• Source: T Coronae Borealis

T Coronae Borealis (T CrB), nicknamed the Blaze Star, is a binary star and a recurrent nova about 3,000 light-years away in the constellation Corona Borealis. It was first discovered in outburst in 1866 by John Birmingham, though it had been observed earlier as a 10th magnitude star. It may have been observed in 1217 and in 1787 as well.




Description



T CrB normally has a magnitude of about 10, which is near the limit of typical binoculars. Well documented outbursts have been seen twice, reaching magnitude 2.0 on May 12, 1866 and magnitude 3.0 on February 9, 1946, though a more recent paper shows the 1866 outburst with a possible peak range of magnitude 2.5 ± 0.5. Even when at peak magnitude of 2.5, this recurrent nova is dimmer than about 120 stars in the night sky. It is sometimes nicknamed the Blaze Star.

T CrB is a binary system containing a large cool component and a smaller hot component. The cool component is a red giant that transfers material to the hot component. The hot component is a white dwarf surrounded by an accretion disc, all hidden inside a dense cloud of material from the red giant. When the system is quiescent, the red giant dominates the visible light output and the system appears as an M3 giant. The hot component contributes some emission and dominates the ultraviolet output. During outbursts, the transfer of material to the hot component increases greatly, the hot component expands, and the luminosity of the system increases.

The two components of the system orbit each other about every 228 days. The orbit is almost circular and is inclined at an angle of 67°. The stars are separated by 0.54 AU.




2016–present activity


On 20 April 2016, the Sky & Telescope website reported a sustained brightening since February 2015 from magnitude 10.5 to about 9.2. A similar event was reported in 1938, followed by another outburst in 1946. By June 2018, the star had dimmed slightly but still remained at an unusually high level of activity. By mid-2023, it faded by 0.35 magnitude; the lowest brightness seen since 2016. A similar dimming occurred in the year before the 1946 outburst, indicating an eruption before September 2024. As of November 2024, such a nova has not yet been observed, although it is believed to be imminent.
Predictions of the next nova:

2026-2027 (made in 1946 either by N.F.H.Knight or W.M. Lindley)
Mid February 2024 to End September 2026 (made in March 2023)
Beginning January 2024 to Mid August 2024 (made in June 2023)
January 2024 (made in August 2023)
End of October 2024 (made in June 2024)
Around 27 March 2025, 10 November 2025, 25 June 2026 or 8 February 2027 (made in October 2024)




References






Further reading


Wallerstein, George; Tanya Harrison; Ulisse Munari; Andrew Vanture (11 May 2008). "The Metallicity and Lithium Abundances of the Recurring Novae T CrB and RS Oph". Publications of the Astronomical Society of the Pacific. 120 (867): 492–497. Bibcode:2008PASP..120..492W. doi:10.1086/587965. S2CID 106406607.
R and T Coronae Borealis: Two Stellar Opposites at Sky & Telescope Archived 2012-04-06 at the Wayback Machine




External links


Blaze Star, www.daviddarling.info
AAVSO: Check Recent Observations (get recent magnitude estimates for T CrB)

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