| 'T' Corona Borealis (T CrB) - A recurrent nova in Corona Borealis likely to erupt Real Soon Now |
| T CrB - Recent papers in Arχiv. |
| T CrB - Distance and position on the sky. |
| T CrB - When ? The $64.000.00 question. |
| update Are We There Yet? |
| End of document |
'T' Corona Borealis (T CrB) - a Recurrent Nova, about to recur.
This came off DrBecky's YT channel, which is good fun and well worth the effort. Another useful link is a seminar held for the AAVSO (A
merican A
ssociation of V
ariable S
tar O
bservers - don't worry, unlike most Americans, they acknowledge there is a Rest Of the World) on the subject last year. Essentially, if you're a variable star observer, in the Northern hemisphere, they want you to be checking it as a regular part of your sweeps (news announcement). If you've got a spectroscopic rig on your telescope, particularly calibrated for UV spectroscopy that can detect neon lines (see seminar video), then your observations are particularly encouraged.
The last two times (or maybe 4, or 5 - there are interesting hints of pre-1800 CE observations) this star went into "eruption", it passed from well below naked-eye visibility (good binocular visibility though - it doesn't need a big scope) to about the 50th-brightest star in the sky in a matter of (at most) a couple of hours. (That's from two events, involving 4 observers - 2 discoverers, and two who were too early ; so it's a good bet for this time around too.) Thus, even if you don't catch it in eruption, yours could be the last pre-eruption brightness record - which itself is a very valuable datum.
Dr Becky and the seminar provide the details on the star ; no point in me repeating their statements here. There's a small chance of the eruption this time being a supernova (type 1-SN, even - the ones used as "standard candles" for distance measurement across the universe), which adds to the importance of understanding it as well as possible. In theory, the system could go through many of these eruptions before eventually triggering the SN - but how many ... theory doesn't have a good answer for that.
It's not hard to find - follow the full length of the handle of the Plough asterism ("Big Dipper" in America - as if "dippers" were more common implements than ploughs ; odd that) from the Plough-share, through the "wedge" of Boötes (with red Aldebaran at the tip of the wedge) but not as far as the "Square of Hercules" ; Corona Borealis is the semi-circle of stars between Boötes and Hercules. Get to know what the area looks like. When the system "goes", there will be a new star there. (At the time of writing (2024 Apr. 27.55056), the AAVSO reported a brightness of 10.034 - which means it hasn't "gone" yet. When it goes, it'll make it to about magnitude 2. THe AAVSO website above lets you interrogate their database (but please don't melt their servers if you hear of the eruption having started - scientists and actual contributors will need it - unmelted!)
Here is a "finder chart" of the area (astronomical convention : bigger blobs = brighter stars). The field of view is 15 degrees square, so your fist at arms-length will approximately cover the arc of stars comprising the Corona Borealis and the target a finger's width to the south (away from the Pole Star !? ) from the semicircle of the "Northern Crown".Get used to what this part of the sky looks like. Some time this year, for a week to 10 days, it's going to look visibly different. Just maybe, you'll be able to see it by daylight. The constellation is about circumpolar from the UK, so you should be able to see what is happening without checking your clock first. Which includes the state of the clouds.
I missed an important point. Going on past events, the eruption will last between a week and 10 days.
Recent papers in Arχiv.
Obviously, I should look at what has recently been published on Arχiv about T.CrB. And, to my surprise, it's already in my search history. What do we have ?
I should note that the naming is a little lax. The "T CrB" ("identifier" in "constellation") code is variably capitalised. The star has different names in various catalogues as well, but "T CrB" is concerned with the variable star. The HD catalog name (for example) might be used if you were working specifically on the (relatively) normal star, not the variable in the system. But if you were looking at the position (does it wobble?), you might look at the GAIA catalogue entry.
Arχiv references encode the year, month and sequence-within-month as "YYmm.sequence". So you've got the date in the reference.
| Code | Title | Comment |
|---|---|---|
| https://en.wikipedia.org/wiki/Nova#Recurrent_novae | Nova | Wiki article on recurrent novæ. Includes a list of the known recurrent novæ. |
| https://en.wikipedia.org/wiki/T_Coronae_Borealis | T CrB | Wiki article on T CrB |
| https://arxiv.org/search/?query=T+CRB&searchtype=all&source=header | Arχiv search | Returns a list of 128 results (today ; this will change). |
| arXiv:2312.04342 | Accretion in the recurrent nova T CrB: Linking the superactive state to the predicted outburst | The 1946 had a dip then a brightening of about 1mag in the years before the 1946 eruption, and similar trends have been seen in 2023, leading to the current expectations. |
| arXiv:2308.13668 | The recurrent nova T CrB had prior eruptions observed near December 1787 and October 1217 AD | Discussed in the "webinar" referreed to above. |
| arXiv:2307.00255 | The "super-active" accretion phase of T CrB has ended | More discussion of the recent changes. |
| arXiv:2207.14743 | Stringent limits on 28SiO maser emission from the recurrent nova T Coronae Borealis | Looking for signs of "mineral dust" being cooked by the variable star. |
| arXiv:2009.11902 | Increasing activity in T CrB suggests nova eruption is impending | This event has been expected for some time! |
The blue entry above adds context in the Abstract, with my [annotations] :
T CrB is known to display the SiO [basic unit of silicate minerals] fundamental vibrational feature at 8μm. [microwave radio signal] When the anticipated eruption occurs, it is possible [possible!] that the shock produced when the ejected material runs into the wind of the red giant in the system may be traced using SiO maser emission.
So ... they're measuring the "quiet" state signal (nothing much visible) so they can compare any "eruption" state signal to the measurements already "in the can". "We find no evidence for such emission." is useful "negative" science.
T CrB - position on the sky and range.
Up in the main message, I described how to find the object "on the sky" :
- follow the full length of the handle of the Plough asterism ("Big Dipper" in America - as if "dippers" were more common implements than ploughs ; odd that) from the Plough-share, through the "wedge" of Boötes (with red Aldebaran at the tip of the wedge) but not as far as the "Square of Hercules" ; Corona Borealis is the semi-circle of stars between Boötes and Hercules. And don't forget - on previous "eruptions", the star became about the 50th (to 30th) brightest on the sky, for a week and a bit.
That's not quite the complete story. For fullness you'd normally also want to know the range. People tend to get (unduly) worried about potential big explosions in our backyard.
The Wikipedia page (link above) cites a report from the GAIA team of a parallax of 1.2127 ± 0.0488 mas, which equates to a distance of 802 parsecs (± 30 parsecs) or 2598.48 (± 97) light years.
Which is close enough for me to think it interesting, even if it's not quite far enough to be convincingly safe. But a strongly beamed explosion ... could be interesting. The results of the eruption could be very interesting.
Back to Article List.
When ? The $64.000.00 question.
When making predictions, the "when" bit of the prediction isa always important. When the star entered it's "active" phase (as seen about 1938 to 1946) in 2016, fingers were pointed at 2024. When the star entered the brightness dip (see the "seminar" in the man section) phase, the date was revised to 2024, May, with a ± of about 0.5 years (6 months). We're currently nearing the mid-point of that range, but no updates on the expected time. So ... weeks to months, possibly days to hours. I'll check the figures again when I submit this to Slashdot. (Checked for brightening on JD 2460428.55208 = 2024 Apr. 28.05208 mag 9.905 ± 0.0052 - not Gone yet!). Saved submission in this blog, to see how the editors mangle it. The "check for brightening" string should be pretty unique.
Back to Article List.
UPDATE Are We There Yet?.
So, has it gone yet?
I check the AAVSO site every so often. (And I deliberately don't provide a direct link, to aboid melting their servers.)
2024-05-10 22:25 +000 (my clock)
Star JD Calendar Date Magnitude Error Filter Observer Collapse All Expand All T CRB 2460440.933050 2024 May. 10.43305 9.976 0.003 V CSEB Details... T CRB 2460440.931128 2024 May. 10.43113 9.969 0.003 V CSEB Details...
It hasn't gone yet. Does it's light curve show any interesting features (in the last couple of days)? (I only ask for the last couple of week's worth, and just the commonest bands. Server melting, plus response time.
There were a few reports of nehanced brightness (visible magnitude up to about 8, R band up to about 7) a few days ago, but that looks like noise. Not gone, yet.
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