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Heads Up on T CRB

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#1 BrooksObs

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Posted 28 February 2018 - 09:33 AM

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.

 

BrooksObs


Edited by BrooksObs, 28 February 2018 - 03:16 PM.

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#2 smithrrlyr

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Posted 28 February 2018 - 11:45 AM

Very interesting, and all the encouragement I need to keep up regular visual observations.  I hope that those with appropriate equipment will also be able to keep a regular eye on the spectrum of the star.  T CrB has apparently had some episodes of spectroscopic activity even during its long interval of photometric calm and Munari et al. noted some pronounced spectroscopic changes during the star's 2015 brightness increase.  The Munari et al. paper is freely available at https://arxiv.org/pdf/1602.07470.pdf .


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#3 robin_astro

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Posted 28 February 2018 - 06:15 PM

I hope that those with appropriate equipment will also be able to keep a regular eye on the spectrum of the star. 

Amateur spectroscopic coverage looks to be pretty good based on the number of spectra in the ARAS database

http://www.astrosurf...iotics/TCrB.htm

Also some in the BAA database

https://britastro.org/specdb/data.php

 

Cheers

Robin


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#4 Aquarellia

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Posted 01 March 2018 - 11:44 AM

Very interesting post.

 

It's one of my prefered target, I mean for my only visual estimation.  Indeed I saw -and reported- those recent brief rises.  

I give lectures in the world of amateur astronomers mainly in France and to push them to observe variable stars I show the following sketch (the up one):

 

maybe.jpg

 

And I ask them what's this constellation ?

the bottom sketch gives then the newlook of Corona Borealis where T-CRB is the new "alpha".

Michel


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#5 DHEB

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Posted 01 March 2018 - 02:46 PM

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.

 

BrooksObs

Thanks for these interesting thoughts. The "mean" quiescent magnitude has indeed slowly increased over the last 5 years or so. On the other hand, the light curve also shows a slight dimming from the mid nineties to about 2013. See the light curve below. T CrB is a star to monitor at every possible opportunity. I agree that it might give us a surprise any time.

Attached Thumbnails

  • screenshot.png

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#6 Keith g

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Posted 03 March 2018 - 09:34 AM

Your thoughts do make common sense BrooksObs when you think of it, just over 70 years have passed since 1946, well enough time for the accretion disk to build up enough material for the next eruption. I think in some years time we will see that the visual brightness rises over the last few years are linked to this. Every opportunity I get I glimpse at corona borealis, awaiting the next outburst of T Crb.

 

You've given me encouragement to keep observing this star !

 

Keith.


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#7 smithrrlyr

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Posted 05 April 2018 - 02:07 PM

The brightness of T CrB has decreased lately to about 9.9 or 10.0 in visual.  The pattern over the past thousand days is messy, but these diminutions in brightness seem to be followed by rises in brightness that can see the star approach magnitude 9.0, as noted by BrooksObs.  It will be interesting to see whether this happens again in the next few weeks.  It is interesting that a well-observed prior dip and mini-outburst happened about one of the star's 228 day orbital periods ago, but a tie-in with the orbital period is not so clear for some other recent variations.


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#8 BrooksObs

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Posted 06 April 2018 - 08:26 AM

Indeed, T CrB is current experiencing a deep dip in brightness. I caught it last evening at magnitude 9.8 myself. I would note that over the decades decades that I've followed this star its normal behavior was always to vary in brightness of a quite limited range with long duration cycles. Of late, however, all this has dramatically changed. Marked variations are occurring in just months, the range has distinctly increased and the mean magnitude has been slowly but steadily increasing for the past three or so years - all signals that the star is awakening from its three-quarters of a century slumber and readying itself for a new outburst.

 

BrooksObs


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#9 DHEB

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Posted 12 April 2018 - 02:18 AM

I visually estimated T CrB last night at 10.0 mag. Looking at the light curve, it seems that the last time an similar dimming has been recorded was between July and August 2017. Following that the star brightened relatively fast up to 9.0 mag in September 2017. Who knows, we might be witnessing some early pre-outburst instabilities. Amazing!
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#10 RobboK

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Posted 19 April 2018 - 07:34 PM

I made it out at about 10.0 last night, 19 Apr 2018.  It's pretty low in the north for me but should be visible for a month or two from here. I took a few shots as well, attached.  Just imagine, it's likely to be considerably brighter than Epsilon CrB (marked) when it does eventually go off.  Interesting time coming up!

 

Cheers -

 

Rob

 

T CrB, 19 Apr 2018 text sm.jpg

 

T CrB, 19 Apr 2018, 15-00 UT lines wide sm.jpg


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#11 Aquarellia

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Posted 20 April 2018 - 03:47 AM

I made it out at about 10.0 last night, 19 Apr 2018.  It's pretty low in the north for me but should be visible for a month or two from here. I took a few shots as well, attached.  Just imagine, it's likely to be considerably brighter than Epsilon CrB (marked) when it does eventually go off.  Interesting time coming up!

 

Cheers -

 

Rob

 

attachicon.gif T CrB, 19 Apr 2018 text sm.jpg

 

attachicon.gif T CrB, 19 Apr 2018, 15-00 UT lines wide sm.jpg

Indeed Rob, my last 3 visual estimations are +10.0 too

Here from Provence T-CrB is near the zenith in the morning quite bad for my back with my long refractor smile.gif

 

Michel


Edited by Aquarellia, 20 April 2018 - 03:49 AM.

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#12 happylimpet

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Posted 20 April 2018 - 04:19 AM

No visual estimates (does mv>4 count?) but I'm grateful to this thread for the heads-up. I always take a look and noticed that as of last night it certainly wasnt bright!!!!



#13 Aquarellia

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Posted 20 April 2018 - 04:46 AM

No visual estimates (does mv>4 count?) but I'm grateful to this thread for the heads-up. I always take a look and noticed that as of last night it certainly wasnt bright!!!!

You mean "mv" fainter than +4 ?? We are far from this magnitude today.  Visual estimation are done via a telescope or binoculars, this is not only naked eye visions.  So fainter than +4 is not very useful.

But you'r right, mv = +10 is the lower's magnitude I saw about this variable and as stated by BrooksObs it's why we have to follow the evolution carefully.

 

Michel



#14 happylimpet

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Posted 23 April 2018 - 07:39 AM

You mean "mv" fainter than +4 ?? We are far from this magnitude today.  Visual estimation are done via a telescope or binoculars, this is not only naked eye visions.  So fainter than +4 is not very useful.

But you'r right, mv = +10 is the lower's magnitude I saw about this variable and as stated by BrooksObs it's why we have to follow the evolution carefully.

 

Michel

I know. It was my little joke.



#15 RobboK

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Posted 04 July 2018 - 07:26 PM

Here's a link to a newly-released paper on T CrB, "Dramatic change in the boundary layer in the symbiotic recurrent nova T Coronae Borealis", addressing recent changes.

https://arxiv.org/abs/1807.01304

 

Cheers -

 

Rob


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#16 DHEB

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Posted 05 July 2018 - 01:52 AM

Thanks for this pointer. Looks very interesting!

#17 Keith g

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Posted 07 October 2018 - 11:14 AM

Hi all, well all is still relatively quiet with T Crb, I viewed it again last night at magnitude 9.7.

 

Keith.



#18 smithrrlyr

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Posted 05 May 2019 - 05:26 AM

T CrB is beginning to be accessible to evening observers, and it has continued its rather erratic behavior, bouncing between V = 9.6 and 10.1.  I put it at 9.7 this morning.  It is certainly showing enough activity to make one want to see what it does next.  The plot shows observations from the AAVSO database for the past 60 days. The black circles are visual observations.  Green are V-band CCD observations.  Blue are B-band CCD observations. T_CrB.JPG

 


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#19 Keith g

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Posted 28 August 2019 - 05:37 PM

Well the wait continues, I visually observed it at magnitude 9.7 this evening August 28th

Keith.
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