T Corona Borealis in history

On topic of stars up and leaving our field, with the h/t to Breitbart: T Corona-Borealis (mediaevally -Ariadnae) is set to blow... soon. This was first published in May 1866 then, watched by better instruments, February 1946. Thence in 1977 one R[onald?] Webbink tracked a previous observation in Rev. Francis Wollaston's 1789 catalog, confusing it with HD 143707 = Herschel V 75; Bradley Schaefer confirms 1787 December 28 (hey: good job with organising the year first, we programmers salute you).

If this interpretation of Wollaston's (mis)note holds, we might have a pattern. Schaefer additionally sees a radiant star noted by a monk Burchard for AD 1217 as being, actually, T Co-Bo; noting that observers well into modern times routinely saw trails spouted off of supernovae like that famous Crab blowup AD 1054 and Kepler's own 1604.

For that nova in 1217, Schaefer assumes this recurrence: 7×81.4, 78.5, 79.7 years. Much weight is placed on that ×; he must expect additional eruptions within a year or two of 1706, 1625, 1544, 1462, 1381, 1299... AD.

So let's look to the system. Their semimajor is 0.54 AU. 1 AU = 214 solar radii; so the red giant here is orbiting at 116 M_☉. I assume the two formed together so are the same age, the 1.37 M_☉ white dwarf exploding first. The red giant's own radius is 75 M_☉. Its mass is still 1.12 M_☉; which means their barycentre is closer to the dwarf, with the giant seeming to orbiting the dwarf. That giant should have expanded out beyond 1 whole AU, like they say of our own Sun. I assume that it was during its redgianting when most of that hydrogen was sucked-up by the companion. Both stars then slowed in the mire toward their present proximity.

And there's my problem. As a star continues to gobble matter, flareups should gradually peter out as available matter decreases. So if they happen, like, ~80 years apart in modern times they might have happened more-frequently in the Middle Ages. The white dwarf has already cleared most of the mass. And the overall Keplerian ratio has been depleted as so much of what's left is going nova and escaping at lightspeed, literally so with much of the mass.

Schaefer continues prior to that monk: 1137, 1055, 974, 892, 811, 730, 648, 567, 485, 404, 323, 241, 160, and 78 AD. Of these AD 648 and 730 would fall in my purview. The Syrians, at least, saw no new-stars worthy of Hoyland's mention in Seeing Islam. 740s? maybe. 670s? sure! And the 620s-30s be rife with portents, which we can take or leave.

Looking afield to Ralph and Dagmar Neuhaeuser, we get (no aurorae in any catalog found from AD 719 to 733); then a portent in the sky seen in Constantinople, and seen and heard(!) among the Tang. Although ... the Neuhaeusers say aurora, not nova. Their notices for the early 800s don't look much better for the nova hypothesis.

For the Tang comets we go to Williams. These accounts for Borealis all have the hairy star moving around the field, never just staying in "Kwan Soo". A nova can't do that.