7] The orbit has a period of 0.33381379 days[5] and an inclination of 88.2° to the line of sight to the Earth, resulting in an eclipsing binary.[3] The nova eruption is believed to have been driven by mass transferred from the secondary star to the white dwarf.[8] 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.[9]


  1. ^ a b 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. ^ a b Robinson, E.L. (July 1975). "Preeruption light curves of novae". The Astronomical Journal. 80: 515–524. doi:10.1086/111774. Retrieved 26 December 2020.
  3. ^ a b c d 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 (eds.). 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.
  4. ^ Selvelli, Pierluigi; Gilmozzi, Roberto (February 2019). "A UV and optical study of 18 old novae with Gaia DR2 distances: mass accretion rates, physical parameters, and MMRD". Astronomy & Astrophysics. 622: A186. doi:10.1051/0004-6361/201834238. Retrieved 26 December 2020.
  5. ^ 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. S2CID 14597316.
  6. ^ Özdönmez, Aykut; Ege, Ergün; Güver, Tolga; Ak, Tansel (May 2018). "A new catalogue of Galactic novae: investigation of the MMRD relation and spatial distribution". Monthly Notices of the Royal Astronomical Society. 476 (3): 4162–4186. arXiv:1802.05725. doi:10.1093/mnras/sty432. Retrieved 26 December 2020.
  7. ^ Smith, D.A.; Dhillon, V.S.; Marsh, T.R. (May 1998). "The mass of the white dwarf in the old nova BT MON". Monthly Notices of the Royal Astronomical Society. 296 (3): 465–482. doi:10.1046/j.1365-8711.1998.00743.x. Retrieved 21 January 2021.
  8. ^ 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. S2CID 2616606.
  9. ^ 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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