Strange Quarks

A couple of months ago I was asked to give an update at the July 2 2025 ASSA general meeting about T CrB, the binary star system that is anticipated to reach magnitude 2 or 3 when it goes into outburst as a recurrent nova (one of only 10 known), which it has done a few times before at roughly 80 year intervals.

In the meantime, we had two bright southern hemisphere novae (around magnitude 5) in June, so my T CrB talk turned into an update about 3 novae: T CrB, V462 Lup, and V572 Vel. The second and third were the subject of my last two posts.

My update was followed by a great talk about variable star photometry with the Seestar S50 by a former colleague, Andrew Murphy. The slides for his talk (and a course project) are here, as of 20 July 2025.

Here’s the PDF for the talk I gave, with thanks to Kym Thalassoudis for allowing me to include his images of V462 Lup and V572 Vel:

Here are the Powerpoint slides as well:

We may still be waiting for T CrB, but within less than a month we’ve seen 2 bright southern hemisphere novae: V462 Lup and now PNV J10251200-5331109 (aka V572 Vel)!

Technically it’s still classed as a possible nova (PNV) before spectroscopic confirmation, although there was a positive Gamma-ray Space Telescope observation overnight while I was sleeping.

Australian John Seach (NSW) discovered this (at magnitude 5.7), and Andrew Pearce (WA) independently found it (magnitude 5.5) on June 25 .

This object has eta Carina at its upper left in this Stellarium screenshot, and below it the “false cross” which consists of stars from Carina and Vela.

This smaller field of view provides more detail with 3 stars at the upper left of the false cross asterism (if the cross was standing upright) at bottom of the picture.

The observing campaign for PNV J10251200-5331109 (aka V0572 Vel) reports the progenitor star as likely being a 22.2 blue star with large amplitude variability.

The sky conditions were not great last night, but I estimated the nova candidate at 4.8 through 15×70 binoculars, through gaps in cloud with DSLR photometry pending.

Rotate this 20 degree FOV AAVSO finder chart 90 degrees right to get the false cross asterism in the same orientation as the screenshots above.

This 8 degree FOV finder chart provides the comparison stars of interest at the moment within a binocular field or two.

As I write this there have been less than 40 observations submitted to the AAVSO International Database.

After being away for a couple of days, I read an email yesterday from Andrew Wendelborn (ASSA) before seeing the official announcements, so thanks for the early heads-up Andrew! The timing worked out well in general.

A nova, now designated V462 Lup, was discovered on June 12 by the ASAS-SN survey at magnitude 8.7 and has since risen to around magnitude 5.5. It has apparently not yet peaked. The progenitor star is thought to have been around magnitude 22, and as with all novae, the rapid brightness increase over a few days is impressive (although not as rapid as some).

Lupus, and the nova, are high in the evening sky as shown in this Stellarium screenshot:

The orientation here is at around midnight on June 21 2025 but Lupus is visible from early evening. This Stellarium screenshot shows the region around the nova corresponding to the image at top.

With the help of this AAVSO finder chart I have made a few visual estimates and there is some DSLR photometry pending. The visual light curve as of the early hours of June 21 is shown below with two of my binocular visual estimates in purple, the last one just a few hours ago:

Meanwhile, T CrB is still quiet.

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.