On 2025 January 17 the TNS (Transient Names Server) registered a bright possible supernova as AT2025brr. The object was found by ZTF (Zwicky Transient Factory) who measured a brightness of 15.7 mag in g-band and 13.9 mag in r-band. The brightness in both bands remained unchanged until end of March 2025 (the date of this article). No classification of this bright discovery was made.

I found the constant brightness levels in both bands and the absence of any possible galaxy very strange. Also, the strong red colour was quite unusual for a new-found and probably young supernova. So I compared the area around the position of AT2025brr on several surveys using AladinLite (see the screenshots below. The star is marked by a white arrow.). Soon I realised that an apparently red star moved very quickly over the sky and would appear at the position of AT2025brr at the beginning of 2025. The star is really a High Proper Motion (HPM) star, probably a red dwarf star not far from the sun. Clicking on the position of AT2025brr in Aladin reveals no HPM star. The DSS shows the star as a short trace with a blue and a red end. Its proper motion is (based on my crude measurements on the plates of POSS 1 and POSS 2)

RA 3165 mas/yr (eastward)
DE -3825 mas/yr (southward)

The resulting proper motion is about 5 arcseconds per year. That star is very speedy - and well known, too. It is known as TEEGARDEN'S STAR. Unfortunately, the database Simbad states a position a little farther than two arminutes away from the position of AT2025brr. This was of course the star's position at J2000.0 and the possible reason why AT2025brr was not identified as Teegarden's star right away. And yes, searching Simbad at the position of AT2025brr with a larger radius than the default 2 arcminutes would have revealed Teegarden's star. But who suspects a HPM star there?

POSS 1 blue plate, 1951 Nov 27

POSS 1 red plat, 1951 Nov 27e

POSS 2 red plate, 1990 Nov 09

POSS 2 blue plate, 1991 Oct 16

2MASS

allWISE. Position of AT2025brr is marked by a cross.

PanSTARRS DR1. Position of AT2025brr is marked by a cross.