I recently I took some time and reviewed AAVSO's entire long-term visual database for the recurrent nova T CRB and in doing so noticing something quite interesting. Having experienced outbursts that attained a magnitude of 2-3 in 1866 and again in 1946, with expectations of another such event around 2026, data taken over the past couple of years displays a very interesting and most unexpected trend.
The pre-outburst phase of T CRB's 1946 eruption is fairly well documented, most thoroughly through data by the late Leslie Peltier of Delphos, Ohio, who carefully followed the star's activity from the early 1920's up through the outburst phase. There are two very brief instances of minor brightenings based on seemingly spurious observations by others during this period, but since AAVSO reports of the era did not include the comparison stars used to make the brightness determinations it is impossible to cross check the source of these undoubtedly erroneous data. Nevertheless, observations by the most trustworthy AAVSO observers show the nova consistently near magnitude +10.0 (with very slight fluctuations) right up to just a few nights before the onset of the 1946 outburst.
The 1866 event was unanticipated and therefore its behavior during early stages of the eruption are undocumented. That of 1946 is much clearer, Peltier having made his final pre-outburst sighting on 1946 Feb. 2.4UT at a magnitude of +9.9. The star was next caught in mid-rise on 1946 Feb. 4.5 at +5.1 and apparently attained peak brightness several days later as indicated by observations of +3.0 and 3.3 reported on 1946 Feb. 9. The nova's brightness rapidly subsided reaching +6.0 within a week and fully returned to its pre-outbutst level after a couple of years. It remained hovering near +10.0 with only minor fluctuations for almost the next 70 years.
Something altogether different has been occurring with T CRB lately. Many of us are aware that the star has unexpectedly undergone 2 or 3 recent brief rises to near +9.0 , then fallen back recently. Something I've not seen mention of elsewhere, however, is the alteration in the star's mean quiescent brightness. During the past 3 years T CRB has displayed a very steady rise in its quiescent state elevating it by over half a magnitude. Such an alteration is not indicated, or even hinted at, at any time over the previous 70 years of intensive monitoring. Neither is such a pre-outburst rise represented in the data leading up to the 1946 outburst.
The above leads me to believe that the next outburst event will come sooner than 2026...perhaps decidedly sooner. Dwarf novae, cousins to the recurrent novae, often exhibit enhanced activity, either an abrupt brightness rise or fall, immediately preceding an outburst. Admittedly, we know precious little about recurrent novae behavior during the pre-outbust stage, but after my long association with variable star activity if I were to venture a guess, I'd say that T CRB should be monitored intently during the next year, or two.
Edited by BrooksObs, 28 February 2018 - 03:16 PM.