2024-04-27 (2) Back to the backlog. Collection.

Well, I've got a backlog to try to work my way through. Thick end of 100 days, which would be pushing 10,000 papers, if I looked at everything. But I've already blindly thrown about 90% of that over the side. Probably including some tatties. Oh well. Modify the default template with the "fonty" stuff.

Nothing attractive in the first part of the pile. But I should go back to the previous post and add anything I see in the archives for T.CrB.

Did the T CrB (see - even i'm not consistent in the abbreviation used!) submission to Slashdot - with a Tyop in the title. Quick look through another day's worth of IArχiv, then bedtime. Bit of a collection post.

Article List.

Articles read and things studied this month, April 2024.

Link	Description
HTML	Recent HTML Learnings - 2024-04
T CorBor	Article submitted to Slashdot
Quadruple massive star system	Arχiv, non-planar system (decided against it)
NGC 708	A 10-billion solar mass black hole in a low dispersion galaxy with a Kroupa IMF (decided against it)

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Recent HTML Learnings - 2024-04

I learned a little about using external fonts, specifically from Google, but I should be able to generalise it, if it's worthwhile. (I'm dubious enough about Google's committment to keeping these fonts generally available, or any of their self-interested "philanthropy", but that'll be another thing to work on.)

This block should be in a silly font. "Google Monoton ". Nope, I'm borked again. Forgotten how to make it work. [...]

Fixed it now. Different funny font, "Jacquard 12 Charted" at 30 pix.

Back to RTFM, and improve my notes.

Where did I (initially) go wrong? I've got (1) the link in the HEAD section, then (2) the font family chosen in the (CSS)STYLE section. (I use PRE for demonstration. Meh.)

The example given encloses the URL for the stylesheet link in only one set of quotes - which is problematic when there are spaces in the font name. Let's get rid of that (and put single-quotes on the outside) for starters.

Yep, that did it. So, names with spaces now.

That looks a bit odd. (Note the different quote marks.) rel="stylesheet" href='https://fonts.googleapis.com/css?family=Monoton|Major Mono Display' works, but I'm sure there were warnings about mixing names with spaces in there. Oh well. Lesson learned, into the default header it goes.

I've also done a little paragraph-level formatting with p style="font-size:30px ; font-family:'Jacquard 12 Charted'" above. Note the arrangement of different quotes in there.

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T Corona Borealis - submitted

The naked-eye shy will (briefly) host a new star. Fuck - check the BODY and you'll have a tyop in the title!

Well, I do hope the editors do catch that. At least I'm a lot more polite about them than the average Slashdotter.

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A Quadruple System with A Massive Star

Arχiv 2403.12771

Looks moderately interesting. Total system mass ~25 M_☉, of considerably differing sizes, thus MS-durations. Not co-planar (now that's surprising - worse then Pluto-Sun-Jupiter, without the tail-wags-doggery). There's a chain of logic implied from the distribution of system masses to the range of bound NS-NS and NS-BH potential future systems, and a difference between expected [NS] and [BH] occurrence rates seen in GW mergers. Which will need more brain cell than I have tonight. This morning, even.

Abstract

Hierarchical massive quadruple systems are ideal laboratories for examining the theories of star formation, dynamical evolution, and stellar evolution. The successive mergers of hierarchical quadruple systems might explain the mass gap between neutron stars and black holes. Looking for light curves of O-type binaries identified by LAMOST, we find a (2+2) quadruple system: TYC 3340-2437-1, located in the stellar bow-shock nebula (SBN). It has a probability of over 99.99\% being a quadruple system derived from the surface density of the vicinity stars. Its inner orbital periods are 3.390602(89) days and 2.4378(16) days, respectively, and the total mass is about (11.47 + 5.79) + (5.2 + 2.02) = 24.48 M_☉. The line-of-sight inclinations of the inner binaries, B$_1$ and B$_2$, are 55.94 and 78.2 degrees, respectively, indicating that they are not co-planar. Based on observations spanning 34 months and the significance of the astrometric excess noise ($D>2$) in Gaia DR3 data, we guess that its outer orbital period might be a few years. If it were true, the quadruple system might form through the disk fragmentation mechanism with outer eccentric greater than zero. This eccentricity could be the cause of both the arc-like feature of the SBN and the noncoplanarity of the inner orbit. The outer orbital period and outer eccentric could be determined with the release of future epoch astrometric data of Gaia.

Looks worth a read.

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Triaxial Schwarzschild Models of NGC 708: a 10-billion solar mass black hole in a low dispersion galaxy with a Kroupa IMF

2403.12144

I met Kroupa IMFs last week - oit's the 4-class IMF, with different power laws indices for each successive mass class.

Look at this one too. Might help me modelling the IMF (and other models).

That's enough for tonight.

Got up to the start of March (mostly by throwing lists away un-examined). I need to thin down (or increasingly specialise) IArχiv for the weighted list. No more work here, just separate posts tomorrow on the "interesting" stuff.

Back to Article List.

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2024-04-27 (Update -06-05) T CorB - a recurrent nova.

Articles studied this April - some of which might go to Slashdot.

'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?

update 2Are We There Either?

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'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.

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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

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.

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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.

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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.

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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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UPDATE Are We There Yet?.

It hasn't 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!?"

(stolen from Flanders & Swann)

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