Strange Quarks

I’ve been observing the constellation Corona Borealis (CrB) as often as possible since late February at around 5 or 6am. Daylight Saving Time ended here just over a week ago. With CrB gradually becoming observable earlier, if I’m still awake at 1am (fairly often), I can observe it (with binoculars) before I go to bed now.

In an October 2024 article in the Research Notes of the American Astronomical Society, When will the Next T CrB Eruption Occur? by Jean Schneider, the author writes:

By going more carefully into the dates of occurrence of the past eruptions, one finds that the successive events date separations are an integer multiple of the orbital revolution period.

…

In summary, the eruptions are not strictly periodic, but the eruptions were all separated by an integer multiple of the orbital period 227.5687 days.

From that, I tentatively infer that the eruption date after 1946 February 9 should be 2431861 + N*227.5687 where N is an integer close to 128, if the orbital period remains constant.

The upshot was predictions for the T CrB eruption of March 27 2025, Nov 10 2025 or June 25 2026. The popular press latched onto this article and suggested a greater certainty than was warranted. It’s now a few weeks after the first of these dates and no nova eruption has occurred yet.

We will see about November. In the meantime, we wait.

I started observing the constellation of Corona Borealis (CrB) again this week, in preparation for the recurrent nova T CrB (aka The Blaze Star) to erupt. This was the first time I’ve done so since early October 2024, when the constellation left Adelaide’s evening sky.

On February 20th from around 5:15am, I spent 45 minutes or so reacquainting myself with the region through hand-held 7×50 binoculars, reminding myself of the comparison stars I’ll use to estimate the change in brightness of the nova, and the asterisms that will help me remember where they are.

Even pre-eruption, T CrB is observable in a small telescope at around magnitude 10, but from suburban skies, anything fainter than magnitude 6.5 or 7 is difficult through 7×50 binoculars, especially when twilight approaches. Still, it’s perfectly good enough to be able to say whether the nova event has happened.

As a reminder, the nova was anticipated before the end of 2024, but nature doesn’t always cooperate with our expectations. When the eruption does happen, T CrB will be visible without the aid of binoculars or telescopes, as bright as alpha CrB aka Alphecca (see the image below).

Why start observing it again now? For two reasons.

• That part of the sky is observable from here again, even if at 5am.
• There is recent evidence from spectroscopic observations that the rate of accretion of material around the white dwarf from the “donor” star in the pair that makes up T CrB (or any nova system) is significantly increasing. Such an increase, if it’s happening, may be a sign that the thermonuclear runaway is close.

Even so, there is not universal agreement that this result implies the nova is imminent.

Given Murphy’s Law, it will be entirely possible to miss the initial brightening, since observing 2 or 3 times a night (as I was doing last year for awhile) is not so easy in the wee hours, given the need to sleep and work, not to mention that some nights/mornings will be cloudy!

Still, it won’t stop me, and many others, from trying and in any case, the nova will be easily observable for several days either to the naked eye or with binoculars.

Here’s hoping we’ll have a bright nova (the brightest of all known recurrent novae) sometime in 2025!

I gave another talk about T CrB earlier this month and hoped I would be speaking post eruption by then.

We’re still waiting, and we’re about to lose it in the early evening sky.

I’ve been checking the area with binoculars most clear nights and doing some photometry with my Seestar S50.

Even if we miss the main event, we have another shot at seeing the nova rise about 100 days post-eruption.

In September 2024, a nova was independently discovered in Scorpius by Koichi Itagaki (Japan) and Andrew Pearce (Western Australia). Its designation is V1725 Sco.

I like to think of the lovely asterism (arbitrary star grouping) in which the nova appears (arrowed above) as:

The visual band light curve below shows the nova’s (partial) rise to around magnitude 9.5 in early September to around magnitude 13 almost a month later.

I made (and submitted to AAVSO) 6 observations of the nova with my Seestar.

The differential photometry aperture rings (red bullseye) are centred on the nova and the green highlighted stars are reference stars. Note the deliberate defocus, so that the light of the stars is spread across multiple sensor pixels, as is common for “one-shot colour” sensors such as the S50, DSLRs and others. My tests so far suggest this may be less necessary than for the DSLR photometry I’ve done in the past, possibly because of the differences between sensor sizes and the number of arc seconds per pixel.

One of the things I love about doing variable star photometry is the endless variation in the star fields being imaged, and the endlessly varying asterisms I see and can imagine about.

I gave a talk on June 5 2024 to ASSA about the imminent nova T Corona Borealis.

One of the things I showed (reproducing a result from Brad Schaefer’s 2023 paper) was the similarity between the light curves around the eruptions of 1866 and 1946. The VStar plot below shows visual band data for the two eruptions in which the difference between the two eruption peaks has been added to the times of the 1866 observations.

I also showed the similarity between observations leading up to the 1946 eruption (the rise and dip) and recent observations:

and the two overlaid:

How much time remains before the next eruption is uncertain, but the signs are that it’s only weeks or in the worst case, a few months away.

T Corona Borealis — T CrB for short — is one of ten known recurrent novae. At a distance of around 3000 light years, it was first discovered as a nova eruption in 1866 by John Birmingham. Outbursts occur approximately once every 80 years. It may have been observed in 1217 and in 1787 as well.

T CrB is expected to explode again this year reaching naked eye visibility, around magnitude 2 or 3. The last outburst was in 1946. As always when we talk about astronomical objects, these events happened long ago, 3000 years ago in this case, with the evidence only expected to reach us this year due to the speed of light.

This is likely to be the brightest nova of a generation, certainly of the known recurrent novae. It will quickly rise from a visual band magnitude of 9 or 10 within a day or two to become visible to the naked for a few days, remaining a binocular object for a week or thereabouts, then returning to its pre-eruption magnitude within a month or so.

Exactly when it will brighten is uncertain and is discussed by nova expert Brad Schaefer and others in this AAVSO article, but the prediction is 2024.4 +/- 0.3, so May or June, but it could be earlier or later.

There was a pre-eruption dip in the light curve, 1.1 years before the 1946 outburst. A similar dip happened in March 2023 as shown in the last two years of T CrB observations in V and B bands, more prominent in the B band.

T CrB is located low in the north-eastern sky from Adelaide starting in the late evening. This Stellarium screenshot shows the circumstance for Apr 8 at midnight when T CrB is around 15 degrees above the horizon. Waiting an hour or two will help make observing easier with T CrB culminating at around 29 degrees above the horizon, but the region is viewable from around 11:30pm with a clear NE horizon.

This unprocessed, untracked image was taken with my DSLR (Canon 1100D, 100mm lens, f2.0, ISO 100, 10 secs) on Apr 7 at 2am, so it’s a little further rotated anti-clockwise than the Stellarium view above. The red arrow points to where T CrB will become visible and the green arrow points to alpha CrB (Alphecca). This shows the bright stars of the constellation of Corona Borealis.

Here is an AAVSO finder chart, with stars only down to magnitude 5. You’ll need to rotate it slightly clockwise to match the views above.

The comparison star marked 22 is the magnitude 2.2 star Alpheccca (alpha CrB). Izar and Arcturus (epsilon and alpha Bootis) do not appear in this finder chart, and are at upper left of the constellation Corona Borealis in this orientation. T CrB may approach Alpheccca in brightness.

I’ll be looking out for T CrB whenever I can stay up late enough or get up early enough until the outburst happens, using just the unaided eye in the first instance. Once visible in outburst, I’ll make estimates with 7×50 binoculars and time-permitting, DSLR images for subsequent photometry, submitting both to the AAVSO International Database.

Messages will also be posted on the AAVSO nova forum when the T CrB outburst happens.