Il semble bien que l’intensité de la raie H_alpha augmente sensiblement depuis l’été dernier !
Which my Français-de-chien translates as "It seems that the intensity of the H_alpha line [in the emission spectrum] is considerably stronger now than last summer. Which was specifically one of the things Schaeffer was mentioning as needing close monitoring in his alert of 10 months ago. It hasn't "gone" yet, but that's what would be expected in the run-up to an outburst.
Merci beaucoup à Alain Lecacheux at [PSM observatory], Alain Figer, Al Grycan and Jean Lecacheuxfor the "heads-up!"
Overall, given the rapid and drastic increase in intensity and width of the Hα profile, we strongly anticipate that the T CrB outburst may occur soon.
Spectroscopy on Jan 15, 29 and Feb 07 continue to show rapid increases in the H&aplha; line, in both intensity and width (indicating a larger size of the accretion disc).
In other words, thinga are hotting-up.
Similar changes have been observed in other "cataclysmic variables" in thye run-up to recent outbursts, though none have the historical record of reaching naked-eye visibility that T CrB has. You probably won't need to carry sunglasses all night, unless you're wanting to pose.
I don't see other mention of T CrB in other ATels back to mid-January.
I checked recent results from AAVSO at about 17:30 local time.
Star
JD
Calendar Date
Magnitude
Error
Filter
Observer
T Crb
2460647.06597
2024 Dec. 02.56597
<6.0
0.1
V
HQA
T Crb
2460647.03
2024 Dec. 02.53000
9.8
-
Vis
BRG
T Crb
2460646.96597
2024 Dec. 02.46597
<5.6
-
Vis
TRIB
T Crb
2460646.45344
2024 Dec. 01.95344
11.341
0.0048
B
DEY
Inevitably, we're under 8/8ths cloud cover here.
18:10 (JD 2,460,647.26182) Not managing to get an updated measurement listing. But that's a fifth of a day ago. (0.19 JD), 4 and a bit hours. Is there a problem in the hardware?
My "Astro-COLIBRI" is reporting an "unclassified optical transient", but that's at a Dec of 31.57° N, which is … actually, that is in the right range (25~35) for the constellation. But T Corb is at dec 25.9°, so … I'm going to have to convert between RA systems.
OK,converter written, the optical transient ("AT2024addv") was only 5 degrees off in declination - which is a plausible error, but 36° off in right ascension, which is not a plusiible error. But the AAVSO website hasn't posted any more results as of 19:15. Then Firefox crashed. [SIGH]
Anything on other astronomy news sites? S&T? Nope. Astronomy.Com ? nope. CBAT ? Nope.
Has T CorB "gone"?
It looks like that was just a glitch - some blockage in AAVSO's pipeline just while the brightest magnitude readings had been posted for ages were at the top of the list. Overnight postings eventually went back to the norm of around 10 mag (Vis). Which is what you expect, but in this case we're poised for a rapid rise cataclysmic eruption.
Oh well, I got one bit of necessary stuff built into my worksheets. Now need the reverse function.
'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 (American Association of Variable Star Observers - 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.
Recent additions to Arχiv concerning the recurrent nova T.CrB
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.
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.
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.
I check the AAVSO site every so often. (And I deliberately don't provide a direct link, to avoid 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 enhanced 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.
But today's check of the AAVSO site was interesting.
2024-06-05 14∶25∶09 BST (my clock)
It hasn't gone yet. But ... I'm sure that the brightness oscillation is increasing in both frequency, and amplitude. Which is a pretty good sign of something that can't go on much longer without something breaking. That's a "model-free prediction" - whatever the forces involved are, something is going to break at some point.
Are we approaching a turning point in the B luminosity (blue curve above, representing usig a blue-transmitting filter when estimating the magnitude ; "visible" is no flter (apart from the inherent slight colour of the glass) ; red and green as obvious, but with specified standard filter ranges)? And if so ... will the star "go at the turn around in the B curve? Or at the maximum slope of the B? Or will the B just never start to slow in it's brightening?
"Isn't it Exci-e-ting ... to lose a little weight!?"
