Sun, 03/03/2019 - 19:36
In my last received Data Usage Report, an anonymous professional astronomer used my observations for an observing run on T Coronae Borealis. It served as a good reminder that it would be good (especially now) to keep an eye on this star as we go forward.
The only two outbursts of this recurrent nova (1866, 1946) occurred 80 years apart. The last outburst was 73 years ago. I will be casting a watchful eye toward T CrB as the weather permits and look forward to when the Northern Crown puts on an addtional jewel in its wreath of stars.
Does anyone know why T CrB has not been seen in outburst prior to 1866? With a peak brightness in outburst of mag 2-3V, this star should have been easily seen with the naked eye, even in ancient times.
I too have pondered on that question. Why has no one apparently reported such a bright nova in that position before 1866? If we accept that 80 years is the recurrence time, 80 years before 1866 was in 1786. At that time there were already plenty of modern astronomers with optical instruments, at least in Europe. If there was an outburst someone should have seen it. Also before the telescope era, a new mag 2-3 star may not have passed unnoticed, as you say. May be there were no outburts previous to 1866? Or perhaps there were outburst that were much fainter and thus went undetected? Or perhaps we have not yet found some lost records of ancient astronomy where an outburst is recorded? This star is just too interesting!
In Comprehensive photometric histories of all known galactic recurrent novae Bradley Schaefer mentions (and rejects) an alleged 1842 T CrB outburst observed by Herschel.
Other than that, the hypotetical 1786 outburst could go unnoticed the same way many other novae, reported in Chinese or Japanese sources, left no trace in Western astronomical records. Not being a historical astronomy expert, I wonder:
a) Did Oriental sources recorded some event of this sort?
b) How many Novae reports could we find in 17th, 18th century European sources?
Maybe Novae were considered just not interesting phenomena.
I have now found and downloaded Schaefer's article. It is a long read at 99 pages, but surely seems a good one! Thanks for poiting it out!
I have no answers to the questions you pose.
In fact, Oriental (Chinese, Korean and Japanese) records of "guest stars" are considered the main sources forf historical supernovae and novae. I'm not an expert of this subject, but Wikipedia points to:
Zhentao Xu, David W. Pankenier (2000) "East-Asian Archaeoastronomy: Historical Records of Astronomical Observations of China, Japan, and Korea", ISBN 90-5699-302-X, Chapter 6, "Guest Stars"
("Guest star" was a term for any transients, including comets. I think the majority of guest stars that were stationary on the sky were supernovae, mainly because they remain bright for longer than novae.)
This makes me think: T CrB has a very short t3 of only 6 days, according to Brad Schaefer's Table 1. The peak may be magnitude 2.5, but by six days after peak, it's almost out of naked-eye range. This makes it easy to miss eruptions of T CrB...
Thanks for the reminder. I believe many of us variable star observers are conscious of the fact that it may not take long for T CrB to enter outburst stage again and keepn an eye on it. It is nevertheless a good thing to remind us all of that.
I noticed this paper on last night's astro-ph preprint server:
Increasing activity in T CrB suggests nova eruption is impending
The authors predict the next eruption for 2026 +/- 3 years. It looks as though the star is being very well covered in multiple filters --- probably B,V,I are the essential ones, though having good U-band data (for U-B color indices) or spectra near H-alpha might allow mass-transfer activity to be seen more clearly.
Koji Mukai writes: "This makes me think: T CrB has a very short t3 of only 6 days, according to Brad Schaefer's Table 1. The peak may be magnitude 2.5, but by six days after peak, it's almost out of naked-eye range. This makes it easy to miss eruptions of T CrB."
Yes, if the optical peak occurred around solar conjunction or during a spell of bad weather, then the whole eruption could have been easily missed in the 18th century and before. And of couse we do not know when T Coronae Borealis erupted for the very first time (could it have been in 1866?).
And remember, Mira gets as bright as second or third magnitude for several days or weeks almost every year but was not officially discovered until 13 August 1596 by David Fabricius. How could this bright variable star go unnoticed for centuries and millennia?
Brian Skiff writes: "The authors predict the next eruption for 2026 ± 3 years."
Maybe astronomers expected already back in 1946 the third recorded eruption for around 2026. ;-)
In March 2016, it was noted that T CrB was brighter than usual by about half a magnitude. AAVSO Special Notice #415 was issued to draw attention to T CrB and ask for good coverage going forward. In the Notice a very interesting paper by U. Munari et al. was referenced and information in it summarized, including that the next outburst might occur in 2026. Please see the Notice and read the paper referenced therein.
Since March 2016, T CrB has continued to be about half a magnitude brighter; it has not returned to pre-March 2016 levels. Observations of this extremely interesting star in all bands are encouraged going forward.